Microbiology Superexam TOPNOTCH

Respiratory fatigue will eventually set in and bring about acidosis. This will affect the P50 value in the oxyhemoglobin dissociation curve. The P50 value represents the oxygen pressure at which hemoglobin: A. is almost fully saturated with oxygen B. releases oxygen at the capillary level C. binds oxygen to 50% saturation of its binding sites D. binds oxygen released by tissues E. Both A and C

108 C. Page 35 of Topnotch Handout. P50 is the pO2 at which Hemoglobin is 50% saturated.

All of the following non-essential amino acids are synthesized from the transamination of alpha-ketoacids except: A. Glutamate B. Glycine C. Alanine D. Aspartate E. All of the above

112 B. Page 40 of Topnotch Handout. Alanine, aspartate, and glutamate are synthesized from the transamination of alpha-ketoacids.

DNA replication is a semi-conservative process where in each strand serves as a template for the complementary daughter strand and each strand becomes part of the daugther strand. This process usually occurs during which part of the cell cycle? A. G0 phase B. G1 phase C. G2 phase D. S phase E. M phase

118 D. Page 54 of Topnotch Handout. This occurs during the S phase of the cell cycle.

Which of the following antibiotics used in TB inhibits RNA synthesis: A. Streptomycin B. Rifampicin C. Isoniazid D. Pyrazinamide E. Ethambutol

119 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Page 59 of Topnotch Handout. Rifampicin binds to the Beta subunit of bacterial DNA- dependent RNA polymerase and thereby inhibits RNA synthesis. Streptomycin binds to the 30s subunit and distorts its structure thereby interfering with the initiation of protein synthesis.

The greatest quantitative source of high energy phosphate in aerobic organism is? A. Oxidative phosphorylation B. Substrate level phosphorylation C. Pentose Phosphate pathway D. Citric acid cycle E. Beta-oxidation

126 A. Oxidative phosphorylation occurs only in aerobic organism

What is/are the effects of epinephrine in the body as a result of stressful stimuli? A. Stimulation of phosphorylase via generation of cAMP B. Increase in glycogenolysis C. Inactivation of pyruvate kinase D. All of these. E. A & B only.

131 D. Epinephrine, together with glucagon, cortisol, and growth hormone counteract the actions of insulin. It increases gluconeogenesis and glycogenolysis. Cyclic AMP is formed from ATP by adenylyl cyclase and acts as an intracellular 2nd messenger in response to hormones such as epinephrine, NE, and glucagon. Phosphorylase in muscle is activated in response to epinephrine acting via cAMP. Pyruvate kinase is an irreversible reaction in glycolysis and is inhibited by high levels of epinephrine, glucagon and ATP.

How many ATPs are produced by NADH in the liver? A. 1 B. 2 C. 3 D. 4 E. 5

133 C. Liver, kidney and heart utilizes the Malate-aspartate shuttle producing 3 ATPs=1 NADH. Skeletal muscle and brain uses glycerol-phosphate shuttle 1 NADH=2 ATP. (SIMILAR TO PREVIOUS BOARD EXAM CONCEPT)

The following are effects of insulin except: A. Stimulation of glycogen synthase. B. Inhibition of phosphofructokinase-2 C. Inhibition of glycogen phosphorylase D. Decreased activity of fructose 1,6 biphosphatase E. Activation of carboxylation of acetyl-CoA to malonyl-CoA

136 B. Effects of insulin: WELL FED STATE. Increased in glycogenesis (glycogen synthase), decreased glycogenolysis (inhibition of glycogen phosphorylase), decreased gluconeogenesis (decreased activity of Fructose-1,6-biphosphatase), increase fatty acid synthesis (activation of acetyl CoA carboxylase involved in Acetyl coa --> Malonyl CoA). Option B is the answer. Insulin activates PFK-2 which activates PFK-1, which catalyzes the rate-limiting step in glycolysis

RVD, a 60 year old man with hypertension and diabetes mellitus came in due to chest pain, you know that the cause of his chest pain is lactic acid accumulation in the heart muscle. How many ATPs are generated by the cardiac muscle in anaerobic respiration? A. 4 B. 2 C. 16 D. 8 E. 10

149 B. Anaerobic glycolysis yields only 2 ATP per molecule of glucose

Acetyl Co-A combines with which substrate to enter the Kreb's cycle? A. Oxaloacetate B. Malonate C. Citrate D. Succinate E. Alpha keto-glutarate

160 A. The first step in Kreb's cycle is when Acetyl Co-A combines with oxaloacetate to form citrate catalyzed by citrate synthase

9. Which of the following vitamins is/are needed by pyruvate dehydrogenase to convert Pyruvate to Acetyl CoA before it enters the Kreb's cycle? A. B1 B. B2 C. B3 D. B5 E. All of the above

169 E pyruvate dehydrogenase needs Thiamine (B1), FAD (B2), NAD (B3), Coenzyme A (B5), and lipoic acid

Which of the following nucleotides are pyrimidines found in an RNA molecule? A. Uracil and Cytosine B. Thymine and Cytosine C. Uracil ang Guanine D. Adenine and Guanin E. Thymine and Guanine

177 A. pyrimidines are cytosine, uracil, and thymine. Uracil and cytosine are for RNA while cytosine and thymine are for DNA

Which among these amino acids is polar and uncharged? A. serine B. threonine C. tyrosine D. A and C E. All of the above

197 E serine, threonine and tyrosine contain hydroxyl groups making it polar but uncharged.

Hormones that bind to cytoplasmic receptor A. cortisol B. aldosterone C. testosterone D. A and B E. None of the above

198 D. Among all the hormones that bind to intracellular receptors, only aldosterone and cortisol have receptors located in the cytoplasm. Others are in the nucleus.

What amino acid plays a crucial part in hemoglobin's affinity to oxygen? A. Glycine B. Tyrosine C. Histidine D. Leucine E. Proline

213 C. Histidine located at F8 and E7 positions of hemoglobin participate in oxygen binding.

The Van Den Bergh reaction measures: A. Glycosylated hemoglobin B. Bilirubin C. Creatinine D. Amylase E. Ck-MB

217 B. More specifically, it measures the amount of conjugated bilirubin in the blood.

which of the following sites of respiratory chain does Barbiturates act? A. Complex I B. Complex II C. Complex III D. Complex IV E. ATP synthase

223 A. barbiturates exert its inhibitory effect by binding to complex I. Malonate is an inhibitor of complex II, Antimycin A and Dimercaprol is for Complex III, Hydrogen sulfide, carbon monoxide and cyanide inhibits complex IV and lastly oligomycin inhibits ATP synthase.

What is the most common glycolytic enzyme deficiency? A. Glucokinase B. Pyruvate kinase C. Glucose phosphate isomerase D. Phosphoglycerate kinase E. Phosphoglycerate mutase

225 B. Pyruvate kinase deficiency is responsible for about 96% of patient suffering from glycolytic enzyme defect.

In Kreb cycle, which of the following dehydrogenase catalyze the last step for CO2 production? A. Isocitrate dehydrogenase B. Malate dehydrogenase C. Succinate dehydrogenase D. Alpha ketoglutarate dehydrogenase E. None of the above

228 D. in kreb cycle, it is necessary to reduce citrate ( a C6 atom) to oxaloacetate ( C4 atom). There are only two sites for CO2 production. The first step is catalyzed by isocitrate dehydrogenase and the last is by the alpha ketoglutarate dehydrogenase. All the other proceeding dehydrogenase will only reduce FAD or NAD without forming CO2.

this lack of enzyme is responsible why the liver cannot utilize its own ketone bodies? A. Acetoacetate: succinyl CoA transferase B. B- ketothiolase C. HMG CoA lyase D. B hydroxybutyrate dehydrogenase E. None of the above

232 A. acetoacetate: succinylCoa transferase or thiophorase is responsible for conversion of acetoacetate to its CoA derivative. This is present in almost all tissues but absent in the liver.

which of the following is an essential amino acid? A. asparagine B. aspartate C. arginine D. Cysteine E. Alalnine

237 C. Essential amino acid: phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, arginine, leucine, lysine.

Which of the following substances is known to inhibit complex 2 succinate -q-reductase of the electron transport chain? A. amobarbital B. malonate C. antimycin A D. dimercaprol E. cyanide

245 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. At that time we were asked about complex 3 and 4 inhibitors Antimycin and cyanide respectively. Dimercaprol also inhibits complex 3. Amobarbital inhibits complex 1

which of the following storage forms of energy in skeletal muscle provides energy for the first few seconds of muscle activity or exertion? A. muscle glycogen B. free glucose C. phosphocreatine D. fatty acids E. ketone bodies

246 C. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. The most immediate source of energy in the first few seconds of muscular activity is phosphocreatine, muscle glycogen is then used next and over long periods of activity, fatty acids start to be used as the main source.

The term forensic pertains to: A. Crime B. Investigatory C. Autopsy D. Law E. Criminal

25 D. SIMILAR TO BOARD EXAM CONCEPT. This seems to be the only none-Biochemistry related question asked during our Board Examination in Biochemistry.

The following substances are known to be antioxidants preventing lipid peroxidation and buffers against free radical production EXCEPT A. glutathione B. vitamin D C. vitamin C D. vitamin E E. vitamin B1

251 E SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Vitamin B1 is the least implicated vitamin as an antixoidant among the choices

From which metabolic intermediate does the synthesis of cholesterol begin with? A. acetylCoA B. HMG-CoA C. mevalonate D. squalene E. lanosterol

255 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Cholesterol synthesis starts with joining of 2 molecules of Acetyl CoA to form AcetoacetylCoA with the enzyme acetoacetylCoA thiolase eventually forming HMG-CoA and so on. All the others are intermediates further down the pathway.

If an amino acid with a nonpolar side chain has a pk1 of 2.3 and a pk2 of 9.1, what will be its expected net charge in an alkalinized urine with a pH of 8.5? A. +2 B. 0 C. -1 D. +1 E.

261 B. At this pH, the COOH group of the amino acid will have already given up its H+ making the net charge 0.

Which of the following functions as a reservoir of apolipoproteins? A. VLDL B. HDL C. LDL D. Chylomicrons E. IDL

266 B. HDL is a reservoir of apoCII and apo E

Alex is a thin 24-year old male who began avidly taking 2 eggs every morning in order to build up his muscle bulk. This might put him at risk of a deficiency of which of the following vitamin? A. B3 B. B5 C. B6 D. B7 E. B9

30 D. B3 - niacin; B5 - pantothenic acid; B6 - pyridoxine; B7 - biotin; B9 - folic acid

Which of the following minerals is essential for the activity of the enzyme glutathione peroxidase? A. Molybdenum B. Manganese C. Iron D. Selenium E. Copper

300 D. In the form of selenocysteine, selenium is essential for the activity of the anti-oxidanrt glutathione peroxidase

Serum levels of which ketogenic amino acid are increased in Maple Syrup Urine Disease? A. I B. L C. K D. V E. Y

31 B. I - Isoleucine; L- Leucine; K - Lysine; V - Valine; Y - Tryptophan

Supplementation of which trace mineral appears to improve the glycemic control of patients with type II diabetes mellitus? A. Chromium B. Copper C. Zinc D. Selenium E. Molybdenum

317 A. chromium is the component of low molecular weight chromodulin which potentiates the effect of insulin by facilitating insulin binding to its receptor and receptor tyrosine kinase signalling. Devlin pp 1114

Formation of Nitric oxide requires which of the following substances? A. Asparagine B. Acetylcholine C. Citrulline D. Arginine E. Glycine

318 D. Nitric oxide formerly known as EDRF is formed by the enzyme NO synthase. It uses arginine as a substrate for oxidation to produce citrulline and NO. Harpers pp 580

The following are the characteristics of smooth muscle except? A. Caldesmon promotes interaction of actin and myosin B. Contains rudimentary sarcoplasmic reticulum C. Extracellular fluid Ca is important for contraction D. Exhibits latch state E. none of the above

319 A. Caldesmon is a regulatory protein ubiquitous in the smooth muscle.at low calcium concentration, it binds to tropomyosin and actin thereby preventing the interaction of actin and myosin. Harpers 27th ed p 579-580

Deficiency of this fatty acid leads to decreased vision and altered learning behavior. A. linoleic acid B. omega 6 fatty acid C. arachidonic acid D. linolenic acid E. none of the above

322 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Linolenic acid / omega 3 fatty acid deficiency results in decreased vision and altered learning behavior. Linoleic acid / omega 6 fatty acid is a precursor to arachidonic acid is thus essential in prostaglandin synthesis.

What is true regarding the pentose phosphate pathway? A. The enzymes involved are mitochondrial. B. Oxidation is achieved by dehydrogenation using NAD+ as an electron acceptor. C. Like the TCA cycle, this pathway yields ATP. D. This pathway can account for the complete oxidation of glucose. E. Glutathione reductase contains selenocysteine at its active site.

328 D. The enzymes involved in the pentose phosphate pathway are cytosolic. NADP+ is the electron acceptor, and this cycle does not yield ATP. Harper Biochemistry 28th edition p.175-1

Lipase whose activity is increased by glucagon? A. Pancreatic lipase B. Lipoprotein lipase C. Hormone-sensitive lipase D. Hepatic lipase E. None of the above

33 C. Pancreatic lipase - activated by trypsin; Lipoprotein lipase - activated by insulin; Hepatic lipase acts on the remaining lipids carried on lipoproteins in the blood to regenerate LDL.

The following are true regarding non-alpha-amino acids, except? A. GABA functions as an inhibitory neurotransmitter in brain tissue B. Catabolism of uracil yields B-alanine. C. Catabolism of thymine yields B-aminoisobutyrate. D. none of the above

331 D. All statements are true. Harper Biochemistry 28th edition pp.266-268

What is true about cardiac muscle but not of smooth muscle? A. syncytial B. nerve impulse initiates contraction C. troponin system present D. caldesmon an important regulatory protein

335 C. Both cardiac and smooth muscle are syncytial. Nerve impulse initiates contraction in skeletal muscle. Troponin system is present in skeletal and cardiac muscle. Caldesmon is important in smooth muscle only. Harper Biochemistry 28th edition p.555 table 49-3

RBCs make use of this glucose transporter: A. GLUT 1 B. GLUT 2 C. GLUT 3 D. GLUT 4

338 A. Harper Biochemistry 28th edition p. 596

Not true regarding anti-oxidants and free radicals: A. Anti-oxidants can also be pro-oxidants. B. Radical damage is a known cause of atherosclerosis. C. Oxygen radicals are the most damaging radicals in biological systems. D. Beta carotene is an antioxidant at high concentrations of oxygen.

339 D. Beta carotene is an autocatalytic pro-oxidant at higher concentrations of oxygen and is only an antioxidant at low oxygen concentrations. Harper Biochemistry 28th edition pp. 482-485

Which of the following is a omega 3 fatty acid? A. Linoleic acid B. Linolenic acid C. Arachidonic acid D. Oleic acid E. All of the above

34 B. The other choices are omega-6 fatty acids.

With regards to isomerism, glucose and galactose are: A. epimers, differing only at carbon 2 B. isomers C. enantiomers D. anomers

340 B. Glucose and galactose are epimers, differing only at carbon 4. Choice A refers to glucose and mannose.

True of the peptide bond, except: A. Formed by a reaction of the α-COOH and α-NH2 of two amino acids B. Has a partial double bond character C.Generally in the cis configuration D. Rigid and planar

341 C. Characteristics of the peptide bond: - attaches the α-COOH to the α-NH2 of another - very stable, can only be disrupted by hydrolysis through prolonged exposure to a strong acid or base at elevated temperatures - polar and can form hydrogen bonds - partial double bond character, which makes the bond rigid and planar - generally in the trans configuration Reference: Topnotch Biochem Handouts

Which of the following compounds inhibit biological oxidation by dissociating respiration from ATP synthesis? A. Antimycin A B. 2,4 dinitrophenol C. Carbon monoxide D. Malonate

345 B. Uncouplers act by dissociating respiration from ATP synthesis. Examples of uncouplers are 2,4 dinitrophenol, aspirin, and thermogenin (brown fat). Antimycin A - inhibits Complex III Carbon monoxide - inhibits Complex IV Malonate - inhibits Complex II

Which of the following is true of the amino acids valine, leucine, and isoleucine? A. Characterized with a polar but uncharged side chain B. Classified under branched chain amino acids C. All are nutritionally non essential D. Possess ionizable functional groups

346 B. Valine, leucine and isoleucine are branched chain amino acids, with nonpolar, uncharged side chains; they are non ionizable and are considered nutritionally essential.

Hemoglobin and proteins composed of several subunits assume this level of protein structure: A. Primary B. Secondary C. Tertiary D. Quaternary

347 D. Primary, secondary, and tertiary levels of protein structure are composed of only one polypeptide chain.

This protein digestive enzyme has the capacity to activate its own zymogen: A. Pepsinogen B. Elastase C. Trypsin D. Chymotrypsin

349 C. Trypsin is capable of activating trypsinogen (its zymogen) into more trypsin, which in turn activates other protein digestive enzymes.

Classic galactosemia can cause cataract formation due to the following, except: A. UDP-Glc:galactose-1PO4 uridyltransferase deficiency B. Accumulation of galactitol inside the lens cells C. Action of aldose reductase forming galactitol D. Ability of galactitol to diffuse out of the lens cell

350 D. Galactitol, once formed from galactose by aldose reductase, accumulates within the lens and causes early cataract formation found in classic galactosemia.

Which type of mutation causes premature termination of protein synthesis because of the creation of a stop codon during the genetic change? A. Missense B. Neutral C. Nonsense D. Silent

357 C.

Muscle relaxation that takes place after actin-myosin dissociation is due to: A. Binding of calcium to troponin C B. Depletion of ATP in the muscle C. Increased formation of creatine phosphate D. Binding of ATP to the S-1 head of myosin to form a myosin-ATP complex

358 D.

Because of the amphipathic nature of bile acids, their role in lipid digestion includes the following, except: A. Serve as detergents binding to fat globules as they are broken down by peristaltic action of the GI tract B. Suspends dietary fat in smaller particles in the aqueous environment in the small intestines C. involved in the packaging of TAGs into chylomicrons D. solubilize the TAGs into micelles and transport them to the intestinal cell surface

359 C. Bile acids are not involved in the packaging of TAGs into chylomicrons, which takes place inside the intestinal epithelial cell.

The Enzyme Commision and IUBMB classifies enzymes based on their: A. Functional groups B. Reactions catalyzed C. Tertiary and Quaternary structure D. Metabolic pathways they belong to E. Locations in the body

36 B.

This component of total energy expenditure plays the most significant role in the total energy requirement of an individual: A. Physical activity B. Thermic effect of food C. Diet induced thermogenesis D. Basal energy expenditure

360 D. 60% of energy is used to maintain Resting or Basal metabolic rate. 30% for physical activity, and 10% for diet-induced thermogenesis or thermic effect of food. Reference: Topnotch Biochem Handouts

Reduced glutathione (GSH) is composed of which of the following amino acids EXCEPT? A. Glycine B. Cysteine C. Glutamate D. Serine E. None of the above

361 D. Reduced glutathione is a tripeptide-thiol (γ- glutamylcysteinylglycine) present in most cells which can chemically detoxify hydrogen peroxide Lippincott 5th pg 148

The following are TRUE of the urea cycle EXCEPT A. The rate limiting step of the cycle is catalyzed by carbamoyl phosphate synthetase I B. CPS I absolutely requires N-acetyl glutamate C. There are two ATP requiring enzymes and one of them is argininosuccinate synthetase D. It can be used to synthesize citrulline, ornithine and aspartate E. Carbon dioxide and free ammonia provides for the atoms of urea

362 D. CPS I absolutely requires N-acetyl glutamate as an allosteric activator. In the urea cycle, 3 molecules of ATP are required but ultimately 4 ATP equivalents are consumed, (2 ATP for CPS I and 1 ATP for argininosuccinate synthetase [converted to AMP hence 2 equivalents used]). The cycle can also be used to synthesize ornithine, citrulline, arginine, fumarate and urea. Lippincott 5th pg 254

The following are TRUE regarding prokaryotic transcription EXCEPT A. Transcription starts at the promoter which contain consensus sequences such as the -35 sequence and the TATAAT box B. Termination of transcription can be spontaneous through formation of a hairpin loop C. RNA polymerase needs a primer to initiate transcription D. Transcription proceeds from a 5’ to 3’ direction and is identical to the sense strand with U replacing T E. All are correct

364 C. RNA polymerase does not need a primer and has no proofreading activity in contrast to DNA polymerase. Lippincott 5th 419-421

The electron transport chain is embedded in the inner mitochondrial membrane. Which of the following is/are the mobile electron carrier/s? A. NADH dehydrogenase B. Coenzyme Q C. Cytochrome b/c1 D. Cytochrome c oxidase E. B and D

368 B. Mobile electron carriers: coenzyme Q and cytochrome c. Lippincott 5th pg 74

Which of the following is/are TRUE of Vitamin A? A. Rhodopsin consists of 11-trans retinal and opsin B. Vitamin A deficiency can produce nightblindness, xerophthalmia and pseudotumor cerebri C. Retinol and retinal can readily be interconverted and can be derived from retinoic acid D. A and C E. All of the above

374 C. Rhodopsin consists of 11-cis retinal and opsin; Pseudotumor cerebri is caused by excessive intake of vitamin A Lippincott 5th pg 384-386

Which of the following amino acids is/are non-polar? A. Phenylalanine B. Proline C. Tryptophan D. A and B E. All of the above

379 E glycine, alanine, valine, leucine, isoleucine, phenylalanine, tryptophan, methionine, proline: non polar Lippincott 5th pg 2

Which of the following enzymes participate in both glycolysis and gluconeogenesis? A. Phosphofructokinase-1 B. Hexokinase C. Phosphoglycerate kinase D. Pyruvate kinase E. Glucokinase

382 C. The other choices participate in non-reversible steps of glycolysis only.

In diabetes mellitus, excess glucose is converted to sorbitol, causing some of its complications including cataract and neuropathy. Sorbital accumulates in the body because its metabolism is very slow, occurring only in the liver and which other body organ? A. Seminal vesicle B. Brain C. Pancreas D. Choroid body E. Kidney

388 A. Sorbitol is metabolized by sorbital dehydrogenase into fructose. Remember that fructose is one of the secretions of the seminal vesicles for the seminal fluid.

Which of the following enzymes can be seen in cancer cells and is partly responsible for their unlimited replicative potential by preventing the shortening of the highly repetitive DNA sequences at the ends of their chromosomes? A. DNA polymerase III B. Telomerase C. Primase D. DNA A protein E. Replicase

389 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE.

A ganglioside may contain all of the following except: A. a ceramide structure B. glucose or galactose C. phosphate D. Sialic acid E. Sphingosine

39 C. Glycosphinglipids do not contain phosphate. Gangliosides, by definition, contain sialic acid

Which of the following is the precursor of the active form of vitamin D that is found naturally occurring in the skin? A. Cholecalciferol B. Ergocalciferol C. Sitocalciferol D. Calcitriol E. Dihydroergocalciferol

391 A. Cholecalciferol, also known as 7-dehydrocholesterol, is the naturally occurring form of vitamin D in animals and human skin. It serves as the precursor for calcitriol, the active form of vitamin D. Ergocalciferol is the form of vitamin D obtained from vegetables.

Which of the following amino acids is the precursor of catecholamines such as dopamine, norepinephrine and epinephrine? A. Asparagine B. Glutamate C. Methionine D. Serine E. Tyrosine

393 E SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE.

Which of the following amino acids is purely ketogenic? A. Phenylalanine B. Tryptophan C. Tyrosine D. Isoleucine E. Leucine

397 E Purely ketogenic: Lys and Leu. Both ketogenic and glucogenic: Phe, Tyr, Ile, Trp (mnemonic: F-Y-I-W).

Arsenic does not inhibit an enzyme in this metabolic pathway? A. Pyruvate decarboxylation B. Citric acid cycle C. Oxidative phosphorylation D. Pyruvate dehydrogenase pathway E. None of the above

40 C. Arsenic inhibits the pyruvate dehydrogenase enzyme in the pyruvate decarboxylation pathway (Swanson conversion. It also inhibits alpha-ketoglutarate dehydrogenase in the TCA cycle.

Which of the following is a co-factor of glutathione peroxidase? A. Molybdenum B. Pyridoxine C. Selenium D. Copper E. Vitamin C

400 C.

Which of the following substances inhibits the Electron Transport chain via the Ubiquinol: Ferricytochrome Oxidoreductase Complex? A. Barbiturate B. Malonate C. Dimercaprol D. Cyanide E. Oligomycin

401 C. Dimercaprol (and Antimycin A) inhibits the Ubiquinol: Ferricytochrome Oxidoreductase Complex simply known as Complex III. Babiturate: Complex I; Malonate: Complex II, Cyanide Complex IV; Oligomycin: ATP synthase (Previous Board Ques)

Which of the following is true regarding Enzymes? A. First-order kinetics is followed when the substrate concentration is above Km B. Temperature does not affect the reaction rate C. The Km is directly proportional to the substrate affinity D. Vi is the substrate concentration at which Km is half the maximal Velocity E. Enzymes that follow the Michaelis-Menten kinetics presents with a hyperbolic curve?

402 E

What Glucose transporter is present in Erythrocytes? A. GLUT-1 B. GLUT-2 C. GLUT-3 D. GLUT-4 E. GLUT-5

403 A. GLUT1: Erythrocytes, brain, kidney, colon, placenta; GLUT2 Liver, pancreas, SI, kidney; GLUT-3 Brain, kidney, placenta; GLUT-4 Heart and skeletal muscle, adipose tissue; GLUT5: SI

What is the default product of fatty acid synthesis? A. Linoleic acid B. Arachidonic acid C. Formic acid D. Palmitic acid

428 D. Be thrilled with quick and simple questions like this =).

The rate-limiting step in the Krebs cycle involves the conversion of isocitrate to alpha-ketoglutarate. The enzyme responsible for this step is: A. Isocitrate dehydrogenase B. Alpha-ketoglutarate dehydrogenase C. Aconitase D. Succinate thiokinase

431 A. More often than not, you'll get clues from the question. Even without studying Krebs, the answer is already obvious from the question itself. MEMORIZE all the rate-limiting enzymes and steps.

What is the amino acid precursor of glutathione and GABA? A. Glutamate B. Glutamine C. Methionine D. Glycine

433 A. Must know the other important amino acid precursors: PHENYLALANINE --- tyrosine (another amino acid), L-dopa, dopamine, norepinephrine, epinephrine; TYROSINE --- thyroxine, melanin; TRYPTOPHAN --- niacin, serotonin, melatonin; METHIONINE --- homocysteine. (high yield)

The type of mutation which results in a new codon specifying a different amino acid which may or may not cause variation in protein function is known as: A. Frameshift B. Nonsense C. Missense D. Silent

437 C. Frameshift means there is deletion or addition of a base which results in protein products that are shorter than normal and hence usually non-functional. Non-sense, on the other hand, refers to formation of a new stop codon making the protein shorter and also non-functional. A silent mutation involves a new codon specifying the same amino acid and therefore has no effect in the protein function.

Most potent counter-regulatory hormone that stimulates gluconeogenesis A. Insulin B. Cortisol C. Growth hormone D. Epinephrine E. Thyroxine

44 B.

A newborn was brought to a clinic by her mother due to vomiting every after feeding. PE revealed that the newborn had severe jaundice and enlarged liver. NB screening result was positive for galactosemia and lactose-containing substances are removed from the diet. In this case, lactose is toxic to the NB because: A. Excess galactose shuts glucose metabolism B. Galactose is toxic even in little amounts C. Galactose is converted to galactitol D. Excess glucose accumulated in the blood E. Excess galactose is converted to sorbitol

442 C. Classic Galactosemia occurs in the absence of galactose 1-phosphate uridyltransferase resulting to accumulation of galactitol. The manifestations are vomiting and diarrhea after milk ingestion, hypoglycemia, liver disease and cirrhosis, lethargy and hypotonia and mental retardation.

A 1 year-old boy was seen at the ER with severe difficulty of breathing. His blood sugar was normal. Glycogen structure was normal although excessive concentrations in abnormal vacuoles in the lysosomes is found. He had also massive cardiomegaly and he died from heart failure. The most probable enzyme deficient in the patient leading to diagnosis is: A. glucose-6-phosphatase B. debranching enzyme C. branching enzyme D. acid maltase E. glycogen phosphorylase

447 D. Pompe Disease or Type II Gylcogen storage disease is caused by deficiency in acid maltase or lysosomal α1- 4 and α1:6 glucosidase. Manifestations include muscle hypotonia, death from heart failure by age 2

Key enzyme in amino acid metabolism which is responsible for release of nitrogen as free ammonia, for subsequent detoxification in the urea cycle: A. Glutamate dehydrogenase B. Pyruvate dehydrogenase C. Alpha-ketoglutarate dehydrogenase D. Succinate dehydrogenase E. Glutaminase

450 A. Through glutamate dehydrogenase, glutamate is oxidatively deaminated to liberate free ammonia.

In an adult, the energy requirement for protein is: A. 10 to 35% B. 15 to 30% C. 25 to 30% D. 20 to 35% E. 45 to 65%

454 A. Energy requirements in Humans: Fat=20 to 35%, Carbohydrate=45 to 65%, Protein=10 to 35%

In order to oxidize fatty acids through B-oxidation in the mitochondria, fatty acids must be ferried through the mitochondrial membrane by: A. Acetyl CoA B. Thiokinase C. Thiolases D. Carnithine E. Citrate

455 D. Carnithine shuttle transports fatty acids from cytoplasm to mitochondria which uses 2 ATPs in Beta exidation.

Gamma-glutamyl-cysteinyl-glycine is A. A potent anti-oxidant B. Needs pentose-phosphate pathway to be regenerated C. Similar to Vitamin E D. Both A and B E. AOTA

46 D. Gamma-glutamyl-cysteinyl-glycine is glutathionine. It is potent anti-oxidant and needs NADPH from PPP to be regenerated.

A 6 year-old girl was brought to the OPD due to skin breaks and blisters which noted to occur during minor scratching. This is a dystrophic form which is due to mutations affecting the structure of collagen type: A. Type I B. Type III C. Type IV D. Type V E. Type VII

460 E Epidermolysis bullosa is characterized by skin breaks and blisters as a result of minor trauma with mutations affecting the structure of Type VII collagen. Type I collagen is affected in osteogenesis imperfecta, Type III collagen in Ehlers-Danlos syndrome and Type IV collagen structure is affected in Alport syndrome.

Which of the following is a known inhibitor of complex I of the electron transport chain? A. amytal B. malonate C. Antimycin A D. cyanide E. None of the choices

461 A. Amytal is a complex I inhibitor, while others are inhibitors of the following: malonate - complex II; Antimycin A - complex III; cyanide - complex IV

The following are essential amino acids that are both ketogenic and glucogenic except: A. phenylalanine B. tyrosine C. tryptophan D. isoleucine E. None of the choices

469 B. all of the choices are both ketogenic and glucogenic, and all are essential amino acids except tyrosine.

Final common pathway by which electrons are passed to the mitochondria to generate ATP A. Glycolyis B. TCA C. ETC D. B-oxidation E. Uronic pathway

47 C.

Among the following pyrimidine bases, which one is present only in the RNA? A. cytosine B. thymine C. uracil D. guanine E. Adenine

475 C. Cytosine, uracil, and thymine are pyrimidine bases, but uracil is present only in RNA while thymine is present only in DNA. Adenine and guanine are purine bases.

In metabolic pathways, catabolic reaction is an example of: A. Endergonic reaction B. Exergonic reaction C. Amphibolic reaction D. A and B only E. B and C only

478 B. Catabolic reaction is an exergonic reaction. Anabolic reaction is an endergonic reaction. Amphibolic is the link between anabolic and catabolic reactions.

Which of the following statements about the urea cycle is FALSE? A. Urinary urea is increased by a diet rich in protein. B. The two nitrogen atoms that are incorporated into urea enter the cycle as ammonia and aspartate. C. ATP is not required for the reaction in which arginosuccinate is converted to arginine. D. Urea is produced directly by the hydrolysis of ornithine.

489 D. Urea is formed during the pathway wherein arginine is converted to ornithine.

Urine test for ketones detect: A. acetoacetate B. beta-hydroxybutyrate C. acetone D. all of the above

492 A. This is the reason why serum ketones are more accurate than urine ketones.

Which is NOT a feature of the genetic code? A. Each codon specifies only 1 amino acid. B. Tryptophan and methionine is encoded by only 1 codon. C. The genetic code is conserved throughout evolution. D. It is overlapping.

498 D. The genetic code is unambiguous, degenerate (except methionine and tryptophan), nonoverlapping/commaless, and universal.

Most of dietary fat are composed of A. TAG B. Free fatty acid C. Cholesterol D. Phospholipid E. Glycerol

50 A. 90% of dietary fats are composed of triacylglycerol

A deficiency in this micronutrient results in hypogonadism and decrease in adult hair whether axillary, facial, or pubic. A. copper B. zinc C. manganese D. selenium

500 B. Zinc deficiency results in delayed wound healing, hypogonadism, decrease in axillary, facial and pubic hair, dysgeusia and anosmia.

1. A sphingolipid which is present in high amounts in myelin sheath: A. Sphingomyelin B. Glycerol C. Lysophosphatidylcholine D. Cholesterol E. Phosphatidylinositol

501 A. Harper's 27th ed., 126. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE (board question, feb 2014)

3. The enzyme responsible for the yellow color of a maturing hematoma: A. Heme oxygenase B. Heme reductase C. Biliverdin reductase D. Glucoronosyl ttransferase E. a-aminolevulinate synthase

503 C. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Heme oxygenase - enzyme system responsible for catabolism of heme from all of the heme proteins Heme reductase Biliverdin reductase - reduces the methyne bridge b/w pyrrole III and pyrole IV of biliverdin to a methylene group to produce bilirubin a yellow pigment Katzung 27th ed., 287 Glucoronosyl ttransferase - catalyzes conjugation of bilirubin a-aminolevulinate synthase - rate-controlling enzyme in porphyrin biosynthesis in mammalian liver

6. Which of the following statements regarding enzymes is not true? A. Enzymes are protein catalysts that increase the velocity of a chemical reaction but are not consumed in the process. B. Isoenzymes like hexokinase and glucokinase are physically distinct versions of a given enzyme that catalyze the same reaction. C. Enzymes do not change the energy of the reactants and products and the equilibrium of the reaction. D. Enzymes are highly specific in the reactions they catalyze. E. Enzymes increase the free energy of activation.

506 E Enzymes lower the free energy of activation.

8. Which of the following substances increase the permeability of the inner mitochondrial membrane to protons causing a decrease in proton gradient and an increase in oxygen consumption with resultant production of heat but cessation of ATP synthesis? A. 2,4-dinitrophenol B. brown fat C. aspirin D. all of the above E. none of the above

508 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. All of them are uncouplers. First Aid 2013, p. 102.

13. Which of the following is not true regarding lipoproteins? A. Chylomicrons transport triglyceride and cholesterol from intestine to tissues following a meal. B. LDL transport cholesterol into the cells. C. VLDL transport endogenous triglyceride from liver to tissues. D. HDL is responsible delivering cholesterol back to the intestines for excretion. E. None of the above

513 D. HDL picks up cholesterol accumulating in blood vessels (reverse cholesterol transport) to the liver and streroidogenic tissues via scavenger receptor (SR-B1).

14. This is the most common lysosomal storage disease wherein there is a deficiency of glucocerebrosidase enzyme. Patient may present with hepatosplenomegaly, aseptic necrosis of femur and macrophages look like crumpled tissue paper microscopically. A. Niemann-Pick disease B. Gaucher's disease C. Taysachs disease D. Hurler's syndrome E. Hunter's syndrome

514 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Niemann-Pick- deficient in sphingomyelinase enzyme; Taysach's- deficient in hexosaminidase A; Hurler's- deficient in a-L- iduronidase, a mucopolysaccharidoses; Hunter's - Idoronate sulfatase deficiency

17. The following amino acids can be converted to glucose except: A. Lysine and Isoleucine B. Tryptophan and Tyrosine C. Isoleucine and Alanine D. Leucine and Lysine E. Alanine and Arginine

517 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE: Glycogenic Amino acids: Alanine, Arginine, Asparagine, Cysteine, Glutamate, Histidine, Methionine, Proline, Serine, Threonine, Valine Ketogenic: Leucine and Lysine Glycogenic and Ketogenic: Phenylalanine, Tyrosine, Isoleucine, Tryptophan (FYIW)

A noncompetitive enzyme inhibitor A. Decreases Vmax and increases Km. B. Decreases Vmax and has no effect on Km. C. Has no effect on Vmax or Km. D. Has no effect on Vmax and increases Km. E. NOTA

52 B. A noncompetitive inhibitor binds to the enzyme at a site other than the substrate binding site, so it has little measurable effect on the enzyme’s affinity for substrate, as represented by the Km. However, the inhibitor has the effect of decreasing the availability of active enzyme capable of catalyzing the reaction, which manifests itself as a decrease in Vmax.

What enzyme converts Norepinephrine to Epinephrine? A) Dopamine B-hydroxylase B) Dopa decarboxylase C) Norepinephrine hydroxylase D) Phenylethanolamine -N-Methyl transferase

526 D.

In glycogen, glucose residues form a straight chain via which of the following? A) a-1,4 linkages B) a-1.6 linkages C) a-1,4 linkages with glycogenin at the non-reducing end D) a-1,6 linkages with UDP-glucose at any end

540 A.

Sorbitol dehydrogenase is an enzyme which converts sorbitol to fructose. Aside from the liver, this enzyme is also found in significant quantities in the: A. Ovaries B. Retina C. Schwann cells D. Pancreas E. Seminal vesicles

548 E Remember that fructose is used by semen as fuel.

Collagen is rich in which of the following amino acids: A. Lysine B. Serine C. Threonine D. Leucine E. Proline

550 E Proline facilitates kinking.

Signs and symptoms similar to pellagra are seen in Hartnup disease due to impaired transport of this amino acid: A. Tyrosine B. Threonine C. Tryptophan D. Valine E. Cystine

553 C. Pellagra is due to niacin deficiency. Remember that tryptophan is required for niacin synthesis.

Too much of a good thing can be bad for you. Excessive ingestion of this vitamin for example can cause headache and nasuea related to increased CSF, hepatomegaly, thickening of long bones and hypercalcemia, and excessive dryness and desquamation of skin. A. Vitamin A B. Vitamin D C. Vitamin E D. Vitamin K E. Niacin

558 A.

Rate-limiting step in urea cycle A. CPS 1 synthase B. CPS 2 synthase C. Isocitarate dehydrogenase D. Both A and B E. AOTA

56 A. CPS 1 synthase - urea cycle CPS 2 synthase - pyrimidine synthesis Isocitarate dehydrogenase - TCA

Which of the following organs or tissues does NOT need to be supplied with glucose for energy production during a prolonged fast? A. Lens B. Brain C. RBCs D. Liver E. Cornea

57 D. Only the liver and kidneys can synthesize glucose by gluconeogenesis. All the other organs listed are dependent on provision of glucose from blood, either supplied by the diet or by gluconeogenesis in liver and the kidneys.

the irreversible inhibition of cyclooxygenase enzyme system in platelets by aspirin is by virtue of: a. acetylation b. hydroxylation c. sulfation d. conjugation

573 A. Acetyl salicylate causes acetylation of the COX enzyme rendering it ineffective permanently.

Denaturation is the disruption of a protein's structure (secondary structure and above). This could be accomplished by any of these mechanisms EXCEPT? A. Decreasing pH B. Increasing pH C. Cooling D. Addition of heavy metals E. Addition of detergents

590 C. Altering pH whether increasing or decreasing it disrupts the protein structure. However only heating will result in denaturation, cooling would decrease the velocity of the catalyzed reactions but the structure of the protein is unchanged.

A group of four cavers were rescued today after spending five days lost underground with no food. Which of the following metabolites were used for fuel by their bodies just before they were rescued? A. Glucose B. Glycogen C. Fatty Acids D. Ketone bodies E. Glycerol

595 D. Glucose is the main energy fuel in the well-fed state. Glycogen stores are only sufficient for 18-24 hrs. Prolonged fasting will make the body used ketones as its main energy fuel

What vitamin is required for the synthesis of niacin from typtophan? A. Thiamine B. Riboflavin C. Pantothenic acid D. Pyridoxine E. Cobalamin

628 D. Pyridoxine of B6 is required for the synthesis of niacin from tryptophan.

Which of the following statements about nitrogen metabolism is correct? A. Cysteine "spares" methionine; that is ingestion of cysteine reduces the need for methionine in the diet B. The enzyme glutamate dehydrogenase catalyzes the transamination of glutamate C. Creatine requires glycine, ornithine, and methionine for the synthesis of its carbon skeleton D. Formiminoglutamate (FIGLU) is an intermediate in glutamine degradation E. All of the above

634 A. because of the sulfur of methionine is used for cysteine synthesis, as cysteine increases in the diet, less methionine is required. Glutamate DH catalyzes the addition of ammonia to alpha ketoglutarate to form glutamate. For creatine synthesis, arginine, not ornithine, is required. FIGLU is produced during the degradation of histidine.

Hemoglobin A1C (HbA1C) is being used in clinics to monitor a diabetic patient's compliance in taking his/her medications. On what amino acid residue does glycosylation of erythrocytes occur? A. Glycine B. Alanine C. Valine D. Lysine E. Leucine

647 D. When blood glucose enters the erythocytes, it glycosylates the ξ-amino group of Lysine residues and the amino terminals of hemoglobin.

This vitamin deficiency may result secondary to decreased absorption of tryptophan, also known as Hartnup disease. A. Thiamine B. Riboflavin C. Niacin D. Pyridoxine E. Folic acid

679 C. Tryptophan is a precursor for synthesis of Niacin (Vit B3).

2. Which of the following amino acids are not found in glutathione? a. cysteine b. glutamic acid c. glycine d. aspartate e. all of the above

82 D.

The pH at which majority of amino acid exists in a form where it has an equal number of positive and negative charges and thus is electrically neutral is called the: A. pK1 B. pK2 C. pK1 + pK2 D. pIE. pH

1 D. A zwitterion is a molecule with a positive and a negative charge in different locations yielding to a net charge of zero for the whole molecule. The pI, or the isoelectric pH is the pH at which this isoelectric/zwitterion form of the amino acid predominates. Source: Harper 27th ed p.17

After a meal, insulin levels in the blood become elevated to effect which of the following changes in enzyme activity? A. Glucokinase is dephosphorylated and inactivated B. Glycogen synthase is dephosphorylated and activated C. HMG CoA synthase is phosphorylated and activated D. Acetyl CoA carboxylase is phosphorylated and inactivated E. A and B

10 B. Glucagon phosphorylates, insulin dephosphorylates. (My mnemonic is DIG-P) This results to either activation or inactivation of particular enzymes in certain pathways. Make sure you master this concept and which enzyme/pathways are activated or inactivated by insulin and glucagon. They can easily ask 5-10 different varieties of these sort of questions.

20. Which of the following vitamins is given to a child to prevent metaplasia of surface epithelium? a. A b. B c. C d. D e. E

100 A. Harper’s Biochemistry 28th edition p. 469

Further studies showed that the patient in the above case suffers from Familial Hypercholesterolemia Type IIa this defect is brought about by which mechanism: A. LCAT deficiency B. Defect in LDL-receptor C. Lipoprotein lipase deficiency D. Decreased production of apo-B48 and 100 E. Inefficient reverse cholesterol transport

106 B. Page 28 of Topnotch Handout. In Type II a Familial hypercholesterolemia there is a deficiency or defect in the LDL-receptors causing increased LDL. A and E are defects in Familial a-Lipoprotein deficiency/ Tangiers disease. C is seen in Type I Familial lipoprotein lipase deficiency. D is seen in Abetalipoproteinemia.

A 17 y/o Japanese male who is fond of eating sushi was noted to have diarrhea, abdominal pain, vomiting, weight loss, and fatigue. He was diagnosed to have D. Latum infestation, causing a deficiency in which of the following: A. Iron B. Folate C. Vitamin A D. Vitamin C E. Cobalamin

115 E Page 48 of Topnotch Handout. D. Latum infestation which is usually obtained from eating raw fish can cause a deficiency in Vitamin B12/cobalamin.

The first proponent of the double helix DNA model A. Watson-Crick B. Wilson-Crick C. Wilkins-Chargaff D. Wilkins-Crick E. Watson-Chargaff

134 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT

Which of the following vitamins has a protective effect by combating lipid peroxidation? A. Vitamin A B. Pyridoxine C. Ascorbic Acid D. Vitamin D E. Vitamin E

139 E SIMILAR TO PREVIOUS BOARD EXAM CONCEPT.

What is the principal cholesterol excreted in human feces? A. Cholic Acid B. Chenodeoxycholic acid C. Coprostanol D. Lithocholic acid E. None of the above

144 C. Cholic acid and chenodeoxycholic acid are primary bile acids secreted in bile, lithocholic acid is a secondary bile acid. Coprostanol is the primary cholesterol in the stool synthesized from cholesterol from the GIT by the gut bacteria.

RDL, a 17 year old female was brought to you due to stunted growth and recurrent fractures, a diagnosis of osteopetrosis was made, biopsy showed osteoclasts lacking carbonic anhydrase activity, what are the substrates of this enzyme? +A. H and sodium B. Potassium and HCO3- C. CO2 and HCl D. CO2 and H2O E. None of the above

159 D. CO2 and H2O are the substrates of carbonic anhydrase to form carbonic acid which in an aqueous solution dissociates into H ions and bicarbonate ions

7. Which of the following sugar molecules is an epimer of D-glucose at carbon number 2? A. fructose B. galactose C. mannose D. ribose E. maltose

167 C. mannose and glucose only differ structurally at carbon number 2

Sphingomyelin is an important constituent of myelin sheath of nerves. What is the backbone structure of sphingomyelin? A. Sphingosine B. Fatty Acid C. Palmitic acid D. oligosaccharide E. N-acetyl neuraminic acid

171 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE

Tay-Sach's disease is a lipid storage disease which can manifest as mental retardation, hypotonia and cherry red macula. Which of th following enzymes is deficient in the disease? A. Alpha-galactosidase B. ceramidase C. Beta-glucosidase D. Hexosaminidase A E. Beta-galactosidase

172 D. (alpha galactosidase: Fabry's disease); (Ceraminidase: Farbers); (beta-glucosidase: gauchers); (beta- galactosidase:Krabbe's disease)

LT, a 24 year old male, went to a blood donation center to donate blood. Upon examination, he found out that he is blood type B. Which of the following glycosphingolipids is found is his RBC? A.N-acetyl-galactosamine B. galactose C. N-acetyl-glucosamine D. B and C E. None

173 B. (type A: N-acetyl galactosamine) (Type B: galactose) (Type AB: both) (Type O:none)

Which of the following techniques involves the use of radioactive DNA probe binding to sample RNA and this is used to measure sizes and amounts of specific mRNA molecules? A. Southern Blot B. Western Blot C. Northern Blot D. Eastern Blot E. ELISA

174 C. Southern blot is for DNA; Northern blot is for RNA; Western blot is for proteins

During transciption, a mutation happened which changed the codon UGG-GGU-UGG-UGG-UGA to UGG-GGU-UGG-UGA-UGA. What kind of mutation happened? A. Silent mutation B. Missense mutation C. Frameshift mutation D. Nonsense mutation E. None of the above

175 D. UGG was changed to UGA which is one of the stop codons

Lead poisoning causes several manifestations like basophilic stipling of RBC, headache, memory loss, nausea, abdominal pain, neuropathy, and lead deposits in some organ systems. Which of the following enzymes is/are inactivated by lead? A. ALA dehydratase B. Ferrochelatase C. ALA synthase D. Uroporphyrinogen E. A and B

176 ELead inhibits FALAD (ferrocheletase and ALA dehydratase)

Which of the following statements about DNA is false? A. DNA serves as storage of genetic information. B. The most common form is the B-DNA C. The 2 strands of the double helix are held in register by H-bond D. Watson, Crick and Wilkins proposed the double-stranded DNA molecule model in the 1950s E. Adenine pairs with guanine while cytosine pairs with thymine

187 E In DNA, adenine pairs with thymine while guanine pairs with cytosine.

Which of the following functions as the storage of genetic material? A. protein B. lipid C. nucleic acid D. carbohydrate E. Both A and C

190 C. giveaway question last boards

Which of the following is the main glucose transporter in the brain? A. Glut 1 B. Glut 2 C. Glut 3 D. Glut 4 E. Glut 5

191 C. Glut 1 and Glut 3 are both found primarily in the brain. Glut 1 is the most abundant and is expressed in high levels in erythrocytes and endothelial cells of the blood brain barrier, whereas Glut3 is expressed mostly in neurons. So yes, I think Glut 3 is the better answer between the two since it is particularly present in the parenchyma of the brain.

Which of the following relies on anaerobic glycolysis as source of energy? A. RBC B. Renal medulla C. Retina D. All of the above E. A and C

192 D. Glycolysis in erythrocytes always terminates in lactate, because the subsequent reactions of pyruvate oxidation are mitochondrial, and erythrocytes lack mitochondria. Other tissues that normally derive much of their energy from glycolysis and produce lactate include brain, gastrointestinal tract, renal medulla, retina, and skin.

Amyloid seen in Alzheimers is an example of what level of protein structure? A. Primary B. Secondary C. Tertiary D. Quaternary E. All of the above

195 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE.

This is the most important product of the pentose phosphate pathway. A. ATP B. NADPH C. Ribose-5-phosphate D. GTP E. NADH

210 C. Ribose-5-phosphate is a precursor of the nucleotides DNA and RNA.

What functional group is absent in DNA rendering it more stable in alkali solutions? A. 1-carbonyl group B. 2-hydroxyl group C. 1-phosphate group D. 2-sulfate group E. 1-alkyl group

212 B. In contrast to RNA, DNA has no 2-hydroxyl group. Hence, its name 2-deoxyribonucleic acid.

which of the following correctly describes Glucokinase? A. Found in hepatocytes B. High affinity to glucose C. Low Vmax D. Can be inhibited by glucose 6 phosphate E. None of the above

224 A. Glucokinase is predominantly found in the liver and beta cells of the pancreas. It has a higher Km compared to Hexokinase, therefore it only phosphorylate glucose during high glucose load ( after meal consumption). It has a high Vmax such that it effectively remove glucose from portal blood. furthermore, it is not allosterically inhibited by its product Glucose 6 phosphate. all the other choices describes Hexokinase which is most tissues of the body.

A 1 month old male presents with severe hypotonia and cardiomegaly, which enzyme deficiency most likely represent this type of glycogen storage disease. A. Glucose 6 phosphatase B. Acid maltase C. Glycogen debranching enzyme D. muscle phosphorylase E. none of the above

229 B. Glycogen storage disease type II aka Pompe disease is a fatal condition most commonly manifested during the first month of life. It primarily affects the heart muscle causing cardiomyopathy. This is secondary to deficiency of acid maltase of alpha 1-4 glucosidase.

what type of cell is affected in terms of glucose transport if there is an insulin deficiency states? A. Neurons B. Pancreatic acinar cells C. Adipocytes D. Erythrocytes E. Hepatocytes

234 C. Among the GLUT transporters, it is only GLUT 4 that is insulin dependent. It is primarily distributed in two major cell population: the adipocytes and myocytes. Pancreatic acinar cells particularly beta cells and hepatocytes uses Glut 2 receptors, Neuorns and RBC uses GLut 1 receptors.

Which of the following precursors is the one converted into vitamin D3 in the skin by activation with the help of sunlight? A. 7-dehydrocholesterol B. 3-hydroxycholesterol C. 25-dehydrocholesterol D. 1,25 - dihydroxycholecalciferol E. pregnenolone

242 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE, The presence of this compound in human skin enables humans to manufacture vitamin D3 from ultraviolet rays in the sun light, via an intermediate isomer pre-vitamin D3.

Which of the following characterizes the enzyme glucokinase? A. Low Vmax B. High Km C. Inhibited by glucose-6-phosphate D. Present in most tissues E. All of the above

281 B. Characteristics of Glucokinase: 1. Present only in liver parenchymal cells and islet cells of pancreas, 2. inhibited by fructose-6-phosphate, 3. High km (low affinity), 4. high vmax, .

Bile acid conjugation with glycine or taurine takes place in which organelle? A. golgi apparatus B. endoplasmic reticulum C. cytosol D. peroxisomes E. none of the above

327 D. Harper Biochemistry 28th edition p.229

Triacylglycerols comprise the majority of which lipoprotein? A. Chylomicrons B. VLDL C. IDL D. LDL E. HDL

376 A. CM 90%; VLDL 60%; LDL 8%; HDL 5% triacylglycerols Lippincott 5th pg 232

Carbamoyl phosphate synthetase I is the rate-limiting enzyme in the urea cycle. This enzyme is found in which part of the cell? A. Cytosol B. Mitochondria C. Golgi body D. Smooth ER E. Peroxisome

394 B.

A Gold olympic medalist for boxing has suffered an injury and was eventually admitted, you were his admitting physician and upon ordering his diet requirements you computed it according to his average dietary energy intake which is: A. 25 kcal/kg/day B. 30 kcal/kg/day C. 35 kcal/kg/day D. 40 kcal/kg/day E. 45 kcal/kg/day

405 D. Energy intake=Energy expenditure. Sedentary:30; Moderately active:35; Very Active:40.

Glucose-6-phosphate dehydrogenase deficiency is characterized by hemolytic episodes secondary to poor defense against oxidative stress. The most common precipitating factor to hemolysis among these patients is: A. Drugs B. Diet (fava beans) C. Infection D. Spontaneous, undetermined

422 C.

In the intestine, primary bile acids are dehydroxylated to form secondary bile acids. Which of the following is a secondary bile acid? A. Cholic acid B. Cholic acid + taurine C. Chenodeoxycholic acid D. Lithocholic acid

429 D. Just remember, cholic acid and chenodeoxycholic acid are primary bile acids, whereas deoxycholic and lithocholic acids are secondary bile acids. When primary bile acids are conjugated with either taurine or glycine, they become bile salts. Secondary bile acids are formed when bacteria act upon (deconjugate and dehydroxylate) the bile salts.

Tangier's disease is characterized by: A. Hypo-alphaprotenemia B. Deficiency of LDL cholesterol C. Affected people have xathomas D. Common genetic condition E. NOTA

43 A. Tangier's Disease is a rare genetic condition due to a deficiency of HDL. This disease is also known as familial alpha lipoprotein deficiency. People affected often have mild hypertrigylceridemia, neuropathy and premature atherosclerosis

Which RNA viral genome encodes a precursor protein that is cleaved to form a protein core: A. tat B. gag C. pol D. rev E. env

449 B. gag gene encodes a precursor protein that is cleaved to form a protein core, tat gene is for activation of transcription of viral genes, pol encodes for enzymes reverse transcriptase, protease intregrase and ribonuclease, env codes for envelope glycoproteins, rev is for transport of late mRNAs to cytoplasm

The normal glycogen stores last for how long? A. 6 hours B. 18 hours C. 26 hours D. 36 hours E. 48 hours

45 B.

A defect in peroxisomal activation of very long-chain fatty acid which leads to its accumulation in the blood and tissues: A. Zellweger syndrome B. X-linked adrenaleukodystrophy C. Refsum's Disease D. Jamaican vomiting sickness E. Fatty liver

452 B. X-linked adrenaleukodystrophy occurs with defect in peroxisomal activation of VLCFA leading to its accumulation in the blood and tissues. Initial abnormalities are apathy and behavioral change. Late findings include visual loss, spasticity, ataxia and death a few years after onset of neurologic symptoms. Zellweger syndrome is a rare inheroted absence of peroxisomes in tissues. Refsum's disease is a defect which results in accumulation of phytanic aid. Jamaican vomiting sickness is caused by eating unripe fruit of akee tree which contains hypoglycin. Fatty liver is due to alcoholism which leads to fat accumulation in the liver.

It is the average daily dietary intake level that is sufficient to meet the requirements of >95% of all individuals in a life stage and gender group: A. Dietary requirement B. Total caloric requirement C. Recommended daily allowance D. Total energy requirement E. Estimated average requirement

453 C. Recommended Daily Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the requirements of >95% of all individuals in a life stage and gender group.

Which of the following is an essential fatty acids? A. Linoleic acid B. isoleucine C. phenylalanine D. valine E. All of the above

467 A. linoleic, linolenic and arachidonic acid are the essential fatty acids. Other choices are essential amino acids.

In the Landsteiner ABO blood system, what determines specificity of blood type A? A. N-acetyl-galactosamine B. galactose C. N-acetyl-glucosamine D. A and B E. All of the choices

470 A. type A= N-acetyl-galactosamine; type B = galactose; type AB = N-acetyl-galactosamine and galactose

Approximately, proteins comprised what percentage of energy requirements in human? A. 10-25% B. 45-60% C. 20-35% D. 40-45% E. 50-55%

472 A. 10-35% = protein; 20-35% = fat; 45-65% = carbohydrates

What is the fat soluble vitamin that is considered the most toxic vitamin? A. Vitamin A B. Vitamin D C. Vitamin E D. Vitamin K E. Vitamin B

473 B. Vit. D is the most toxic vitamin while Vitamin E is the least toxic vitamin.

What is the smallest type of RNA? A. tRNA B. mRNA C. rRNA D. snRNA E. None of the choices

477 A. tRNA is the smallest RNA. mRNA is the largest RNA. rRNA is the most common type of RNA. snRNA is a subset of RNA for gene regulation.

An excess of this vitamin causes sensory neuropathy: A. Vitamin A B. Vitamin B C. Vitamin C D. Vitamin D

481 B. Ironically, intake of pyridoxine (B6) which prevents peripheral neuropathy can result in sensory neuropathy with altered sensation of touch and pain if taken in excess.

Which of the following is a ketogenic amino acid? A. isoleucine B. valine C. lysine D. alanine

487 C. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Only leucine and lysine are purely ketogenic. Isoleucine gives rise to both ketogenic and glucogenic fragments.

12. These are compounds that are mirror images of each other. A. isomers B. anomers C. epimers D. enantiomers E. All of the above

512 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE.( 2 questions of this type) Isomers - compounds that have the same chemical formula but different structures. Epimers are compounds that differ in the 3-d configuration around only one specific carbon atom with the exception of the carbonyl carbon. Enantiomers/optical isomers/stereoisomers- are pairs of structures that are mirror images of each other and are designated as D- and L-sugars. Anomers are convertible between a linear and a ring form.

16. Which of the following regarding glycogen is not true? A. In the muscle, the role of glycogen is to provide free glucose for export to maintain the blood concetration of glucose. B. Glycogen is the major storage carbohydrate in animals. C. Glycogenolysis is not the reverse of glycogenesis, but is a separate pathway. D. Insulin inhibits glycogenolysis and stimulates glycogenesis. E. McArdle's syndrome is a glycogen storage disease presenting with poor exercise tolerance and decreased blood lactate after exercise

516 A. Harper's 27th ed., 161. In the liver the role of glycogen is to provide free glucose for export to maintain the blood concentration of glucose; in muscle, the role of glycogen is to provide a source of glucose 6-phosphate for glycolysis in response to the need for ATP for muscle contraction.

A 3-month-old boy is brought for a well-child examination. He has poor head control. Examination shows generalized hypotonia. The point of maximal impulse is at the left anterior axillary line. The liver edge is palpated 4 cm below the right costal margin. The spleen is not palpable. Which of the following is the most likely diagnosis? A) Congenital muscular dystrophy B) Glycogen storage disease, type II (Pompe's disease) C) GM1 gangliosidosis D) Infant botulism

523 B.

A molecule of palmitate will yield how many ATP? A)12 B) 38 C) 39 D) 129

527 D.

A 25-year-old man eats 20 raw eggs a day to increase protein for his bodybuilding routine. This unusual diet affects the activity of which of the following enzymes? A) Acetyl-CoA carboxylase B) Acyl-CoA dehydrogenase C) Fatty acid synthase D) Fatty acid thiokinase

533 A. Raw eggs >> biotin deficiency >> biotin cofactor for carboxylation reactions

Some humans are unable to generate NADPH from glucose metabolism but are able to synthesize ribose from fructose-6-phosphate. Which of the following enzymes are essential? A) G6PD B) Glutathione reductase C) Enolase D) Transketolase

535 D.

Which of the following is not a characteristic of the genetic code? A) It is a triplet code B) It is nonoverlapping and without punctuation C) It is degenerate in that one codon may code for more than one amino acid D) It is universal

538 C. one amino acid is translated by a codon = unambiguous; degenerate = one amino acid may be generated by more than one codon

Humans can't synthesize Vitamin C due to the absence of this enzyme A. Gulonolactone reductase B. Gulonolactone oxidase C. Gulonolactone ligase D. Gulonolactone synthase E. NOTA

54 B. The inability of humans to synthesize L-ascorbic acid is known to be due to a lack of L-gulono-gamma- lactone oxidase, an enzyme that is required for the biosynthesis of this vitamin.

Which of the following immunoglobulins opsonizes bacteria making them easier to phagocytose? A. IgE B. IgM C. IgG D. IgA E. IgD

543 C. Main antibody in the secondary response. Also fixes complement, which enhances bacterial killing, and neutralizes bacterial toxins and virus (Harper's p.594)

A 28/F, whose partner was recently diagnosed with HIV-AIDS, comes in and requests to be tested for the presence of HIV. To confirm an HIV infection, you would need to order a test which employs: A. Enzyme linked immunoassay B. Genomic outhern blot C. Northern blot D. Western blot E. VNTR analysis

555 D.

The major pathway of amino groups disposal in human is by: A. Urea B. Ammonia C. Creatinine D. Uric acid E. AOTA

58 A.

Which compounds act as inhibitors for Cytochrome Oxidase (Complex IV) of the Electron Transport Chain? A. CO B. CN C. H2S D. All of the Above E. None of the Above

581 D. All compounds are inhibitors of cytochrome oxidase.

In the formation of oleic acid, aside from enzymes located in the cytoplasm which organelle is needed for its synthesis? A. Peroxisomes B. Lysosomes C. Endoplasmic Reticulum D. Golgi Bodies E. Mitochondria

588 C. The end of fatty acid synthesis in the cytoplasm is the formation of the 14-C palmitic acid. Further elongation can be done in both the SER and mitochondria but insertion of double bonds, such as in Oleic acid can only be done in the ER. Peroxisomes are needed to oxidize fatty acids with double bonds.

A 25 yr old obese person had just ate one cup of fried rice, 2 pieces of fried chicken and a mixed berry shake. Which enzymes are dephosphorylated and active? A. Hexokinase B. Phosphofructokinase-1 C. Glucose-6-phosphatase D. Fructose 1,6-bisphophatase E. Glycogen phosphorylase

594 B. The person is in the well-fed state so we know that the metabolic pathways active are glycolysis and glycogenesis and not gluconeogenesis and glycogenolysis which are active in the fasting state. Hexokinase is not the rate-limiting step of glycolysis and is not subject to phosphorylation and dephosphorylation so the answer is PFK-1, the rate limiting step of glycolysis.

Which precursors of nucleotide synthesis is necessary for both purine and pyrimidine synthesis? A. Glutamine B. Aspartic acid C. Carbon dioxide D. All of the above E. None of the above

597 D. All are needed for either purine or pyrimidine synthesis. For purine synthesis, there is the addition of glycine and tetrahydrofolate as necessary components.

What is known as the Central Dogma of Molecular Biology? A. The Genetic Code has been conserved from the early stages of evolutions with only slight changes in the manner of which the code is translated. B. DNA is replicated semi-conservatively with the daughter DNA strands containing half of the original strands. C. The Genetic Code is specific, universal, degenerate/redundant and non-overlapping. D. Southern blot is used to identify DNA, Northern blot to identify RNA and Western blot to identify proteins E. DNA is replicated in the nucleus, transcribed to mRNA, and then translated to proteins in the ribosomes.

599 E The central dogma involves DNA replication to form copies of DNA, DNA transcription to mRNA. mRNA serves as a template for the translation of proteins.

Which of the following amino acids lacks an amino group in its structure? A. Histidine B. Arginine C. Tryptophan D. Proline E. None of the above

608 D. Proline has an imino group in its structure.

Your patient has muscular weakness and degeneration of the optic nerve. Your tentative diagnosis is Leber’s hereditary optic neuropathy. If this is the correct diagnosis, which of the following pathways will contain the defect? A. tricarboxylic acid cycle B. electron transport chain C. glycolysis D. gluconeogenesis E. pyruvate dehdyrogenase multienzyme complex

610 B. Leber's hereditary optic neuropathy is caused by an abnormality involving complex III of ETC. This is characterized by acute onset of unilateral visual loss which may become bilateral.

Which of the following enzyme/s involved in heme synthesis is/are inhibited by lead intoxication, thereby causing anemia? A. aminolevulinic acid synthase B. aminolevulinic dehydratase C. ferrochelatase D. A and B E. B and C

617 E Lead inhibits ALA dehydratase and ferrochelatase.

Water is considered a dipolar molecule because? A. It can act both as a proton donor and a proton acceptor B. It has a partial positive and negative charges unequally distibuted in its structure C. It is made up of two elements- oxygen and hydrogen D. it can exist in a solid (ice) as well as the liquid state E. all of the above

624 B. water is a dipole- a molecule with electrical charge distributed asymmetrically it its structure.

What enzyme converts Norepinephrine to Epinephrine? A. Dopamine B-hydroxylase B. Dopa decarboxylase C. Norepinephrine hydroxylase D. Epinephrine decarboxylase E. Phenylethanolamine -N-Methyl transferase

627 E PNMT converts NE to E, with SAM (S adenosyl methionine) which adds CH3 and serves as a donor for the conversion.

A molecule of palmitate will yield how many ATP? A. 12 B. 38 C. 39 D. 126 E. 129

637 E

α1-antitrypsin is said to be a protective factor against developing emphysema. What proteolytic enzyme does this substance inhibit? A. Fibrillin Kinase B. Desmosinase C. Elastase D. Elastinase E. Protease

648 C. Elastase destroys alveolar walls, resulting to emphysema. Î'1-antitrypsin regulates this enzyme and serves as a protection.

Lactose is from? A. Glucose + Glucose B. Galactose + Glucose C. Galactose - Glucose D. Galactose - Fructose E. Galactose + Maltose

652 B. It is a common mistake that medical students believe that Galactose is the dissacharide form of Lactose (which is the other way around). Lactose is the condensation product of Galactose plus Glucose. Galactose is only a monosaccharide, just like Glucose.

The following are the only ketogenic amino acids? A. Lysine, Leucine B. Isoleucine, Lysine C. Tyrosine, Methionine D. Leucine, Arginine E. None

665 A. The only ketogenic amino acids are Leucine and Lysine. Ile, Thr, Phe, Tyr and Trp are both ketogenic and glucogenic. Others are purely glucogenic.

This process occurs both in the cytoplasm and mitochondria: A. Glycolysis B. Heme synthesis C. B-oxidation of fatty acids D. ketogenesis E. None of the above

670 B. Processes that occur both in the cytoplasm and mitochondria includes Heme synthesis, Urea cycle and Gluconeogenesis.

Major reactants for heme synthesis includes: A. Glutamine, glycine, aspartate B. Aspartate, glutamine C. 2 acetyl CoA D. Glycine, succinyl CoA E. None

677 D. Glutamine, glycine and aspartate are the reactants for purine synthesis, aspartate and glutamine for pyrimidine synthesis, acetyl CoA for FA synthesis.

There are several types of mutation which involves any permanent heritable change in the DNA base sequence of an organism. What type of mutation causes a possible decrease in protein function because the new codon specifies for a different amino acid? A. Silent B. Missense C. Nonsense D. Frame shift

687 B. Answer: B. Missense (Biochemistry, Topnotch Handouts)

Which of the following conditions involve severe diminution or absence of most oxidoreductases of the respiratory chain as this affects all complexes of the ETC? A. MELAS B. Fatal Infantile Mitochondrial Myopathy C. Leber's Hereditary Optic Neuropathy D. Kearns-Sayre Syndrome

689 B. Answer: B. Fatal Infantile MitoChondrial Myopathy (Biochemistry, Topnotch Handouts)

Hepatocytes deliver ketone bodies to the circulation because they lack which of the following enzymes? A. Beta-hydroxybutyrate dehdrogenase B. Hydroxymethyglutaryl-CoA-lyase C. Hydroxymethylglutaryl-CoA-synthetase D. Succinyl-CoA-acetoacetate-CoA-tranferase E. Beta-ketothiasolase to hydrolyze acetoacetyl-CoA

695 D. Succinuylo CoA Acetoacetate CoA transferase is the long name of thiophorase which is an enzyme not found in the liver

There is but a single enzyme-catalyzed reaction in the human body known to generate carbon monoxide as one of its products. Which of the following enzymes represents the CO-producing reaction? A. Biliverdin reductase B. Coproporphyrinogen oxidase C. Heme oxygenase D. Protoporphyrin oxidase E. Uroporphysin decarboxylase

699 C. Heme is oxidized, w/ heme ring being opened by endoplasmic reticulum enzyme, heme oxygenase.

What step of the Krebs cycle utilizes substrate level phosphorylation? A. Succinate to Fumarate B. Succinate to Oxaloacetate C. Alpha keto glutarate to Succinyl CoA D. Fumarate to Malate E. None of the above

71 E The Krebs cycle has only 1 step that uses substrate elvel phosphorylation to produce 1 mol of GTP namely Succinyl-Coa to Succinate by succinate thiokinase.

What lipoprotein is responsible for reverse cholesterol transport? A. Chylomicron B. VLDL C. LDL D. HDL E. IDL

75 D. HDL or the good cholesterol mediates reverse cholesterol transport from periphery to liver.

If 20% of DNA consists Guanosine nucleotides, how many percent are thymidine nucleotides? A. 20% B. 30% C. 40% D. 50% E. Cannot be identified from given information

8 B. According to Chargaff’s rule, the concentration of A nucleotides equals T nucleotides while C nucleotides equals G nucleotides. 100% - 20% (G) â€" 20%(C) = 60% (A+T) 60% / 2 = 30%

8. Which of the following is NOT induced by insulin in the regulatory and adaptive enzymes associated with carbohydrate metabolism? a. PFK 1 b. pyruvate carboxylase c. pyruvate kinase d. glucokinase e. pyruvate dehydrogenase

88 B. Harper’s Biochemistry 28th edition p. 168

17. A 32 year old female presented with hepatic encephalopathy and Kayser Fleischer rings. Which of the following enzymes contain copper? a. amine oxidase b. superoxide dismutase c. cytochrome oxidase d. tyrosinase e. all of the above

97 E Harper’s Biochemistry 28th edition p. 573

Smith-Lemli-Opitz syndrome is a common autosomal recessive multiple malformation syndrome. In this syndrome there is a deficiency in what enzyme? A. HMG-CoA reductase B. Acetyl-CoA acetyltransferase C. 3-hydroxy-3-methylglutaryl-CoA reductase D. 7-dehydrocholesterol reductase E. 3-hydroxy-3-methylglutaryl-CoA synthase

101 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Pathway on page 24 of Topnotch Handout. Smith-Lemli-Opitz syndrome (SLOS) is a well-known malformation syndrome with principal characteristics of psychomotor and growth retardation, cleft palate, hypospadias, postaxial polydactyly, and a distinctive craniofacial appearance consisting of microcephaly, ptosis, inner epicanthal folds, anteverted nares, and micrognathia. Mutations in the DHCR7 gene cause Smith-Lemli-Opitz syndrome.The DHCR7 gene provides instructions for making an enzyme called 7-dehydrocholesterol reductase. This enzyme is responsible for the final step in the production of cholesterol.

Which of the following is the rate limiting step in catecholamine synthesis? A. DOPA decarboxylase B. Dopamine hydroxylase C. Tyrptophan hydroxylase D. Phenethanolamine N-methyltransferase E. Tyrosine hydroxylase

102 E SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Pathway on page 31 of Topnotch Handout. The rate limiting step is Tyrosine hydroxylase.

Sanfilippo syndrome is one of the autosomal recessive mucopolysaccharidoses. It is characterized by mental retardation, hyperactivity and eventual loss of motor function. Each of the 4 types has a specific deficiency in the following enzymes, EXCEPT: A. Iduronate sulfatase B. heparan sulfamidase C. N-acetylglucosaminidase D. N-acetylglucosamine sulfatase E. N-acetylglucosamine

103 A. Page 44 of Topnotch Handout. Iduronate sulfatase is a deficiency in Hunters syndrome not in Sanfilippo.

Which of the following is part of the Electron transport chain and is also found in the Tricarboxylic acid pathway: A. NADH dehydrogenase B. Succinate dehydrogenase C. Ubiquinol:ferricytochrome oxidoreductase D. Cytochrome oxidase E. Cytochrome a/a3

104 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Page 6 of Topnotch Handout. Succinate dehydrogenase is the enzyme in converting succinate to fumarate in the Kreb's cycle and its product is FADH2. It is also known as Complex II of the ETC.

A 27 y/o female patient went in for an executive check up. Laboratory results showed elevated LDL. Which statement is true regarding LDL.: A. Transports cholesterol from the peripheral tissues to the liver. B. Delivers cholesterol to steroidogenic tissues via SR-B1 C. Taken up by tissues through receptor mediated endocytosis D. Shuttles apo-CII and apo-E in blood E. Mediates uptake of chylomicron remnant

105 C. Page 27 of Topnotch Handout. LDL binds to specific receptors on extrahepatic tissues and on the liver where they are endocytosed. A,B and D are functions of HDL. E is a function of Apo-E

A 70 y/o male was brought to the ER presenting with severe congestive cardiac failure. He has been unwell for about a week and has been vomiting for the previous 5 days. He was on no medication. He was hyperventilating and was very distressed. His vital signs are: BP 80/60, HR 85, RR 30. ABG showed pH 7.58, pCO2 21 mmHg, pO2 154 mmHg, HCO3 14 mmol/l How will his current condition affect the Oxygen saturation curve of hemoglobin : A. The oxygen binding curve will assume the shape of a hyperbola similar to myoglobin B. There will be a rightward shift of the oxygen binding curve C. The position of the oxygen binding curve will not be altered in any way D. There will be a leftward shift of the oxygen binding curve E. Both A and C

107 D. Page 35 of Topnotch Handout. The patient is in Respiratory alkalosis in response to the dyspnea hence there will be a shift to the left of the oxygen binding curve. pH: pH is greater than 7.44 so an alkalaemia is present. The cause is an alkalosis Pattern: pCO2 & bicarbonate are both low suggesting either a metabolic acidosis or a respiratory alkalosis. As we already know an alkalosis is present then the primary disorder is a respiratory alkalosis. Asessing the compensation for a respiratory alkalosis (using rule 4 - "the 5 for 10" rule): The expected HCO3 is (24 - 10) = 14. Formulation: respiratory alkalosis

Alpha-tocopherol has the following functions: A. Protects membrane lipids from peroxidation B. Promotes epithelial cell proliferation and differentiation C. Increases calcium reabsorption in kidneys and bone resorption D. Used as co-factors in redox reactions E. Used as cofactor for acyl transfers

109 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Page 47 of Topnotch Handout. Alpha tocopherol is also known as Vitamin E. It functions as an antioxidant in the lipid phase, protects membranes from peroxidation and prevents oxidation of LDL. B is a function of Vitamin A. C is a function of Vitamin D. D is a function of Vitamin B2/Riboflavin. E is a function of Vitamin B5/Panthotenate.

Which is the main source of NADPH for Lipogenesis? A. Pentose Phosphate Pathway B. Krebs Cycle C. Urea Cycle D. Gluconeogenesis E. A and C

11 A. NADPH is utilized in many pathways in the cell such as lipogenesis, nucleic acid metabolism, and even in the pathways utilized by the innate immunity. There are 2 sources of NADPH â€" the Pentose phosphate pathway and the malic enzyme. The PPP is most significant. Source: Harper 27th ed p199

The importance of the Glucose Alanine cycle in the muscle in relation to amino acid metabolism is that: A. It is the mechanism by which excess nitrogen from muscles is transfered to the liver by transamination of pyruvte B. It is used for the synthesis of glucose in the muscle to replenish energy supply of the liver C. The carbon skeletons of alanine will be transaminated to pyruvate for glycolysis D. Pyruvate is reduced to lactate which is eventually transported to the liver E. All of the above

110 A. Page 39 of Topnotch Handout. The glucose alanine cycle is used for the removal of excess nitrogen from peripheral tissues through alanine. The excess nitrogen will reach the liver through transamination of pyruvate to produce alanine (occurs in the muscle) then in the liver, alanine is converted back to pyruvate which may undergo gluconeogenesis and is transorted back to the muscles.

Which of the following is a true statement regarding the Krebs-Henseleit cycle : A. It is the final common pathway for the aerobic oxidation of ALL nutrients B. It provides majority of ATP for energy C. It occurs in the inner mitochondrial membrane D. It is a pathway for removal of nitrogenous waste in the body E. Both A and B are correct

111 D. Page 39 of Topnotch Handout. Krebs-Henseleit cycle is also known as the Ornithine or Urea cycle, which functions in the removal of nitrogenous waste products in the body. A and B are both true for Kreb's cycle. C is true for the ETC.

A 25 y/o male was diagnosed to have staghorn calculi. This condition may be due to a common inherited defect of renal tubular amino acid transporter for the following amino acids in the PCT of the kidneys, except: A. Arginine B. Lysine C. Ornithine D. Cystine E. Cysteine

113 E Page 41 of Topnotch Handout. Cystinuria is a common inherited defect of renal tubular amino acid transporter for cystine, ornithine, lysine and arginine in the PCT of the kidneys. Excess of cystine in the urine may lead to precipitation of cystine kidney stones and cause staghorn calculi.

Fats are the best storage form of energy because they have ___________ energy content : A. 6 kcal/gram B. 7 kcal/gram C. 8 kcal/gram D. 9 kcal/gram E. 10 kcal/gram

114 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Page 46 of Topnotch Handout. Fats have 9 kcal/gram energy content. Carbohydrates, proteins and ketones contain 4 kcal/gram, while ethanol contains 7 kcal/gram.

A 50 y/o male patient with colorectal cancer was given Fluorouracil. This is a pyrimidine analog drug which acts on rapidly dividing cancerous cells and they undergo cell death via thymineless death. Hence this drug is known to act on the enzyme in the De Novo Pyrimidine synthesis necessary for the: A. Synthesis of carbamoyl phosphate B. Methylation of deoxyuridine monophosphate to form thymidine monophosphate C. Formation of orotidine monophosphate D. Synthesis of UTP and CTP E. All of the above

116 B. Page 51 of Topnotch Handout. 5-FU acts in several ways, but principally as a thymidylate synthase (TS) inhibitor. Interrupting the action of this enzyme blocks synthesis of the pyrimidine thymidine, which is a nucleoside required for DNA replication. Thymidylate synthase methylates deoxyuridine monophosphate (dUMP) to form thymidine monophosphate (dTMP). Administration of 5-FU causes a scarcity in dTMP, so rapidly dividing cancerous cells undergo cell death via thymineless death.

A 7 month old infant presents with presented with fever and paralysis of his left arm 3 months after receiving his third oral poliovirus vaccine. Past history included chronic thrush presenting in the absence of antibiotic therapy or breastfeeding at 3 months, chronic diarrhea from 4 months, and recurrent otitis media. He was at the 90th percentile for height and weight, similar to his parents. He was noted to have poor feeding and poor weight gain. This is characteristic of SCID: A. Adenosine deaminase deficiency B. HGPRT deficiency C. Low activity of orotidine phosphate decarboxylase D. x-linked recessive disorder caused by deficiency of ATP-dependent membrane transporter for copper E. Hexosaminidase deficiency

117 A. Page 52 of Topnotch Handout. Adenosine deaminase deficiency leads to severe combined immunodeficiency due to increased levels of dATP inhibiting ribonucleotide reductase and inhibiting formation of deoxyribonucleotides. B is for Lesch- Nyhan syndrome. C is seen in Orotic aciduria. D is for Menkes syndrome. E is in Tay-sachs.

Cyanide inhibits which of the following complex of the electron transport chain? A. NADH Q oxidoreductase B. Q cytochrome c oxidoreductase C. Cytochrome C oxidase D. Succinate Q reductase E. None of the above

12 C. Inhibitors: Complex I â€" Barbiturates Complex II â€" Malonate Complex III â€" Antimycin A and dimercaprol Complex IV â€" H2S, Cyanide, CO Source: Harper 27th ed p107

This heat stable DNA polymerase used in PCR replicates the DNA sequence following each primer: A. Swivelase B. Gyrase C. Taq polymerase D. Ligase E. Helicase

120 C. Page 60 of Topnotch Handout. Taq polymerase is a thermostable DNA polymerase named after the thermophilic bacterium Thermus aquaticus. As an enzyme able to withstand the protein-denaturing conditions (high temperature) required during PCR. Taq's optimum temperature for activity is 75â€"80°C, with a half-life of greater than 2 hours at 92.5°C, 40 minutes at 95°C and 9 minutes at 97.5°C, and can replicate a 1000 base pair strand of DNA in less than 10 seconds at 72°C.

The following amino acids are important in creatine biosynthesis except: A. Methionine B. Arginine C. Glycine D. Lysine E. None of the above

121 D. Creatinine is formed in muscle from creatine phosphate by irreversible, non-enzymatic dehydratio, and loss of phosphate. Glycine, arginine, and methionine all participate in creatine biosynthesis. (Harpers) SIMILAR TO PREVIOUS BOARD EXAM CONCEPT

Which of the following is NOT a function of Vitamin C? A. Antioxidant B. Regulation of cell cycle C. It is necessary for conversion of dopamine to norepinephrine D. Coenzyme in hydroxylation of proline and lysine in collagen synthesis E. None of the above

122 B. Ascorbic acid role/functions are the following : coenzyme in hydroxylation of proline and lysine in collagen synthesis, antioxidant, enhances absorption of iron. Regulation of cell cycle is a function of Biotin. (Harpers). "Ascorbic acid is the coenzyme for copper containing hydroxylases and a ketoglutarate linked iron containing hydroxylases. Dopamine B- hydroxylase is a copper-containing enzyme involved in the synthesis of the catecholamines, norepinephrine, and epinephrine, from tyrosine in the adrenal medulla and central nervous system. During hydroxylation the Cu+ is oxidized to Cu2+; reduction back to Cu+ specifically requires ascorbate, which is oxidized to monodehydroascorbate. Harpers p. 495. Regulation of cell cycle is a function of biotin. Harpers"

Which of the following is INCORRECT regarding hormone-sensitive lipase? A. It catalyzes hydrolysis of triacylglycerol stores in adipose tissue. B. Its activity is mainly inhibited by insulin by stimulating phosphodiesterase and lipase phosphatase. C. Deficiency of this enzyme will cause severe chylomicronemia. D. It is activated by cAMP-dependent protein kinase and removes fatty acid from carbon 1 and carbon 3 of triacylglycerol. E. Its action yields free fatty acids and glycerol.

123 C. Deficiency of lipoprotein lipase will cause severe chylomicronemia (Harpers, Topnotch handouts)

What is the rate-limiting step in catecholamine synthesis? A. Phenylalanine hydroxylase B. DOPA decarboxylase C. Phenylethanolamine N-methyl transferase D. Tyrosine hydroxylase E. Dopamine beta-oxidase

124 D. Tyrosine hydroxylase is the rate-enzyme if catecholamine biosynthesis; it uses tetrahydrobiopterin and molecular oxygen to convert tyrosine to DOPA. (Pubmed: Archives of Biochemistry and Biophysics, April 2011). SIMILAR TO PREVIOUS BOARD EXAM CONCEPT

Which of the following enzyymes is common to both glycolysis and gluconeogenesis? A. Phosphoglycerate kinase B. Fructose-1,6-biphosphatase C. Glucokinase D. Pyruvate carboxylase E. Pyruvate kinase

125 A. All the enzymes listed are specific to either glycolysis or gluconeogenesis. Glucokinase/Hexokinase, Phosphofructokinase, and pyruvate kinase catalyzed irreversible reactions unique to glycolysis. Fructose- 1,6-biphosphatase and pyruvate carboxylase are irreversible enzymes in gluconeogenesis.

Which of the following is true regarding myoglobin? A. It follows a sigmoidal curve. B. Its main function is for oxygen transport. C. It is mainly affected by allosteric receptors. D. It is found in the the muscles and red blood cells. E. It shows saturation in the oxygen dissociation curve.

127 E Myoglobin follows a hyperbolic curve. Its main function is for oxygen storage. It is mainly found in heart and muscle. Its structure is composed of 1 polypeptide only. In contrast, hemoglobin follows a sigmoidal curve and shows cooperativity. It is mainly found in the red blood cells and is affected by allosteric effectors whose interaction with one site of hemoglobin affects the binding of oxygen to heme groups at other location. It has 4 polypeptides.

Which of the following is true regarding glycemic index? A. It is described as the increase in blood glucose after a test dose of a carbohydrate compared with that after an equivalent amount of glucose. B. Foods that high glycemic index are considered to be more beneficial since they cause less fluctuation in insulin secretion. C. Carbohydrates that are absorbed less rapidly have a higher glycemic index. D. Fructose and sugar alcohols have high glycemic index. E. None of the Above

128 A. Carbohydrates that are absorbed less rapidly are food that have low glycemic index and are thus more beneficial since it causes less fluctuation in insulin secretion. Fructose and sugar alcohols are examples of carbohydrates with low glycemic index.

Which statement is true regarding competitive inhibition? A. Km is constant. B. Inhibitor binds to allosteric site of the enzyme and halts the enzyme catalysis. C. Vmax is lowered. D. Reversal of the inhibition is through increasing the substrate. E. Inhibitor changes the shape of the enzyme so it cannot bind to the substrate.

129 D. Only option D is correct. All others are description of non-competitive inhibitor.

Which of the following is not an essential fatty acid? A. Linoleate B. Alpha-linolenate C. Both D. Neither E. Fatty acids are not essential in diet and can be synthesized from carbohydrates and proteins

13 D. Both are essential FA. Source: Harper 27th ed p204

The most important step in cholesterol excretion: A. Bile acid secretion B. Provision of glycerol-3-phosphate C. Action of hormone-sensitive lipase D. Biosynthesis of mevalonate E. Action of lipoproteins

130 A. The provision of glycerol 3-phosphate regulates esterification. Hormone-sensitive lipase catalyzes hydrolysis of triacylglycerol to form fatty acids and glycerol. Biosynthesis of mevalonate (enzyme is HMG- CoA reductase is part of cholesterol synthesis. Lipoprotein are important in transport About 1 g of cholesterol is eliminated from the body per day. Approximately half is excreted in the feces after conversion to bile acids. The remainder is excreted as cholesterol.

The main difference of glucokinase from hexokinase A. It promotes increased hepatic utilization of glucose following a meal. B. It has a low Km and thus, a high affinity for glucose. C. It acts at a constant rate under all normal condition. D. It has a lower Vmax compared to hexokinase. E. It is saturated under normal conditions and acts to provide glucose-6-phosphate to meet the cell's need.

132 A. Only option A is correct. The rest are characteristics of hexokinase. Glucokinase is present only in liver and islet cells of pancreas, inhibited by fructose 6 phosphate, has high Km/low affinity, high Vmax, and removes glucose from blood following a meal.

The process by which a particular segment of DNA is copied by the RNA polymerase? A. Replication B. Translation C. Transcription D. Initiation E. Elongation

135 C. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT

A 20-month old child born full terrm via vaginal delivery, was brought to the hospital due to inability to sit up. She was diagnosed to have Tay-Sach's disease. Which of the following enzymes is deficient in this condition? A. Hexosaminidase A B. β-galactosidase C. Ceramidase D. Sphingomyelinase E. α-galactosidase

137 A. β-galactosidase -- Krabbes; Ceramidase --Farber'ss disease; Sphingomyelinase --Niemann-Pick; α- galactosidase -- Fabry's SIMILAR TO PREVIOUS BOARD EXAM CONCEPT

A 10-month old infant was admitted due to vomiting and decreased sensorium after her mother gave him an orange juice. On history, he was born full term after an uncomplicated pregnancy, solely breastfed for the first 6 months. Urine was noted to contain non-reducing sugars. What is the patient's most likely condition? A. Essential fructosuria B. Classic Galactosemia C. Aldolase B deficiency D. Galactokinase deficiency E. Aldose reductase deficiency

138 C. Fructose intolerance is an autosomal recessive disorder resulting from deficiency in Aldolase B. Patient present wirh hypoglycemia, jaundice, cirrhosis and vvomiting due to accumulation of fructose 1-P phosphate. (Decrease glycogenolysis, and decrease gluconeogenesis). In Essential fructosuria, there is a defect in fructokinase. However, it is more benign and asymptomatic. Galactokinase deficiency presents with galactosuria and cataracts in early childhood. Classic galactosemia may present with vomiting, diarrhea after milk ingestion (not after ingestion of fruit juice).

Starch is a polymer of which of the following? A. Glucose B. Galactose C. Fructose D. Tryptophan E. Cellulose

14 A. Source: Harper 27th ed 116

Which of the following antibiotics prevents binding of aminoacyl-tRNA to the A site? A. Chloramphenicol B. Streptomycin C. Tetracycline D. Rifampicin E. Clindamycin

140 C. Chloramphenicol - inhibits peptidyltransferase; Streptomycin - interferes with initiation of protein synthesis, Rifampicin - binds to bacterial RNA polymerase, inhibiting RNA synthesis; Clindamycin - inhibit translocation

Which of the following is not a participant in creatinine formation? A. Lysine B. Arginine C. Methionine D. Glycine E. None of the above

141 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. The AA lysine is not involved in creatinine formation

Which of the following enzymes is elevated in Gout? A. HGPRT B. Adenosine deaminase C. Xanthine Oxidase D. A & B E. None of the above

142 C. The activity of xanthine oxidase is elevated in gout because elevated activity of this enzyme causes increased formation of uric acid thus precipitating attacks of gout. The rest are enzymes which shunt purine derivatives back into the available nucleic acid pool and thus deplete xanthine oxidase of its substrate.

The sequencing of a genetic make up of an individual is known as? A. Genetics B. Genomics C. Gene Therapy D. Genetic Engineering E. None of the above

143 B. Genetics is the study of genes, heredity, and genetic variation in living organisms. Genomics is the study of the genetic make-up of an individual

How many base pairs are there in the human genome? 10A. 3 x 10 11B. 3 x 10 12C. 3 x 10 9D. 3 x 10 8E. 3 x 10

145 D. Reference: Harper's biochem

What is the enzyme is defective in Smith-Lemli-Opitz syndrome? A. HMG-CoA reductase B. 25-Hydroxyvitamin D3 1-alpha-hydroxylase C. HMG CoA synthase D. Acetyl CoA carboxylase E. 7-dehydrocholesterol reductase

146 E SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. The enzyme 7- dehydrocholesterol reductase is deficient in patients with Smith-Lemli-Opitz syndrome

Which of the following cells do not synthesize heme despite being mature? A. Erythroid Bone Marrow B. RBC C. Yolk Sac D. Liver E. Spleen

147 B. RBCs when they reach maturity do not synthesize heme anymore as they rely on the preformed heme inside the cytoplasm, the other options are the progenitor sources of the RBCs and therefore synthesize heme.

RM, a 30 year old political activist was imprisoned, he was brought to the infirmary due to weakness, upon questioning, you learned that he was deliberately withheld food for 2 weeks, thus when the brain is deprived of glucose at this point in time, which of the following is expected to happen? A. Glycolysis B. Fatty acid synthesis C. Cholesterol synthesis D. Ketogenesis E. A & B

148 D. At this point, ketogenesis predominates which produces ketone bodies to serve as the body's main energy source.

If the enthalpy change is negative and the entropy change is positive in a particular reaction, will this proceed spontaneously? A. Yes, always B. No, always C. Maybe, but only at high temp D. Maybe, but only at low temp E. Cannot be determined with the given information

15 A. Thermodynamics is still chemistry! Don’t sacrifice this topic, they can still ask a few questions on this. Know when a reaction is spontaneous, the definitions of entropy and enthalpy and the basic laws of thermodynamics. Source: Topnotch handout in biochemistry

Pyruvate is oxidized to which substrate to enter the Kreb's cycle? A. Acetyl CoA B. Lactic Acid C. Phosphoenolpyruvate D. Glyceraldhyde 3-Phosphate E. Oxaloacetate

150 A. Acetyl CoA is formed when Pyruvate is oxidized by pyruvate dehydrogenase in aerobic respiration, in the absence of aerobic respiration as in hypoxia or lack of mitochondria (e.g. RBC) the pyruvate is not oxidized but is reduced by LDH to lactate.

What is the complex amino acid alcohol found in sphingomyelin? A. Sphingosine B. Ceramide C. Phosphatidylserine D. Phosphatidylinositol E. Lysophosphatidylcholine

151 A. Sphingosine is the complex amino acid alcohol found in sphingomyelin, ceramide is a combination of sphingosine and a fatty acid.

Sickle cell is an example of point mutation in the gene coding for the globin molecule. What is the amino acid implicated in the polymerization of hemoglobin in sickle cell disease A. Aspartic acid B. Glutamic acid C. Isoleucine D. Valine E. Phenylalanine

152 D. Valine is the amino acid that substituted glutamic acid in the normal Hgb molecule.

An infant was brought to your clinic because of yellowish discoloration of the skin, upon PE, you noted jaundice. Labs indicated elevated levels of direct bilirubin and liver biopsy showed darkly stained hepatocytes, what is the most likely cause? A. Crigler-Najjar syndrome B. Dubin-Johnson syndrome C. Rotor syndrome D. Gilbert's syndrome E. None of the above

153 B. Crigler-Najjar and Gilbert's syndrome are defects in the conjugation of bilirubin while Rotor syndrome also causes elevated direct bilirubin but the liver biopsy shows that the hepatocytes are not darkly stained unlike in Dubin-Johnson syndrome.

A patient came in to the ER suspected of suffering from a MI, you know that the mechanism of action of which of the following involves the inhibition of ADP binding to its receptor in the platelet cell membrane? A. Aspirin B. Tirofiban C. Abciximab D. Clopidogrel E. Dipyridamole

154 D. Clopidogrel inhibits the ADP receptor on platelet cell membranes

These are enzymes whose main function is to catalyze the union of 2 molecules with hydrolysis of ATP A. Ligases B. Lyases C. Hydrolases D. Oxidoreductases E. None of the above

155 A.

All of the following require the co-factor biotin except: A. pyruvate ---> oxaloacetate B. pyruvate ---> acetyl CoA C. acetyl CoA ---> malonyl CoA D. propionyl CoA ---> succinyl CoA E. None of the above

156 B. It is catalyzed by pyruvate dehydrogenase and does not require biotin as co-factor.

Our understanding today of DNA was made possible through the contribution of? A. Oliver and Wilbur Wright B. Jane Goodall and Marie Leakey C. Gregor Mendel and James Watson D. James Watson and Francis Crick E. None of the above

157 D. James Watson and Francis Crick were the first to describe the double helical structure of DNA.

2,3-Bisphosphoglycerate formation is catalyzed by which enzyme? A. Phosphoglycerate kinase B. Phosphoglycerate mutase C. Phosphotriose isomerase D. Bisphosphoglycerate mutase E. Glyceraldehyde 3-phosphate dehydrogenase

158 D. Bisphosphoglycerate mutase catalyzes the conversion of 1,3-BPG to 2,3-BPG

A 6 month old infant presented with hyperacusis (exaggerated startle response), cherry red spot on the macula and froglike position. What substance is expected to accumulate in the brain? A. GM2 Ganglioside B. Hexoseaminidase A C. Sphingomyelin D. Glycosphingolipids E. No accumulation

16 A. Be familiar with the clinical presentation as well as enzyme deficiency and substance which accumulates for lysosomal storage diseases. (favorite cases are taysach’s, neimann pick, gaucher’s) They can ask similar 2 or 3 step analysis types of question in biochemistry or pediatrics/IM or even patho. This is a case of Tay Sach’s. The enzyme deficient is Hexoseaminidase A and the substance GM2 ganglioside accumulates in the brain. Note the buzzwords - exaggerated startle response and cherry red spot in the macula. They do not present with hepatomegaly. Source: Harper 27th ed p.215 Clinical case adapted from first aid for the pediatrics clerkship 2nd ed.

Oxidative phosphorylation which involves several compounds and complexes that transfer electron between mitochondrial membranes is an efficient process of ATP production in aerobic species. Therefore when one of its components is blocked, ATP production may cause pathologic disturbance. Which of the following compounds inhibits ATP synthase? A.Barbiturates B.Oligomycin C.Cyanide D.Malonate E.Hydrogen Sulfate

161 B. oligomycin inhibits complex 5 or atp synthase. Barbiturates inhibit complex 1. cyanide and hydrogen sulfate inhibits complex 4. malonate inhibits complex 3.

How many net ATPs will be produced in a single glucose molecule when a cell undergoes anaerobic glycolysis? A. 2 B. 3 C. 4 D. 5 E. 0

162 A. 4 will be produced 2 ATPs will be used (SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE)

3. NADH is an important compound for ATP production in both aerobic and anaerobic glycolysis. What is the net NADH produced in a cell undergoing anaerobic glycolysis? A. 0 B. 1 C. 2 D. 3 E. 4

163 A. 2 NADH will be produced but they will be used in converting pyruvate to lactate (SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE)

4. Which of the following enzyme is both involved in gluconeogenesis and glycolysis? A. PFK 1 B. Hexokinase C. Pyruvate dehydrogenase D. Phosphoglycerate kinase E. None of the above

164 D. phosphoglycerate kinase can convert 1,3- bisphosphoglycerate to 3-phosphoglycerate in glycolysis and vice versa for gluconeogenesis (SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE)

5. Smith-Lemil-Opitz syndrome (SLOS) is an autosomal recessive inborn error of cholesterol synthesis which causes broad spectrum of effects ranging from mild intellectual disability and behavioral problems to lethal malformations. Which of the following enzymes is defective in SLOS? A. HMG Co A reductase B. HMG Co A synthase C. 7-dehydrocholesterol reductase D. 11-dehydrocholesterol synthase E. carnitine transport

165 C. Previous board exam question concept. This is an autosomal recessive disorder characterized by multiple malformation syndrome caused by mutation of 7-dehydrocholesterol reductase

6. What is the Body Mass Index of a 34 year old male patient who has a weight of190 lbs and a height of 5 foot 10 inches? A. 27.3 B. 32.2 C. 26.6 D. 31.4 E. 25.5

166 A. BMI= wt in kg/ height in m2.. Factor for pounds to kg is 2.2 while inches to meter is 0.0254

8. Which among the following amino acids is not essential for human survival for as long as all the essential amino acids are present in a normal person’s diet? A. threonine B. tryptophan C. tyrosine D. lysine E. Leucine

168 C. Essential amino acids are Phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, arginine, leucine, lysine ( PVT TIM HALL always Argues never Tyres)

Patient presents with arthritis and connective tissue pigmentation. On letting his urine stand, his urine is noted to darken. Which enzyme is deficient in this patient? A. Tyrosine aminotransferase B. Phenylalanine hydroxylase C. Homogentisate oxidase D. Branched chain ketoacid dehydrogenase E. A and C

17 C. This is a case of alkaptonuria. Source: Harper 27th ed p 259

10. Which among the lipoproteins has the greatest concentration of proteins? A. chylomicrons B. HDL C. LDL D. VLDL E. IDL

170 B. the higher the density, the more its protein component

Which of the following nucleotides is a purine found in DNA but not in RNA? A. thymine B. Uracil C. Adenine D. Guanine E. None of the above

178 E purines are guanine and adenine and both are found in DNA and RNA. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE

Which of the following amino acids is purely ketogenic? A. Tyrosine B. Arginine C. Histidine D. Methionie E. Lysine

179 E purely ketogeneic amino acids are the two Ls (lysine and leucine), purely glucogenic are WIFY(tryptophan, isoleucine, phenyalanine and tyrosine) SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE

The following is ATP, Biotin and CO2 requiring: A. Pyruvate dehydrogenase B. Acetyl CoA Carboxylase C. HMG CoA reductase D. SGPT E. All of the above

18 B. These 3 enzymes need 3 things to function (ATP, Biotin, CO2): Acetyl CoA carboxylase, propionyl carboxylase, pyruvate carboxylase. My mnemonic is the ABC enzymes. Source: Topnotch lecture

Sickle cell anemia involves a mutation substituting thymine for adenine which causes the coding of Valine instead of glutamate at position 6 of the hemoglobin beta chain. Which of the following best describes the amino acid change in the disease? A. from non-polar amino acid to polar amino acid B. from polar amino acid to non-polar amino acid C. from acidic amino acid to basic amino acid D. from basic amino acid to acidic amino acid E. from essential amino acid to non-essential amino acid

180 B. glutamate is a polar amino acid while valine is nonpolar. Valine will tend to fold the hemoglobin so that it will position itself to the internal parts of the hgb

Creatine is derived from the following amino acids except? A. methionine B. lysine C. arginine D. glycine E. None of the above

181 B. (SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE.). Creatine can be derived from methionine, arginine and glysine. Choline is derived from methionine. Carnitine is from methionine and lysine. Carnosine and anserine are from alanine. Spermine and spermidine are from methionine.

Which of the following is found in the basement membrane? A. Chondroitin sulfate B. Hyaluronic acid C. Dermatan sulfate D. Heparan sulfate E. Heparin

182 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE.. Heparan sulfate is found in the basement membrane of the kidney where it plays a major role in determining the charge selectiveness of glomerular filtration. Memorize this! Hyaluronic acid- found in synovial fluid, vitreous humor, loose connective tissue. Chondroitin sulfate- cartilage, bone, cornea. Keratan sulfate- cornea. Heparan sulfate- skin fibroblast, aortic wall. Dermatan sulfate- wide distribution.

True statement about fructose intolerance. A. It is autosomal recessive B. It is caused by deficiency of aldolase B C. Symptoms include hypoglycemia, jaundice, vomiting D. There is accumulation of fructose-1-phosphate E. All of the above

183 E SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE.. topnotch biochem handout page 17.

The last step in the synthesis of cortisol is catalyzed by what enzyme? A. 17-α hydroxylase B. 21 hydroxylase C. 11-β hydroxylase D. 1- hydroxylase E. 25- hydroxylase

184 C. The order of enzymes used in cortisol synthesis: 17 -> 21 -> 11. Please refer to steroid hormone synthesis pathway diagram for better comprehension. You can easily eliminate 1-hydroxylase and 25-hydroxylase because they are involved in Vit.D activation, not in cortisol synthesis.

What is the only amino acid that undergoes oxidative deamination in order to yield free ammonia? A. arginine B. glutamine C. asparagine D. aspartate E. glutamate

185 E Glutamate undergoes oxidative deamination to yield free ammonia which will be used in the urea cycle.

In the liver, how many ATPs can be produced from 1 mol of glucose via aerobic glycolysis? A. 6 B. 10 C. 2 D. 8 E. 38

186 D. 2 from substrate level phosphorylation and 6 from 2 NADH that undergo oxidative phosphorylation. Take note the transport shuttle used here is malate- aspartate shuttle (because it is in the liver), so 1 NADH yields 3 ATP. Whereas if glycerol phosphate shuttle is used, 1 NADH yields only 2 ATP.

Which of these is true during fasting state? A. Glycogen synthase is dephosphorylated B. Glycogen synthase is active C. Glycogen phosphorylase is phosphorylated D. Glycogen phosphorylase is inactive E. None of the above

188 C. In fasting state, glycogen synthase is inactive and phosphorylated while glycogen phosphorylase is active and dephosphorylated.

What enzyme is defective in Richner-Hanhart syndrome? A. Tyrosine aminotransferase B. Fumarylacetoacetate hydrolase C. Phenylalanine hydroxylase D. Homogentisate oxidase E. Arginosuccinate synthase

189 A. Tyrosinemia has 2 types: Type 1 is caused by a defect on the enzyme fumarylacetoacetate and affects hepatorenal. Type 2 (aka Richner-Hanhart Syndrome) is caused by defect in tyrosine aminotransferase and has oculocutaneous effects. Note: expeCt at least 1 question about never-before-heard eponyms.

Patient presents with urine smelling of maple syrup or burnt sugar and is diagnosed with maple syrup urine disease. Which of the following is not necessary for the function of the enzyme deficient in this disease? A. Thiamine B. Lipoic acid C. FAD D. Biotin E. None of the above

19 D. The patient is deficient of branched chain ketoacid dehydrogenase. BCKD, like pyruvate dehydrogenase and succinate dehydrogenase require the following for function: Thiamine, Lipoic acid, CoA, FAD, NAD Familiarize yourself with these 3 enzymes and the 5 components required for their function. It’s also a popular question. Source: Topnotch lecture

Which of these enzymes is used in both glycolysis and gluconeogenesis? A. Hexokinase B. Phosphoglycerate kinase C. Phosphofructokinase I D. Pyruvate kinase E. Glucokinase

193 B. phosphoglycerate kinase catalyzes a reversible reaction, thus utilized in both glycolysis and gluconeogenesis.

True statement about Kreb's Cycle except? A. 1 mol of ATP is produced via substrate level phosphorylation B. 3 NADH and 1 FADH2 are produced per turn C. The rate limiting step is catalyzed by isocitrate dehydrogenase D. The enzyme that catalyzes substrate level phosphorylation is succinate thiokinase E. α-ketoglutarate dehydrogenase is an enzyme complex that requires vitamins B1, B2, B3, B5 and lipoic acid

194 A. 1 mol of GTP (not ATP) is produced via substrate level phosphorylation in the Kreb's cycle.

A patient was diagnosed with a hereditary condition affecting the mitochondria. What would be the most likely manifestation? A. myopathy B. mental retardation C. stroke D. seizure E. MI

196 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE.

What is the mechanism of action of tetracycline? A. Inhibits DNA-dependent RNA polymerase B. Inhibits prokaryotic peptidyltransferase and peptide bond formation C. prevents binding of aminoacyl-tRNAs to the A site D. Binds to 30s subunit and blocks the formation of initiation complex E. binds to 50s subunit and inhibit translocation

199 C. A- rifampicin. B- chloramphenicol. D- Aminoglycoside. E. Clindamycin and macrolides

Glutathione is an important molecule for the clearance of free radicals in the body. It consists of only 3 amino acids. Which of the following polypeptides is the primary structure of glutathione? A. Glutamyl â€" cysteinyl â€" glycine B. Glutamine â€" cysteinyl â€" glycine C. Glutamine â€" threonyl â€" methionine D. Glutamine â€" cysteinyl â€" methionine E. None of the above

2 A. Remember the 3 amino acids which make up Glutathione. (Similar principle/concept to previous exam questions) The most important amino acid is cysteine which contains the active -SH group. Source: Harper 27th ed p. 19

Patient has an autosomal recessive genetic disease which makes him markedly susceptible to sunlight with subsequent formation of multiple skin cancers and premature death. The inherited defect involves repair of damaged DNA, particularly thymine dimers. Cells cultured from the patient has low activity of which of the following DNA repair mechanisms? A. Mismatch repair B. Base excision repair C. Nucleotide excision repair D. Double strand break repair E. All of the above

20 C. This is a case of xeroderma pigmentosum. Source: Harper 27th ed p345

What do adipose tissues use for the synthesis of TAG? A. diacylglycerol B. Phosphatidic acid C. Through a reaction catalyzed by glycerokinase D. DHAP E. Acetyl coa

200 D. Glycerokinase is only present in liver. DHAP is an intermediate of glycolysis which undergoes reduction to become glycerol phosphate.

Zero-order kinetics of enzyme reactions occur when: A. Substrate concentration is above Km B. Velocity of enzyme reaction is below Vmax C. Allosteric effectors are present D. The Lineweaver-Burke plot assumes a sigmoidal curve E. Enzyme inhibitors are not present

201 A. In zero-order kinetics, the rate of reaction depends on the availability of enzyme and not in the substrate concentration. This occurs when all enzymes are active; that is, when the substrate concentration is above Km.

In oxidative phosphorylation, energy is generated when hydrogen accumulates in the ________. A. Cytosol B. Mitochondrial matrix C. Intermembranous space D. Inner mitochondrial membrane E. Outer mitochondrial membrane

202 C. The electron transport chain occurs in the mitochondrial matrix. However, the proton gradient created by the accumulation of hydrogen atoms occurs in the intermembranous space.

Which of the following is NOT true of anabolic reactions? A. Endergonic B. Convergent C. Î"G > 0 D. Non-spontaneous E. Synthesis of compounds occurs.

203 B. Anabolic reactions are divergent.

Which among the following is amphibolic? A. Glycolysis B. TCA C. ETC D. PPP E. Urea cycle

204 B. Amphibolic means a link between anabolic and catabolic systems. The TCA is an amphibolic cycle.

Which enzyme catalyzes a reversible reaction in glycolysis? A. phosphoglycerate kinase B. phosphofructokinase-1 C. hexokinase D. pyruvate kinase E. glycogen synthase

205 A. Choices B, C, and D catalyze irreversible reactions in glycolysis.

What is an important role of phosphofructokinase-2 in the well-fed state? A. It promotes glycogenesis B. It inactivates insulin C. It forms fructose-2,6-bosphosphate D. It inhibits glycolysis E. It metabolizes sucrose into fructose and glucose.

206 C. In the well-fed state, fructose-2,6-bisphosphate is the most potent activator of PFK-1, the rate-limiting enzyme in glycolysis, so that the glycolytic cycle will continue.

Which form of arsenic inhibits dehydrogenases by its affinity to lipoic acid? A. Univalent B. Divalent C. Trivalent D. Tetravalent E. Pentavalent

207 C. Arsenite (the trivalent form of arsenic) forms a stable complex with the thiol (-SH) groups of lipoic acid, make this compound unavailable to serve as a coenzyme.

Which TCA enzyme is located in the inner mitochondrial membrane? A. Aconitase B. Alpha-ketoglutarate dehydrogenase C. Succinate thiokinase D. Succinate dehydrogenase E. Fumarase

208 D. Succinate dehydrogenase is the only enzyme of the TCA that is not found in the mitochondrial matrix. Instead, it functions in the inner mitochondrial membrane.

In glycogenesis, bonds between glucose residues are formed at the non-reducing end of the growing chain. This is carbon ____. A. 1 B. 2 C. 3 D. 4 E. 5

209 D. Elongation of a glycogen chain involves the transfer of glucose from UDP-glucose to the non-reducing end of the growing chain, forming a new glycosidic bond between the anomeric hydroxyl of carbon 1 of the activated glucose and carbon 4 of the accepting glucosyl residue. Hence, the alpha(1â†'4) linkages.

Chemical added to natural gas that confers its distinctive odor? A. Sulfur B. Chlorine C. Methane D. Mercaptan E. Phenol

21 D. SIMILAR TO BOARD EXAM CONCEPT. Natural gas is odorless. To detect leaks, mercaptan is added to the gas to make it smell like rotten eggs.

What form of hemoglobin is produced when 2,3-BPG forms salt bridges with hemoglobin thus promoting oxygen release? A. T form B. R form C. S form D. C form E. A form

211 A. When 2,3-BPG combines with hemoglobin, it forms salt bridges leading to the formation of the T ('taut") form of hemoglobin. This form has lesser affinity to oxygen. Oxygen is, thus, released for use by the tissues.

Sucrose is a non-reducing sugar because __________. A. It is not a pentose B. It has no hydroxyl group C. It is a disaccharide D. It's anomeric carbon is not free E. Its enantiomers do not exist

214 D. The reducing property of sugars is determined by its free anomeric carbon.

What is the important role of pyruvate carboxylase in the Krebs Cycle? A. It depletes pyruvate thereby allowing glycolysis to continue B. It prevents flooding of intermediates in the TCA C. It conserves carbon atoms by generating two molecules of carbon dioxide D. It inhibits lactate dehydrogenase E. It ensures that enough oxaloacetate is present

215 E Pyruvate carboxylase catalyzes the conversion of pyruvate to oxaloacetate so that enough oxaloacetate is present to combine with pyruvate in the Krebs cycle.

This glycosaminoglycan is implicated in atherosclerosis as it is known to bind LDL in arteries. A. Heparan sulfate B. Keratan sulfate C. Dermatan sulfate D. Chondroitin sulfate E. Hyaluronic acid

216 C. Dermatan sulfate appears to be the major GAG synthesized by arterial smooth muscle cells, cells which are known to proliferate in atherosclerotic lesions.

Which B vitamin is part of fatty acid synthesis? A. B1 B. B2 C. B3 D. B5 E. B6

218 D. Pantothenate or vitamin B5 is a component of the fatty acyl coA synthase complex of fatty acid synthesis.

Which of the following is TRUE regarding uncouplers of the ETC? A. A proton gradient is formed; however, no ATP is generated. B. Uncouplers decrease the permeability of the intermembranous space to hydrogen atoms. C. There is increased oxygen consumption. D. Uncouplers affect complexes I to IV of the ETC. E. Acetylsalicylic acid is not an uncoupler.

219 C. Uncouplers increase the permeability of the inner mitochondrial membrane to hydrogen ions. As a result, no protein gradient is formed. Complex V is affected. Aspirin is an uncoupler.

Marize did not take any food for eight hours in preparation for a lipid profile test. Which of the following is likely to be occuring inside her cells right now? A. Glycogen phosphorylase b is unphosphorylated. B. cAMP levels are increased. C. Pyruvate is converted to lactate. D. PFK-2 is unphosphorylated. E. Fructose 2-6 bisphosphatase is unphosphorylated.

22 B. SIMILAR TO BOARD EXAM CONCEPT. Fasting increases the glucagon:insulin ratio. Glucagon acts via a G-protein coupled receptor whose alpha subunit adenylate cyclase, increasing intracellular levels of cAMP. cAMP activates protein kinase A. This enzyme, in turn, activates phosphorylase kinase, which then phosphorylates glycogen phosphorylase b, converting it into the active form called phosphorylase a. Protein kinase A will also phosphorylate the enzymes fructose-2,6-bisphosphatase and phosphofructokinase-2. This covalent phosphorylation initiated by glucagon activates the former and inhibits the latter. Conversion of pyruvate in lactate happens in anaerobic metabolism, which does not necessarily occur only in fasting. There were about 10 questions involving insulin, glucagon, feeding and fasting in Biochemistry during our Biochemistry exam

In DNA transcription, the template strand is also known as the ________. A. Coding strand B. Non-coding strand C. Intron D. Exon E. None of the above

220 B. The template strand is the one that is read/copied/transcribed during DNA transcription to form the mRNA transcript. It is also known as the non- coding strand and is complementary to the mRNA transcript. The other strand is called the coding strand because this strand bears the exact same code as the mRNA transcript (with the exception of T for U changes).

Which of the following is true about myoglobin except? A.it contains a tetrapyrrole ring connected to its individual components through methylene bridges B. it it similar to the secondary-tertiary structure of the hemoglobin C. it exhibits bohr effect during extreme oxygen deprivation D. oxidation of Fe2 to Fe3 completely destroys its biologic activity E. it has only one domain therefore it is monomeric.

221 C. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Bohr effect is dependent cooperative interaction between hemes of more than one domain.this is only represented in hemoglobin which has a tetrameric structure. Letter A is correct since myoglobin contains a heme protein. B- is also correct, since the only major difference between hemoglobin and myoglobin is that the latter has only domain while the former exhibits 4 domains. their alpha helix and tertiary configuration is very similar. both myoglobin and hemoglobin needs a reduced state of iron (ferrous form) to allow binding of oxygen for storage or for transport.

which of the following is true about a competitive enzyme inhibitor? A. It can be best extrapolated using Michaelis Menten equation B. It increases the value of the Km C. It affects the Vmax by one half during high levels of inhibitor compared to original substrate D. it acts by decreasing the number of free substrate molecules availabole to bind to the enzyme E. all of the above are correct

222 B. Competitive inhibition is best extrapolated using line weaver burk plot since it can easily demonstrate the values of Km and Vmax. It is also called as substrate analog they bind to the catalytic site decreasing the number of free enzyme molecules availabe for substrate binding. kinetics will show that affinity will be decreased as manifested by increase in Km ( note that Km and affinity has inverse relationship) and with no effect to the Vmax regardless of the amount of the inhibitor

which of the following is an effect of high glucagon states? A. Phosphorylation of PFK2 leading to decrease activity B. Phosphorylation of Fructose 1,6 biphosphatase leads to decrease activity C. Decrease levels of Protein kinase A D. all of the above E. none of the above

226 A. high glucagon/insulin ratio will promote gluconeogenesis through a cascade of events: increase cAMP leads to increase Protein Kinase A which will inactivate PFK2 and activate FBP both via phosphorylation.

which of the following enzyme catalyze the formation of GTP via substrate level phosphorylation in Kreb cycle? A. Succinate dehydrogenase B. Succinyl CoA synthetase C. Aconitase D. Isocitrate dehydrogenase E. Fumarase

227 B. Succinyl CoA synthetase or succinate thiokinase converts succinyl CoA to succinate in mammalian tissues resulting to phosphorylation of GDP to GTP.

Ryan experiences bloating and abdominal cramps whenever he eats dairy-containing products. Which of the following is true about his condition? A. Galactose accumulate in his small intestine. B. Increased levels of hydrogen may be detected in his breath. C. Stool pH is increased. D. There is a deficiency of a specific disaccharide from the brush border. E. Administration of lactulose will lead to improvement of his symptoms.

23 B. SIMILAR TO BOARD EXAM CONCEPT. Lactase intolerence is caused by a deficiency of lactase (a disaccharidase) in the intestinal brush border. Lactose is unable to be broken down into glucose and galactose, and thus accumulates in the gut. It is eventually fermented by bacteria to form hydrogen, methane and carbon dioxide, leading to various abdominal symptoms. 3 questions pertaining to lactase deficiency were asked during our Biochemistry exam

which of the following is a correctly paired enzyme deficiency among mucopolysaccharidoses except? A. Hurler syndrome : a-L iduronidase B. Hunter syndrome: N - acetyltransferase C. Sly syndrome: B- Glucuronidase D. Sanfilippo syndrome: Heparan sulfamidase E. none of the above

230 B. Hunter syndrome is the only X linked type of mucopolysaccharidosis characterized by deficiency in iduronate sulfatase. It presents with mental retardation, variable physical deformities however, minimal to no corneal clouding. It is secondary to accumulation of dermatan sulfate and heparan sulfate.

which of the following is a false statement regarding acetyl CoA carboxylase? A. It is activated by palmitate B. It is inhibited by phosphorylation during high glucagon/insulin ratio C. It requires biotin D. It is the rate limiting step in fatty acid synthesis E. only A and C are incorrect statement

231 A. acetyl CoA carboxylase is activated by citrate and inhibited by its product palmitate.

A 27 y/o female presents with hypertriglyceridemia with a normal or low cholesterol count. Which of the familial syndrome will explain the abnormal lipid profile of the patient? A. LDL receptor defect B. Lipoprotein lipase deficiency C. overproduction of VLDL D. apolipoprotein E deficiency E. none of the above

233 B. A- is a pathologic basis of familial hyperbetalipoproteinemia. In this disease, the cholesterol rises (inc LDL) while the clearance of chylomicrons and VLDL is normal ( Normal TAG). B- impaired clearance of VLDL and chylomicrons by an absent or abnormal lipoprotein lipase will lead to increase TAG. since less is transformed into LDL, cholesterol will be normal or low. overproduction of VLDL alone will lead to increase in both Cholesterol and TAG. Apolipoprotein E deficiency decreasing the clearance of VLDL remnant, will result to increase VLDL,LDL and TAG.

Which of the following intermediate products of heme synthesis will accumulate if the patient suffers from lead intoxication? A. Succinyl CoA B. Uroporpholinogen C. Aminolevulinic acid D. porphobilinogen E. All of the above

235 C. Lead intoxication affects two enzyme in the heme synthesis. It is ALA dehydratase and ferrochelatase. The former combines two molecules of d-ALA to form Porphobilinogen, while ferrochelatase catalyzes the incorporation of ferrous iron to the Protoporphyrin IX to form heme. therefore both B and D will be deficient.succinyl CoA along with glycine will not accumulate since its conversion to d-ALA is irreversible by the enzyme ALA synthase ( rate limiting step)

which of the following is true regarding Phenylketonuria ? A. It can be secondary to dihydrobiopterin reductase deficiency B. Blood phenylalanine levels rises significantly at Day 2 postnatal life. C. There would be normal levels of catecholamines in the blood D. tyrosine need not be supplemented E. none of the above

236 A. Hyperphenylalaninemia (PKU) can arise from either absence of phenylalanine hydroxylase(PH) which convert phenylalanine to tyrosine or absence of its enzyme cofactor tetrahydrobiopterin. Blood phenylalanine levels accumulates only after Day 3 or Day 4 of life. absence of PH will make tyrosine essential AA, without complete supplementation, there would be a depletion of catecholamine levels since tyrosine is deficient.

what bacterialDNA polymerase is responsible for gap filling and synthesis of lagging strand during replication? A. DNA pol I B. DNA pol II C. DNA pol III D. DNA pol IV E. DNA pol V

238 A. there are only three types of bacterial DNA polymerase. Pol I is responsible ofr gap filling and lagging strand synthesis. Pol II is for DNA proofreading and repair. Pol III is for leading strand synthesis

which of the following is false about the Genetic code? A. One amino acid is encoded only by one codon B. There are no punctation marks in the reading of the code C. A specific codon indicates only one specific amino acid D. It is universal E. none of the above

239 A. one amino acid can be encoded by more than one codon.this is the degenerate feature of a genetic code.

Which of the following amino acids contain a phenol ring? A. Tyrosine B. Phenylalanine C. Histidine D. Tryptophan E. Proline

24 A. SIMILAR TO BOARD EXAM CONCEPT. Aromatic amino acids: Phenylalanine - benzene ring; Histidine - Imidazole ring; Tryptophan - Indole ring; Proline contains a ring structure, but is not classified as an aromatic amino acid

which of the following is true about type 1 muscle fiber? A. Fast contraction rate B. Predominant in soleus and erector spinae muscle C. High energy utilization D. High myosin ATPase activity E. Short duration of action

240 B. type 1 are slow twitch muscle fiber widely distributed along the antigravity muscles. It is important in maintaining posture. All the other choices describes Type II fast twitch or glycolytic fibers.

Sphingomyelin is a substance participating in nerve conduction and insulation, what is its predominant fatty acid composition? A. palmitic acid B. stearic acid C. lignoceric acid D. nervonic acid E. sphanganine

241 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE, very difficult to answer because there are a lot to consider especially type of tissue involved, but assuming human neural tissue, based on journals from pubmed the most predominant fatty acid is stearic acid C18 with lignocericC24 and nervonic C24:1 coming next

Which of the following is a common enzyme in both gluconeogenesis and glycolysis A. pyruvate carboxylase B. pyruvate kinase C. phosphoenolpyruvate carboxykinase D. phosphoglycerate kinase E. fructose 1,6 bisphosphatase

243 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Of all the enzymes given only phosphoglycerate kinase is common to both pathways, pyruvate kinase is glycolytic, the others are involved in gluconeogenesis

The committed step in the glycolytic pathway is catalyzed by the enzyme phosphofructokinase 1, the following substrates and or substances positively regulates or allosterically activates this enzyme EXCEPT A. citrate B. 5'AMP C. fructose 2,6 bisphosphate D. fructose 6 phosphate E. none of the above (all are positive regulators)

244 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. All are positive regulators except citrate and ATP which represent high energy states therefore exerting negative feedback regulation on the glycolytic pathway. Fructose 2,6 bisphosphate is the strongest positive allosteric activator

The disease characterized as having a deficiency of homogentisic acid oxidase manifesting with dark discoloration of the urine when allowed to stand and can cause damage to cartilage (ochronosis), heart valves and kidney stones. A. homocystinemia B. homocystinuria C. maple syrup urine disease D. alkaptonuria E. alport's disease

247 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Homocystinemia and homocystinuria are manifestations of cystathionine synthase deficiency and other enzymes involved in methionine metabolism, may also be seen with B9 B12 deficiencies. Alkaptonuria is a basement membrane disease, maple syrup urine disease is deficiency of branched chain amino acid dehydrogenase

Which of the following genes act as a tumor suppressor gene which regulates cell apoptosis and the dysfunction of which is implicated in the pathogenesis of a lot of human cancers? A. BCR-ABL B. RAS C. RET D. C-kit E. p-53

248 E SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. P53 also known as the guardian of the genome regulates promotes cell apoptosis when there is irreversible DNA damage. All the other genes are oncogenes which function in promoting growth when mutated promotes uncontrolled cellular growth.

Juan was trapped inside a collapsed building after an earthquake. Having been trapped with no access to food and water, his main source of energy for the first 24 hours following the event would be derived from which of the following sources? A. muscle glycogen B. muslce protein C. liver glycogen D. ketones E. gluconeogenesis

249 C. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. A lot of questions on starvation and metabolic integration. First 24 hours glycogen is the main source. After that gluconeogenesis to maintain blood glucose, then fats and ketones and then breakdown of proteins after prolonged starvation. Muscle glycogen cannot be utilized as free glucose by other organs because of lack of glucose 6 phosphatase.

Juan was trapped inside a collapsed building after an earthquake. Having been trapped with no access to food and water, and experienced prolonged starvation, other than glucose what predominant source of energy will his brain be utilizing? A. protein B. glycosphingolipids C. free fatty acids D. ketone bodies E. glycogen

250 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. The brain can obtain up to 70% of its energy from ketone bodies with prolonged starvation. Fatty acids cannot be utilized by the brain.

The following hormones act via intracellular nuclear receptors binding to DNA response elements EXCEPT A. Estrogen B. insulin C. thyroid hormone D. vitamin D E. cortisol

252 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. All steroid based hormones have intracellular nuclear receptors. Insulin binds to a cell membrane receptor associated with tyrosine kinase

Which of the following cell profiles are usually associated with chronic autoimmune diseases and cancers like hodgkin's lymphoma? A. CD4(+) CD8(-) B. CD4(-) CD8(-) double negative C. CD4(-) CD8(+) D. CD4(+) CD8(+) double positive E. all of the above

253 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE, difficult one, from research I found the answer to be double positive, meaning cells have both CD4 CD8 characteristics evading thymic immune regulation causing diseases like autoimmune and malignancies.

What is the most active potent form of androgen involved in the development of male external genitalia and also found predominant in the prostate and hair follicles? A. testosterone B. dihydrotestosterone C. dehydroepiandrosterone D. androstenedione E. none of the above

254 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE, dihydrotestosterone or DHT is the active form of testosterone and the most potent. Androstenedione is a precursor with androgen properties, Dehydroepiandrosterone or DHEA is secreted in the adrenal and gonads where it also acts as an intermediate for estrogen and androgen synthesis

Increasing insulin levels has which of the following effects on the different enzyme systems? A. glycogen phosphorylase will be dephosphorylated B. AcetylCoA carboxylase will be inhibited C. pyruvate dehydrogenase is phosphorylated D. glycogen synthase is phosphorylated E. pyruvate carboxylase is activated

256 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE, know the functions of the hormones by heart, a lot of metabolic integration. Insulin predominantly dephosphorylates enzymes to activate them or inhibit them. Glucagon Epinephrine predominantly phosphorylates enzymes to activate them via cAMP Protein Kinase A pathway. Increase Insulin like in the well fed state will cause storage of energy as glycogen therefore glycogen phosphorylase the one responsible for breakdown is inhibited and dephosphorylated form, opposite is true with glycogen synthase where it is activated and dephosphorylated, acetylcoa carboxylase is activated because insulin promotes energy storage by lipogenesis, pyruvate dehydrogenase is dephosphorylated and activated because insulin promotes glucose entry and utilization, insulin promotes glycolysis and inhibits gluconeogenesis therefore pyruvate carboxylase should be inhibited no new glucose needs to be made in a well fed state.

Which of the following statements are true regarding skeletal muscle? A. skeletal muscle is unable to contract in the absence of extracellular calcium influx stimulating the release of calcium from the sarcoplasmic reticulum B. action potential travels down the T-tubules closely related to the 2 terminal cisternae of the sarcoplasmic reticulum releasing calcium into the cytoplasm C. the dihydropyridine receptor opens and releases the calcium from the sarcoplasmic reticulum into the cytoplasm to stimulate excitation contraction coupling D. calcium released from the sarcoplasmic reticulum binds to troponin T allowing actin myosin interaction to occur E. all of the above statments are correct

257 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE, suprisingly there was a lot of physiology question in the biochemistry exam, muscle physiology had 3-5 questions alone. Skeletal muscle does not need extracellular calcium, dihydropyridine receptors sense the action potential causing the Ryanodine receptors in the SR to open and release calcium, calcium binds to troponin C

Which of the following biochemical processes exclusively occur in the mitochondria of the cell? A. glycolysis B. pentose phosphate pathway C. tricarboxylic acid cycle D. urea cycle E. fatty acid synthesis

258 C. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE, glycolysis and fatty acid synthesis occurs in the cytoplasm, urea cycle has steps in both the cytoplasm and mitochondria, pentose phosphate pathway in the cytoplasm

What is the predominant pathway utilized by red blood cells for energy? A. beta oxidation B. embden meyerhoff pathway C. luebering rapoport pathway D. hexose monophosphate shunt E. Citric acid cycle

259 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE, specifically answer should be anaerobic glycolysis since RBCs don’t have mitochondria. Lueberin rapoport pathway - pathway involved in the formation of 2,3 BPG.

The following electrophoresis technique is used in the study of DNA-binding proteins: A. Northern blot B. Western blot C. Southern blot D. Western blot E. Southwestern blot

26 E For the different blotting techniques, remember the mnemonic SNoW DRoP: Southern - DNA, Northern - RNA, Western - Protein

This important coenzyme A involved in various biochemical reactions is derived from which of the following substances? A. vitamin B1 B. vitamin B2 C. vitamin B3 D. vitamin B5 E. vitamin B6

260 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE, what was asked was FAD B2 and NAD B3. memorize the coenzymes and vitamin derivatives, this is after all both biochemistry and nutrition

A patient with long-standing Diabetes mellitus type 2 is diagnosed with peripheral neuropathy. The absence of this enzyme in the presence of hyperglycemia is said to be responsible: A. sorbitol dehydrogenase B. aldose reductase C. fructokinase D. aldolase B

262 A. Sorbitol dehydrogenase converts sorbitol to fructose. Absence of this enzyme in the presence of hyperglycemia will result in increased sorbitol in the tissue.

Which of the following characterizes the lagging strand but not the leading strand in DNA replication? A. Requires an RNA primer B. Synthesized in a 5’ to 3’ direction C. Requires DNA ligase activity D. Bound by single-stranded DNA binding proteins

263 C. A B and D are required by both strands

A diet rich in which of the following dietary fats is most responsible for a decrease in LDL levels: A. polyunsaturated omega 3 fatty acids B. monounsaturated fatty acids C. saturated fat D. transfat

264 B. Monounsaturated fatty acids and omega 6 PUFA lowers LDL levels.

Which of the following is true about enzyme kinetics? A. Allosteric enzymes show a sigmoidal curve B. A numerically small Km indicates low affinity for substrate C. Enzymes that follow Michaelis-Menten kinetics show a sigmoidal curve D. An irreversible competitive antagonist leads to an increase in Km E. None of the above

265 A.Review enzyme kinetics. Michaelis-menten shows a hyperbolic curve. Irreversible inhibitor lowers Vmax

A patient is diagnosed with megaloblastic anemia and undergoes several laboratory tests. Which of the following differentiates cobalamin from folic acid deficiency? A. Homocystinuria B. Increased MCV C. Decreased Hgb D. Increased methylmalonic acid levels E. Decreased activity of methionine synthase

267 D. All the others may also be found in folic acid deficiency

Interconversion of sugars between fructose 6-P, xylulose 5-P, Ribose 5-P, and Glyceraldehyde 3-P is made possible by which pathway? A. Hexose monophosphate shunt B. Embden Meyerhoff pathway C. Pentose Phosphate pathway D. A and B E. A and C

268 E HMP shunt or Pentose phosphate pathway

The reaction catalyzed by the enzyme phosphoglucose isomerase (glucose 6-P â†'fructose 6-P) in the glycolytic pathway has a standard free energy +400 cal/mol. If isolated from the other enzymatic reactions from the pathway under standard conditions, which of the following conclusions may be derived: A. The reaction is in equilibrium B. The reaction mostly proceeds from right to left C. More fructose 6-P is produced D. A predominantly forward reaction takes place E. No reaction takes place

269 B. A + standard free energy mostly proceed from right to left and vice versa for a (-) standard free energy

Characteristic of the genetic code that can account for silent mutations? A. Non-ambiguous B. Universal C. Non-overlapping D. Degenerate E. Commaless

27 D. Non-ambiguous/specific - a certain codon codes always codes for the same amino acid; Universal - codons always code for same amino acid from generation to generation and between species; Redundant/degenerate - A given amino acid may have more than one triplet codon coding for it; Non- overlapping/commaless - DNA is read from a starting point as a continuous sequence of bases, taken three at a time without any gaps

Arsenic poisoning inhibits the conversion of pyruvate to acetyl-coA. It will also inhibit the following: A. reaction catalyzed by isocitrate dehydrogenase B. conversion of phosphoenolpuruvate to pyruvate C. synthesis of ribose 5-phosphate D. catabolism of branched-chain amino acids E. None of the above

270 D. Arsenic inhibits lipoic acid an essential component of the enzymes pyruvate dehydrogenase, alpha- ketoglutarate dehydrogenase, and branched chain dehydrogenase

A patient presenting with fasting hypoglycemia and accumulation of intracellular glycogen with abnormal structure at branch points has which disorder: A. Glycogen phoshorylase deficiency B. Pompe disease C. Glucose 6-Phosphatase deficiency D. Cori disease E. McArdle disease

271 D. Cori disease or deficiency in debranching enzyme

Myoglobin is a globular, flexible molecule found predominantly in slow-twitch muscle fibers. It is composed of alpha-helical secondary structure that is stabilized by: A. Disulfide bonds B. Hydrophobic interactions C. Ionic interactions D. Hydrogen bonds E. All of the above

272 D. All the others bonds that stabilize tertiary and quaternary structures

An infant presenting with increased orotic acid levels, hyperammonemia, and neurologic manifestations will most likely have which deficiency? A. Ornithine transcarbamylase B. N-acetylglutamate C. Carbamoyl phosphate synthase I D. Carbamoyl phosphate synthase II E. Bifunctional pyrimidine synthesis enzyme

273 A. The presence of hyperammonemia differentiates ornithine transcarbamylase deficiency from deficiency of pyrimidine synthesis enzyme deficiency that cause orotic aciduria

What is the rate-limiting enzyme in the TCA cycle? A. Alpha-ketoglutarate dehydrogenase B. Malate dehydrogenase C. Succinate dehydrogenase D. Isocitrate dehydrogenase E. None of these

274 D.

A person is in his second day of religious fasting, which of the following metabolic pathway is primarily responsible for maintaining glucose concentration in the circulation: A. breakdown of glycogen stores B. ketones synthesis C. uptake and phosphorylation of glycerol by the liver D. Embden Meyerhoff pathway E. Pentose phosphate pathway

275 C. Glycogen stores good for 12-18 hours only. After that, gluconeogenesis is responsible for maintaining glucose levels

Collagen undergoes extensive posttranslational modification. Which of the following occurs outside the cell? A. Triple helix formation B. Cleavage of C-terminal sequence C. Hydroxylation of lysine and proline D. Removal of signal sequence E. Glycosylation of lysine

276 B. All others occur inside the cell

Glycogenesis is enhanced by: A. enzyme phosphorylation B. activation of protein phosphatase C. increased cAMP concentration D. activation of protein kinase A E. All of the above

277 B. All others enhance gluconeogenesis

Which of the following amino acids is a direct donor of NH3 in urea synthesis? A. Aspartate B. Glutamate C. Glutamine D. Arginine E. Alanine

278 A. Aspartate directly donates NH3 in urea synthesis

In gluconeogenesis, reversal of the glycolytic enzyme pyruvate kinase involves two reactions, the second of which is catalyzed by phosphoenolpyruvate carboxykinase which utilizes a source of energy from a substrate level phosphorylation such as the reaction catalyzed by: A. alpha-ketoglutarate dehydrogenase B. malate dehydrogenase C. phosphofructokinase 1 D. succinate thiokinase E. A and B

279 D. Succinate thiokinase is responsible for substrate level phosphorylation that produces GTP, which is preferentially used by phosphoenolpyruvate carboxykinase

Which of the following is a nucleoside? A. Hypoxanthine B. Xanthine C. Inosine D. cAMP E. Adenine

28 C. SIMILAR TO BOARD EXAM CONCEPT. Bases/Nucleobases: Nitrogenous bases = guanine, adenine, thymine, uracil, cytosine, xanthine, hypoxanthine; Nucleosides: base+sugar = guanosine, adenosine, thymidine, cytidine, uridine, inosine; Nucleotides: base+sugar+phosphate = ATP, GMP, UDO, cAMP. 3 similar questions were asked during our Biochemistry exam

Hypogonadotrophic dwarfism and acrodermatitis enteropathica is caused by: A. Vitamin E deficiency B. Vitamin A excess C. Zinc deficiency D. Ascorbic acid deficiency E. Vitamin A deficiency

280 C.

Which of the following amino acids does not undergo transamination at some point in its catabolism? A. Histidine B. Valine C. Tryptophan D. Aspartate E. Lysine

282 E All amino acids with the exception of LYSINE and THREONINE participate in transamination

Which of the following is true regarding Vitamin K? A. It is a water soluble vitamin B. It is not synthesized in the human body C. Plays an essential role in coagulation D. Present at high concentration in cow's or breast milk E. Important in management of hemorrhagic disorders by prolonging the coagulation time.

283 C. Vitamin K, a fat soluble vitamin, is an essential cofactor for the synthesis of factors II, VII, IX and X. It DECREASES/SHORTENS the coagulation time (particularly the PT). It is synthesized by the normal gut flora and is present at low concentration in cow's/breast milk.

Which of the following pathways produces carbon monoxide as a by-product? A. Heme Catabolism B. Glycogenolysis C. Fatty Acid Synthesis D. Urea Cycle E. Hexose Monophosphate Shunt

284 A. Heme catabolism is first carried out by the enzyme heme oxygenase which produces an equimolar amount of biliverdin, with ferric iron and carbon monoxide being released

How does azithromycin inhibit bacterial protein synthesis in order to extert its antibacterial effect? A. Interferes with the initiation of protein synthesis B. Inhibits the DNA depended RNA polymerase C. Inhibits translocation by irreversibly binding to a site on the 50s ribosome D. Inhibits the enzyme peptidyltransferase E. Blocks the binding of aminoacyl TRNA to the acceptor site

285 C. A - aminoglycoside, B - Rifampicin, D - Chloramphenicol, E- Tetracycline

Chronic Alcoholism often leads to fatty liver by consuming what coenzyme which is needed for beta oxidation of fatty acids? +A. NAD B. NADH C. NADPH D. FAD E. FADH2

286 A. As part of alcohol metabolism, ethanol is oxidized to acetaldehyde by the enzyme alcohol dehydrogenase to produce acetaldehyde, this is coupled with NAD being reduced to NADH2. NAD is also essential in one of the oxidative steps in the beta oxidation of fatty acids. If NAD is consumed by means of chronic alcohol consumption, the beta oxidation will not proceed hence accumulation of fat within the hepatocytes (steatosis)

What is the biochemical mechanism behind the development of seizures in individuals with hepatic encephalopathy? A. Elevated levels of alpha ketoglutrate hence producing increased ATP production B. An increase in the level of the neurotransmitter glycine inside the brain C. Nitrogenous substances shunted out of the brain resulting in depletion of ammonia levels D. Increased synaptic release of glutamate E. None of the above

287 D. Hepatic encephalopathy results in the shunting of nitrogenous material INSIDE the neurons. The increased ammonia levels shift the transamination reaction to the synthesis of glutamate rather than alpha ketoglutarate, hence the TCA will not proceed leading to DEPLETION of ATP. Glutamate is an EXCITATORY neurotransmitter and its elevated levels can stimulate the cortical neurons producing seizure episodes. GABA is also increased in individuals with hepatic encephalopathy as it is produced through decarboxylation of glutamate. However it is an inhibitory neurotransmitter and is primarily responsibe for COMA in advanced stages. Glycine is an inhibitory neurotransmitter in the spinal cord

Cataracts are common in poorly controlled diabetic individuals due to what biochemical mechanism? A. Decreased sorbitol levels which produce cellular degradation of the proteins in the lens B. Insulin deficiency inhibits synthesis of proteins in the lens C. Osmotic shift due to the increased levels of sorbitol inside the lens D. Absence of the enzyme aldose reductase which is responsible for sorbitol metabolism E. Both C and D are correct

288 C. Poorly controlled diabtetics have elevated levels of glucose in the blood. The glucose accumulates inside the lens (the lens does not require insulin for glucose uptake), which is eventually metabolized to sorbitol through the enzyme ALDOSE REDUCTASE. The lens lack the enzyme SORBITOL DEHYDROGENASE which metabolizes sorbitol further to fructose

Increased formation of ketone bodies during starvation is due to? A. Decreased levels of circulating glucagon B. Increased levels of free fatty acids in the blood C. Decreased levels of acetyl-CoA in the blood D. Decreased activity of hormone sensitive lipase E. Inhibition of beta oxidation of fatty acid

289 B. Free fatty acids are increased due to the increased activity of hormone sensitive lipase (stimulated by Glucagon, in the fasting state). Acetyl-CoA is the end product of fatty acid oxidation which is a substrate needed for ketone body synthesis

What is the rate-limiting step of ketogenesis? A. Carbamoyl phosphate synthetase I B. Carbamoyl phosphate synthetase II C. Acetyl CoA carboxylase D. Acetyl CoA decarboxylase E. HMG CoA synthase

29 E Rate limiting steps: Urea cycle - Carbamoyl phosphate synthetase I; De novo pyrimidine synthesis - Carbamoyl phosphate synthetase II; Fatty acid synthesis - Acetyl-CoA carboxylase. Only 1 rate- limiting enzyme type question appeared during our Biochemistry exam

Which of the following chemotherapeutic drugs acts by inhibiting the enzyme thymidylate synthase? A. Gemcitabine B. Paclitaxel C. Bleomycin D. Vincristine E. 5-FU

290 E 5FU inhibits thymidylate synthase leading to a "thymineless" cell death,

Which of the following is true about the enzyme acetyl-CoA carboxylase? A. It requires thiamine for the carboxylation of acetyl-CoA B. It is located mainly in the matrix of the hepatic mitochondria C. It utilizes citrate as a substrate D. It produces malonyl-CoA E. It catalyzes the rate limitting step in the beta oxidation of fatty acids

291 D. ACC requires BIOTIN as a coenzyme. It is found in the CYTOPLASM. It utilizes ACETYL-COA as a substrate. It is the rate limiting step of FATTY ACID SYNTHESIS

An infant diagnosed with Von Gierke's disease has the following characteristics EXCEPT? A. Cannot utilize hepatic gluconeogenesis to maintain blood glucose levels B. Characterized by a deficiency of the enzyme glucose-6-phosphatase C. Can utilize the muscle glycogen to maintain blood glucose levels D. Develops lactic acidosis due to the hypoglycemia E. None of the above

292 C. Von Gierke's disease: deficiency in glucose-6- phosphatase which is an enzyme utilized in gluconeogenesis and glycogenolysis. Affected infants develop hypoglycemia and if severe enough could progress to lactic acidosis. Muscle glycogen cannot be used (even in normal individuals) to produce free blood glucose since muscle lacks glucose-6- phosphatase

Which of the following substances inhibit Complex III of the Electron Transport Chain? A. Barbiturates B. Dimercaprol C. Cyanide D. Hydrogen Sulfide E. Malonate

293 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE: Complex I inhibitors (Barbiturate, Piericidin A, Amytal, Rotenone), Complex II inhibitors (Malonate, Carboxin, TTFA), Complex III inhibitors (Dimercaprol, Antimycin A) Complex IV inhibitors (Cyanide, Carbon monoxide, Sodium azide, Hydrogen sulfide)

An individual with lipoprotein lipase deficiency would have which of the following changes in blood lipid levels? A. Elevation of plasma HDL level B. Elevation of chylomicron level C. Decreased triglyceride levels D. Elevated LDL levels E. Decreased VLDL levels

294 B. If the activity of lipoprotein lipase is decreased, both plasma chylomicrons and VLDL would become elevated

An infant who was initially normal at birth began to develop lethargy, hypothermia and apnea. He was later found out to have a deficiency of the enzyme arginosuccinate synthase. Which of the following would be expected? A. High blood levels of arginine B. Low blood levels of ammonia C. Low blood levels of aspartate D. High blood levels of ornithine E. High blood levels of citrulline

295 E Arginosuccinate synthase catalyzes the condensation of citrulline with L-aspartate to form arginine. Any intermediates before this step would accumulate while all those that occur afterwards would have decreased levels

Patients with xeroderma pigmentosum suffer DNA damage upon exposure to UV light through formation of which of the following? A. Pyrimidine dimers B. Purine dimers C. Deoxyribose dimers D. Anhydrous bonds in the DNA E. All of the above

296 A. UV light causes formation of pyrimidine dimers in DNA

The carbon skeleton of triacylglycerol can be used for gluconeogenesis by entering the pathway as what substrate? A. 3-phosphoglycerate B. Glucose-6-phosphate C. Fructose 1,6-bisphosphate D. Dihydroxyacetone phosphate E. Phosphoenolpyruvate

297 D. Glycerol is released during TAG hydroysis, Glycerol is phosphorylated to glycerol phosphate which is then oxidized to form dihydroxyacetone phosphate.

The neurologic manifestations seen in Niemann Pick disease are associated with the accumulation of which of the following? A. Gangliosides B. Cerebroside C. Prostaglandin D. Leukotriene E. Sphingomyelin

298 E Niemann Pick disease - deficiency of sphingomyelinase enzyme

A 24 year old male medical student complains of bilateral white discharge from his breast. Which of the following is true about his probable condition ? A. There is excessive production of ADH by his posterior pituitary B. His testosterone levels are markedly decreased C. His disease condition would respond by administering Bromocriptine D. Oxytocin levels are markedly elevated E. There is most likely a tumor present that involves the posterior pituitary

299 C. Prolactinoma - most common functioning pituitary tumor, located in the anterior pituitary gland. Most are microadenoma and is the only pituitary tumor that can be treated medically with dopamine analogs (such as Bromocriptine)

Which of the following amino acid is incorrectly paired with its side chain? A. Tyrosine â€" Thiol group containing B. Tryptophan â€" indole group containing C. Proline â€" imino group containing D. Arginine â€" guandino group containing E. Histidine â€" imidazole group containing

3 A. Tyrosine does not contain a thiol group. Tyrosine contains a phenol group. Source: Harper 27th ed p. 18

Which of the following is true about mammalian pyruvate dehydrogenase complex under physiologic condition ? A. It is composed of 3 types of catalytic enzyme subunits B. Phosphorylation of this enzyme will increase the formation of acetyl CoA C. the presence of epinephrine will activate the PDH in adipose tissue D. high NADH/NAD ratio will promote active form of the complex E. pyridoxal phosphate is an esential cofactor of the complex

301 A. pyruvate dehydrogenase complex is one of the most highly regulated enzyme in terms of carbohydrate metabolism. It is a mitochondrial enzyme complex composed of 3 catalytic subunits namely: pyruvate dehydrogenase, dihydrolipoyl transacetylase, and dihydrolipoyl dehydrogenase. cofactors essential for the complex include the ff: FAD, thiamine pyrophosphate, lipoamide,Coenzyme A (pantothenic acid), and NAD. the process involves the conversion of pyruvate to acetyl CoA along with release of CO2 and NADH as byproduct. accumulation of its product ( acetylCoA,NADH) will inactivate the complex via competitive feedback. furthermore, phosphorylation of the enzyme by protein kinase will also inactivate the complex. the reverse is true about dephosphorylation. catecholamines particularly epinephrine will stimulate PDH in the cardiac tissue while insulin will stimulate this adipose tissue PDH. Devlin biochemistry pp 540-542 6th ed.

Which of the following intermediate substances in the kreb cycle will accumulate when fluoroacetate enters the mitochondrial matrix? A. Alpha ketoglutarate B. citrate C. Isocitrate D. Succinyl CoA E. None of the abvoe

302 B. the administration of fluoroacetate will inhibit the enzyme aconitase found in the mitochondrial matrix. This enzyme is part of the kreb cycel responsible for converting citrate into isocitrate. Therefore, citrate will accumulate as a result. On the otherhand, arsenic inhibit alpha ketoglutarate dehydrogenase complex resulting to accumulation of alpha ketoglutarate and deficiency in succinyl CoA. harpers 27th ed pp 145- 146.

Which of the following is an effect of salicylate overdose in the oxidative phosphorylation process? A. It binds to the ATP synthetase preventing the H reentry into the mitochondrial matrix B. It inhibits the electron transport via complex I by blocking the transfer from Fe-S to Q C. competitively inhibits the succinate Q reductase( Complex II) D. it promotes increase permeability of the inner mitochondrial membrane E. inhibits the cytochrome c oxidase (complex IV) resulting to inability to transfer electrons to oxygen atom

303 D. supradoses of aspirin (salicylates) will uncouple the electron transport chain by promoting permeabilty of the inner mitochondrial membrane to hydrogen. This will result to loss of hydrogen gradient despite continous process of ETC. in effect, much of the energy produced in the electron transfer will dissipate as heat and consequently leads to fever on the part of the patient. the same mechanism is involved in ingestion of 2,4 dinitrophenol and during brown fat thermogenesis via thermogenin protein in neonates.barbiturates, ptericidin A, rotenone are inhibitors of complex I, carboxin, TTFA, malonate are to Complex II; antimycin A and dimercaprol (BAL) are to Complex III while hydrogen sulfide, CO, and Cyanide are to complex IV. oligomycin on the otherhand inhibits the H reentry in the ATP syntethase. Harpers 27th ed pp 107-108

which of the following enzymes is highly active in the seminal vesicles? A. Sorbitol dehydrogenase B. Aldolase B C. Aldose reductase D. Glycerol 3 phosphate dehydrogenase E. None of the above

304 A. (SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE). The major energy source of spermatozoa is fructose. This is produced by the cells of the seminal vesicles from glucose by two step process. First is by NADPH dependent reduction of glucose to sorbitol( aldose reductase) followed by NAD dependent oxidation of sorbitol to fructose (sorbitol dehydrogenase). of the two enzymes, the activity of the former is comparable to all other cells while the latter enzymes is specifically active in seminal vesicles. Devlin 6th p 615

Which of the following is the end product of isoleucine,valine and methionine metabolism? A. Acetyl CoA B. Succinyl CoA C. Propionyl CoA D. Methylmalonyl CoA E. None of the above

305 C. propionyl CoA is the end product of the ff metabolism: isoleucine, valine, methionine, odd chain fatty acid oxidation and side chain of cholesterol degradation. Conversion of proprionyl CoA to methylmalonyl CoA is by the biotin requiring enzyme propionyl CoA carboxylase. further conversion of methylmalonyl CoA to succinyl CoA is by Vit B12 requiring methylmalonyl CoA mutase. Devlin 6th ed p777

how many ATP/s is/are required to produce urea in Kreb Henseleit Cycle? A. 1 ATP B. 2 ATP C. 3 ATP D. 4 ATP E. No ATP needed.

306 D. Kreb Henseleit cycle or the urea cycle requires 4 ATPs to produce and excrete urea. Two ATPs are required in the formation of carbamoyl phosphate and 2 ATPs for the formation of arginosuccinate. Refer to your handouts for the diagram. Devlin 6th ed pp 752

which of the following amino acid is an essential component in the de novo synthesis of phosphatidylcholine? A. arginine B. threonine C. serine D. Methionine E. None of the above

307 D. phosphatidylcholine is an essential component of cell membranes, myelin sheath and mature pulmonary surfactant. It is formed by phosphorylation of choline obtained from the diet followed by addition of 3 methyl groups. The activated form of methionin (S- adenosyl methionine) is the only amino acid that can donate methyl groups.

true about sphingolipidoses except? A. There is upregulation in the synthesis of stored lipids B. Most are autosomal recessive C. Accumulation of GM2 ganglioside is caused by hexosaminidase A deficiency D. Deficiency of alpha galactosidase is the cause of fabry's disease E. none of the above

308 A. sphingolipidosis is a group of inherited disorder characterized by accumulation of complex lipids. This is primarily due to defective lyososomal degradation pathway. It particularly affect the CNS because of its reliance to complex lipid myelination processes. The synthesis of stored lipids is intact and not upregulated. Most are autosomal recessive except for fabry disease ( deficiency in a galactosidase) which is x linked recessive.Tay sach disease presenting mental retardation, cherry red macula and muscular weakness, is due to deficiency in hexosaminidase A leading accumulation of GM2 ganglioside.

Which of the following processes does not occur during mobilization of stored fats and fatty acid oxidation? A. cAMP mediated activation of hormone sensitive lipase B. Upregulation of glycerol kinase in the adipocytes C. Transfer of acyl group from coenzyme A to carnitine for transfer to the mitochondrial matrix D. shortening of the fatty acid chain via sequential oxidation,hydration,oxidation, thiolysis reaction E. none of the above

309 B. adipocytes does not have glycerol kinase instead glycerol is transported to the liver wherein it is phosphorylated to produce dihydroacetone phosphate which then can be converted to metabolic precursors for glycolysis or gluconeogenesis. Lippincott 2nd ed pp 181-182

failure in the addition of this signal sequence to lysosomal proteins leads to characteristic mental retardation, coarse facial features, and multiple joint restriction of I cell disease. A. Glyceraldehyde 3 phosphate B. apolipoproteins A2 C. Galactoacylceramide D. Mannose 6 phosphate E. none of the above

310 D. I cell disease is characterized by accumulation of lysosomal proteins in the serum due to failure of the latter to be compartmentalized in the lysosomes. This is due to absent addition of mannose 6 phosphate that is responsible for internalization of these enzymes.

During eukaryotic DNA replication, what type of polymerase is responsible for the synthesis of RNA primer in both leading and lagging strand? A. Pol alpha B. Pol beta C. Pol gamma D. Pol delta E. Pol epsilon

311 A. important eukaryotic polymerase enzymes in DNA replication are as follows: alpha - formation of RNA primers for both leading and lagging strands, delta- elongation of leading strand, epsilon - elongation of lagging strand, gamma - replication of mitochondrial DNA.

which of the following enzyme- product pair is inhibited even by low concentration amanitin (amanita phalloides mushroom) poisoning ? A. RNA pol I/ tRNA B. RNA pol II/mRNA C. RNA pol III/rRNA D. RNA pol I/rRNA E. RNA pol II/ snRNA

312 B. alpha amanitin inhibits eukaryotic RNA polymerase II enzyme that is responsible for the formation of mRNA. RNA pol I forms the rRNA while RNA pol III is for tRNA,snRNA and 5S ribosomal RNA. Lippincott 2nd ed p 384.

During bacterial RNA synthesis, what is the promoter region for RNA polymerase to bind that is located 10 bases upstream from transcription start site? A. Sigma factor B. CAAT box C. Pribnow box D. TATA box E. Rho factor

313 C. for prokaryotic organisms, the promoter regions in the DNA are the pribnow box ( 8-10 nucleotide upstream) and -35 sequence while for the eukaryotics it is the CAAT box (80 nucleotide upstream) and TATA/hogness (25 nucleotide upstream) box. On the otherhand, sigma factor is a component of the RNA polymerase responsible for recognizing the specific promoter region in the DNA strand while rho factor promotes termination of RNA synthesis.

The atoms of the purine ring are contributed by the following except? A. Aspartic acid B. glutamine C. CO2 D. Thiamine pyrophosphate E. Tetrahydrofolate

314 D. purine ring atoms are contributed by the following: aspartate, glycine, glutamine, N10 formyltetrahydrofolate and carbon dioxide. For pyrimidine ring it is contributed by glutamine, aspartic acid and CO2 lippincott 2nd ed p 345

what is the specific mechanism on how clindamycin exerts its effect in protein synthesis? A. Binds to 30s subunit inhibiting initiation of protein synthesis B. Blocks the interaction between aminoacyl tRNA to the mRNA ribosome complex C. irreversible binding to 50s subunit preventing translocation D. inhibits 50s peptidyl transferase preventing translocation E. none of the above

315 C. (SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE) A- streptomycin,B- tetracycline, D- chlorampenicol. Lippincott 2nd ed p 396

the compromise in the energy production seen in wet beriberi is primarily due to what altered process? A. Absence of cofactor in the transketolase activity B. Inhibition of PDH and alpha ketoglutarate complex C. Lack of cofactor supply during oxidation and reduction reactions D. inhibition of transamination reaction leading to underutilization of amino acids during gluconeogenesis E. all of the above

316 B. wet beriberi is a type of severe thiamine deficiency characterized by high output heart failure, neuromuscular symptoms and weakness. The lack of energy generation by the cells is due to inhibition of PDH and a ketogluterate dehydrogenase complex leading to decrease in the levels of ATP and reducing equivalents. transketolase reaction is also catalyzed by thiamine however it is not involved in energy generating pathway but rather it is required in HMP. transamination reaction requires pyridoxine as a cofactor. oxidation reduction reactions uses riboflavin (FAD) and niacin (NAD and NADP) Devlin 6th ed pp 1102-1103

True of alpha-thalassemia: A. Beta chain accumulates and precipitates. B. Gamma chain production is decreased. C. It is transmitted in an autosomal dominant fashion. D. Hemoglobin C disease results if 3 alleles are affected. E. Definitive diagnosis may be done through karyotyping.

32 A. In alpha thalassemia, one or more genes involved in alpha-globin production are defective, leading to relative excess of beta globin and gamma globin chains. Despite being a structural disease, it is transmitted in a autosomal recessive manner. Hemoglobin H (beta globin tetramers) may result from 3 deleted alleles. Hemoglobinopathies are usually diagnosed by hemoglobin electrophoresis.

A 4 weeks old neonate presents to your clinic with generalized hypotonia, respiratory distress, dilated jugular veins, and displaced apex beat. Laboratory shows normal glucose levels, uric acid and blood lactate level. which of the following enzyme is deficient in this patient? A. glycogen debranching enzyme B. muscle glycogen phosphorylase C. alpha 1,4 glucosidase D. glucose 6 phosphatase E. none of the above

320 C. this is a classic case of Pompe disease caused by deficiency of a 1,4 glucosidase aka acid maltase. It is a form of enzyme defect wherein there is accumulation of glycogen granules inside the lysosomes. It doesn’t present with hypoglycemia and lactic acidosis since enzymes for glycogen metabolism are intact. the most common presentation is cardiomyopathy with heart failure. no treatment is available and death usually occurs at 1 mo of age. Devlin p 621.

Which glycolytic enzyme catalyzes a reversible reaction? A. glyceraldehyde phosphate dehydrogenase B. hexokinase C. phosphofructokinase-1 D. pyruvate kinase E. none of the above

321 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Glyceraldehyde phosphate dehydrogenase yields 1,3-bisphosphoglycerate using glyceraldehyde-3-phosphate as its substrate.

The following are causes of conjugated hyperbilirubinemia, except: A. Dubin Johnson syndrome B. Rotor syndrome C. biliary atresia D. Gilbert syndrome E. no exception

323 D. In Dubin Johnson syndrome, the gene encoding MRP- 2, involved in the secretion of already conjugated bilirubin into bile, is mutated. Rotor syndrome is characterized by chronic conjugated hyperbilirubinemia and a normal liver histology. Biliary atresia is a form of biliary tree obstruction and a cause of conjugated hyperbilirubinemia which results in the regurgiation of bilirubin glucuronide into hepatic veins and lymphatics. Gilbert syndrome is caused by mutations in the gene encoding bilirubin- UGT. Harper Biochemistry 28th edition p.282

True regarding the biochemical events occurring during muscle contraction: A. The S-1 head of myosin hydrolyzes ATP to ADP and P1, which remain bound. B. Formation of the actin-myosin-ADP-P1 complex promotes the release of P1, inititating the power stroke. C. Myosin-ATP has a low affinity for actin, which is thus released. D. all of the above E. none of the above

324 D. Harper Biochemistry 28th edition p.550

What is the most potent positive allosteric activator of phosphofructokinase-1, and an inhibitor of fructose-1,6-bisphosphatase? A. fructose-2,6-bisphosphate B. fructose-6-phosphate C. glucose D. acetyl CoA E. none of the above

325 A. Harper Biochemistry 28th edition p.168

In the fed state, the following enzymes' activities are expected to increase, except: A. phosphofructokinase-1 B. pyruvate dehydrogenase C. glucokinase D. glycogen synthase E. cAMP dependent protein kinase

326 E In the fasting state, glucagon stimulates the production of cAMP, activating cAMP-dependent protein kinase, which in turn inactivates PFK-1 and activates fructose-2,6-bisphosphatase by phosphorylation. Harper Biochemistry 28th edition p.169

Which is a true statement? A. Gilbert syndrome is the most common cause of unconjugated hyperbilirubinemia. B. Phenobarbital is effective in the treatment of Crigler Najar type I. C. Crigler Najar type II is the benign form. D. A hemolytic condition is suspected when urinalysis reveals increased amount of conjugated bilirubin but no urobilinogen. E. none of the above

329 C. Neonatal physiologic jaundice is the most common cause of unconjugated hyperbilirubinemia. Phenobarbital has no effect in the treatment of Crigler Najar type I. An obstructive condition is suspected when urinalysis reveals increased amount of conjugated bilirubin but no urobilinogen.

The following are glucogenic, except: A. leucine B. propionyl CoA C. lysine D. A & B E. A & C

330 E Ketogenic only: Leu & Lys. Propionyl resude from an odd chain fatty acid is the only part of a fatty acid that's glucogenic.

Which is a true statement? A. Pyruvate is reduced to form lactate. B. Lactate is oxidized to form pyruvate. C. all of the above D. none of the above

332 C. In the reduction of pyruvate to lactate, NADH+ acts as the electron donor; whereas oxidation of lactate uses NAD+ as the electron acceptor.

The following amino acids are catabolized via a multimeric enzyme complex closely resembling pyruvate dehydrogenase, except: A. leucine B. isoleucine C. lysine D. valine

333 C. The catabolism of leucine, isoleucine, and valine involves reactions analogous to catabolism of fatty acids. There is an involvement of the enzyme branched chain alpha keto acid dehydrogenase, a multimeric enzyme complex of a decarboxylase, transacetylase, and a dihydrolipoyl dehydrogenase closely resembling pyruvate dehydrogenase. Harper Biochemistry 28th edition pp.257-258

Of the following steps in the processing of the fibrillar collagen precursor, which one takes place extracellularly? A. cleavage of the signal peptide B. formation of the triple helix C. quarter staggered alignment assembly D. formation of intrachain and interchain disulfide bonds in extension peptides

334 C. Harper Biochemistry 28th edition p.529 table 48-3

True regarding skeletal muscle, except: A. Skeletal muscle can utilize ketone bodies during starvation. B. Skeletal muscle can contribute to blood glucose. C. Its proteolysis during starvation supplies amino acids for gluconeogenesis. D. Glucagon is unable to stimulate glycogenolysis in skeletal muscle.

336 B. Harper Biochemistry 28th edition p.562 table 49-12

The following clotting factors are properly paired with their common name, except: A. III - tissue factor B. IV - calcium C. V - proaccelerin D. VI - proconvertin

337 D. There is no factor VI. Proconvertin / cothromboplastin / serum prothrombin convertion accelerator (SPCA) is factor VII. Harper Biochemistry 28th edition p. 585 table 51-1

Which of the following is NOT a tyrosine derived hormone? A. Vasopressin B. Prolactin inhibiting hormone C. Thyroxine D. Epinephrine

342 A. Tyrosine is a precursor of L-dopa, dopamine (also known as Prolactin Inhibiting Hormone or Prolactin Inhibiting Factor), norepinephrine, epinephrine, thyroxine and melanin. Vasopressin, or anti-diuretic hormone, is a peptide hormone composed of 9 amino acids, and is not directly derived from tyrosine.

Enzymes as biologic catalysts accelerate biochemical reactions by: A. Lowering the net free energy change (Î"G0) of the reaction B. Lowering the free energy of activation C. Altering the thermodynamic properties of the reaction D. Decreasing the Km of the enzyme for its substrate

343 B. Enzymes act by lowering the free energy of activation, but do not change the energy of the reactants and products, nor the equilibrium of the reaction. Reference: Topnotch Biochem Handouts

All of the following complexes in the Electron Transport Chain are sites of ATP synthesis, except: A. NADH dehydrogenase B. Cytochrome b-c1 complex C. Succinate-CoQ dehydrogenase D. Cytochrome aa3 complex

344 C. Protons are pumped to the intermembranous space to create a gradient (therefore, produce ATP) in 3 complexes: - Complex I or NADH dehydrogenase - Complex III or Cytochrome b/c1 complex - Complex IV or Cytochrome a/a3 or cytochrome oxidase Complex II (Succinate dehydrogenase) does not produce ATP.

Which of the following is true of Km? A. Corresponds to the substrate concentration when initial velocity is Vmax/2 B. Its value increases when the affinity of the substrate to the enzyme increases. C. Corresponds to the reciprocal value of the y-axis in the Lineweaver Burk plot. D. is equal to the value of Vmax when the enzyme is fully saturated with the substrate

348 A. Km, or the Michaelis constant, is the substrate concentration at which the initial velocity is half the maximal velocity (Vmax/2). Km increases when the affinity to the substrate is low, and decreases when the affinity is high. In the Lineweaver Burk plot, the Km is the reciprocal value of the x-axis. Km is always half of Vmax, and is never equal to its value.

A man manifests with short stature. His wife has normal stature, but all his daughters are short and bow-legged. All his sons are normal. The probable mode of inheritance of this disease is? A. Autosomal dominant B. Autosomal recessive C. Mitochondrial D. X-linked dominant E. X-linked recessive

35 D. The disease described fits the profile of Vitamin-D resistant rickets, which is transmitted in a x-linked dominant fashion. 1 genetic question in our Biochemistry exam.

Carbamoyl phosphate synthase I differs from Carbamoyl phosphate synthase II in that the former: A. Is involved in pyrimidine de novo synthesis B. Is stimulated by PRPP C. Is found in the cytosol D. Is a mitochondrial urea cycle enzyme

351 D. All the other choices except D describe CPS II, the rate limiting enzyme in de novo pyrimidine synthesis.

Which apolipoprotein is vital in the clearance of TAGs from chylomicrons and VLDL by lipoprotein lipase? A. Apo E B. Apo C-II C. Apo A-1 D. Apo B-48

352 B. Apo C-II activates lipoprotein lipase for the clearance of triacylglycerols from chylomicrons and VLDS. Apo E - mediates uptake of the chylomicron remnant Apo A-1 - found in HDL; activates LCT/PCAT to produce cholesterol esters Apo B-48 - functions in chylomicron assembly and secretion Reference: Topnotch Biochem Handouts

A 30 year old patient was seen by his physician because of hypertension. Aside from the high blood pressure, lab tests revealed elevated blood cholesterol but normal triglycerides. He was diagnosed as a case of Familial Hypercholesterolemia. The elevated cholesterol in this condition is mainly due to: A. Absence of feedback inhibition on the committed step of cholesterol synthesis B. Defect in LDL receptor and receptor-mediated endocytosis of LDL cholesterol C. Decreased lipoprotein lipase activity D. Absence of apoprotein B-48, C-II and E

353 B. Familial Hypercholesterolemia, which manifests as high LDL levels in laboratory determinations, is due to a deficiency in the LDL receptor. This confers an increased risk of atherosclerosis and coronary heart disease.

Which condition promotes a rightward shift of the hemoglobin saturation curve? A. Decrease in intracellular pH of 7.2 B. Core body temperature of 32°C C. pCO2 of 25 D. Decreased 2,3 BPG concentration

354 A.An increase in CO2, hydrogen ions (acidosis), 2,3-BPG, temperature, and exercise, promotes a shift to the right of oxygen-hemoglobin dissociation curve.

The following biochemical events take place during exercise, except: A. High CO2 and low O2 concentration in the muscle inhibit diffusion of CO2 from the tissues to the RBC +B. Increased [H ] from lactic acid formation will promote O2 release by oxyhemoglobin C. Increase in CO2 will favor deoxyhemoglobin formation, promoting O2 unloading to the tissues D. Increased heat generated in the muscles shifts the oxyhemoglobin binding curve to the right resulting to O2 unloading at the tissue level.

355 A. High CO2 within the muscles during exercise should promote diffusion of CO2 from the tissues to the RBC.

The structural feature of myoglobin that distinguishes it from hemoglobin: A. Quaternary protein composed of alpha and beta globin chains stabilized by non-covalent interactions B. A single polypeptide chains folded to form a globular protein C. A central cavity occupied by 2,3 bisphosphoglycerate D. Salt bridges on the 4 terminal carboxyl groups of the tetramer

356 B. All the other choices except B describe hemoglobin.

HMG-CoA is involved in the synthesis of: A. Cholesterol B. Ketone bodies C. Palmitate D. A and B E. All of the above

363 D. The first two reactions in the cholesterol synthetic pathway are similar to those in the pathway that produces ketone bodies. They result in the production of HMG CoA through HMG CoA synthase. HMG CoA synthase is the limiting enzyme of ketone body synthesis while HMG CoA reductase is the limiting enzyme of cholesterol synthesis. Lippincott 5th pg 220

A 14/F recently broke up with her boyfriend. Due to this she ingested silver jewelry cleaner causing her to lose consciousness after a few minutes. She was immediately taken to the ER. On PE, she was still unconscious and had cherry red cold clammy skin. The patient most likely had inhibition of: A. NADH dehydrogenase B. Succinate dehydrogenase C. Cytochrome b/c1 D. Cytochrome c oxidase E. Coenzyme Q

365 D. Silver jewelry cleaner usually contains cyanide and this causes inhibition of Cytochrome c oxidase (Complex IV). Other substances which inhibit complex IV include sodium azide, hydrogen sulfide and carbon monoxide. NADH dehydrogenase (Complex I), Succinate dehydrogenase (Complex II), Cytochrome b/c1 (Complex III). Lippincott 5th pg 75

True of lipid metabolism EXCEPT A. Short and medium chain fatty acids are absorbed into the enterocyte through micelles B. Digestion of lipids begins in the stomach through acid stable lingual lipase and gastric lipase C. Short and medium chain fatty acids are released directly into the portal circulation bypassing the lacteals D. Pancreatic lipase preferentially cleaves the fatty acids at carbons 1 and 3 forming 2-monoacylglycerol plus free fatty acids

366 A. Short and medium chain length fatty acids do not require the assistance of mixed micelles for absorption by the intestinal mucosa. Lippincott 5th pgs 173-177

Simvastatin is a reversible competitive inhibitor of the rate-limiting step in cholesterol biosynthesis. What change would you expect for Lineweaver-Burke plot? A. The x-intercept would be closer to the zero due to an apparent increase in Km B. The x-intercept would be farther from zero due to an apparent increase in Km C. The y-intercept would be closer to zero due to an apparent decrease in Vmax D. The y-intercept would be farther from zero due to an apparent decrease in Vmax

367 A. Competitive inhibition would cause an apparent increase in Km causing -1/Km to move closer to zero. Choice D would be expected for non-competitive inhibition. Lippincott 5th pgs 60-61

The following are TRUE regarding the HMP shunt EXCEPT? A. Phase 1 reactions are irreversible B. The main products of phase 2 reactions are ribulose 5-P, glyceraldehyde 3-P and fructose 6-P C. The only product of phase 1 reactions is NADPH D. B and C E. No exception

369 D. Phase 1 reactions produce NADPH and ribulose 5-P; Phase 2 reactions produce ribose 5-P not ribulose 5-P Lippincott 5th pg 146

Which of the following transporter systems utilize secondary active transport? A. SGLT-1 transporter B. GLUT-2 transporter C. GLUT-4 transporter D. Cystic Fibrosis Transporter Receptor (CFTR) E. GLUT-5

37 A. GLUT transporters facilitate diffusion, while CFTR use the primary active transport mechanism.

Which essential amino acid is both ketogenic and glucogenic? A. Threonine B. Tyrosine C. Tryptophan D. Leucine E. Lysine

370 B. Leucine and lysine are ketogenic and essential; Threonine glucogenic and essential; Tyrosine both glucogenic and ketogenic but nonessential Lippincott 5th pg 262

Which of the following is/are TRUE regarding RNA? A. Postranslational modification of mRNA includes the addition of a polyadenylate tail and a methylguanosine cap B. snRPs are responsible for the removal of exons and the joining of introns C. RNA polymerase II synthesizes mRNA and miRNA D. A and C E. All of the above

371 D. introns are removed while exons are joined together Lippincott 5th pg 422

What percentage of total caloric intake of fat has been associated with reduced risk of chronic disease while still providing adequate amounts of the nutrient? A. 45-65% B. 10-20% C. 10-35% D. 20-35% E. 5-10%

372 D. AMDR for adults is 45â€"65% of their total calories from carbohydrates, 20â€"35% from fat, and 10â€"35% from protein Lippincott 5th pg 360

Cephalin is made up of: A. two phosphatidic acid residues and a glycerol backbone B. phosphatidic acid and ethanolamine C. phosphatidic acid and glycerol D. phosphatidic acid and choline E. None of the above

373 B. Cephalin/phosphatidylethanolamine; A - cardiolipin; C - phosphatidylglycerol; D - lecithin/phosphatidylcholine Lippincott 5th pg 202

NADPH required for fatty acid synthesis comes from the: A. Hexose monophosphate pathway B. Cytosolic malic enzyme C. Succinyl dehydrogenase D. A and B E. All of the above

375 D. Hexose monophosphate pathway is the major supplier of NADPH for fatty acid synthesis but cytosolic malic enzyme or NADP+ dependent malate dehydrogenase also produces cytosolic NADPH Lippincott 5th pg 186

Which of the following is/are the needed substrate/s in de novo purine synthesis? A. Aspartate B. Carbon dioxide C. Glutamate D. A and B E. All of the above

377 D. Sources of the atoms in the purine ring include aspartate, carbon dioxide, glutamine, glycine and N10- THF. Pyrimidine ring: aspartate, carbon dioxide, glutamine Lippincott 5th pg 293 and 302

Which of the following is/are INCORRECTLY matched? A. Northern blot: RNA B. Southern blot: DNA-binding proteins C. Western blot: protein D. A and B E. None of the above

378 B. Southwestern blot for DNA-binding proteins

Alcohol metabolism produces large amounts of NADH which inhibit gluconeogenesis by? A. shifting the pyruvate-lactate equilibrium towards lactate B. Favoring the producion of oxaloacetate from malate C. Inhibiting the electron transport chain D. All of the above E. None of the above

38 A. NADH shifts oxaloacetate to malate.

Which of the following is/are TRUE regarding hemoglobin? A. One gram of hemoglobin is capable of binding 1.34 mL of O2 B. Binding of an oxygen molecule to one heme group increases the oxygen affinity of the other groups C. The deoxy form of hemoglobin is constrained and has low affinity for oxygen D. A and B E. All of the above

380 E deoxy/taut (T) form - low affinity; oxy/relaxed (R) form - high affinity for oxygen Lippincott 5th pg 28

Which of the following are non-polar amino acids? A. Leucine B. Phenylalanine C. Methionine D. All of the above E. None of the above

381 D. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Non-polar amino acids: Gly, Ala, Phe, Trp, Met, Pro. Uncharged, polar amino acids: Cys, Tyr, Ser, Thr, Asn, Gln. Basic amino acids: His, Arg, Lys. Acidic amino acids: Glu, Asp.

Which of the following substances is a known inhibitor of complex III of the electron transport chain? A. Amytal B. Carboxin C. Malonate D. Actinomycin A E. Sodium azide

383 D. Complex I inhibitors: barbiturate, piericidin A, amytal, rotenone. Complex II inhibitors: malonate, carboxin, TTFA. Complex III inhibitors: antimycin A, dimercaprol. Complex IV inhibitors: cyanide, carbon monoxide, sodium azide, hydrogen sulfide.

What is the rate-limiting enzyme in glycolysis? A. Hexokinase B. Phosphofructokinase C. Phosphoglycerate kinase D. Pyruvate kinase E. Both A and B

384 B.

Which of the following is a cofactor of xanthine oxidase? A. Molybdenum B. Pyridoxine C. Selenium D. Copper E. Vitamin C

385 A.

Which of the following vitamins is required for proper hydroxylation of amino acid residues in collagen? A. Vitamin A B. Vitamin B6 C. Vitamin C D. Vitamin D E. Vitamin E

386 C.

Apo-CII can be found in the following lipoproteins except: A. Chylomicron B. VLDL C. LDL D. HDL E. None of the above

387 C. Apo-CII is an activator of lipoprotein lipase and is naturally found in chylomicrons and VLDL. HDL is used to shuttle Apo-CII.

Which of the following fatty acids is essential and is needed for proper development of vision and learning behavior? A. Linolenic acid B. Linoleic acid C. Oleic acid D. Arachidonic acid E. Stearic acid

390 A. Linolenic acid = omega-3 fatty acid

How much oxygen does 1 g of hemoglobin carry? A. 1.00 mL B. 1.25 mL C. 1.34 mL D. 1.55 mL E. 1.67 mL

392 C. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE.

Fructose enters glycolysis as what intermediate substance in this pathway? A. Dihydroxyacetone phosphate B. Fructose-6-phosphate C. Fructose-1,6-bisphosphate D. Glucose E. 2-phosphoglycerate

395 A. Fructose is phosphorylated by fructosekinase into fructose-1-phosphate. Fructose-1-phosphate is then cleaved by aldolase B to form dihydroxyacetone phosphate (which can now enter glycolysis) and glyceraldehyde. Glyceraldehyde can be phosphorylated by triokinase into glyceraldehyde-3- phosphate (which can also now enter glycolysis).

Which of the following substances would you expect to accumulate when there is a deficiency of homocysteine methyltransferase, such as in cases of homocyteinuria? A. N5-methyltetrahydrofolate B. Methionine C. N10-formyltetrahydrofolate D. Cysteine E. S-adenosylmethionine

396 A. Homocysteine and N5-methyltetrahydrofolate accumulate when there is a deficiency of homocysteine methyltransferase. This enzyme is required to transfer a methyl group from N5- methylTHF to homocysteine to form methionine and tetrahydrofolate.

Which of the following is not a common precursor in both de novo purine and pyrimidine synthesis? A. Aspartate B. Glutamine C. Glycine D. Carbon dioxide E. None of the above

398 C. Precursors of purine: Asp, Gln, Gly, CO2, N10- formyltetrahydrofolate or N5,N10- methenyltetrahydrofolate. Precursors of pyrimidineL Asp, Gln, CO2

Which of the following vitamins is most likely to be deficient in patients who underwent gastrectomy? A. Vitamin C B. Vitamin A C. Vitamin B6 D. Vitamin B12 E. Vitamin E

399 D. Intrinsic factor, which is required for vitamin B12 absorption in the ileum, is produced by parietal cells in the gastric fundus.

A neonate, born at home, with no newborn care administered is rushed to the ER for heavy bleeding from the umbilical stump and recent onset generalized seizures. What vitamin deficiency is responsible for this? A. Vitamin A B. Vitamin D C. Vitamin E D. Vitamin K E. Vitamin C

4 D. This is a classic case of hemorrhagic disease of the newborn. They can present with seizures for intracranial hemorrhage. Source: Harper 27th ed p 495

Utilization of Galactose by the body enters the Embden-Meyerhof Pathway thru which Intermediate? A. Citrate B. Glucose-6-Phosphate C. Fructose-6-phosphate D. Succinyl CoA E. Fumarate

404 B. Galactose is converted to Galactose-1-phosphate by galactokinase/hexokinase, Gal-1-Phosphate is then converted to Glucose-1-phosphate by Hexose-1- phosphate uridyltransferase and is then converted again to Glucose-6-phosphate by Phosphoglucomutase, Embden Meyerhof pathway is the other name for Glycolysis, A,D and E are intermediates of the Kreb's Cycle.

Fat provides how many percentage of the energy requirements in humans? A. 10-35% B. 10-20% C. 20-35% D. 20-50% E. 45-65%

406 C. Carbohydrates: 45-65%; Protein 10-35%(SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE)

Which of the following amino acids will be most likely found in the interior of a protein? A. Cysteine B. Leucine C. Isoleucine D. B and C E. All of the above

407 D. Leucine, Isoleucine, Valine, Alanine, Glycine, Phenylalanine, Tyrosine, Methionine and Proline are all Non-polar Amino acids, hence can be found in the interior of a protein.

The following statements are true regarding the utilization of Pyridoxine by the human body, EXCEPT: A. Coenzyme for Glycogen phosphorylase B. Coenzyme for ALA Reductase C. Synthesis of Niacin from Tryptophan D. Synthesis of GABA from Glutamate E. Coenzyme of Cystathione synthase

408 B. All are correct except B which is supposed to be "Coenzyme for ALA synthase"

A pediatric patient presented to you with noted Basophilic stippling on RBC, Memory loss, Peripheral Neuropathy, and lines in the gums, due to your diligent history, you extracted from the patient's mother that the walls of their house had several "chapped" paints, which the patient may have ingested. Which of the following enzymes in heme synthesis is inhibited by the said suspected ingested substance? A. ALA Dehydratase B. ALA reductase C. ALA synthase D. Uroporphyrinogen decarboxylase E. Uroporphyrinogen synthase

409 A. This is a classic case of Lead poisoning. ALA dehydratase together with ferrochelatase are both inhibited by lead. (similar to a SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLEion)

Which of the following is true? A. Brain cells prefer fatty acid as fuel source B. Cardiac muscle prefer glucose as fuel source C. Adipose cells prefer ketone bodies as fuel source D. One-half of the glycogen stores is in the muscles E. NOTA

41 E Brain cells prefer glucose as fuel source. Cardiac muscle prefer fatty acid as fuel source. Adipose cells prefer fatty acid as fuel source. 3/4 to 4/5 of glycogen are stored in skeletal muscles.

An 8 month-old patient presented to you with noted black conjunctival pigment, upon examination you noted that the patients diaper had black stains. What enzyme is most likely deficient in this patient? A. Dihydropteroate synthase B. Cystathione synthase C. Phenylalanine hydroxylase D. Homogentisic Acid Oxidase E. Tyrosine hydroxylase

410 D. This is a classic case of Alkaptonuria, an Inborn error of metabolism.

Which of the following Apolipoproteins is a cofactor for Lipoprotein Lipase? A. A-1 B. B-100 C. C-II D. B-48 E. E

411 C.

A female african-american patient presented to you with anemia, tissue anoxia, and painful crises, Upon doing a PBS, the pathologist noted several misshapen RBCs, forming crescent shapes. Which of the following is true regarding the pathophysiology of this disease? A. Lysine is substituted for Glutamate in the 6th position B. Lysine is substituted for Glutamate in the 8th position C. Valine is substituted for Glutamate in the 6th position D. Valine is substituted for Glutamate in the 8th position E. There is a mutation in the development of Ankyrin/Spectrin

412 C. This is a classic case of Sickle Cell Anemia, caused by a point mutation in both genes coding for the B chain that results in the replacemnt of Glutamate by Valine in the 6th position.

When old RBCs are degraded by the spleen, Free hemoglobin is produced. One of the following binds extracorpuscular hemoglobin, preventing free hemoglobin from entering the kidneys: A. Ferritin B. Transferrin C. Albumin D. Haptoglobin E. Hemopexin

413 D. Haptoglobin prevents loss of free hemoglobin thru the kidneys, thus conserving the Iron present in hemoglobin which would otherwise be lost in the body.(SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLEion)

Jaundice is a clinical sign when there is systemic yellowish discoloration. This is prevented by its catabolic pathway, which of the following enzymes convert bilirubin into a colorless compound? A. Urobilinogen reductase B. B-Glucuronidase C. UDP-Glucose Dehydrogenase D. Biliverdin reductase E. Cytochrome P450

414 B. B-Glucuronidase is an enzyme present in intestinal bacteria, which converts conjugated bilirubin to a colorless substance called Urobilinogen and is then converted to Stercobilin (Feces) or Urobilin (Urine) (SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLEion)

This is a branch of medical science wherein it involves the design of computer algorithms and construction of databases that enable biomedical scientists to access and analyze the growing avalanche of biomedical data A. Genomics B. Genetics C. Bioinformatics D. Computational Biology E. Human Genome Project

415 C. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE

Eicosanoids are important groups of physiologically and pharmacologically active compounds, including Prostaglandins, thromboxanes, leukotrienes and lipoxins. Which of the following Fatty acids can Eicosanoids be derived from? A. Linoleic Acid B. Palmitic Acid C. Linolenic Acid D. Oleic Acid E. Stearic Acid

416 A. Linoleic Acid is an essential fatty acid which is the precursor of a membrane phospholipid, Arachidonic Acid which is the main component for the synthesis of Eicosanoids.

Sickle Cell Anemia is a mutation were an amino acid in a sequence has been replaced by a different amino acid, What type of mutation is indicated in this case? A. Silent B. Missense C. Nonsense D. Transition E. Transversion

417 B. Silent-New codon, same amino acid; Nonsense-Stop codon; Transition-Purine-Purine change; Transversion-Purine-Pyrimidine Change(PSIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE)

This rule indicates that the total amount of purines equals the total amount of pyrimidines in a sequence: A. Shine-Dalgarno's Rule B. Chargaff's Rule C. Pribnow's Rule D. Hogness' Rule E. Sanger's Rule

418 B. In any sample of dsDNA, the amount of Adenine equals to the amount of Thymine, the amount of Guanine equals to the amount of Cytosine.

Tetracycline is an antibiotic which inhibits protein synthesis in prokaryotes, specifically, on what aspect of protein synthesis does it act? A. Inhibits prokaryotic peptidyltransferase B. Binds to the 50s subunit and distorts its structure C. Binds to the B-subunit of bacterial DNA-dependent RNA polymerase D. Prevents binding of aminoacyl tRNAs to the A site E. Inactivates Elongation Factor-2

419 D.

True 5-Fluorouracil A. Causes thymineless death B. Used as a chemotherapeutic agent for colonic carcinoma C. Inhibitis thymidylate synthase D. Both B and C E. AOTA

42 E

You and your friends went to Vikings for an eat-all-you-can buffet, during your fed state the following biochemical reactions are currently occuring in your body except: A. Increased Protein synthesis by the muscles B. Increased Triglyceride synthesis and storage C. Replenished its glycogen stores D. Decreased Glucagon:Insulin ratio E. Increased Epinephrine levels

420 E Increased Epinephrine levels are seen in the fasting state, which promotes Glycogenolysis to maintain normal blood glucose levels

To maintain normal protein and energy balance in the body, the carbon skeletons of amino acids are catabolized yielding different intermediates including ketone bodies. Which of the following amino acids is exclusively ketogenic? A. Phenylalanine B. Leucine C. Isoleucine D. Methionine E. All of the above

421 B. Leucine and lysine are the only ketogenic amino acids. They can be degraded directly to become acetyl CoA by ketogenesis (acetoacetate). They cannot be converted to glucose since the carbon atoms in the ketones are ultimately degraded to carbon dioxide. Phenylalanine and isoleucine, as well as tyrosine and tryptophan are both ketogenic and glucogenic; while methionine and the rest of the amino acids are glucogenic.

A 9-month old female was observed to have excessive REDUCING sugars in the urine. She was also noted to be jaundiced, hypoglycemic, acidotic, and with elevated AST. There was significant improvement upon removal of the sugar from her diet. The patient is most likely suffering from deficiency of: A. Aldolase B B. Fructokinase C. Glucokinase D. Galactose-1-phosphate uridyltransferase A

423 A. The first clue here is the involvement of a REDUCING sugar, and fructose should be our main consideration. There are only 2 metabolic disorders involving fructose that we should know - essential fructosuria (fructokinase deficiency) which is essentially benign and asymptomatic, and hereditary fructose intolerance in which aldolase B is deficient. Absence of aldolase B leads to intracellular trapping of fructose 1- phosphate which results in vomiting, severe hypoglycemia, jaundice, hemorrhage and finally, hepatic failure. Removal of dietary fructose on the other hand serves as the main therapy.

Peptide bonds covalently join amino acids to form proteins. They are amide linkages between the alpha-carboxyl group of 1 amino acid and the alpha-amino group of another. Which of the following statements about peptide bonds is true? A. Rapid exposure to strong acids is required to hydrolyze peptide bonds non-enzymatically. B. They can be broken by exposure to high concentrations of urea. C. Trypsin can cleave peptide bonds on the amino end of proteins. D. They possess a partial double-bond character. E. All of these are true.

424 D. The partial double-bond feature of peptide bond makes the structure of protein rigid and planar at the same time, just enough to allow assumption of certain configurations. Prolonged exposure to strong acid or o base at elevated temperatures (at 110 C for 24 hours) is required to hydrolyze these bonds non- enzymatically. Urea cannot break down these bonds whereas trypsin can cleave them only at the carbonyl side of either arginine or lysine.

Deficiency of which of the following vitamins predisposes a patient to anemia? A. Iron B. Vitamin B2 C. Vitamin B6 D. Vitamin D

425 C. Vitamin B6 (pyridoxine phosphate) is a co-factor in the formation of delta-aminolevulinic acid, the rate- limiting step in heme synthesis; and is catalyzed by ALA synthase. This is also the reason why isoniazid therapy in which pyridoxine deficiency may be common, can result in anemia. Iron, although essential in heme synthesis, is not considered a vitamin but a mineral. (Always remember the rule, CHOOSE THE BEST ANSWER). Vitamin is organic, mineral is not.

A 24-year old asymptomatic patient was noted to have decreased hemoglobin and hematocrit. Her RBC indices were MCHC 26%, MCV 74 fL - hypochromic, microcytic. At this point, your most likely consideration for the cause of anemia would be: A. Iron deficiency B. Folate deficiency C. Spherocytosis D. Acute blood loss from menstruation

426 A. It may not be your typiCal biochem question but you should know that anything can be asked in any subject, and biochem is no exception. Our main hint here is the RBC indices indicating a hypochromatic, microcytic type of anemia. You should only remember 5 anemias exhibiting this picture and the mnemonic is CLITS - anemia of Chronic disease, Lead poisoning, Iron deficiency anemia, Thalassemia and Sideroblastic anemia. For megaloblastic (macrocytic) anemias, just remember folate and vitamin B12 deficiency, and pernicious anemia. Acute blood loss and spherocytosis is often times normocytic and normochromic. Keeping this in mind, you'll get a very good chance in answering questions not only in biochem, but more likely in physio, patho, IM, and pedia.

Bilirubin is conjugated in the liver mainly for the purpose of: A. Increasing the levels of delta bilirubin which is the less toxic form. B. Making it more water-soluble for easier excretion. C. Inhibiting its binding with albumin to reduce risk of jaundice. D. Keeping its value less than 0.1 mg/dL in the blood. E. All of these.

427 B. Keep yourself from choosing "all of the above" that easily. You have to really read through and analyze. The goal of bilirubin conjugation is to make it more soluble in water (plasma) so that it can be easily excreted (direct bili/B2). Delta bilirubin is bilirubin covalently bound to albumin, which is also non-toxic but cannot be excreted; it happens in prolonged periods of hyperbilirubinemia. Indirect bilirubin naturally binds with albumin for transport to the liver for conjugation. Bilirubin levels must be below 2.5 mg/dl to prevent development of jaundice.

Which secondary messenger system is utilized by the hormone glucagon? A. Tyrosine kinase B. cGMP-guanylate cyclase C. None, it binds intracellularly D. cAMP-adenylate cyclase

430 D. Must remember at least 2 examples for each secondary messenger system: glucagon and epinephrine (β and α2) for cAMP pathway; ANP and NO for cGMP; insulin and growth factors for tyrosine kinase; epinephrine α1 for IP3/DAG; and glucocorticoids and thyroid hormone for the intracellular pathway.

The last step in the enterohepatic circulation involves: A. Removal of taurine/glycine from the bile salt compound. B. Reabsorption of about 95-99% of primary and secondary bile acids in the ileum with excretion of some unesterified cholesterol. C. Dehydroxylating action of intestinal bacteria on primary bile acids with their conversion to secondary bile acids in equal molar amounts. D. The 7-alpha-hydroxylation of cholesterol as catalyzed by cholesterol 7-alpha hydroxylase. E. None of these.

432 B. The answer lies in the main purpose of the enterohepatic circuit and that is to reabsorb majority of bile acids and recycle them in the liver while also serving as the mean for excreting body cholesterol.

The enzyme responsible to replace the stretches of highly repititive DNA found at the ends of linear chromosomes in cells in order to avoid aging as seen in cancer and germline cells is: A. Elongase B. Transcriptase C. Telomerase D. Polymerase

434 C.

This is a disease condition resulting from formation of thymine dimers secondary to exposure to UV without its normal removal by UV-specific endonuclease: A. Epidermolysis bullosa B. HNPCC C. Xeroderma pigmentosum D. FAP

435 C.

What constitute the central dogma? A. Replication, DNA synthesis, proofreading B. Replication, transcription, translation C. Transcription, translation, modification D. Translation, modification, labeling and secretion E. All of these may constitute the central dogma.

436 B.

Cystinuria is an inherited condition characterized by formation of kidney stones brought about by defects in the renal tubular amino acid transporter for: A. Ornithine B. Arginine C. Cystine D. All of these E. None of these

438 D. Cystinuria is the most common genetic error of amino acid transport. It has defective kidney tubule reabsorption of the amino acids cysteine, ornithine, lysine and arginine (mnemonic: COLA). There is precipitation of cystine to form kidney stones which can cause urinary tract obstruction. Under the microscope, you can appreciate cystine as hexagonal- shaped crystals in the urine, looking much like your favorite "Piattos" chips.

In the regular human diet, the estimated energy requirement coming from fat is set at: A. 10-25% B. 20-35% C. 45-65% D. >60%

439 B. This topic is must know. For carbohydrate, it is 45- 65% and for protein 10-35%. The expected total energy required per day for a sedentary person is set at 30 kcal/kg/day; for the moderately active and in- patients, 35 kcal/kg/day; and for the very active, 40 kcal/kg/day.

Hemoglobin is different from myoglobin by: A. Having oxygen dissociation curve that is sigmoidal in shape B. Possessing 4 polypeptides in the form of globins C. Exhibiting allosteric effects D. Being utilized for oxygen transport rather than storage E. All of these

440 E Myoglobin on the other hand, has only 1 polypetide, it has a hyperbolic-shaped oxygen dissociation curve and functions mainly as storage for oxygen both in heart and skeletal muscles. Myoglobin is the EARLIEST detectable cardiac element found in plasma during MI.

Electrons are passed down the transport chain to create proton gradient which results to ATP synthesis. Several inhibitors stop electron flow from substrate to oxygen. Inhibitor/s of Cytochrome oxidase include/s: A. Cyanide B. Malonate C. Hydrogen sulfide D. A and B E. A and C

441 E Electron Transport Chain Inhibitors: Complex I- Barbiturate, Piericidin A, Amytal, Rotenone, Complex II-Malonate, Carboxin, TTFA, Complex III-Antimycin A, Dimercaprol, Complex IV-Cyanide, Carbon monoxide, sodium azide, hydrogen sulfide

All are true of the pentose phosphate pathway, EXCEPT: A. It provides the route for metabolism of 5-carbon sugars B. It is the source of ribose 5-phosphate for nucleotide synthesis C. It is only functional in red blood cells D. It is the source of reduced NADP E. It is active in tissues that produce lipids

443 C. Pentose phosphate pathway occurs in the cytoplasm of RBCs, liver, adipose tissue, adrenals, thyroid, testes, lactating mammaries and tissues that are producing lipids.

A non-competitive inhibitor of an enzyme: A. Increases Km and decreases affinity B. Decreases Km and increases affinity C. Increases Vmax D. Decreases Vmax E. None of the above

444 D. Non-competitive inhibitor results to decreased Vmax but it does not affect KM and affinity.

In prokaryotic RNA synthesis, the function of the "rho" factor: A. It initiates the binding of RNA polymerase B. It participates in proper termination of transciption C. It binds repressor to the promoter region D. It increases the rate of RNA synthesis E. It eliminates binding of RNA polymerase to promoter region

445 B. rho factor is required for termination of transcription of genes.

In contrast to RNA polymerase, DNA polymerase: A. Synthesizes RNA primer to initiate DNA synthesis B. It fills in the gap between Okazaki fragments C. Synthesizes in a 3' to 5' direction D. Does not edit as it synthesizes E. Does not require a primer

446 B. DNA polymerase synthesizes DNA in both strands, the leading and lagging strands, catlyzes chain elongation, proofreads the newly synthesized DNA, read template in 3' to 5' direction and synthesize in 5' to 3' direction. Primase not DNA polymerase synthesizes short stretches of RNA called primers.

The oxidation of pyruvate to acetyl coA by pyruvate dehydrogenase is dependent on this vitamin co-factor: A. Biotin B. Niacin C. Thiamine D. Vitamin C E. Vitamin A

448 C. Conversion of pyruvate to acetyl CoA is through the pyruvate dehydrogenase complex which requires the presence of 5 co-enzymes including: thiamine, FAD, NAD, Pantothenic acid and lipoic acid.

All of these enzymes act on protein substrates in the small intestines A. Trypsin, chymotrypsin, elastase B. Pepsin, trypsin, chymotrypsin C. Amylase, pepsin, trypsin D. Elastase, pepsin, amylase E. Pepsin, chymotrypsin, elastase

451 A. polypeptides and amino acids are digested further in the small intestines by elastase, carboxypeptidase, trypsin, chymotrypsin; pepsin is in the stomach, amylase is for digestion of carbohydrates

The common biochemical pathology seen in Creutzfeld-Jakob disease and Alzheimer's Disease: A. Improper folding of affected proteins due to absence of chaperones B. Mutated apolipoprotein E is the primary cause C. Aggregation of infected proteins forming neurofibrillary tangles D. Secondary helical structure of affected proteins are transformed to B sheet E. Fatal neurodegenerative disease due to accumulation of amyloid plaques

456 D. Creutzfeld-Jakob disease is a fatal neurodegenerative disease Caused by an altered version of normal protein to a pathologiC Conformation whiCh is riCh in B-sheets. Alzheimer disease is progressive cognitive and behavioral impairment due to accumulation of amyloid plaques and neurofibrillary tangles. Similar to CJB, alzheimer's disease also is rich in B-sheet prone to self- aggregation. Harper's, 27th Ed. p38.

This inborn error of metabolism is manifested by convulsive seizures, lens subluxation, damage of the arterial walls, myocardial infacrtion and skeletal deformities: A. I-cell Disease B. Marfan syndrome C. Homocystinuria D. Cystinuria E. Porphyrias

457 C. Homocystinuria is an inborn error of metabolism which is manifested by convulsive seizures, lens subluxation, damage of the arterial walls, myocardial infacrtion and skeletal deformities; I-cell Disease is due to accumulation of partially degraded glycoproteins in lysosomes manifested as severe mental retardation, coarse facial features, Marfan syndrome is due to defect in the gene encoding for fibrillin resulting to lens subluxation, aortic dilatation, archnodactyly, Cystinuria is due to inherited defect or renal tubular amino acid transporter leading to formation of staghorn calculi, porphyrias is due to defect in heme synthesis resulting to photosensitivity and overt blistering after sun exposure.

The rate-limiting step of fatty acid oxidation is: A. Activation of fatty acid B. Transport of fatty acyl CoA to mitochondria C. Formation of malonyl CoA D. Provision of fatty acid E. None of the above

458 B. Transport of fatty aCyl CoA to mitoChondria is the rate-limiting step in B-oxidation whiCh is Catalyzed by Carnitine aCyltransferase. Activation of fatty acids is the only step in the complete degradation of a fatty acid that requires energy from ATP. Harper's, 27th Ed. p187.

Deficiency of the activities of DNA repair system leading to sunlight sensitivity and susceptibility in persons at risk for Xeroderma pigmentosum is in the: A. Base excision repair system B. Nucleotide excision repair system C. Double-strand break system D. Mismatch repair system E. Multifunctional repair system

459 B. Nucleotide excision repair is used to replace regions of damaged DNA caused by UV light inducing the formation of thymine dimers. A special excision nuclease cuts the DNA upstream and downstream of the defective region. The gap is then filled by a polymerase. Harper's p. 344-345

The Krebs or Citric acid cycle is the final common pathway of the following except: A. carbohydrate B. protein C. lipid D. A and B E. None of the choices

462 E krebs or citric acid cycle is the final common pathway of carbohydrate, protein, and lipid

What is the rate-limiting enzyme in cholesterol synthesis? A. HMG CoA synthase B. HMG CoA reductase C. Acetyl CoA carboxylase D. Carnitine acyltransferase E. cholesterol - 7 - α - hydroxylase

463 B. The following are the rate limiting enzymes for: HMG CoA synthase = ketogenesis; HMG CoA reductase = cholesterol synthesis; acetyl CoA carboxylase = fatty acid synthesis; carnitine acyltransferase = fatty acid oxidation; cholesterol - 7 - α - hydoxylase = bile acid synthesis

Bile acids are synthesized from cholesterol. Which of the following is an example of primary bile acids? A. Lithocholic acid B. Chenodeoxycholic acid C. Deoxycholic acid D. All of the choices E. None of the choices

464 B. chenodeoxycholic acid and cholic acid are the primary bile acids, while lithocholic and deoxycholic acid are the secondary bile acids

What is the "mother hormone" of all steroid hormones? A. pregnenolone B. cholesterol C. hydroxypregnenolone D. progesterone E. Aldosterone

465 A. cholesterol is the precursor of all steroid hormones while pregnenolone is the "mother hormone" of all steroid hormones. Other choices are derivatives of pregnenolone.

Cardiolipin is an important phospholipid characterized as follows except: A. antigenic phospholipid B. Found in mitochondria and cytoplasm C. Found in mitochondria only D. Reacts with antibodies produced against Treponema pallidum E. none of the choices

466 B. Cardiolipin is a phospholipid that is antigenic which reacts with antibodies against Treponema pallidum. It is found only in mitochondria which is essential for mitochondrial function.

A single DNA base substitution resulting to formation of a different amino acid. A. Frame shift mutation B. Nonsense mutation C. Missense mutation D. Silent mutation E. None of the choices

468 C. frameshift mutation involves deletion or addition of a base resulting to a shorter nonfunctional protein. Nonsense mutation results to a stop codon. Missense mutation forms a different amino acid. Silent mutation forms same amino acid.

A 60 year old female diabetic patient was given 20U of regular insulin at bedtime by her daughter. Few hours later, the blood sugar level was at 39mg/dl. In order to increased her blood sugar level, her body should produce what hormone/s? A. glucagon B. epinephrine C. cortisol D. all of the above E. A and C only

471 D. The counter-regulatory hormones of insulin are glucagon, cortisol, epinephrine, and growth hormone.

A 6 year old child presents with pallor. As her attending physician, you request for CBC which revealed a hemoglobin of 9g/dl. What medication/s should you give to this patient. A. Iron B. Vitamin C C. Zinc D. Iron and Vitamin C E. Iron and zinc

474 D. This child is most likely having an iron deficiency anemia. Iron should be given in this patient along with Vitamin C which increases iron absorption.

This disease is caused by low activities of orotidine phosphate decarboxylase and orotate phosphoribosyltransferase which causes abnormal growth and anemia. What type of anemia is present in this disease? A. hypochromic anemia B. microcytic anemia C. megaloblastic anemia D. sideroblastic anemia E. none of the choices

476 C.

NADH produced from aerobic glycolysis proceeds to the electron transport chain. If one molecule of NADH enters a neuron, how many ATP are produced? A. 1 B. 2 C. 3 D. 4 E. 5

479 B. NADH needs a shuttle in order for it to enter the mitochondrial membrane to enter the ETC. There are 2 shuttles used - the malate aspartate shuttle present in liver, kidney, and heart which produces 3 ATP in one NADH; and the glycerol phosphate shuttle present in skeletal muscle and brain which produces 2 ATP in one NADH.

Which of the following is a complex 4 inhibitor A. Amobarbital B. CO C. Antimycin A D. Dimercaprol E. 2,4 dintrophenol

48 B. Amobarbital - Complex 1 inhibitor, CO - complex 4 inhibitor, Antimycin A and Dimercaprol - complex 3 inhibitor. 2,4 dintrophenol - uncoupler

A 3 day old infant presents with vomiting and diarrhea after milk ingestion. Blood sugar level was 40 mg/dl. The infant develops a cataract few days after. What is responsible for the disease. A. Galactokinase deficiency B. galactokinase excess C. Gal-1-P uridyltransferase deficiency D. hexokinase deficiency E. aldolase B deficiency

480 C. Gal-1-P uridyltransferase deficiency causes classic galactosemia which presents with vomiting, diarrhea, hypoglycemia, lethargy, hypotonia, liver disease, and cataracts within a few days of birth. While in galactokinase deficiency, cataracts develop later in early childhood. In aldolase B deficiency, cataract is not characteristic.

Which is FALSE regarding beta bends? A. They are also known as beta turns. B. They fall under secondary structure. C. They are usually composed of proline and alanine. D. Beta bends often promote the formation of antiparallel beta sheets.

482 C. Proline and glycine are frequently found in beta bends; proline because its cyclic structure is ideally suited for the beta turn, and glycine because with the smallest side chain of all the amino acids, it is the most stericallly flexible.

The most appropriate and prompt treatment for galactosemia is: A. Enzyme replacement B. Hormone therapy C. Special infant formula D. Vitamin therapy

483 C. Galactosemia is due to an enzyme deficiency (galactose-1-phosphate uridyl transferase) which leads to accumulation of galactose-1-phosphate in the tissues. Treatment consists of prompt elimination of lactose-containing milk from the diet in infancy.

A 13-year-old healthy Jewish girl, Anne Frank, is found to have mild anemia, leukopenia, and thrombocytopenia. Physical exam reveals an enlarged spleen. Bone marrow exam shows abnormal cells. The diagnosis can be confirmed by measurement of the activity of which of the following enzymes? A. glucocerebrosidase B. sphingomyelinase C. hexosamidase A D. sulfatase A

484 A. This is a case of Gaucher disease. The diagnosis is confirmed by the absence of glucocerebrosidase activity in leukocytes, in cultured skin fibroblasts and liver cells. Spingomyelinase deficiency causes type A Niemann-Pick disease, hexosaminidase A deficiency causes Sandhoff disease, sulfatase A deficiency causes metachromatic leukodystrophy. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE

A 60-kg medical student rides the jeepney daily, spends 8 hours in class sitting down, goes home and studies for another 3 hours or so. What should be his total caloric intake daily in order for him to maintain his current weight? A. 1,200 kcal B. 1,000 kcal C. 1,800 kcal D. 2,400 kcal

485 C. Calorie intake for weight maintenance is as follows according to Schwartz: for sedentary lifestyle: 25 kcal/kg, moderately active lifestyle: 30 kcal/kg, heavy activity lifestyle: 35 kcal/kg. Minus 5kcal each for weightloss and add 5kcal each for weight gain. There were some computations like this during our exam. Biochem lec values as follows: 30 kcal/kg sedentary, 35 kcal/kg moderate, 40 kcal/kg heavy.

A 6-month old child was noted to have slow weight gain and mild delay in achieving developmental milestones. One morning the parents noted that their child seems unable to move the right side of his body. Which condition could explain this child's presentation? A. phenylketonuria B. cystathioninuria C. homocystinuria D. maple syrup disease

486 C. Strokes in the young should increase the suspicion of homocystinuria. It can cause thromboembolic phenomena in the pulmonary and systemic arteries, and particulary the cerebral vasculature.

Which of the following is FALSE regarding gene therapy? A. It is a safe and effective therapy. B. It can be used to treat not only inherited disorders but certain types of cancer and viral infections as well. C. It is the use of DNA encoding for a functional, therapeutic gene to replace a mutated gene. D. Viruses have been used as a vector for gene therapy.

488 A. Several questions regarding gene therapy were asked during our exam. Although gene therapy is a promising treatment option for a number of diseases, the technique remains risky and is still under study to ensure that it is safe and effective.

True of Central Dogma of Molecular Biology A. Translation --> Transcription --> replication B. Replication --> transcription --> translation C. Transcription --> translation --> replication D. Translation --> replication --> transcription E. NOTA

49 B.

Which apolipoprotein activates lecithin-cholesterol acyltransferase (LCAT)? A. E B. A-1 C. C-II D. B-48

490 B. Apolipoprotein A-1 is found in HDL alone.

Paulo ordered two-piece chicken and large fries for lunch. Which among the enzymes would increase in activity? A. Pancreatic lipase B. Lipoprotein lipase C. Hepatic TG lipase D. Hormone-sensitive lipase

491 A. Pancreatic lipase is used for the degradation of dietary TG in the small intestine. LPL is for TG degradation circulating in chylomicrons and VLDLs. HL is for the degradation of TG remaining in IDL. Hormone- sensitive lipase (sensitive to catecholamines, glucagon etc.) is for the degradation of TG stored in adipocytes.

The liver is NOT able to utilize ketone bodies because of the lack of the enzyme: A. thiolase B. thiosuccinase C. thiophorase D. Thionase

493 C. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Thiophorase is an enzyme that converts ketone bodies to acetyl CoA.

Carbon monoxide poisoning inhibits which complex in the mitochondrial electron transport chain? A. Complex II B. Complex III C. Complex I D. None of the above

494 D. Carbon monoxide, together with cyanide, hydrogen sulfide and azides, inhibits cytochrome c oxidase or complex IV. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Know the other complex inhibitors.

Biotin is used as a cofactor for the following enzymes, EXCEPT: A. Pyruvate carboxylase B. Acetyl-CoA carboxylase C. Propionyl-CoA carboxylase D. Succinyl-Coa carboxylase

495 D. The rest of the choices use biotin which adds a 1- carbon group to the substrate.

A middle aged woman presents with depression, progressive dementia, and choreiform movements. You suspect that she is suffering from a trinucleotide repeat expansion disease which is multiple repeats of: A. CGG B. GAA C. CAG D. CTG

496 C. CGG is for Fragile X, GAA is for Friedrich's ataxia, CTG is for myotonic dystrophy.

Which of the following post-transcription modifications take place to produce eukaryotic mRNA? A. Addition of 7-methylguanosine cap on the 5' end B. Polyadenation on 3' end C. Splicing out of introns D. All of the above

497 D. All these steps happen to produce the mature eukaryotic mRNA.

A person at risk for all types of skin cancer would have a defect in: A. Base excision repair B. Mismatch repair C. Nucleotide excision repair D. Any of the above

499 C. Nucleotide excision repair is the primary defect in xeroderma pigmentosum, which prevents repair of pyrimidine dimers because of ultraviolet light exposure.

What is the rate limiting enzyme of ketogenesis? A. HMG-CoA synthase B. HMG-CoA reductase C. HMG-CoA lyase D. HMG-CoA transferase E. All of the above

5 A. HMG CoA reductase is the rate limiting enzyme for cholesterol synthesis. Source: Harper 27th ed p 191

2. These vitamins are toxic in excess: A. Vitamin A and B B. Vitamin B and C C. Vitamin C and D D. Vitamin A and D E. Vitamin D and E

502 D. There is only a limited capacity to metabolize vitamin A, and excessive intakes lead to accumulation beyond the capacity of binding proteins, so that unbound vitamin A causes tissue damage. Symptoms of toxicity affect the central nervous system (headache, nausea, ataxia, and anorexia, all associated with increased cerebrospinal fluid pressure); the liver (hepatomegaly with histologic changes and hyperlipidemia); calcium homeostasis (thickening of the long bones, hypercalcemia, and calcification of soft tissues); and the skin (excessive dryness, desquamation, and alopecia). Harper's 27th ed., 491-92. Some infants are sensitive to intakes of vitamin D as low as 50 g/day, resulting in an elevated plasma concentration of calcium. This can lead to contraction of blood vessels, high blood pressure, and calcinosisâ€" the calcification of soft tissues. Harper's 27th ed., 93

4. Major end product of nitrogen catabolism in humans: A. glutamate B. urea C. uric acid D. ammonia E. Creatinine

504 B. Harper's 27th ed., 249

5. Most important intracellular buffer: A. bicarbonate B. carbon dioxide C. water D. proteins E. Phosphate

505 D. Buffers are solutions of weak acids or bases and their conjugates that has the ability to resist a change in pH following addition of strong acid or base. Bicarbonate is the most important extracellular buffer. Proteins are the most important intracellular buffer.

7. Inhibitor of Complex III of the electron transport chain: A. Barbiturate and Amytal B. Dimercaprol and antimycin C. Cyanide and hydrogen sulfide D. Malonate and carboxin E. Cyanide and carbon monoxide

507 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. 3-4 questions of this type came out in my boards Complex I inhibitors: Barbiturate, Piercidin A, Amytal, Rotenone Complex II inhibitors - Malonate, Carboxin, TTFA Complex III inhibitors - Antimycin A, Dimercaprol Complex IV inhibitors - Cyanide, Carbon monoxide, sodium azide, hydrogen sulfide

9. Metabolic pathway that provides a source of NADPH required for reductive reactions and also yields ribose for nucleotide synthesis and glycolytic intermediates. A. Hexose monophosphate shunt B. Gluconeogenesis C. Aerobic Glycolysis D. Anaerobic Glycolysis E. Tricarboxylic acid cycle

509 A. HMP of Pentose phosphate pathway is an important source of NADPH and ribose. Gluconeogenesis is responsible for generation of glucose from non- carbohydrate sources as glycerol and amino acid. Glycolysis is breakdown of carbohydrates into glucose molecules that can be absorbed by the body. Tricarboxylic acid cycle or Kreb's cycle produces 3 NADH, 1 FADH2, 2 CO2, and 1 GTP per acetyl-CoA. First Aid 2013, p.103

Lactic acid is considered to be a weak acid because: A. It is insoluble in water at standard temperature and pressure. B. It fails to obey the Henderson-Hasselbalch equation. C. The equilibrium between the acid and its conjugate base has a pKa of 5.2.. D. The lactate anion has minimal tendency to attract a proton. E. NOTA

51 C. Weak acids like lactic acid never completely dissociate. The indicated pKa of 5.2 is consistent with the idea that the lactate anion retains a strong affinity for protons, a hallmark of a weak acid. The lactate anion is highly water-soluble. All weak acids obey the Henderson- Hasselbalch equation.

10. Deficiency of this enzyme results in intracellular accumulation of sorbitol, causing osmotic damage in the form of cataracts, retinopathy and peripheral neuropathy seen in uncontrolled diabetics : A. Aldose reductase B. Sorbitol dehydrogenase C. Lactase D. Galactokinase E. Fructokinase

510 B. First Aid 201, p. 105 Aldose reductase sorbitol dehydrogenase Glucose â†' Sorbitol â†' Fructose + NADPH NAD

11. A newborn presents with dark ears and brown-pigmented sclera. Mother also complains that his urine turns black on exposure to air. Which enzyme is deficient? A. Melanin synthase B. Phenylalanine hydroxylase C. Homocysteine methyl transferase D. Tyrosinase E. Homogentisic oxidase

511 E SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. This is a case of alkaptonuria, AKA ochronosis wherein there is a deficiency of homogentisic oxidase. First Aid 2013, p.108 tyrosonase is deficient in albinism

15. Adipose tissue and muscles lacks this enzyme which explains why it cannot export glucose into the blood stream: A. HMG CoA reductase B. Fatty acid synthetase C. Glycogen phosphorylase D. Hexokinase E. Glucose 6-phosphatase

515 E Harper's 27th ed 161. In liver (and kidney) but not in muscle, glucose 6 phosphatase hydrolyzes glucose 6- phosphate, yielding glucose that is exported, leading to an increase in the blood glucose concentration.

18. Which of the following statements show degeneracy in the genetic code? A. Six different codons specify serine. B. For any specific codon, only a single amino acid is indicated. C. The reading of the genetic code during the process of protein synthesis does not involve any overlap of codons. D. Once the reading of the genetic code is commenced at a specific codon, the message is read in a continuous sequence of nucleotide triplets until translation stop codon is reached. E. Codons differing only in the 3rd base positions may code for the same tRNA/amino acid.

518 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Degenerate/Redundant - Most amino acids are coded by multiple codos except methionine and tryptophan which are encoded by only 1 codon (AUG and UGG, respectively). Unambiguous- Each codon specifies only 1 amino acid. Commaless/non-overlapping- read from a fixed starting point as a continuous sequence of bases. Universal -genetic code is conserved. First aid 2013, p.66. Choice E depicts wobble or the ability of certain anti-codons to pair with codons that differ at the 3rd base.

19. If the cytosine content of a double-helical DNA is 30% of the total bases, the thymidine content would be: A. 60% B. 50% C. 40% D. 30% E. 20%

519 E Chargaff's rule: In DNA molecules the concentration of deoxyadenine nucleotide equals that of thymidine nucleotides (A=T), while the concentration of deoxy guanosine nucleotides equals that of deoxycytidine nucleotides (G=C). Harper's 27th ed., 311.

20. This enzyme is responsible for the release of free fatty acids from adipose in fasting states and is inhibitted by insulin. A. Pancreatic lipase B. Lipoprotein lipase C. Hormone-sensitive lipase D. Gastric lipase E. Lingual lipase

520 C. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Pancreatic lipase acts on dietary TAG, Lipoprotein lipase acts on TAG chylomicrons and VLDL. Hormone sensitive TAG acts on TAG stored in adipose and is activated by glucagon. Lingual lipase originates from the back of the tongue. - Biochem Topnotch handouts

A 23-year-old male develops steatorrhea, weight loss, and bloody diarrhea. He notes that his diarrhea is worse when he eats breads or cereals. A gastroenterologist performs a biopsy during a colonoscopy, which reveals celiac disease. This disorder is most directly due to which of the following? A) excess lipids in the feces B) deficiency of enterokinase C) defective transport of amino acid cysteine D) hypersensitivity to the protein gluten

521 D. Celiac disease

A 32-year-old man with alcoholism is brought to the emergency department by friends because he has been unable to stand without support and has had "funny eye movements"; they report that he has been drinking approximately 18 beers daily over the past month and has been increasingly confused over the past 5 days. He is awake and confused but is noncombative. His speech is slurred, and his breath smells of alcohol. His temperature is 37.2 C (99 F), blood pressure is 180/60 mm Hg, pulse is 110/min, and respirations are 18/min. Physical examination shows sixth cranial nerve palsy, horizontal diplopia, strabismus, and an asymmetric horizontal-gaze evoked nystagmus. Neurologic examination shows no focal weakness or numbness. When helped up and told to walk, he has a broad-based, uncertain gait. When asked how he arrived at the emergency department, he relates that "I drove to this place to visit some friends." The most likely cause of these findings is a deficiency of which of the following? A) Folic acid B) Magnesium C) Vitamin B1 (thiamine) D) Vitamin B12 (cyanocobalamin)

522 C.

A 1-week-old newborn has had poor feeding, vomiting, and progressive lethargy over the past 4 days. She was born at term; pregnancy, labor, and delivery were uncomplicated, and she had no congenital anomalies. She is being breast-fed. She has a healthy 2-year-old brother; a sister died at 10 days of age after a full-term birth. Examination shows decreased muscle tone and poor responsiveness; reflexes are normal. Serum bicarbonate level is 8 mEq/L, pH is 7.15, and plasma ammonia level is 10 times the upper limit of normal. Which of the following is the most likely cause? A) Mitochondrial disorder B) Mucopolysaccharidoses disorder C) Organic acid metabolism disorder D) Renal tubular acidosis

524 C.

A 1-year-old infant came to the physician due to fever. On physical examination, the patient has epicanthal folds, flat facial profile, macroglossia and presence of simian crease. Further history revealed that the patient was born from a 48-year-old mother. What is the most common cause of this chromosal disorder? A) Nondisjunction B) Robertsonian translocation C) Mosaicism D) Chromosomal deletion

525 A. Trisomy 21 >> most common is nondisjunction in 95 % of cases.

Typtophan is an amino acid with the largest side chain containing an indole ring. It is a precursor of what substances? A) Niacin B) Melatonin C) Serotonin D) All of the above

528 D.

Desmolase is the rate limiting enzyme in androgen and steroid synthesis. It is responsible for what reaction? A) Conversion of progesterone to 11 deoxycorticosterone B) Conversion of pregnenolone to 17 hydroxypregnenolone C) Conversion of cholesterol to pregnenolone D) Conversion of DHEA to Androstenedione

529 C. desmolase >> cholesterol to pregnenolone

Aspartame is composed of what amino acid? A. Phenylalanine B. Asparagine C. Glutamic acid D. Alanine E. Tyrosine

53 A. Aspartame: Phenylalanine + Methanol + Aspartic Acid

A 45-year-old male is hospitalized for treatment of myocardial infarction. His father and a paternal uncle also had heart attacks at an early age. His cholesterol is elevated, and lipoprotein electrophoresis demonstrates an abnormally high ratio of low- to high-density lipoproteins (LDL to HDL). Which of the following is the most likely explanation for this problem? A) Mutant LDL receptors are deficient in cholesterol uptake B) Mutant LDL is not responding to high cholesterol levels C) Mutant caveolae proteins are not responding to high cholesterol levels D) Mutant HDL is not responding to high cholesterol levels

530 A. Familial hypercholesterolemia

A healthy 28-year-old woman comes to physician for advice on losing weight. She is 150 cm ( 4ft 11in) tall and 56 kg (124 lb): BMI 25kg/m2. Physical examination reveals no other abnormalities. Physician recommends a diet that will restrict her daily intake by 500 kilocalories. Which of following processes is most likely to increase in this patient as a reuslt of following this diet? A) Adipocyte glucose uptake B) Cerebral keotne utilization C) Hepatic lipid oxidation D) Muscle glucose uptake

531 C. liver will burn lipids to provide energy for gluconeogenesis

A 4-year-old girl with a history of mental retardation is brought to the physician because of poor vision. Physical examination shows long limbs, tall stature, and kyphosis. Funduscopic examination shows bilateral lens dislocations. Laboratory studies are most likely to show a selective elevation of which of the following amino acids in serum? A) Cystathionine B) Methionine C) Cysteine D) Phenylalanine

532 B. Marfan-like habitus >> homocystinuria >> cystathionine synthase deficiency >> accumulated homocysteine is alternatively metabolized to methionine by homocysteine methyl transferase and cofactor B12

A 44 year old alcoholic was brought to the emergency department by his friends. During their usual gathering at the local bar, he passed out and his friends were unable to revive him. The physician ordered an injection of Thiamine , followed by overnight parenteral glucose. The next morning the patient was alert and coherent, serum thiamine was normal, and blood glucose was 73 mg/dl (4mM). The patient was then sent home. At the time of discharge from the hospital, which of the the following proteins would have no significant physiologic activity in this patient? A) Malate Dehydrogenase B) Glucokinase C) alpha-ketoglutarage dehydrogenase D) GLUT 1 transporter

534 B. Glucokinase >> glucose storage >> fbs is 73 so you don’t need storage

Okazaki fragments are formed on the ______ strands and in the ______ direction. A) Leading; 3’-5’ B) Lagging; 3’-5’ C) Leading; 5’-3’ D) Lagging; 5’-3’

536 B.

Two couples present to the ER with severe nausea, vomiting, and diarrhea. One of the patients admits that she served salad at the dinner party to which she had added a few mushrooms that she picked outside. With such information, it is likely that their symptoms are a result of inhibition of what molecular event? A) RNA polymerase II B) RNA polymerase I C) RNA splicing D) RNA polymerase III

537 A. a-amanitin from Amanita phylloides >> inhibits RNA polymerase II

A 4-month-old boy is being evaluated for seizures, psychomotor retardation, and hypotonia. Work-up reveals elevated serum levels of lactate alanine, pyruvate, and ketoacids. Based on the clinical presentation, pyruvate carboxylase activity is measured using fibroblasts from a skin biopsy and is found to be markedly decreased. This enzyme is normally used to directly synthesize which of the following molecules? A) Pyruvate B) Oxaloacetate C) Malate D) Acetyl CoA

539 B. pyruvate carboxylase >> converts pyruvate to OAA >> enters TCA or gluconeogenesis

A 65/M, heavy smoker, presented with a 5 month history of vague epigastric pain and nausea; associated with weight loss and pruritus. Lately, patient has also started to experience back pain and appeared jaundiced. On PE, you note icteric conjunctivae and epigastric tenderness. An abdominal ultrasound reveals a pancreatic head mass. Expected results of biochemical testing include the following except: A. Increased direct bilirubin B. Present urine bilirubin C. Trace fecal urobilinogen D. Increased total bilirubin E. Increased urine urobilinogen

541 E In complete obstruction of the bile duct, no urobilinogen is found in the urine, since bilirubin has no access to the intestine, where it can be converted to urobilinogen. In this case, the presence of bilirubin (conjugated) in the urine without urobilinogen suggests obstructive jaundice, either intrahepatic or posthepatic. The commonest cause of obstructive (posthepatic) jaundice are cancer of the head of the pancreas and a gallstone lodged in the common bile duct. (Harpers 26e p.284)

The above patient was noted to lose 10 kg in 5 months. On PE, you note obvious wasting. Which of the following is NOT true regarding the biochemical and metabolic changes in cancer cachexia? A. The tumor releases lactate which is recycled into glucose consuming 6 ATPs / glucose recycles. B. There is upregulation of uncoupling proteins, leading to thermogenesis and oxidation of fuels. C. There is futile cycling of lipids. Hormone sensitive lipase is activated which breaks down triglycerides to FFA, which ae then re-esterified at ATP cost. D. In cachexia, protein synthesis is reduced but catabolism is unaffected. E. None of the above

542 D. A - C describe the three mechanisms by which cancer causes cachexia. In cachexia, protein catabolism is INCREASED; this differentiates it from marasmus in which protein synthesis is reduced but catabolism is unaffected (Harpers p.479).

A 24/M came in for pre-employment examination. On PE, you note that the patient is over the 95th percentile for height; and he has a slight scoliosis, skin striae and pectus excavatum. Ausculation reveals a heart murmur. You then order a 2D echo which shows an enlarged aortic root, aortic valve regurgitation and mitral valve prolapse. You suspect a genetic condition in which there is abnormal production of a glycoprotein, leading to abnormalities in the mechanical stability and elastic properties of connective tissue. Production of which of the following glycoproteins is defective? A. Elastin B. Collagen C. Fibronectin D. Fibrillin E. Laminin

544 D. Patient has Marfan's syndrome.

A neonate is admited to the intensive neonatal care and incubated due to jaundice. He was born to a 30-year old G3P2 who is known to be Rh-negative with an Rh-positive sexual partner. The mother has not received anti-D prophylaxis during the current pregnancy. You are suspecting Rh incompatibility. Which of the following serum proteins is expected to be decreased in the neonate? A. a1-antitrypsin B. C reactive protein C. Haptoglobin D. Ceruloplasmin E. a2-macroglobulin

545 C. Haptoglobin was asked during the last board exam. This protein prevents loss of free hemoglobin into the kidney; conserving Fe present in Hg. Levels are decreased in hemolytic anemia because of increased free Hg levels (Hg-Hp complex has a short half life of 90 mins vs 5 days for normal halptoglobin). Increased levels are seen in chronic inflammatory states (haptoglobin is an acute phase reactant)

A 78/M, car mechanic, presented with a 24 hour history of progressive headache, vomiting and dizziness. On examination, he is awake, but appears confused and has generalized weakness. His carboxyhemoglobin level is 18%. You diagnose the patient as having carbon monoxide poisoning. Carbon monoxide is dangerous because it is a potent inhibitor of which complex in the electron transport chain. A. NADH dehydrogenase B. Oxygen dehydrogenase C. Succinate dehydrogenase D. Ubiquinol:ferricytochrome oxidoreductase E. Cytochrome oxidase

546 E MNEMONIC: CO (carbon monoxide) inhibits CO (cytochrome oxidase / complex IV).

A 24/F who came in for dysuria and frequency was prescribed cotrimoxazole. Two days later, she develops nausea and exhaustion and comes back to the ER after passing "tea-colored" urine. She was also noted to be jaundiced. Work-ups reveal that the patient has anemia, azotemia, deranged liver function and unconjugated hyperbilirubinemia. She is diagnosed as having drug-induced hemolytic anemia. You suspect that the patient has an inherited condition that makes her unable to tolerate oxidative stress leading to red cell hemolysis. This condition is due to a deficiency in the key enzyme in which of the following biochemical reactions: A. Glycolysis B. Tricarboxylic acid cycle C. Gluconeogenesis D. Serial oxidative phosphorylation in the electron transport chain E. Pentose phosphate pathway

547 E Patient has G6P deficiency. G6PD is the key enzyme in the oxidative phase of PPP.

Which of the following dyslipoproteinemia is a condition apparently beneficial to health and longevity? A. Familial dysbetalipoproteinemia B. Familial hypertriacylglycerolemia C. Familial hyperalphalipoproteinemia D. Familial type III hyperlipoproteinemia E. All increase risk of atherosclerosis and coronary disease.

549 C. Remember that ApoA is the major lipoprotein of HDL aka good cholesterol. In hyperalphalipoproteinemia, (ApoA = alpha) there is increased concentration of HDL, conferring longevity to the lucky patient.

Certain drugs are thought to increase membrane fluidity directly, resulting in impaired neurotransmission that may be the basis for their therapeutic effects. Which class of drugs acts by this direct mechanism? A. Hallucinogens B. Stimulants C. Sedatives D. Opiates E. Anesthetics

55 E Anesthetics are highly lipid-soluble and experiments with isolated membranes indicate that these molecules can dissolve in the hydrophobic center of the membrane bilayer. This causes a measurable increase in the membrane fluidity by disrupting the packed structure of phospholipids tails; thus, It inhibits neurotransmission (pain sensations) in neurons. Hallucinogens and opiates may also affect membrane fluidity, but their effects occur by indirect mechanisms, resulting from changes in the protein or lipid composition of the membranes.

A newborn presenting with vomiting and hypotonia has been found to have severe lactic acidosis. Serum analysis reveals elevated lactate and alanine. You are considering a biochemical condition characterized by a deficiency in: A. Muscle phosphofructokinase B. Pyruvate kinase C. Pyruvate carboxylase D. Pyruvate dehydrogenase E. Lactate dehydrogenase

551 D. This is the most common biochemical cause of congenital lactic acidosis. Because enzyme is deficient, pyruvate is shunted towards lactate production. Patients present with lactic acidosis and neurologic disturbance. Alanine increases from conversion of pyruvate to alanine by alanine aminotransferase.

An 8 month old male of Ashkenazi Jewish heritage was referred to you for developmental delay. Parents noted that by 7 months, he had poor head control and remained inattentive to surroundings. Parents also noted unusual eye movements and staring episodes. The patient was already referred to an ophthalmologist who observed a "cherry-red spot" within a pale macula. You suspect that the patient has an inherited deificency in which of the following enzymes: A. Sphingomyelinase B. Arylsulfatase A C. Hexosaminidase A D. B-galactosidase E. B-glucosidase

552 C. Patient has Tay-Sach's disease (hexosaminidase A deficiency) characterized by mental retardation, blindness and muscular weakness. Buzz phrase: cherry red spot in the macula.

A newborn is seen with blisters and erosions covering the entire body. It was noted that handling of the baby easily causes tearing of the skin. You suspect an inherited condition characterized by mutations affecting a protein which forms delicate fibrils that anchor the basal lamina to the dermis. Which protein is abnormally produced in this condition? A. Type I collagen B. Type II collagen C. Type III collagen D. Type IV collagen E. Type VII collagen

554 E Patient has epidermolysis bullosa.

A 20/M comes in for knee pain and swelling. On PE, you noted dark spots in his sclera. On probing, the patient reports that when he leaves his urine standing, it turns black. You suspect an inherited condition characterized by a deficiency in an enzyme necessary for the catabolism of this amino acid. A. Tyrosine B. Threonine C. Leucine D. Serine E. Glycine

556 A. Patient has alkaptonuria due to deficiency in homogentisate oxidase. Homogentisate is a product of tyrosine catabolism. Oxidation of homogentisate leads to darkening of the urine. Oxidation of homogentisate to benzoquinone acetate poiymerizes and binds to connective tissue, leading to arthritis and pigmentation (ochronosis).

A 28/M, with a history of recurrent nephrolithiasis, comes in due to severe intermittent right flank pain and hematuria. On examination, you note CVA tenderness on the right. Urinalysis reveals hexagonal crystals upon cooling of acidified urine sediment. The patient tells you that a physician who saw him for a previous bout of nephrolithiasis was considering an inherited condition. You suspect that the patient may have a condition characterized by impaired renal tubular absorption of which of the following amino acids: A. Ornithine B. Arginine C. Lysine D. Cystine E. All of the above

557 E Cystinuria No transporter for COAL Cystine, Ornithine, Arginine, Lysine

Activation of erythrocyte transaminases is an accepted index of nutritionals status of this vitamin: A. Thiamine B. Pyridoxine C. Riboflavin D. Biotin E. Folic acid

559 B. The question could be rephrased as such: 'which of the following vitamins is a co-factor in transaminase reactions?' Answer would be pyridoxine.

It has been common practice to prescribe multivitamins for patients with peripheral neuropathy, complaining of "pangangalay." However, the use of multivitamins for this indication is not evidence-based. Moreover, excessive intake of this vitamin is commonly associated with sensory neuropathy. A. Thiamine B. Pyridoxine C. Riboflavin D. Biotin E. Folic acid

560 B.

1. The main source of Estrogen in a 27 year old primigravid patient is from: A. placenta B. Maternal adrenals C. fetus D. Peripheral aromatization of DHEA

561 A. Estriol is only produced in significant amounts during pregnancy as it is made by the placenta from 16-OH DHEAS, an androgen steroid made in the fetal liver and adrenal glands

Hemoglobin is a functional protein belonging to what structural order? A. primary B. secondary C. tertiary D. quaternary

562 D. Quaternary structures are composed of at least 2 polypeptide chains. Hemoglobin is composed of 2 alpha and 2 beta chains and is therefore quaternary in nature.

This amino acid is considered the most basic among the group: A. Histidine B. Lysine C. Arginine D. Glycine

563 C.

The major inhibitory neurotransmitter of the Brain is derived from a decarboxylation reaction requiring pyridoxal phosphate. The amino acid A. Glutamine B. Glycine C. Glutamate D. Lysine.

564 C. Glutamate, the major stimulant in the CNS is consequently carboxylated by L-glutamic decarboxylase into GABA, the major inhibitory transmitter of the CNS

In alpha thalassemia (-/-, -/-) the hemoglobin formed composed of B4 (beta4) is referred to as : A. HbH B. HbS C. Hb Barts D. Hb C

565 A. In Alpha thalassemia, accumulation of 4 beta chains is referred to as HbH, whereas 4 gamma chains is referred to as Hb Bart’s. Both can exist in this condition.

True of Noncompetitive inhibition a. Formation of product continues b. The Km of the enzyme targeted decreases c. The Km of the enzyme targeted increases d. The Vmax of the enzyme targeted remains unchanged

566 A. In noncompetitive inhibition, formation of the product continues. Allosteric inhibition causes the Vmax to decrease. However, Km remains unchanged.

Gibbs free energy predicts the spontaneity of a reaction that is about to take place. The factors to be considered are the following except: a. enthalpy b. temperature c. entropy d. none of the above

567 D. The formula of Gibbs free energy is enthalpy minus temperature x entropy

A Gibbs free energy change of 0 means that the reaction is: a. Spontaneously occurring b. Non-spontaneous that requires coupling with an exothermic reaction c. In equilibrium d. No significance

568 C. Zero Gibbs free energy change means that the reaction is in equilibrium

beta oxidation of palmitic acid into acetyl coA residues occur in which site of the cell? a. cytosol b. peroxisome c. mitochondrial matrix d. both a and c

569 C.

terminal digestion of carbohydrates into monosaccharides occur in which site of the gastrointestinal tract? a. brush border of the intestines b. duodenal lumen when acted upon by pancreatic enzymes c. enterocytes d. in the mouth by the enzyme ptyalin

570 A. Terminal digestion occurs in the brush borders due to the presence of disaccharidases

which of the following is true of phosphatidylinositol? a. synthesized from free inositol and CDP-diacylglycerol b. it is an unusual phospholipid in that it contains arachidonic acid in Carbon 1 and stearic acid on carbon 2 c. the arachidonic acid present is bound and unaccessible for prostaglandin synthesis d. all of the above

571 A. PI is synthesized from free inositol and CDP-DAG. It is an unusual phospholipid in that it contains stearic acid on C-1 and Arachidonic acid on C-2. It serves as a reservoir for prostaglandin synthesis.

which component of phosphatidylinositol degradation of the secondary messenger complex is responsible for Protein kinase C activation? a. Diacylglycerol b. IP3 c. PHosphatidylinositol 4,5 diphosphate d. calcium

572 A. The products IP3 and DAG mediate the mobilization of intracellular Ca and the activation of Protein kinase C, respectively.

which among the following is considered a primary bile acid a. lithocolic acid b. cholic acid c. deoxycholic acid d. ursodeoxycholic acid

574 B. Two primary bile acids are: chenodeoxycholic and cholic acid.

the most common enzyme deficiency in Congenital Adrenal hyperplasia is: a. 11-hydroxylase b. 17- hydroxylase c. 21-hydroxylase d. Aromatase

575 C. 21-hydroxylase deficiency

Deficiency of this vitamin causes hemolytic anemia: a. Vitamin A b. vitamin D c. vitamin E d. vitamin K

576 C. Vitamin E deficiency causes hemolytic anemia; on the other hand, excess Vitamin K may also cause hemolysis.

Warfarin inhibits vitamin K dependent clotting factors by direct inhibition of: a. vitamin K epoxide reductase b. glutamyl carboxylase c. Lipid absorption of vitamin K in the GI tract and the liver d. protein synthesis of factors 2,7,9,10

577 A. Vitamin K Epoxide reductase inhibition is the main mechanism of Warfarin

a disorder of purine metabolism characterized by hyperuricemia, self-mutilation, and neurologic features with involuntary movements is mainly due to a defect of what enzyme? a. glucose 6-phosphatase b. HGPRT c. Adenine phosphoribosyl transferase d. ribonucleotide reductase

578 B. Lysch Nyhan Syndrome is due to the deficiency of the Purine Salvage Mechanism caused by HGPRT deficiency.

Adenosine deaminase deficiency causes this disorder among children characterized by both Tcell and Bcell dysfunction: a. Severe combined immunodeficiency b. combined variable immunodeficiency c. DiGeorge syndrome d. X-linked agammaglobulinemia

579 A.

which among the following amino acids does not contribute directly to the synthesis of a purine ring? a. glycine b. glutamine c. aspartate d. valine

580 D. Valine does not contribute any carbon to the purine ring.

Which irreversible enzymes in glycolysis is coupled to the release of energy and requires different enzymes to catalyzed the reverse reactions in the pathway of gluconeogenesis? A. Hexokinase B. Phosphofructokinase C. Pyruvate Kinase D. All of the above E. None of the above

582 C. Although all 3 enzymes catalyzed irreversible steps in glycolysis, only pyruvate kinase is exergonic or is coupled to the release of energy. Hexokinase and PFK are in the energy investment stage of the Glycolysis.

The reaction rates of adding substance A in a solution with known enzyme kinetics can be exemplified using the Lineweaver-Burk Plot (1/Vi=(Km/Vmax)(1/S) + 1/Vmax). When adding substance A, the ordinate of the Lineweaver-Burk plot increases while the abscissa remains the same. Substance A can then be classified as a? A. Complete Agonist B. Partial Agonist C. Competitive Antagonist D. Non-competitive Antagonist E. Uncompetitive Antagonist

583 D. Remember the equation y=mx+b where m is the slope of the line and b is the y-intercept (ordinate). Increasing the ordinate will result in a decrease in Vmax (since we get the reciprocal of Vmax as the ordinate). A decrease in Vmax while Km (-1/Km is the abscissa or x-intercept) remains the same is characteristic of Non-competitive inhibition.

In the intestinal brush border which monosaccaharide can only used the GLUT-5 (facilitated diffusion) and not the SGLT transporter (active co-transport)? A. Glucose B. Mannose C. Galactose D. Dextrose E. Fructose

584 E All monosaccharides can use the GLUT-5 transporter while only aldoses can use the SGLT transporter. Fructose is the only ketose sugar in the group. Glucose=Dextrose. Glucose, galactose and mannose are aldoses

Aerobic glycolysis in the heart produces a net total of how many ATP molecules for each molecule of glucose? A. 30 B. 32 C. 34 D. 36 E. 38

585 E Aerobic glycolysis produces either 36 or 38 ATP molecules for each molecule of glucose depending on the shuttle used. The liver, kidney, and the heart uses the malate aspartate shuttle so each NADH produce in glycolysis in the cytoplasm nets 3 ATP. The skeletal muscle and the brain uses the gycerol phosphate shuttle so each NADH only produces 2 ATP.

A patient always experienced pain and cramps after exercise. Initial work-up shows normal ECG tracing,electrolytes were within normal limits and normal lactate levels. The patient's urine had a brownish color. The patient likely has which glycogen storage disease? A. Von Gierke's B. Pompe's C. Cori's D. McArdle's E. Andersen's

586 D. The signs and symptoms are typical of McArdle's disease (Cramps+Myoglobinuria (brownish discoloration) with no lactate acidosis)

Which of the following statements are TRUE for lipids? A. All lipids are substances that are hydrophobic. B. The melting temperature of fatty acids is directly proportional to the number of double bonds. C. Lipids such as cholesterol can be used by the body to obtain energy through β-oxidation. D. Lipids are the main component of cellular enzymes needed for metabolism. E. Fatty acid metabolism occurs in the cytoplasm.

587 A. The melting temperature is inversely proportional to the number of double bonds. Cholesterol is not used to obtain energy, only fatty acids and glycerol. Proteins, not lipids are the main components of enzymes. Fatty acid synthesis occur in the cytoplasm but β-oxidation occurs in the mitochondria.

Which of the following is not an essential amino acid? A. Histidine B. Threonine C. Leucine D. Asparagine E. Methionine

589 D. PVT TIM HALL, always ARGues, never TYRes. Asparagine can be synthesized from aspartate.

Bloatedness in lactose intolerance is due to A. Increased production of gas by the gut B. Lactose reduced to lactitol and converted to lactone C. Bacterial fermentation of undigested lactose in the gut D. Osmotically driven gfluid shift in the gut E. AOTA

59 C.

What amino acid is the precursor of the main inhibitory neurotransmitter of the spinal cord? A. Serine B. Glycine C. Glutamate D. Glutamine E. Tryptophan

591 A. The main inhibitory neurotransmitter of the spinal cord is glycine. Serine is necessary for its synthesis.

Maple syrup disease is a disorder characterized by blocked degradation of branched chain amino acids. It is therefore important to limit the following amino acids EXCEPT? A. Lysine B. Leucine C. Valine D. Isoleucine E. None, all needs to be limited

592 A. Lysine is not a branched chain amino acid.

A 5-yr old boy has distinctive coarseness in his facial features, including a prominent forehead, a nose with a flattened bridge, and an enlarged tongue. There are developmental delays and nervous system problems. Biochemical testing reveals there is a defect in the degradation of dermatan sulfate and keratan sulfate. Genetic testing shows there is a polymorphism in the gene encoding for iduronate-2-sulfatase. The patient most likely has? A. Hunter's Syndrome B. Hurler's Syndrome C. Morquio's Syndrome D. Scheie's Syndrome E. Sly Syndrome

593 A. Enzyme defects: Hunter's Syndrome: Iduronate Sulfatase Hurler's Syndrome and Scheie's Syndrome: α- iduronidase Morquio's Syndrome: Galactose-6-sulfatase Sly Syndrome: β-Glucuronidase

An athlete who has extensive training of 8 hours per day has a higher energy requirement than people who have sedentary lifestyles. Most of the energy requirement is used for? A. Metabolism in skeletal muscles during physical activity for rapid and sustain effort B. Metabolism in cardiac and respiratory cells to maintain adequate oxygen and nutrient delivery to all cells of the body C. Metabolism in nerve cells needed to conduct electrical impulses and control bodily functions D. Metabolism in the GIT to extract nutrients needed to sustain the energy requirements E. Metabolism in cells to maintain homeostasis such as the maintenance of the Na/K pump

596 E No matter the physical activity, the basal metabolic rate accounts for at least 50% of energy requirements. Most of the basal metabolic rate is used for the maintenance of cellular functions such as the maintenace of the cellular electrolyte composition by the Na/K pump.

You are task to elucidate the identity of a heriditary disease X. A father inflicted with the disease does not transmit it to any of his children. An afflicted mother transmit it to all her offsprings. The disease most likely shows this characteristic? A. X-linked B. Autosomal Dominant C. Autosomal Recessive D. Mitochondrial E. Variable Penetrance

598 D. Mitochondrial diseases are always maternally derived since the mitochondria of a child all comes from the mother. Remember the only contribution of the sperm is its haploid DNA.

An infant presents with hepatosplenomegaly and failure to thrive. A liver biopsy was done which revealed accumulation of polysaccharide with few branch points because of a deficiency for an important enzyme in carbohydrate metabolism. What is the diagnosis for this patient? A. Von Gierke Disease B. Andersen’s Disease C. Tarui’s Disease D. Fabry’s Disease E. Her’s Disease

6 B. Glycogen storage diseases: enzyme deficienct: signs and symptoms/buzzwords - Von Gierke’s disease: Glucose 6 phosphatase deficiency: severe hypoglycemia (because glucose generated from all pathways (gluconeogenesis and glycogenolysis) is trapped in the hepatocyte and cannot be released into the blood) - Pompe’s disease: acid maltase: heart failure - Cori’s disease: debranching enzyme: accumulation of branched polysaccharide - Anderson’s disease: branching enzyme: accumulation of polysaccharide with few branch points - McArdle syndrome: muscle phosphorylase: poor exercise tolerance, accumulation of muscle glycogen Her’s disease: liver phosphorylase: accumulation of liver glycogen, mild hypoglycemia (because only glycogenolysis is impaired, gluconeogenesis can replenish glucose) Source: Harper 27th ed p. 166

Severe combined immunodeficiency are sensitive to allosteric inhibition of which of the following enzymes of purine nucleotide metabolism? A. Xanthine oxidase B. Dihydrofolate reductase C. Adenosine deaminase D. Ribonucleotide reductase E. Hypoxanthine-guanine phosphoribosyltransferase

60 D. dATP-induced allosteric inhibition of ribonucleotide reductase, which catalyzes reduction of the 2′- hydroxyl groups on ADP and GDP to form dADP and dGDP

In biotechnology, restriction enzymes are enzymes that cleave certain locations in the DNA sequence that helps identify the presence of genetic polymorphisms. They preferentially target which sites in the DNA molecule? A. Sites where there is a high GC content B. Sites where there is a palindromic sequence C. Sites that have altered DNA bases such as thymidine dimers D. Sites that have trinucleotide repeats (CAGs, etc.) E. Sites that are "trash" or those that do not encode proteins

600 B. Restriction enzymes target palindromic sequences or those sequence that are mirror images of each other .. Ex AAAAGTCGACAAAAA TTTTCAGCTGTTTTT

Water is the universal solvent. This is because water: A. is an excellent nucleophile B. is amphoteric C. has high dielectric constant D. is a dipole E. All of the above

601 C. Having a high dielectric constant permits water to decrease force of attraction between charged and polar species. Water as a dipole means it has electric charge distributed asymetrically about its structure. Water as an excellent nucleophile means it can cleave amide, glycoside or ester bonds. Water as an amphoteric means it acts both as an acid and a base.

The following are electron transport chain uncouplers, EXCEPT: A. Aspirin B. Thermogenin C. 2, 4-dinitrophenol D. Oligomycin E. None of the above

602 D. Uncouplers are agents that allow dissipation of hydrogen ions across the inner mitochondrial membrane without production of ATP. These substances include aspirin, 2,4 DNP and thermogenin (brown fat)

Enzyme 1 has Km (michaelis constant) of 4, while Enzyme 2 has Km of 2. Assuming that Enzymes 1 and 2 act on the same substrate, which of the following is correct? A. Enzyme 1 has greater substrate affinity than Enzyme 2 B. Enzyme 2 has greater substrate affinity than Enzyme 1 C. Enzyme 1 and 2 have the same substrate affinity D. Affinity cannot be determined by Km E. None of the above

603 B. A greater Km value indicates lesser affinity of the enzyme for a given substrate. Km is substrate concentration at which the speed of reaction is half the maximal velocity (Vmax/2)

After a high carbohydrate meal, blood glucose level increases. In the brain, how many ATPs will be produced from 1 molecule of glucose after complete oxidative glycolysis? A. 32 B. 34 C. 36 D. 38 E. Cannot be determined

604 C. Liver, kidney and heart utilizes the malate-aspartate shuttle, thereby producing 38 ATPs over-all (NADH will be converted to 3 ATPs). Skeletal muscle and brain utilizes the glycerol-phosphate shuttle, thereby producing only 36 ATPs (NADH will be converted to 2 ATPs only).

The liver cannot utilize ketones as a source of energy, due to the absence of which enzyme/s? A. Thiophorase B. Succinyl CoA - Acetoacteyl CoA transferase C. Acetoacetyl - acyl transferase D. A and B E. B and C

605 D. Thiophorase (also known as succinyl coa - acetoacetyl coa transferase) is needed for tissues to utilize ketones as source of energy. Liver lacks this enzyme.

Which of the following apoproteins attached to lipoproteins are responsible for activation of lipoprotein lipase? A. Apo C-II B. Apo B-100 C. Apo B-48 D. Apo E E. B and C

606 A. Apo C-II activates lipoprotein lipase. Apo B serves as a receptor ligand for LDL (B 100) or Chylomicrons (B 48). Apo E facilitates uptake of lipoproteins by the liver.

A preterm newborn male was observed to be dyspneic after 12 hours of life during your NICU rotation. You noted chest indrawing, alar flaring and cyanosis. As the intern-in-charge, you suggested chest x-ray to be done, revealing "white out lungs." Which of the following is/are most probably decreased in this patient? A. Phosphatidylcholine B. Dipalmitoylphosphatidylcholine C. Dipalmitoyllecithin D. A and B E. B and C

607 E Dipalmitoylphosphatidycholine (aka dipalmitoylecithin) is the major lung surfactant. Inadequate levels lead to respiratory distress syndrome in the newborn, more commonly observed among preterms.

The following are synthesized from tryptophan, EXCEPT: A. Melanin B. Melatonin C. Niacin D. Serotonin E. B and C

609 A. Tryptophan is the precursor for niacin, serotonin and melatonin. Melanin is synthesized from tyrosine.

Vitamin B1 or Thiamine pyrophosphate is a cofactor in several of these enzymes/steps EXCEPT: A. Pyruvate to Acetyl-Coenzyme A B. Pyruvate to Oxaloacetate C. Alpha-Keto Glutarate to Succinyl CoA D. Hexose Monophosphate Shunt Phase 2 E. Branched chain ketoacid dehydrogenase

61 B. Remember the mnemonics ATP. Vit B1 is a co factor of Alpha-ketoglutarate DH of the TCA cycle, Transketolase (Phase 2 of the HMP shunt) and Pyruvate DH complex (pyruvate to Acetyl-CoA). Additonally it is also a co-factor of the the Branched chain ketoacid DH step. Pyruvate to oxacocetate is faciltitated by pyruvate carboxylase which requires biotin instead.

The eukaryotic DNA has the following property/properties: A. Coding regions are not interrupted by intervening sequeces B. All of the cellular DNA is located within the nucleus C. Contains no repetitive sequences D. Replication of double stranded DNA is unidirectional E. None of the above

611 E The eukaryotic DNA has the following properties: 1)coding regions are often interrupted by intervening sequences, 2)more than half of the DNA is unique or nonrepetitive sequences, 3)at least 30% of the genome consist of repitive sequences, 4)1% of cellular DNA is in mitochondria, 5) replication is bidirectional

Which of the following pairs is INCORRECT? A. RNA polymerase I - rRNA B. RNA polymerase II - ssRNA C. RNA polymerase III - tRNA D. A and C E. All are incorrect

612 B. RNA polymerase 1 is used in the transcription of large rRNAs in the nucleolus, II for mRNAs and III for tRNAs

Which of the following pertains to a set of structure genes coding for a group of proteins required for a particular metabolic function along with the regulatory region that controls the expression of the structural genes? A. Promoter region B. Primary transcript C. Rho factor D. Operon E. None of the above

613 D. Promoter regions are part of the DNA where RNA polymerase binds to start transcription. The primary transcript is a linear copy of the transcriptional unit, the segment of DNA between specific initiation and termination sequences. Rho factor is involved in termination of DNA transcription by binding to a C- rich region near the 3'-end of the newly synthesized RNA and migrates along the 5' to 3' direction until termination site is reached.

A sample of DNA-RNA hybrid is to be examined for its component. The best method to utilize is: A. Southern blot B. Northern blot C. Western blot D. Eastern blot E. None of the above

614 B. Southern blot is utilized for purely DNA sample. Northern blot is utlized for RNA and mixed DNA-RNA samples, while Western blot can be utilized for protein-containing sample.

A 6-year old boy was brought to your clinic due to persistent back pain. You noted that he was short for his age and has some degree of skeletal dysplasia. Upon further examination, his mental development was found to be at par with his age. Suspecting a type of mucopolysacchridoses, which of the following is most likely affecting this patient? A. Morquio's syndrome B. Hunter's syndrome C. San fillippo syndrome D. Sly syndrome E. None of the above

615 A. This patient is suffering from mucopolysaccharidoses. Morquio's syndrome is the only mucopolysaccharidoses which does not present with mental retardation or other CNS involvement. Findings usually include skeletal dysplasia and short stature. This is due to deficiency in galactose 6- sulfatase.

A 65-year old diabetic female was brought to the ER due to body weakness, followed by seizures and sudden loss of consciousness. History revealed that she was on insulin therapy for 6 years now and has missed several meals that day due to a bingo tournament she joined in the neighborhood. Blood glucose level was 18 mg/dl. Which of the following can be expected in this patient? A. Increased glucagon B. Increased epinephrine C. Decreased C-peptide D. All of the above E. A and B

616 D. The very low blood glucose of the patient would trigger the release of counterregulatory hormones that are supposed to elevate glucose levels by increasing mobilization of glucose from liver and inducing gluconeogenesis. These counterregulatory hormones include glucagon, epinephrine and cortisol. Since the patient is being maintained on exogenous insulin for sugar control, endogenous insulin secretion can be presumed to be decreased. C peptide is produced only in endogenous insulin. Hence, in this patient, C peptide can be presumed to be decreased,as well.

A 3-month old infant prsented with fair skin, eczema, growth retardation and musty body odor. Which of the following should be done to prevent further worsening of his condition? A. Administration of branched chain amino acid in the diet B. Eliminate branched chain amino acid from the diet C. Administer phenylalanine in the diet and eliminate tyrosine D. Eliminate phenylalanine from the diet and administer tyrosine supplement E. None of the above

618 D. The patient has phenyketonuria. This is either due to deficiency in phenylalanine hydroxylase or decreased tetrahydrobipterin cofactor. This sually presents with mental retardation, growth retardation, fair skin, eczema and musty body odor. Treatment includes elimination of phenylalanine from the diet and administer tyrosine-rich diet

The following amino acids can be converted to ketones, EXCEPT: A. Glycine B. Leucine C. Phenylalanine D. Tryptophan E. B and C

619 A. Strictly ketogenic amino acids are: leucine and lysine. Ketogenic and glucogenic amino acids are: phenylalanine, tyrosine, tryptophan and isoleucine. All others are strictly glucogenic.

This amino acid is weakly basic but uncharged at physiologic pH hence its important role in the functioning of hemoglobin. A. Proline B. Arginine C. Lysine D. Phenylalanine E. Histidine

62 E SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. The 3 basic amino acids are lysine, arginine and histidine. Histidine is a weak base but largely uncharged at physiologic pH. This is an important property in the functioning of hemoglobin.

A mitochondrion was experimentally divided into its individual parts. On examining the inner membrane, which of the following electron transport chain components will NOT be present? A. Complex I B. Complex III C. Cytochrome oxidase D. Cytochome c E. C and D

620 D. All components of ETC are fixed to the inner mitochondrial membrane except for: conenzyme Q and cytochrome C.

A 49 year old man with a 10 year history of poorly controlled diabetes mellitus presents to his physician complaining of changes in his vision. Physical examination reveals opacities on the lens of the eye. Which enzyme most likely contributed to this complication? A. Adenosine deaminase B. Aldose reductase C. Galactose-1-phosphate uridyltransferase D. Hexokinase E. Glucokinase

621 B.Aldose reductase catalyzes the breakdown of glucose into sorbitol. Sorbitol is then metabolized to fructose. In patients with hyperglycemia as in a case of DM, sorbitol accumulation with the cells leads in the rise in the intracellular osmolality, causing water movement in the cell resulting to osmolar swelling and osmotic damage. swelling of the lens fiber can lead into rupture and cataract formation.

A woman gives birth to a full term baby. Upon delivery, her pediatrician, Dra. Casimiro, noticed that the baby is small and has a musty odor. Upon questioning, the woman says that she did not smoke nor drink alcohol during the course of her pregnancy and she only drinks diet soda and water. Which of the following amino acid is most likely to be deficient in the newborn? A. Alanine B. Tyrosine C. Phenylalanine D. Serine E. B and C

622 B. This is a case of Phenylketonuria (PKU). Patients with this kind of disease are unable to convert phenylalanine to tyrosine due to a deficiency of phenylalanine hydroxylase.

Which amino acid would most likely to be found in the interior of the a protein? A. Tyrosine B. Phenylalanine C. Histidine D. Asparagine E. A and C

623 B. Phenylalanine is a non-polar amino acid.

The higher the oxygen affinity of hemoglobin for oxygen, A. The higher its P50 for oxygen becomes B. The more difficult it is to saturate with oxygen C. The more difficult it becomes for oxygen to dissociate from the hemoglobin molecule D. A & B E. none of the above

625 C. The higher the affinity of oxygen for hemoglobin the difficult it becomes to give up or to distribute the oxygen to the tissues.

A drug that is a competitive inhibitor of an enzyme A. Increases the apparent Km but does not affect the Vmax B. Decreases the apparent Km but does not affect the Vmax C. Increases Vmax but does not affect the Km D. Decreases the Vmax but does not affect the Km E. Decreases both Vmax and Km

626 A. a competitive inhibitor competes with a substrate for the active site of the enzyme, in effect increasing the apparent Km. As the substrate concentration is increased, the substrate, by competing with the inhibitor, can overcome its inhibitory effects and eventually the normal Vmax is reached.

Mr. Dorado was diagnosed to have a deficiency of muscle phosphorylase enzyme. An individual with deficiency of this enzyme would; A. Produce a higher than normal amount of lactate during a brief period of intense exercise like push-ups B. Be incapable of performing mild exercises of long duration (a 10-mile walk) C. have lower than normal amounts of glycogen in muscle tissue D. be less dependent than normal on blood glucose to supply energy for exercise E. produce normal amounts of blood glucose in response to increased glucagon

629 E this is a case of McArdle's disease, muscle phosphorylase deficiency. Muscle glycogen could not be oxidized during exercise. Therfore, lactate level would be low and the person could not tolerate intense exercise of brief duration and would rely on fuels from the blood for energy. the person could engage in mild exercises of long duration using these blood fuels. the liver would not be affected because it contains a different phosphorylase enzyme and it could still respond to glucagon by breaking down glycogen.

Which statement is true regarding the Krebs Henseleit cycle? A. 90% occurs n the liver and 10% in the kidney B. The rate limiting step has an absolute requirement for N-acetylglutamate (NAG) as a positive allosteric activator C. The first 2 steps occurs in the cytoplasm and the rest occurs in the mitochondria D. The first nitrogen of urea is from free ammonia while the second nitrogen is donated by gluatamate E. Formation of carbamoyl phosphate is driven by cleavage of 1 mol of ATP

63 B. The urea cycle occurs exclusively in the liver because it has arginase to cleave arginine into urea. The first 2 steps occurs in the mitochondria whereas the remaining enzymes are located in the cytosol. The second nitrogen of urea is from aspartate NOT glutamate. 2 molecules of ATP are req'd to synthesize carbamoly phosphate. Remember: An important concept in the urea cycle is that NAG is an essential activator of CPS I, the rate limiting step.

Which of the following statements about the conversion of glucose to triacylglycerol in the liver is CORRECT? A. Malate serves to transport acetyl units across the mitochondrial membrane B. Reducing equivalents are provided by the reactions of glycolysis C. Reducing equivalents are provided by the malic enzyme (a decarboxylating malate dehydrogenase) D. The glycerol moiety can be derived from dihydroxyacetone phosphate (DHAP) but not from blood glycerol E. 2-Monoacylglycerol is an intermediate

630 C. Citrate transports acetyl unit from mitochondria to cytosol. NADPH is provided by PPP and MALIC enzyme. The liver has glycerol kinase, thus blood glycerol can be used. 2 monoacylglycerol is produced only in intestinal cells.

What reaction/pathway generates the greatest amount of ATP? A. Glycolysis B. Citric acid cycle C. Oxidative Phosphorylation D. Adenylate kinase reaction E. None of the above

631 C.

When it transfers extramitochondrial NADH to the respiratory chain, it generates 2 rather than 3 ATPs A. Malate shuttle B. Glycerophosphate shuttle C. Citrate shuttle D. Both A and B E. None of the above

632 B. Glycerophosphate shuttle 2 ATPs; malate 3 ATPS

A neonate born 4 hours ago is having a difficulty of breathing. The baby was born at 32 weeks AOG. He is tachypneic and is flaring and grunting. The baby's heart rate is 120bpm, BP 100/60 mmHg and respiratory rate is 55 cpm. What is lacking in this patient? A. Dipalmitoyl phosphatidylcholine B. Lecithin C. Elastase D. Collagen E. A and B

633 E Dipalmitoyl phosphatidylcholine is the same as lecithin.

Which of the following statements concerning metabolism of arachidonic acid is TRUE? A. It is converted to prostagalndins by a process that is stimulated by aspirin B. It is coverted to prostaglandins by a process that is stimulated by glucocorticoids C. It is produced from thromboxanes and leukotrienes D. It is derived from palmitate E. it is cleaved from membrane phospholipids by a phospholipase

635 E Arachidonic acid is cleaved from membrane phospholipids by phospholipase A2.

Which of the following statements is TRUE of de novo pyrimidine synthesis but not of de novo purine synthesis? A. The base is synthesized while attached to ribose 5 phosphate B. One carbon fragments are donated by folic acid derivatives C. Carbamoyl PO4 donates a carbamoyl group D. The entire glycine molecule is incorporated into a precursor of the base E. Glutamine donates nitrogen that becomes one of the atoms in the ring

636 C. In pyrimidine biosynthesis, carbamoyl phosphate produced from glutamine, C02 and ATP, reacts with aspartate to form a base which, after oxidation, reacts with PRPP to form a nucleotide.

Which level of protein structure is involved in the pathology of prion diseases? A. Primary structure B. Secondary structure C. Tertiary structure D. Quaternary structure E. A and C

638 B. B pleated sheet= secondary structure

Typtophan is an amino acid with the largest side chain containing an indole ring. It is a precursor of what substances? A. niacin B. melatonin C. serotonin D. A and B E. All of the above

639 E tryptophan is a precursor of niacin, melatonin and serotonin

The ff is true of proline EXCEPT? A. It is considered a secondary amino acid B. It is an imino acid C. It contains a sulfhydryl group that is an active part of many enzymes D. It has an aliphatic side and a non polar side chain E. Its unique geometry contributes to formation of collagen

64 C. Cysteine and not proline contains a sulfhydryl group. Proline has a unique 5 membered ring structure making it a secondary and an imino acid. Its unique and sturdy geometry interrupts the alpha helices of collagen.

Desmolase is the rate limiting enzyme in androgen and steroid synthesis. It is responsible for what reaction? A. Conversion of progesterone to 11 deoxycorticosterone B. Conversion of pregnenolone to 17 hydroxypregnenolone C. Conversion of cholesterol to pregnenolone D. Conversion of DHEA to Androstenedione E. None of the above

640 C. desmolase converts cholesterol to pregnenolone, which is the rate limiting step

Glycosaminoglycans (GAG's) are long, unbranched heteropolysaccharide chains that are generally composed of repeating dissacharide units. Which among the following GAG's is mainly found on synovial fluid and vitreous humor; and plays an important role in permitting cell migration during morphogenesis and wound repair? A. Hyaluronic Acid (GlcNAc, GLCUA) B. Chondroitin Sulfate (GalNAc, GlcUA) C. Keratan Sulfate (GlcNAc, Gal) D. Dermatan Sulfate (GalNAc, IdUA) E. Heparan Sulfate (GalNAc, GlcUA)

641 A. All of the choices given are GAG's. However, in terms of cell migration and wound repair (specifically on synovial fluid and vitreous humor), Hyaluronic Acid is the best answer. Chondroitin sulfate is present on cartilage and cornea. Keratan Sulfate and Dermatan sulfate are responsible for corneal transparency. Heparan Sulfate determines the charge-selectiveness of the renal glomerulus.

After acquiring your Physician PRC license, you decided to go on moonlighting. At the OPD, a mother brought her 4 year old child who presented with short stature, hypermobile joints and widely-spaced teeth. Upon chest examination, you heard a grade 4/6 systolic murmur. You are suspecting a mucopolysaccharidoses syndrome and upon knowing that the patient has NO CNS abnormality, you already know that the patient is suffering from? A. Hurler's Syndrome B. Hunter's Syndrome C. Morquio's Syndrome D. Sanfilippo Syndrome E. Zellweger Syndrome

642 C. Morquio's Syndrome is characterized by accumulation of GAG's in the lysosomes due to galactose-6-sulfatase deficiency, and is the only mucopolysaccharidoses syndrome that is NOT associated with CNS abnormality.

Myoglobin is a heme protein found in heart and skeletal muscle. It acts as reservoir of oxygen in the said locations and releases oxygen in times of hypoxia. The residue of which amino acid is responsible for myoglobin's oxygen-binding capacity? A. Glutamine B. Histidine C. Alanine D. Serine E. Threonine

643 B. Histidine residues play an essential role in O2-binding of myoglobin. Glutamine and Alanine are the main carriers of Nitrogen from peripheral tissues towards the liver. Serine and Threonine are the sites for O- linked glycosylation in the Golgi apparatus.

Which among the following amino acids is a weak base, and therefore has no charge on neutral pH? A. Histidine B. Arginine C. Lysine D. Leucine E. Isoleucine

644 A. Histidine, Arginine, and Lysine are all basic in nature. Arginine and Lysine are positively charged at neutral pH. Leucine and Isoleucine are branched-chain amino acids.

On a research laboratory, you are asked to determine the linear sequence of a specific protein. While doing so, you recalled that the kind of bond you least likely to break is the? A. Hydrogen Bond B. Ionic Bond C. Covalent Bond D. Peptide Bond E. Hydrophobic Bond

645 D. The linear sequence of a protein is called its Primary Structure. It is composed by specific amino acids attached to each other by Peptide Bonds. All other choices are found on higher levels of protein structure.

These are specialized group of proteins required for the folding of many species of proteins. They can also "rescue" proteins that have become thermodynamically trapped in a misfolded dead-end by unfolding hydrophobic regions. A. Domains B. Chaperones C. Motifs D. Protein-guiding Benders E. Hydrophilic β-benders

646 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Motifs are the non-functional combinations of secondary protein structures. Domains are made of Motifs and are the functional forms. Chaperones are the folding-guides and are also called the "rescue" proteins. The rest are just nuisance choices.

In bioenergetics, the measure of heat content of the reactants and products is called Enthalpy. What unit is used to describe it? A. Kelvin B. Joules C. Joules per Kilogram D. Joules per Kelvin E. Joules per Fahrenheit

649 B. Joules is the unit of measurement used for describing Enthalpy. Joules per Kelvin is used to measure Entropy.

This complex of the electron transport chain is the site where one-half of O2 is reduced to water. A. Cytochrome oxidase B. ATP synthase C. NADH dehydrogenase D. Succinate dehydrogenase E. Ubiquinol ferricytochrome oxidoreductase

65 A. Complex IV or cytochrome oxidase is the site where the the final electron acceptor which is 1/2 of oxygen is reduced to water

The electron transport chain (ETC) is the final common pathway by which electrons from the different fuels of the body flow and create energy. What complex of ETC is also an essential part of the Kreb's Cycle? A. Complex I B. Complex II C. Coenzyme Q D. Complex III E. Complex IV

650 B. Complex II is the Succinate Dehydrogenase enzyme. Aside from accepting FADH2 in the ETC, it also participates in the Kreb's cycle. It converts Succinate to Fumarate and yields FADH2 as a reducing equivalent.

Uncouplers are substances that increase the permeability of the inner mitochonadrial membrane to protons. Which among the following statements is/are true about ETC in the presence of uncouplers? A. Continue to produce energy B. Increase ATP synthesis C. Decrease oxidation of NADH D. choices A and B are both correct E. choices B and C are both correct

651 A. In the presence of uncouplers, ETC still continue to produce energy BUT in the form of HEAT and NOT ATP. Uncouplers increase oxygen consumption and oxidation of NADH.

Glucose is the main fuel of most of the cells in the body. Before it can be utilized, some cells need specific transporters to mediate its use. Which among the following glucose transporters is/are present in the brain? A. Glut 1 B. Glut 2 C. Glut 3 D. choices A and B are both correct E. choices A and C are both correct

653 E The brain utilizes Glut-1 and Glut-3 to transport glucose inside the cell. Glut-2 is present in the liver, pancreatic B-cells, kidneys, and basement membrane of the small intestines.

Phosphofructokinase 1 (PFK1) is the rate-limiting step for Glycolysis. Which among the following statements is/are true about this enzyme? A. Activated by excess ATP B. Inhibited by excess Citrate C. Active in Starved state D. Choices A and B are both correct E. Choices A and C are both correct

654 B. During the well-fed state (when there is increased Insulin and decreased Glucagon levels), PFK2 converts fructose-6-phosphate (F-6-P) to fructose-2,6- bisphosphate (F-2,6-BP). Accordingly, F-2,6-BP activates PFK1 and glycolysis will proceed to produce energy from the food we eat. In contrary, when there is excess energy (in the form of ATP and Citrate), PFK- 1 is inhibited.

Pyruvate Dehydrogense enzyme deficiency is the most common biochemical cause of congenital lactic acidosis. Which among the following substances is/are needed by this enzyme as co-factor/s? A. Thiamine bisphosphate B. FAD C. NAD+ D. Choices A and B are both correct E. Choices B and C are both correct

655 E Pyruvate Dehydrogenase enzyme is the link between Glycolysis and Kreb's Cycle. It needs the following co- enzymes: 1. Thiamine pyrophosphate, 2. FAD, 3. NAD+, 4. Coenzyme-A, 5. Lipoic Acid

Gluconeogenesis pathway is technically the reverse of Glycolysis. They just differ in three enzymes. Which among the following groups of enzymes is PRESENT in Gluconeogenesis and NOT in the later? A. PEP carboxykinase + Pyruvate Carboxylase, Fructose-1,6-bisphosphatase, Glucose-6-phosphatase B. PEP carboxykinase + Pyruvate Carboxylase, Fructose-1,6-bisphosphatase, Hexokinase/Glucokinase C. PEP carboxykinase + Pyruvate Carboxylase, Fructose-2,6-bisphosphatase, Glucose-6-phosphatase D. PEP carboxykinase + Pyruvate Carboxylase, Fructose-2,6-bisphosphatase, Hexokinase/Glucokinase E. PEP carboxykinase + Pyruvate Carboxykinase, Fructose-2,6-bisphosphatase, Hexokinase/Glucokinase

656 A. The steps 10, 3 and 1 of Glycolysis are catalyzed by Pyruvate Kinase, PFK-1, and Hexokinase/Glucokinase respectively. In Gluconeogenesis, these enzymes are subtituted by: PEP carboxykinase + Pyruvate Carboxylase, Fructose-1,6-bisphosphatase, and Glucose- 6-phosphatase respectively.

Cellulose is the primary structure of a plant cell wall. Being a stool-former, it is an important part of human diet and is said to be protective from colon cancer. What kind of glycosidic bond is present in cellulose that humans cannot digest? A. α(1->4) linkage B. α(1->6) linkage C. β(1->4) linkage D. β(1->6) linkage E. none of the choices is true

657 C. Cellulose is a polysaccharide consisiting of a linear chain of several hundred to ten thousand of β(1->4) linkage which cannot be digested by humans.

During your rotation in the Department of Pediatrics, you encountered a 5 year-old patient with a chief complaint of loose watery stools accompanied by undocumented fever. During PE, patient is febrile with macular rashes on the chest (Rose Spots). CBC showed lymphocytosis and the Widal Test turned out to be positive. You prescribed Chloramphenicol but the mother told you that the patient experienced bleeding in the past when he took the said medication. What kind of abnormality are you thinking of? A. Glucose-6-phosphatase deficiency B. Glucose-6-phosphate dehydroxylase deficiency C. Glucose-6-phosphate dehydrogenase deficiency D. Glucose-6-phosphate dihydrogenase deficiency E. Glucose-6-phosphatase dehydroxylase deficiency

658 C. Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common disease-producing enzyme abnormality in humans. Precipitating factors involves infection and certain medications.

This is a rare neurologic disorder due to abnormal accumulation of Phytanic Acid. A. Zellweger's Syndrome B. Carnitine palmitoyl transferase I deficiency C. Carnitine palmitoyl transferase II deficiency D. Ornithine transcarbamoylase deficiency E. Refsum's Disease

659 E In excess, Phytanic Acid blocks beta oxidation and causes neurologic symptoms due to improper myelinization. This disorder is called Refsum's Disease.

A patient is suspected of salicylate toxicitiy. Which of the ff statement is true regarding its effects on the ETC? A. There is reduced permeability of the inner mitochondrial membrane to protons hence impaired ATP synthesis B. Respiration dissociates from phosphorylation C. The electron transport chain terminates along with ATP synthesis D. There is direct inhibition of Complex V hence ATP synthesis terminates E. All of the above

66 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE.. Salicylates/aspirin are uncouplers that dissociates oxidation in the respiratory chain from phosphorylation. There is increased permeability of the mitochondiral membrane to protons therefore ATP sysnthesis stops but the respiratory chain continues prducing excessive heat hence hyperpyrexia. Oligomycin and not aspirin is a Complex V inhibitor.

Which among the following codons is/are "stop codon/s"? A. UAA B. UGG C. UAU D. Choices A and B are both correct E. Choices A and C are both correct

660 A. There are only three "stop codons". UAA, UAG and UGA.

This type of chemical bond is formed between 2 amino acidsand destroyed by heating the protein in a strong acid solution for 24 hours. A. Peptide bond B. Phosphodiester bond C. Hydrogen bond D. Disulfide bond E. None of the above

661 A. Peptide bond is formed between two amino acids and is the bonds that form the primary structure of proteins. Phosphodiester bonds exist between nucleotides in a DNA strand. H-bonds exist between water and an electron rich molecule such as sulfur, oxygen, nitrogen and fluoride. Disulfide bonds exist o between cysteine residues in 3 structures.

Precursor of purine amino acids: A. IMP B. OMP C. UMP D. dUMP E. None of the above

662 A. De Novo Purine synthesis uses IMP as precursor molecule while Pyrimidine synthesis uses OMP.

Deficiency in Vitamin B6 would lead to decreased synthesis of the following except? A. Niacin B. GABA C. Epinephrine D. Histamine E. None of the above

663 C. Vitamin B6 (Pyridoxine) is a co-factor in several amino acid biosynthetic pathway including Tryptophan, Histidine, Glycine and Glutamate to produce Niacin, Histamine, Porphyrin and GABA respectively. Tetrahydrobiopterin (BH4) is needed in the synthesis of Epinephrine, to convert Phenylalanine into Tyrosine.

Tyrosine becomes an essential amino acid in the presence of _________? A. Phenylketonuria B. Tryptophan deficiency C. Adenosine deaminase deficiency D. Vit. B6 Deficiency E. None of the above

664 A. In a normal person, Tyrosine is synthesized form Phenylalanine. However in the presence of phenylketonuria, Phe intake is restricted, so Tyrosine must be derived from the diet for the synthesis of catecholamines.

Keloid is made up of what type of collagen? A. I B. II C. III D. IV E. V

666 A. CONTROVERSIAL. It's made up of both type I and III, but more type I rather than III. II) Keloid tissues contained 31.6 +/- 2.2 percent type III collagen as compared to 21.4 +/- 2.7 percent type III present in normal human skin dermis. Alteration of collagen composition and cross-linking in keloid tissues. Di Cesare PE, Cheung DT, Perelman N, Libaw E, Peng L, Nimni ME. Matrix. 1990 Jul;10(3):172-8. PubMed PMID: 2215357

Post - transcriptional modification in eukaryotes, except? A. Capping of 5' end B. Polyadenylation of 3' end C. Splicing of introns D. Splicing of exons E. None of the above

667 D. Co-transcriptional modification is a process in cell biology by which, in eukaryotic cells, primary transcript RNA is converted into mature RNA.

A protein is separated by gel electrophoresis and antibody is bound to a protein. This process describes? A. Southern blot B. Northern blot C. Western blot D. Southwestern blot E. Northwestern blot

668 C. Southern blot uses DNA as sample and DNA as probe. Northern blot uses RNA as sample, DNA as probe and Western blot uses Protein as probe and sample.

This type of inhibition leads to decreased affinity and does not affect efficacy? A. Non - competitive Inhibition B. Allosteric inhibition C. Mixed inhibition D. Competitive inhibition E. None of the above

669 D. Non - competitive inhibition decreases efficacy but does not affect affinity. Allosteric inhibition is a type wherein the substrate binds to a different site from the inhibitor. Mixed inhibition leads to deacreased affinity and decreased efficacy.

Which of the ff statements regarding the carbohydrate structure is true? A. Epimers are compounds that have the same chemical formula different only in structure B. The L enantiomer is the major sugar of the human body C. Galactose and mannose are epimers D. Glucose and Fructose are isomers E. Anomers are convertible between a linear form and ring form through specific enzymatic reactions

67 D. Glucose, galactose, fructose and mannose are all isomers having the chemical formula C6H12O6. Epimers are compounds that differ around only 1 specific carbon atom hence galactose and mannose are NOT epimers bec they differ on 2 carbons atoms. The D enantiomer and not the L is utilzed by the body. Anomers can mutarotate without need for enzymes.

Rate Limiting step in de Novo Pyrimidine Synthesis? A. Carbamoyl PO4 synthetase II B. Glutamine - PRPP amidotransferase C. Carnitine acyltransferase I D. Carbamoyl phosphate synthetase i E. G6PD

671 A. Glutamine - PRPP amidotransferase - de novo purine synthesis Carnitine acyltransferase I - FA oxidation Carbamoyl phosphate synthetase I - FA oxidation G6PD - HMP shunt

Gross ATP production per molecule of glucose during glycolysis through substrate level phosphorylation? A. 2 B. 4 C. 6 D. 8 E. 10

672 B. Two enzymes in glycolysis produce ATP through substrate level phosphorylation: PG Kinase and Pyruvate kinase producing 2 ATPs each, making it a total of 4 ATPs.

Main function of Pentose Phosphate Pathway? A. NADPH production B. ATP production C. Removal of nitrogenous waste D. Transport of FA from cytosol to inner mitochondrial membrane E. None of the above

673 A. The pentose phosphate pathway (also called the phosphogluconate pathway and the hexose monophosphate shunt) is a process that generates NADPH and pentoses (5-carbon sugars). ATP production is through Kreb's cycle and ETC, nitrogenous waste is removed through Urea cycle and FA transport is carnitine shuttle for B-oxidation of FA.

Reactions proceed spontaneously in which of the following? Î"G A. = 0 B. < 0 C. >0 D. Î"H - TÎ"S E. None of the above.

674 B. Spontaneous reactions occur when Î"G is negative, that is <0. Positive Î"G needs energy for it to occur and if Î"G = 0, rate of formation is equal to rate of degradation.

This lipoprotein transports triglyceride from liver to the periphery. A. LDL B. HDL C. VLDL D. Chylomicrons E. Micelles

675 C. LDL transports cholesterol into cells. HDL reverses cholesterol transport, transporting it from the periphery into the liver, chylomicrons transport dietary TG and cholesterol into tissues while micelles are formed through the biliary saponification of dietary fat from the intestinal lumen for absorption into the intestinal brush border.

Component of surfactant produced by type II pneumocytes? A. Phosphatidyl inositol B. Phosphatidyl choline C. Phospholipase D. Glycerophospholipid E. Glycerol

676 B. Dipalmitoyl phosphatidylcholine is the major component of lung surfactant. Phosphatidyl inositol is a reservoir of arachidonic acid in cellular membranes, needed for synthesis of prostaglandins and leukotrienes.

A 6 - month old presents with recurrent sinus infection, chronic cough and pneumonia. CBC showed lymphopenia. This may be caused by a deficiency in which enzyme? A. HGPRT B. Adenine deaminase C. G6PD D. Homogentisic acid oxidase E. HMG CoA synthetase

678 B. This condition is also known as Severe Combined Immunodeficiency (SCID) which is a genetic disorder characterized by the absence of fuctional T- lymphocytes,which results in a defective antibody response.

The ff statement is true regarding glycosis EXCEPT A. It is present in the cytoplasm of all cells B. Phosphorylation of glucose is an irreversible step C. 2 ATP molecules are initially utilized D. Fructose 2,6 Bisphosphate is a potent inhibitor of the rate limiting step E. Only 2 molecules of ATP per glucose is produced under anaerobic conditions

68 D. Fructose 2-6 BP is actualy the most potent allosteric activator of PFK-1, the rate limiting step of glycolysis. All the rest of the statements are true.

Protein - energy malnutrition which occurs more often in children >1y/o, with hair and skin changes, edema and stunted growth. Plasma protein is very low when measured. A. Kwashiorkor B. Marasmus C. Cachexia D. Anorexia E. None of the above

680 A. Kwashiorkor is a form of malnutrition wherein there is adequate intake of calories but with low protein content, which leads to the above symptoms. Marasmus on the other hand is due to lack of calories but with adequate protein.

The model proposed by Watson, Crick and Wilkins consists of a double-stranded helical structure of the B form of DNA. Several bonds maintain the integrity of the DNA molecule. What bond is found in between the purine and pyrimidine bases of its respective linear molecules holding the two strands together of the double-stranded helix? A. Hydrogen bond B. van der Waals C. Hydrophobic interactions D. 3'-5'-phosphodiester bridges

681 A. A. Hydrogen bond (pp. 311, Harper's Biochemistry, 27th ed.) Notes: • van der Waals and hydrophobic interactions - between stacked adjacent base pairs • 3'-5'-phosphodiester bridges - connects monomeric units of DNA to become polymeric forms

In the prokaryotic gene expression, what is the genetic unit coding for the structure of the subunit of a protein molecule, acting as it does as the smallest unit of genetic expression? A. Operon B. Intron C. Cistron D. Exon

682 C. C. Cistron (pp 381, Harper's Biochemistry, 27th ed). SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE.

The occurrence of the 21st amino acid in proteins is uncommon; however, it is present at the active site of several human enzymes that catalyze redox reactions. Replacement of this amino acid with another can result in significantly decreased catalytic activity and might impair a kind of human protein which has been implicated in tumorigenesis, atherosclerosis and Keshan disease. What is this amino acid? A. Isoleucine B. Selenocysteine C. Hydroxyproline D. Selenoleucine

683 B. Answer: B. SelenoCysteine (pp. 243, Harper's Biochemistry, 27th ed.) Notes: Keshan Disease = selenium deficiency cardiomyopathy

The Kreb's-Henseleit Cycle is a pathway present only in the liver useful in the removal of nitrogenous waste products in the body. The "bottleneck" reaction and the metabolite flux of this pathway is reduced when the catalytic efficiency or quantity of what catalyst is decreased? A. Carbamoyl Phosphate Synthetase-1 B. Phosphofructokinase-1 C. Isocitrate Dehydrogenase D. Carnitine Palmitoyl Transferase-1

684 A. Answer: A. Carbamoyl Phosphate Synthetase-1 (Biochemistry, Topnotch Handouts). Notes: This question can be rephrased into: What is the rate- limiting (bottleneck) enzyme for urea cycle? *Kreb's- Henseleit Cycle (Urea Cycle/Ornithine Cycle) is NOT synonymous with Kreb's Cycle (TCA).

5. The different etiologies of jaundice can be classified into prehepatic, hepatic and posthepatic causes. Differentiation of these causes can be evaluated by determination of bilirubin levels in the serum, urine and feces. What is the clinical significance of acholuric jaundice? A. Normal B. Hemolytic Anemia C. Hepatitis D. Obstructive Jaundice

685 B. Answer: B. HemolytiC Anemia (pp. 292, Harper's Biochemistry, 27th ed.) Notes: The presence of bilirubin in the urine is sometimes referred to as Choluria. • Hepatitis and obstruction of CBD = choluric jaundice • Hemolytic anemia = acholuric jaundice • Normal = (obviously) absent jaundice and absent urine bilirubin

Impairment of oxidation of fatty acids gives rise to several diseases. An example of which is Refsum's disease, a rare neurologic disorder due to a metabolic defect resulting in the accumulation of a certain substance found in dairy products and ruminant fat and meat. What is this substance thought to have pathological effects on membrane function, protein prenylation and gene expression? A. Hypoglycin B. Dicarboxylic Acid C. Phytanic Acid D. Polyenoic Acid

686 C. Answer: C. PhytaniC ACid (pp. 194, Harper's Biochemistry, 27th ed.) Notes: • Jamaican Vomiting Sickness = Hypoglycin (from Akee Tree) = inactivates medium- and short-chain acyl-CoA Dehydrogenase • Dicarboxylic Aciduria = w-dicarboxylic acids = lack mitochondrial medium-chain acyl-CoA Dehydrogenase • Refsum disease = Phytanic Acid • Zellweger's (cerebrohepatorenal) syndrome = accum. polyenoic acid in the brain =absence of peroxisomes in all tissues • *This topic came out during Feb 2013 Physician Licensure Exam.

Blotting is a method used to study macromolecules like DNA, RNA and proteins which are separated by gel electrophoresis and transferred into a carrier. The macromolecules can then be visualized by specific probes or staining methods. Which of the following methods is a modification of the Western Blot Technique by detecting posttranslational modification of proteins? A. Eastern Blot B. Polymerase Chain Reaction C. Southwestern Blot D. Northern Blot

688 A. Answer: A. Eastern Blot (pp. 20, Comment Section, Rush University Medical Center, Review of Surgery, 5th edition) Notes: Southern Blot - DNA sample, DNA probe; Northern Blot - RNA or mRNA sample, DNA probe; Western Blot - Protein Sample, Antibody Probe; Eastern Blot - Posttranslational modification of protein (sample); Southwestern Blot - DNA-binding proteins (sample).

Characteristics of glucokinase are the ff: A. It is used as basal absorption of glucose by most tissues B. It can also phosphorylate hexoses other than glucose C. It is saturated under normal conditions D. It has high affinity for glucose compared to hexokinase E. It is the rate limiting step of glycolysis

69 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Glucokinase despite its name can also phosphorylate other hexoses. It has high Km (low affinity for glucose) and high Vmax and is present only in liver and pancreas. It is most active post-prandially. It is the first step but not the rate limiting step of glycolysis. Review the table highlighting the differences between hexokinase and glucokinase.

Immunoglobulins (Ig) play a key role in the defense mechanism of the body. Each class of Ig has its own distinct property for it to confer its specific function. Among the 5 classes, based on its structure, which of the Ig may exist as a dimer? A. IgG1 and IgM B. serum IgA and IgD C. IgM and secretory IgA D. IgD and IgG1

690 C. Answer: C. IgM and seCretory IgA (pp 601, Harper’s Biochemistry, 27th edition) Notes: • serum IgA â€" may exist both as a monomer and a dimer • secretory IgA â€" exist as a dimer with a secretory component • IgM â€" monomer, dimer or pentamer • IgD, IgG, IgE â€" monomer

An adult man suffered from stable angina pectoris for 15 yrs. During which time there was progressive heart failure and repeated pulmonary thromboembolism, on his death at age 63, autopsy disclosed enormous cardiomyopathy (1100 g), cardiac storage of globotriaosylceramide (11 mg lipid/g wet weight) and restricted cardiocytes. Which of the following lipid storage disease would result in these clinical findings? A. Fabry disease B. Gaucher disease C. Krabbe disease D. Niemann-Pick disease type 1A E. Tay-Sachs disease

691 A. Fabry disease is an X-linked disorder that results from a deficiency in alpha-galactosidase A. This leads to deposition of neutral glycosphingolipids. Most affected tissues are heart, kidneys and eyes.

Lipoprotein lipase (LPL) is the endothelial cell-associated enzyme necessary for release of fatty acid from circulating lipoproteins. Which of the following apoplipoproteins is required to activate LPL-mediated release of fatty acids from chylomicrons? A. Apo A B. Apo B100 C. Apo B48 D. Apo CII E. Apo E

692 D. The presence of Apo CII on the surfaces of lipoprotein particles is necessary for the activation of endothelial cell LPL.

Hemochromatosis, a disorder that is the result of excess iron accumulation, is caused by deficiencies in which of the following proteins? A. Divalent metal transporter-1 (DMT-1) B. Human leukocyte antigen (HLA) complex iron protein (HFE) C. Ferritin D. Ferroportin E. Transferrin

693 B. Hemochromatosis is a disorder in iron metabolism that is characterized by excess iron absorption, saturation of iron-binding proteins and deposition of hemosiderin in the tissues.

One important function of nitric oxide is the induction of vascular smooth muscle relaxation in response to acetylcholine. The production of NO requires which amino acid? A. Arginine B. Asparagines C. Cysteine D. Glutamine E. Lysine

694 A. NO is generated from arginine catalyzed ny NOS. Other product is citrulline.

The inability to rapidly synthesize DNA during the process of erythrocyte maturation leads to abnormally enlarged erythrocytes. This disorder referred to macrocytic anemia and is caused by a deficiency in which of the following vitamins? A. Ascorbate B. Biotin C. Folate D. Niacin E. Thiamine

696 C.

Hypersensitive individuals have IgE to specific antigens on the surface of their WBC. When these individuals are challenged with antigen, the antigen-IgE complexes induce synthesis and release of which of the following physiologically potent lipids? A. Arachidonic acid B. Leukotriene B4 C. Platelet activating factor (PAF) D. Prostaglandin E2 E. Thromboxane A2

697 C. PAF is a unique complex lipid of the plasmalogen family and functions in hypersensitivity rxns, acute inflammatory rxns and anaphylactic shock by inc. Vasopermeability, vasodilation and bronchoconstriction.

Which of the following represents the enzyme deficiency that leads essential fructosuria? A. Fructose 1 phosphate aldolase (aldolase B) B. Fructose 1,6 bis phosphate aldolase (aldolase A) C. Fructokinase D. Hexokinase E. 6PFK-1

698 C. Essential fructosuria is an autosomal recessive disorder manifesting benign asymtotomatology due to lack of fructokinase.

A patient who presented with mild jaundice had work up done, which revealed increased direct bilirubin, absent urine urobilinogen, (+) urine bilirubin. Liver biopsy showed liver hyperpigmentation. Which of the following is the most likely diagnosis? A. Crigler- Najjar syndrome B. Gilbert syndrome C. Dubin Johnson syndrome D. Rotor syndrome E. Hepatitis

7 C. Try to master direct and indirect hyperbilirubinemia. It’s a favorite theme and there are many question variations that can be done across many subjects. This is a case of conjugated hyperbilirubinemia (note sometimes, the examinar can be unforgiving and may not put increased direct bilirubin so be familiar with other lab findings too). Rotor syndrome and dubin Johnson syndrome present similarly except dubin Johnson has liver hyperpigmentation (dubin â€" dark liver) Conjugated hyperbil â€" increased direct serum bilirubin, absent urine urobilinogen, (+) urine bilirubin Ex. Obstructive jaundice, dubin Johnson, Rotor syndrome Unconjugated â€" increased indirect serum bilirubin, (+) urine urobilinogen, (-) urine bilirubin Ex. Crigler-Najjar, Gilbert Source: Harper 27th ed p292

In glycogenolysis, the reason why the muscle tissue cannot produce free glucose for release into the blood stream is: A. The cell membrane is selectively impermeable to free glucose B. Increased calcium levels in muscle tissue prevents exocytosis of free glucose C. Absence of glucose-6-phosphatase D. Glycogen phosphorylase is allosterically inactivated by increased glucose 6 phosphate levels E. Debranching enzyme is inacitve in metabolically active msucles hence glucose is prefentially utilized intracellularly

70 C. In the muscle, the enzyme, glucose-6-phosphatase is ABSENT hence glucose 6 phosphate from glycogenolysis enters glycolysis instead. Remember that muscle can perform glycogenolysis but can only utilze the glucose for its own use. The other statements are erroneous explanations.

Obesity, genetic profile and aging all contribute to the development of Type II DM. Which is the most important additive factor for these 3 conditions in the development of type II DM? A. Inc.hepatic gluconeogenesis B. Inc. Pancreatic glucagon secretion C. Impaired renal clearance of glucose D. Inc. Adipose tissue activity E. Muscle resistance to insulin

700 E The overall level of significant influence is at the level of skeletal muscle sensitivity to the action of insulin.

In the fasting state which of the ff occurs? A . Glycogen synthase is phosphorylated B. Decreased cAMP C. Increased phosphofructokinase-2 (PFK-2) D. Increased fructose 2-6 Bisphosphate (F2,6 BP) E. Decreased activity of hormone senstive lipase

72 A. Expect PLENTY of questions regarding the feeding/fasting cycle. Effects of insulin/glucagon? What enzymes are active when phosphorylated/ dephosphorylated? Please master it by heart. In the fasting state, glucagon predominates to raise blood glucose levels. Glucagon increases cAMP and protein kinase A. It acts generally by PHOSPHORYLATING enzymes. Take note: Glycogen synthase when phosphorylated is INACTIVE hence glycogenesis is inhibited. There is also decreased activity of PFK2 and its product F2,6-BP which is the most important alloesteric activator of glycolysis and inhibitor of gluconeogenesis. Hormone senstive lipase is activated by glucagon to release FFA for oxidation

A person ate a heavy meal 30 mins ago, which of the ff occurs? A. Increased activity of carnitine acyltransferase B. Decreased fructose 2-6 Bisphosphate (F2,6 BP) C. Most rare limiting enzymes are in the dephosphorylated state D. Glycogen phosphorylase Is phosphorylated E. Increased NAD/NADH ratio

73 C. In the fed state, insulin predominates. In contrast to glucagon, insulin generally activates enzymes by DEPHOSPHORYLATION. Glycogen phosphorylase, in contrast to glycogen synthase, is active when phosphorylated. Insulin upregulates F2,6BP to stimulate glycolysis increasing NADH. Carnitine acyltranferase is the rate limiting step of fatty acid oxidation and is deactivated

All of the the ff are effects of glucagon EXCEPT? A. Activation of hormone sensitive lipase B. Increased activity of both ketogenesis and ketogenolysis C. Allosteric activation of pyruvate carboxylase by acetyl-CoA D. Glycogen phosphorylase Is phosphorylated E. Activation of protein phosphatase

74 E Again, glucagon (fasting state) generally acts by phosphorylating enzymes. Hormone senstive lipase is activated to release FFA for oxidation. Both ketogenensis and ketogenolysis is active in the fasting state.Pyruvate carboxylase, an irreversible step in gluconeogenesis is activated to increase free glucose levels. Glycogen phosphorlyase is active when phosphorylated. Protein phosphatase is the key effector enzyme of insulin and acts to DEPHOSPHORYLATE other enzymes.

NAPDH produced from the HMP shunt is needed in the ff pathways EXCEPT? A. Fatty acid synthesis B. Nitric oxide syntehsis C. Cholesterol synthesis D. Heme synthesis E. Regeneration of Glutathione

76 D. NADPH from HMP shunt is used for reductive reactions for FA and steroid synthesis, reduction of glutathione, NO synthesis, respiratory burst and CYP450 reactions.

A patient has mental retardation and hypotonia. Further examination revealed a cherry red spot on the macula. Traube's space is obliterated. You are suspecting a type of sphingolipidosis. What enzyme is probably deficient? A. Hexosaminadase A B. Hexosaminadase B C. Glucocerebrosidase D. Galactocerebrosidase E. Sphingomyelinase

77 E SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. For some reason, Tay sachs disease with characteristic cherry red spot is a favorite topic. Differentiate it from Niemann pick diease which also has cherry red spot but with hepatosplenomely as well. Enzyme dieficiencies are: Tay sach's- Hexosaminidase A. Gaucher's- Glucocerebrosidase. Krabbe's- Galactocerebrosidase. Nieman Pick- Sphingomyelinase

This intermediate is common to both ketogenesis and cholesterol synthesis? A. 3-hydroxy 3 methylglutaryl-CoA B. 3 hydroxybutyrate C. Mevalonate 5-phosphate D. Farnesyl pyrophosphate E. Lanosterol

78 A. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. 3-hydroxy 3 methylglutaryl- CoA is termed simply as HMG-CoA and and its production serve as the first step of both cholesterol synthesis and ketogenesis. The other intermediates are part of ketogenesis or choelsterol synthesis but not both.

This is an example of a nucleoside. A. Adenine B. Cytidine C. Thymine D. Adenosine monophosphate E. Uracil

79 B. SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE. Memorize the names of nitrogenous bases with their corresponding nucleoside and nucleotide. Bases are adenine, guanine, thymine, uracil, cytosine. Nucleoside (base plus sugar) are adenosine, guanosine, thymidine, uridine and cytidine. Nucelotide (nucleoside plus phopshate group) are AMP, UMP, TMP etc.

It is a characteristic of eukaryotic mRNA. A. Introns are spliced together B. Long sequence of adenine moelcules at the 5' end C. 3'-CCA sequence D. 7 methyl-guanosyl group at 3' end E. Makes up only 5% of the proportion of the RNA genome

80 E mRNA in eukaryotes are extensively modified: Exons are spliced together and introns are removed, a long sequence of poly A tail at the 3' end and a 7 methyl- guanosyl group at 5' end is added. It also makes up only 5% of the proportion of the RNA genome. 3'-CCA sequence is a unique property of tRNA.

Which of the following is NOT true on how Calcium synchronizes the activation of glycogen phosphorylase? a. cytosolic calcium is responsible for both contraction and glycogenolysis b. muscle phosphorylase kinase activates glycogen phosphatase c. phosphorylase kinase is made up of 4 subunits d. binding of calcium activates catalytic site of gamma subunit e. phosphorylated form is only fully activated in the presence of calcium

81 B. glycogen phosphorylase is activated by muscle phosphorylase kinase Harper’s Biochemistry 28th edition p. 160

3. Which of the following is added to LPG tanks to detect leaks? a. propane b. ethyl mercaptan c. methane d. butane e. acetone

83 B.

Which of the following amino acids does not contain a basic group? a. arginine b. proline c. lysine d. histidine e. none of the above

84 B. Harper’s Biochemistry 28th edition p. 16

5. According to the International Union of Biochemists (IUB) which of the following refers to an enzyme that catalyzes cleavage of C-O bond through atom elimination? a. oxidoreductases b. transferases c. ligases d. lyases e. hydrolases

85 D. ligases - joining together of 2 molecules coupled with hydrolysis of ATP hydrolases - hydrolytic cleavage transferases - transfer of glycosyl, methyl, or phosphoryl groups, etc Harper’s Biochemistry 28th edition p. 52

6. An 8 year old child ingests Full cream milk. After 2 hours, patient was noted to have bloating, flatulence, and soft watery stools. Reduced sugars were found in stools. Which of the following is most likely true? a. disaccharidase enzyme deficiency b. inability to absorb lactose c. inability to break down maltose d. autoimmune destruction of villi e. none of the above

86 A. refers to lactase deficiency Harper’s Biochemistry 28th edition p. 113

9. Which of the following processes is NOT increased by glucagon? a. protein synthesis b. glycogenolysis c. gluconeogenesis d. ketogenesis e. lipolysis

89 A. Harper’s Biochemistry 28th edition p. 172

Covalent modification is one of the most rapid ways of regulating enzyme activity in the cell. During fasting which of the following is expected to occur? A. Phosphorylation of Glucose-6-phosphatase B. Dephosphorylation of Glycogen synthase C. Acetylation D. Methylation E. None of the above

9 A. Acetylation and methylation are covalent modifications on histones to activate or inactivate transcription. Metabolic enzymes are regulated via phosphorylation or dephosphorylation.Glucagon phosphorylates, insulin dephosphorylates. (My mnemonic is DIG-P) This results to either activation or inactivation of particular enzymes in certain pathways. Make sure you master this concept and which enzyme/pathways are activated or inactivated by insulin and glucagon. They can easily ask 5-10 different varieties of these sort of questions.

10. Which of the following is NOT TRUE of regulation of ketogenesis? a. the factors regulating mobilization of free fatty acids are important in controlling ketogenesis b. triacylglycerols are the precursors of ketone bodies in the liver c. regulation of entry of fatty acids into the oxidative pathway is through CPT-1 d. impaired oxidation of fatty acids leads to diseases associated with hypoglycemia e. decreased insulin/glucagon ration promotes B - oxidation of fatty acids

90 B. Free fatty acids are the precursors of ketone bodies Harper’s Biochemistry 28th edition p. 190

11. Which of the following is the regulatory step of bile acid synthesis? a. HMG Coa synthase b. HMG CoA reductase c. 7 alpha - hydroxylase d. sterol 27 hydroxylase e. none of the above

91 C. Harper’s Biochemistry 28th edition p. 229

12. A 6 year old African American presented with dyspnea, painful digits, splenomegaly, anemia and jaundice. Which of the following mutations is most likely present in this patient? a. nonsense b. missense c. frameshift d. silent e. none of the above

92 B. Here, glutamic acid, the normal amino acid in position 6 of the B chain has been replaced by valine. Clearly, this hinders normal function. Harper’s Biochemistry 28th edition p. 357

13. WHich of the following is not a vitamin B12 dependent enzyme? a. methionine synthase b. methylmalonyl CoA mutase c. leucine aminomutase d. alpha ketoglutarate dehydrogenase e. none of the above

93 D. Harper’s Biochemistry 28th edition p. 476

14. A neonate was found to have poor feeding with seizures. Biochemical tests revealed accumulation of very long chain fatty acids and marked reduction of plasmalogen. Mutations in genes encoding peroxisome biogenesis has also been found. Which of the following is the most likely diagnosis? a. adrenoleukodystrophy b. Refsum’s disease c. Zellweger syndrome d. rhizomelic chondrodysplasia punctata e. none of the above

94 C. Harper’s Biochemistry 28th edition p. 493

15. Which of the following is NOT a feature of N - glycosylation? a. the transfer of oligosaccharide occurs in Asn residues b. protein bound oligosaccharide partially processed by glucosidases and mannosidases c. transfer of oligosaccharide occurs post translationally in the golgi d. the enzyme which catalyzes the transfer of oligosaccharide is inhibited by tunicamycin e. none of the above

95 C. transfer can occur cotranslationally in the endoplasmic reticulum Harper’s Biochemistry 28th edition p. 516

16. Which of the following is NOT true in the metabolism of skeletal muscle? a. skeletal muscle has receptors for glucagon b. glucose is resynthesized from lactate through Cori cycle c. free fatty acids are the major source of energy during marathons d. alanine from muscle is destined for gluconeogenesis e. skeletal muscle does not contain glucose 6 phosphatase

96 A. Harper’s Biochemistry 28th edition p. 562

18. A neonate was seen in the NICU for delayed separation of umbilical cord. Which of the following is not a biochemical feature of neutrophils? a. active pentose phosphate pathway b. contains CD11/CD18 integrins in plasma membrane c. uses NADPH oxidase for oxygen independent killing of microbes d. active glycolysis e. moderately active oxidative phosphorylation

98 C. NADPH oxidase is used for oxygen dependent killing of microbes Harper’s Biochemistry 28th edition p. 604

19. Which of the following is NOT true in the metabolism of glycogen? a. CAMP promotes simultaneous activation of phosphorylase and inhibition of glycogen synthase b. insulin inhibits glycogenolysis and stimulating glycogenesis c. glycogenesis and glycogenolysis are the same pathway d. glycogen biosynthesis involves UDP glucose e. branching of glycogen involves detachment of existing glycogen chains

99 C. glycogenolysis is not the reverse of glycogenesis, but is a separate pathway Harper’s Biochemistry 28th edition p. 157

7. Which of the following is TRUE on regulation of glycolysis and gluconeogenesis in the liver? a. most potent positive allosteric activator of PFK 1 and inhibitor of fructose 1,6 bisphosphate is fructose 2,6 bisphosphate b. fructose 2,6 bisphosphate is formed by PFK -2 c. PFK 2 and fructose 2,6 bisphosphatase are different enzymes d. both A and B e. both B and C

D. Harper’s Biochemistry 28th edition p. 168