CHEM 1005 - FINAL MULTIPLE CHOICE
NADPH and glyceraldehyde 3-phosphate are essential for the synthesis of fatty acids and triacylglycerols. Which of the following pathways can supply both of these products? A. Pentose phosphate pathway B. Ketogenesis C. Fructose metabolism D. Glycolysis
A
Which of the following enzymes is regulated by N-acetyl glutamate (NAG)? A. Carbamoyl phosphate synthetase I (CPS I) B. Argininosuccinate lyase C. Carbamoyl phosphate synthetase II (CPS II) D. Ornithine transcarbamylase
A
Which of the following is the full complement of apoproteins present on a mature HDL? A. Apo A; ApoCII; ApoE B. ApoB48; ApoCII; ApoE C. ApoCII; ApoE D. ApoB 100; ApoCII; ApoE
A
A 30-year-old man presented at clinic with a history of intermittent abdominal pain and episodes of confusion and psychiatric problems. Laboratory tests revealed increases of urinary δ-aminolevulinate and porphobilinogen. Mutational analysis revealed a mutation in the gene for uroporphyrinogen I synthase (porphobilinogen deaminase). The probable diagnosis was: A. Acute intermittent porphyria. B. X-linked sideroblastic anemia. C. Congenital erythropoietic porphyria. D. Porphyria cutanea tarda. E. Variegate porphyria.
A. (Explanation: Acute intermittent porphyria is due to mutations in the gene for uroporphyrin I synthase.)
The subcellular site of the breakdown of long-chain fatty acids to acetyl-CoA via β-oxidation is: A. The cytosol B. The matrix of the mitochondria C. The endoplasmic reticulum D. The mitochondrial intermembrane space E. The Golgi apparatus
B
Which of the following is the substrate for ketone synthesis? A. Glucagon B. Acetyl-CoA C. Pyruvate D. Glycerol
B
Which of the following shuttle systems is necessary for the oxidation of long-chain fatty acids? A. Citrate B. Carnitine C. Glycerol-3-Phosphate D. Malate-Aspartate
B
After a high carbohydrate meal, which of the following enzymes will be dephosphorylated and active? A. Hormone-sensitive lipase B. Glycogen phosphorylase C. Acetyl-CoA carboxylase D. Fructose 2,6-bisphosphate
C
The class of drugs called statins have proved very effective against hypercholesterolemia, a major cause of atherosclerosis and associated cardiovascular disease. These drugs reduce plasma cholesterol levels by: A. Preventing absorption of cholesterol from the intestine. B. Increasing the excretion of cholesterol from the body via conversion to bile acids. C. Inhibiting the conversion of 3-hydroxy-3-methylglutaryl-CoA to mevalonate in the pathway for cholesterol biosynthesis. D. Increasing the rate of degradation of 3-hydroxy-3-methylglutaryl-CoA reductase. E. Stimulating the activity of the LDL receptor in the liver.
C
Which of the following enzymes is used directly in the synthesis of dTMP (thymidine)? A. Carbamoyl phosphate synthetase II (CPSII) B. Aspartate transcarbamoylase C. Thymidylate synthase D. Dihydrooratase
C
Tay-Sachs disease is a lipid storage disease caused by a genetic defect in which one of the following enzymes: A. β-Galactosidase B. Sphingomyelinase C. Ceramidase D. Hexosaminidase A E. β-Glucosidase
D
Which of the following is the common intermediate for purine synthesis? A. Orotate monophosphate (OMP) B. Cytidine monophosphate (CMP) C. Hypoxanthine D. Inosine monophosphate (IMP)
D
HMG-CoA reductase is inhibited by A. Insig (binds SREBP and retains it in the ER) B. Elevated levels of sterols/cholesterol C. AMPKinase mediated phosphorylation D. Glucagon E. All the above
E
Hypopigmentation disorder is primarily due to deficient metabolism of which of the following amino acids? A. Homocysteine B. Cysteine C. Methionine D. Arginine E. Tyrosine
E
Metabolism of _____________________ leads to the synthesis of __________________. A. Glycine ; epinephrin B. Threonine ; norepinephrine C. Tyrosine ; serotonin D. Alanine ; homocysteine E. Tryptophan ; melatonin
E
Select the choice that correctly completes the portion of the package insert of the drug allopurinol: "Allopurinol is a structural analog of the natural purine base, hypoxanthine. It is an inhibitor of _________, the enzyme responsible for the conversion of hypoxanthine to xanthine and of xanthine to ________, the end product of purine metabolism in man." A. Dihydroorotase ; dihydroorotic acid B. Carbamoyl phosphate synthetase II; aspartic acid C. Dihydroorotate dehydrogenase; orotic acid D. Orotidylic acid decarboxylase; uracil monophosphate E. Xanthine oxidase; uric acid
E
Select the choice that correctly completes the portion of the package insert of the drug allopurinol: "Allopurinol is a structural analog of the natural purine base, hypoxanthine. It is an inhibitor of _________, the enzyme responsible for the conversion of hypoxanthine to xanthine and of xanthine to ________, the end product of purine metabolism in man." A. Dihydroorotate dehydrogenase; orotic acid B. Carbamoyl phosphate synthetase II; aspartic acid C. Dihydroorotase ; dihydroorotic acid D. Orotidylic acid decarboxylase; uracil monophosphate E. Xanthine oxidase; uric acid
E
What could the consequences of inaccurate mRNA splicing be for the RNA? A. A single base error at a splice junction will cause a large deletion. B. A single base error at a splice junction will cause a large insertion. C. A single base error at a splice junction will cause a large inversion. D. C and E. E. A single base error at a splice junction will change the reading frame and result in mRNA mistranslation.
E
A comatose infant is brought to the emergency department. In the course of the examination, plasma ammonia was found to be elevated 20-fold over normal values. Urine orotic acid and uracil were both greater than normal. A defect of which of the following enzymes is the most likely diagnosis? A. Ornithine transcarbamylase B. N-acetyl glutamate synthetase C. Carbamoyl phosphate synthetase II D. Carbamoyl phosphate synthetase I E. Phosphoribosyl pyrophosphate synthetase (PRPP Synthetase)
A
A defect in the thioesterase subunit of fatty acid synthase would impair which of the following activities of the enzyme complex? A. Liberation of newly assembled palmitate from the enzyme B. Binding of malonyl-CoA to an SH group C. Priming of the enzyme with acetyl-CoA D. Liberation of CO2 from 3-ketoacyl synthase
A
A deficiency in the LDL receptor will result in an initial decrease in which of the following? A. Intracellular cholesterol B. Circulating LDLs C. De novo cholesterol synthesis D. Fatty acid synthesis
A
A deficiency in the LDL receptor will result in an initial decrease in which of the following? A. Intracellular cholesterol B. Circulating LDLs C. Fatty acid synthesis D. De novo cholesterol synthesis
A
A deficiency in vitamin B6 (pyridoxal phosphate) would negatively impact which of the following pathways: Metabolism of cysteine to homocysteine Metabolism of phenylalanine to tyrosine Conversion of methyl malonyl-Co A to succinyl-CoA A. 1 only B. 2 only C. 2 and 3 D. 1 and 2
A
A healthy, well-nourished male consumes a protein-rich meal. Several hours later, the majority of the nitrogen atoms from the protein in his diet would most likely be incorporated into which of the following compounds? A. Urea B. Ketone bodies C. Glycogen D. Nucleotides
A
ATP can be generated by many metabolic pathways in the body. Which of the following processes generates the most ATP? A. Fatty acid oxidation B. Glycolysis C. Glycogenolysis D. Pentose phosphate pathway E. Tricarboxylic acid cycle
A
Gout can present as a complication of von Gierke disease due to which of the following mechanisms? A. Increase synthesis of PRPP B. Increased DNA synthesis C. Decreased excretion of uric acid D. Decreased salvage of purines
A
Nitrogen from amino acid metabolism is incorporated into all of the following compounds except: A. Cholesterol B. Urea C. Nucleotides D. Arginine
A
Phenylketonuria can present due to a deficiency in which of the following required metabolic cofactors? A. Tetrahydrobiopterin (BH4) B. Tyrosine C. Tetrahydrofolate (THF) D. Cobalamin (B12)
A
Secondary bile salts lack a hydroxyl (OH) group when compared to primary bile salts. What is the consequence of the loss of this group? A. Secondary bile salts are less soluble B. Secondary bile salts are more soluble C. The loss of the OH group does not change their functionality D. Secondary bile salts are more readily resorbed in the intestinal lumen
A
Several familial disorders are characteristic of defects in the LDL-receptor that inhibit cellular uptake of LDLs and reduce intracellular cholesterol. In these patients, all of the following are true except: A. HMG-CoA reductase is phosphorylated B. Circulating levels of LDL are elevated C. SREBP is cleaved and activated D. HMG-CoA - reductase is activated
A
The process of β-oxidation and gluconeogenesis are coupled in the fasted state. Which of the following compounds is produced by β-oxidation and is an activator of an enzyme required for gluconeogenesis? A. Acetyl-CoA B. NADH C. FADH2 D. Glycerol
A
Two hikers get lost in the woods, they have not brought any snacks or water with them. As time passes their insulin to glucagon ratio decreases. 24 hours into their fast you would expect the enzymatic activity of both _________ and ________ to be elevated in the liver. A. Glutaminase and carbamoyl phosphate synthetase I B. Glycogen synthase and carnitine palmitoyltransferase I C. Glutamine synthase and Phosphofructokinase 2 (PFK2) D. PEP carboxykinase (PEPCK) and pyruvate kinase
A
Under cellular conditions when cholesterol is low, which of the following is a true statement regarding the sterol response element-binding protein? A. It will be associated with the sterol response element (SRE) on the DNA B. It will be bound to a plasma membrane receptor C. It will be associated with proteins in the ER D. It will be targeted for degradation
A
Under cellular conditions when cholesterol is low, which of the following is a true statement regarding the sterol response element-binding protein? A. It will be associated with the sterol response element (SRE) on the DNA B. It will be bound to a plasma membrane receptor C. It will be targeted for degradation D. It will be associated with proteins in the ER
A
What is the primary lipid component of a VLDL particle? A. Triacylglycerols B. Cholesterol C. Phospholipids D. Cholesterol ester
A
When citrate is shuttled out of the mitochondria for fatty acid synthesis, the initial reaction by citrate lyase generates which of the following products? A. Acetyl-CoA and oxaloacetate B. Pyruvate and malate C. Citrate and oxaloacetate D. Acetyl-CoA and citrate
A
Which of the following best describes the mechanism by which cholesterol is eliminated? A. Cholesterol is used to synthesize secondary bile acids that are eliminated in the feces B. Excess cholesterol can be degraded in the liver back to acetyl-CoA C. Cholesterol is primarily excreted through the kidney in the urine D. Excess cholesterol used to synthesize hormones
A
Which of the following compounds contributes both the sugar and phosphate groups to the nucleotide bases? A. PRPP (5- phosphoribosylpyrophosphate) B. Glucose 6-phosphate C. Inosine monophosphate D. 5- methyl thymidine
A
Which one of the following eicosanoids is synthesized from linoleic acid via the cyclooxygenase pathway? A. Prostaglandin E1 (PGE1) B. Leukotriene A3 (LTA3) C. Prostaglandin E3 (PGE3) D. Lipoxin A4 (LXA4) E. Thromboxane A3 (TXA3)
A
Select the one of the following statements that is NOT CORRECT: A. Bilirubin is a cyclic tetrapyrrole. B. Albumin-bound bilirubin is transported to the liver. C. High levels of bilirubin can cause damage to the brains of newborn infants. D. Bilirubin contains methyl and vinyl groups. E. Bilirubin does not contain iron.
A (Explanation: Bilirubin is a linear tetrapyrrole.)
Which of the following will be elevated in the bloodstream about 2 hours after eating a high-fat meal? A. Chylomicrons B. High-density lipoprotein C. Ketone bodies D. Nonesterified fatty acids E. Very-low-density lipoprotein
A (Explanation: Chylomicrons are synthesized in the intestine and secreted into lymph after a fat meal.)
Which one of the following statements about gangliosides is INCORRECT? A. They are derived from galactosylceramide. B. They contain one or more molecules of sialic acid. C. They are present in nervous tissue in high concentrations. D. The ganglioside GM1 is the receptor for cholera toxin in the human intestine. E. They function in cell-cell recognition.
A (Explanation: Gangliosides are derived from glucosylceramide.)
The recently discovered protein, proprotein convertase subtilisin/kexin type 9 (PCSK9), has been identified as a potential target for antiatherogenic drugs BECAUSE: A. It decreases the number of LDL receptors exposed at the cell surface, thus LDL uptake is lowered and blood cholesterol levels rise. B. It inhibits the binding of apo B to the LDL receptor, thus blocking uptake of the lipoprotein and raising blood cholesterol levels. C. It increases the absorption of cholesterol from the intestine. D. It prevents the breakdown of cholesterol to bile acids in the liver. E. It increases the synthesis and secretion of VLDL in the liver, leading to increased LDL formation in the blood.
A (Explanation: PCSK9 regulates the re-cycling of LDL receptors to the cell surface after endocytosis has taken place. Inhibition of PCSK9 activity, therefore, increases the number of LDL receptor molecules on the cell surface, leading to an increased rate of clearance and lower blood cholesterol levels.)
Select the one of the following statements that is NOT CORRECT: A. Threonine provides the thioethanol moiety for biosynthesis of coenzyme A. B. Histamine arises by decarboxylation of histidine. C. Ornithine serves as a precursor of both spermine and spermidine. D. Serotonin and melatonin are metabolites of tryptophan. E. Glycine, arginine, and methionine each contribute atoms for biosynthesis of creatine.
A (Explanation: Serine, not threonine, provides the thioethanol moiety of coenzyme A.)
Under fasting conditions, acetyl-CoA carboxylase will be inhibited by an increase in which of the following compounds? A. Fatty acyl-CoA B. Citrate C. Malonyl CoA D. Glucose
A (In fasting conditions when lipolysis is active, an increase in fatty acyl-CoA in the cell for the process of β-oxidation will decrease citrate efflux from the mitochondria and activity of acetyl-CoA carboxylase)
A 12-year-old male is brought to his primary care physician. His parents are concerned with his recent decline in school work due to persistent blurred vision. On physical exam, planar xanthomas are noted and laboratory testing reveals extremely low plasma HDL. This presentation would be consistent with a loss of which of the following apoproteins? A. ApoE B. ApoA C. ApoB100 D. ApoB48
B
A 3-year-old male is brought to the emergency department with hypoglycemia following a brief seizure. His parents put him to bed the night before and he had not eaten much dinner. His urine tested positive for dicarboxylic acids, serum-free fatty acids are elevated and there were no detectable ketones in his blood or urine. In this individual, at the time of presentation his ratio of insulin to glucagon is: A. 1 B. >1 C. <1
B
A 4-year-old female presented to the clinic with megaloblastic anemia and failure to thrive. Urinalysis showed significant sediment with extremely high levels of orotic acid. A deficiency in which of the following enzymes would be consistent with this presentation? A. Glutamyl amidotransferase B. Orotate phosphoribosyltransferase C. Carbamoyl phosphate synthetase II D. Thymidylate synthase
B
A 45-year-old male has a mild heart attack and a history of vascular disease. He is placed on a Mediterranean diet and statin therapy. Which of the following will be the most likely result of this therapy? A. Low oxidation of fatty acids B. High blood glucose C. Low blood LDLs D. Low blood glucose E. High blood cholesterol
B
A deficiency in which of the following enzymes would impair the production of S-adenosylmethionine (SAM)? A. Phenylalanine hydroxylase B. Methionine adenosyltransferase (MAT) C. Tryptophan synthase D. Spermidine synthase
B
Fatty acid synthase is a multimeric enzyme complex. Which of the following subunits contains pantothenic acid as a cofactor? A. Ketoacyl synthase B. Acyl carrier protein (ACP) C. Enoyl reductase D. Thioesterase
B
Glucogenic amino acids can be used in the process of gluconeogenesis and will be metabolized to all of the following compounds except: A. Oxaloacetate B. Acetyl-CoA C. Succinyl-CoA D. Fumarate
B
Glutamate can be deaminated by which of the following enzymes: A. Glutamine synthetase B. Glutamate dehydrogenase (GDH) C. Glutaminase D. Arginase
B
Identify the amino acid that is the major contributor to the transport of nitrogen destined for excretion as urea: A. Alanine B. Glutamine C. Glycine D. Lysine E. Ornithine
B
In an individual with a deficiency in the branched-chain ketoacid dehydrogenase complex, metabolism of which of the following amino acids would not likely be impaired? A. Valine B. Tyrosine C. Isoleucine D. Leucine
B
Several familial disorders are characteristic of defects in the LDL-receptor that inhibit cellular uptake of LDLs and reduce intracellular cholesterol. In these patients, all of the following are true except: A. Circulating levels of LDL are elevated B. HMG-CoA reductase is phosphorylated C. SREBP is cleaved and activated D. HMG-CoA - reductase is activated
B
The cellular uptake of LDL increases intracellular cholesterol levels. This has which of the following impacts on de novo cholesterol synthesis? A. Increases dephosphorylation of HMG-CoA reductase B. Increases degradation of HMG-CoA reductase C. Increases activation of SREBP D. Increases activity of HMG-CoA reductase
B
The conversion of ribose bases into deoxy-bases will be occurring under which of the following conditions? A. In the fasted state B. When cells are proliferating C. In the fed state D. Under most conditions
B
When citrate is shuttled out of the mitochondria for fatty acid synthesis, the initial reaction by citrate lyase generates which of the following products? A. Acetyl-CoA and citrate B. Acetyl-CoA and oxaloacetate C. Pyruvate and malate D. Citrate and oxaloacetate
B
Which of the following amino acids is essential? A. Cysteine B. Methionine C. Arginine D. Tyrosine
B
Which of the following compounds is the primary component of a mature HDL? A. Triacylglycerol B. Cholesteryl-ester C. Fatty acids D. Cholesterol E. Glycerol
B
Which of the following enzymes is responsible for transferring triacylglycerol from VLDL to HDL in exchange for cholesterol? A. Microsomal transfer protein B. CEPT (Cholesteryl ester transfer protein) C. Lipoprotein Lipase D. Phosphatidylcholine:cholesterol acyltransferase (PCAT, aka LCAT)
B
Which of the following is not a product of β-oxidation? A. FADH2 B. NADPH C. NADH D. Acetyl-CoA
B
Which one of the following best describes the action of phospholipase C? A. It releases the fatty acyl chain from the sn-2 position of a phospholipid. B. It cleaves a phospholipid into its phosphate-containing head group and a diacylglycerol. C. It releases the head group of a phospholipid, leaving phosphatidic acid. D. It releases the fatty acyl chain from the sn-1 position of a phospholipid. E. It releases the fatty acyl chains from the sn-1 and sn-2 positions of a phospholipid.
B
Select the one of the following statements that is NOT CORRECT: A. PEST sequences target some proteins for rapid degradation. B. ATP and ubiquitin typically participate in the degradation of membrane-associated proteins and other proteins with long half-lives. C. Ubiquitin molecules are attached to target proteins via non-α peptide bonds. D. The discoverers of ubiquitin-mediated protein degradation received a Nobel Prize. E. Degradation of ubiquitin-tagged proteins takes place in the proteasome, a multi-subunit macromolecule present in all eukaryotes.
B (Explanation: ATP and ubiquitin participate in the degradation of nonmembrane-associated proteins and proteins with short half-lives.)
Select the one of the following statements that is NOT CORRECT: A. Selenocysteine is present at the active sites of certain human enzymes. B. Selenocysteine is inserted into proteins by a posttranslational process. C. Transamination of dietary α-keto acids can replace the dietary essential amino acids leucine, isoleucine, and valine. D. Conversion of peptidyl proline to peptidyl-4-hydroxyproline is accompanied by the incorporation of oxygen into succinate. E. Serine and glycine are interconverted in a single reaction in which tetrahydrofolate derivatives participate.
B (Explanation: The insertion of selenocysteine into a peptide occurs during, not subsequent to translation.)
Malonyl-CoA, the first intermediate in fatty acid synthesis, is an important regulator of fatty acid metabolism BECAUSE: A. Its formation from acetyl-CoA and bicarbonate by the enzyme acetyl-CoA carboxylase is the main rate-limiting step in fatty acid synthesis. B. It prevents entry of fatty acyl groups into the matrix of the mitochondria because it is a potent inhibitor of carnitine palmitoyl transferase-I. C. It prevents entry of fatty acyl groups into the matrix of the mitochondria because it is a potent inhibitor of carnitine palmitoyl transferase-II. D. It prevents entry of fatty acyl groups into the matrix of the mitochondria because it is a potent inhibitor of carnitine-acylcarnitine translocase. E. It inhibits the synthesis of fatty acyl-CoA.
B. (Explanation: When the action of carnitine palmitoyl transferase-I is inhibited by malonyl CoA, fatty acyl groups are unable to enter the matrix of the mitochondria where their breakdown by β-oxidation takes place.)
A 35-year-old man with severe hypercholesterolemia has a family history of deaths at a young age from heart disease and stroke. Which of the following genes is likely to be defective? A. Apolipoprotein E B. The LDL receptor C. Lipoprotein lipase D. PCSK9 E. LCAT
B. (Explanation: If the LDL receptor is defective, LDL is not cleared from the blood, causing severe hypercholesterolemia.)
An individual is suspected of having a deficiency in branched-chain ketoacid dehydrogenase. Supplementation of which of the following vitamins or cofactors may help resolve this issue? A. Tetrahydrobiopterin (BH4) B. Thiamine C. Cobalamin D. Folate
B. Thiamine (Feedback: Much like the pyruvate dehydrogenase complex, the branched chain keto acid dehydrogenase also requires the cofactor thiamine.)
A healthy, well-nourished male consumes a protein-rich meal. Several hours later, the majority of the nitrogen atoms from the protein in his diet would most likely be incorporated into which of the following compounds? A. Glycogen B. Nucleotides C. Urea D. Ketone bodies
C
A well, 2-year-old female presents to the clinic with symptoms of a viral illness. Her parents report she has had bouts of vomiting and diarrhea over the last 24 hours. This morning they could barely wake her from her crib and she was very weak. Laboratory tests show low blood glucose (hypoglycemia) and elevated liver enzymes. There are no ketones present in her urine. The child is hospitalized and glucose is administered I.V. Additional laboratory analysis showed elevated medium-chain fatty acylcarnitines in blood and 6-8 carbon dicarboxylic acids in the urine. Which of the following abnormalities is the most likely diagnosis for this child? A. Defect of medium-chain fatty acyl synthetase B. Mitochondrial defect in the electron transport chain C. Defect of medium-chain coenzyme A dehydrogenase D. Carnitine deficiency E. Mitochondrial defect in fatty acid transport
C
Dietary cholesterol is primarily transported in the body by which of the following lipoproteins? A. HDL B. LDL C. Chylomicron D. VLDL
C
In the liver, which of the following key inhibitory events ensures that newly synthesized palmitoyl-CoA is not immediately oxidized? A. Acyl-CoA synthetase by malonyl CoA B. Carnitine acylcarnitine translocase (CAT) by palmitoyl-CoA C. Carnitine palmitoyl transferase-I (CPTI) by malonyl-CoA D. Carnitine palmitoyl transferase-I (CPTI) by palmitoylcarnitine E. Carnitine palmitoyl transferase-II (CPTII) by acetyl-CoA
C
Insulin stimulates lipogenesis through several mechanisms. Which of the following is not an insulin-stimulated process that enhances lipogenesis? A. Decreased levels of cAMP B. Increased activity of acetyl-CoA carboxylase C. Decreased activity of the pyruvate dehydrogenase complex D. Increased glucose transport into the cells
C
Methotrexate is classified as an "antimetabolite." Methotrexate most closely resembles which endogenous compound? A. 5-hydroxytryptamine B. Histamine C. Folate D. Epinephrine E. Aspartic acid
C
NADPH and glyceraldehyde 3-phosphate are essential for the synthesis of fatty acids and triacylglycerols. Which of the following pathways can supply both of these products? A. Glycolysis B. Fructose metabolism C. Pentose phosphate pathway D. Ketogenesis
C
Purine salvage is a key part of purine metabolism. Which of the following enzymes catalyzes the conversion of guanine to guanosine monophosphate (GMP)? A. Glutamine phosphoribosyl amidotransferase B. Orotate phosphoribosyl-transferase C. Hypoxanthine-guanine phosphoribosyl transferase (HGPRT) D. Carbamoyl phosphate synthetase II
C
The de novo synthesis of fatty acids by the fatty acid synthase enzyme complex results in the synthesis of: A. Only long-chain fatty acids B. 16 and 18 carbon saturated fatty acids (C16:0 and C18:0) C. Only palmitic acid (C16:0) D. 16 and 18 carbon unsaturated fatty acids (C16:9,12 and C18:9,14)
C
The process of ketogenesis refers to the conversion of acetyl-CoA to which of the following compounds? A. Malonyl-CoA B. Methylmalonyl-CoA C. β-hydroxybutyrate D. Propionyl-CoA
C
What is the primary lipid component of a nascent HDL particle? A. Triacylglycerols B. Cholesterol C. Phospholipids D. Cholesteryl-ester
C
Which lipoproteins is responsible for the process of reverse cholesterol transport (the movement of cholesterol from the peripheral tissues back to the liver)? A. Chylomicron B. VLDL C. HDL D. LDL
C
Which of the following non-essential amino acids is synthesized as part of the urea cycle? A. Aspartate B. Glutamine C. Arginine D. Asparagine E. Lysine
C
Which of the following represents the correct sequence of events in a cycle of β-oxidation beginning with a saturated fatty acyl-CoA? A. NAD+-coupled oxidation, hydration, FAD-coupled oxidation, thiolytic cleavage B. FAD-coupled oxidation, NAD+-coupled oxidation, hydration, thiolytic cleavage C. FAD-coupled oxidation, hydration, NAD+-coupled oxidation, thiolytic cleavage D. hydration, FAD-coupled oxidation, NAD+-coupled oxidation, thiolytic cleavage E. NAD+-coupled oxidation, FAD-coupled oxidation, hydration, thiolytic cleavage
C
Which of the following statements is consistent with protein catabolism in the fed state? A. Glutaminase activity in the liver will be low B. The conversion of alpha-ketoglutarate to glutamate will be favored in the liver C. High levels of arginine will stimulate the activity of urea synthesis D. Amino acids will be used as a substrate for gluconeogenesis
C
Which one of the following enzymes is inhibited by the nonsteroidal anti-inflammatory drug (NSAID) aspirin? A. Lipoxygenase B. Prostacyclin synthase C. Cyclooxygenase D. Thromboxane synthase E. Δ6 desaturase
C
You and a friend are being chased by a bear. Under these conditions levels of epinephrine are increased due to the metabolism of which of the following amino acids? A. Valine B. Tryptophan C. Tyrosine D. Phenylalanine
C
Which one of the following statements concerning the biosynthesis of cholesterol is CORRECT? A. The rate-limiting step is the formation of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) by the enzyme HMG-CoA synthase. B. Synthesis occurs in the cytosol of the cell. C. All the carbon atoms in the cholesterol synthesized originate from acetyl-CoA. D. Squalene is the first cyclic intermediate in the pathway. E. The initial substrate is mevalonate.
C (Explanation: Cholesterol is synthesized in the endoplasmic reticulum from acetyl CoA. The rate-limiting step is the formation of mevalonate from 3-hydroxy 3-methylglutaryl-CoA by HMG CoA reductase and lanosterol is the first cyclic intermediate.)
For metabolic disorders of the urea cycle, which statement is NOT CORRECT: A. Ammonia intoxication is most severe when the metabolic block in the urea cycle occurs prior to the reaction catalyzed by argininosuccinate synthase. B. Clinical symptoms include mental retardation and the avoidance of protein-rich foods. C. Clinical signs can include acidosis. D. Aspartate provides the second nitrogen of argininosuccinate. E. Dietary management focuses on a low-protein diet ingested as frequent small meals.
C (Explanation: Due to the failure to incorporate NH4+ into urea, clinical signs of metabolic disorders of the urea cycle include alkalosis, not acidosis.)
α-Linolenic acid is considered to be nutritionally essential in humans BECAUSE: A. It is an ω3 fatty acid. B. It contains three double bonds. C. In humans, double bonds cannot be introduced into fatty acids beyond the Δ9 position. D. In humans, double bonds cannot be introduced into fatty acids beyond the Δ12 position. E. Human tissues are unable to introduce a double bond in the Δ9 position of fatty acids.
C (Explanation: Humans (and most mammals) do not possess enzymes able to introduce a double bond into fatty acids beyond Δ9.)
The first reaction in the degradation of most of the protein amino acids involves the participation of: A. NAD+ B. Thiamine pyrophosphate (TPP) C. Pyridoxal phosphate D. FAD E. NAD+ and TPP
C (Explanation: Pyridoxal-dependent transamination is the first reaction in degradation of all the common amino acids except threonine, lysine, proline, and hydroxyproline.)
Which of the following statements about bile acids (or bile salts) is INCORRECT? A. Primary bile acids are synthesized in the liver from cholesterol. B. Bile acids are needed for the breakdown of fats by pancreatic lipase. C. Secondary bile acids are produced by modification of primary bile acids in the liver. D. Bile acids facilitate the absorption of the products of lipid digestion in the jejunum. E. Bile acids are recirculated between the liver and the small intestine in the enterohepatic circulation.
C (Explanation: Secondary bile acids are produced by the modification of primary bile acids in the intestine.)
Select the one of the following statements that is NOT CORRECT: A. Angelman syndrome is associated with a defective ubiquitin E3 ligase. B. Following a protein-rich meal, the splanchnic tissues release predominantly branched-chain amino acids. which are taken up by peripheral muscle tissue. C. The rate of hepatic gluconeogenesis from glutamine exceeds that of any other amino acid. D. The L-α-amino oxidase-catalyzed conversion of an α-amino acid to its corresponding α-keto acid is accompanied by the release of NH4+. E. Similar or even identical signs and symptoms can be associated with different mutations of the gene that encodes a given enzyme.
C (Explanation: The carbon skeleton of alanine contributes the most to hepatic gluconeogenesis.)
Which one of the following is a chain-breaking antioxidant? A. Glutathione peroxidase B. Selenium C. Superoxide dismutase D. EDTA E. Catalase
C (Explanation: A, B, D, and E are classed as preventive antioxidants as they act by reducing the rate of chain initiation.)
The ribonucleotide reductase is important for converting ribose bases to the deoxy form. This conversion is coupled with the oxidation of which of the following compounds? A. NADH B. NADP+ C. Thioredoxin D. Tetrahydrofolate
C. Thioredoxin (Feedback: The reaction is coupled with thioredoxin reductase, reduced thioredoxin and the reductase. In the reaction, thioredoxin is oxidized. This compound is re-reduced by NAPDH so it can be regenerated as part of the reaction.)
A 45-year-old male is found to have elevated serum triglycerides (> 730mg/dL). He tells you he forgot to fast before his visit and he ate a full breakfast of bacon and eggs before the labs were drawn. Which of the following lipoproteins would be the largest contributors to a measurement of plasma triglycerides in this situation? A. Chylomicron remnants and High-density lipoproteins (HDLs) B. LDLs and adipocyte lipid droplets C. VLDLs and LDLs D. Chylomicrons and VLDLs E. High-density lipoproteins (HDLs) and LDLs
D
A 45-year-old male is found to have elevated serum triglycerides of > 730mg/dL. He tells you he fasted for 24 hours before his visit and has only had water to drink. Which of the following lipoproteins would be the largest contributors to a measurement of plasma triglycerides in this situation? A. LDLs and adipocyte lipid droplets B. Chylomicrons and VLDLs C. Chylomicron remnants and High-density lipoproteins (HDLs) D. VLDLs E. High-density lipoproteins (HDLs) and LDLs
D
After they are produced from acetyl-CoA in the liver, ketone bodies are mainly used for which one of the following processes? A. Excretion as waste products B. Energy generation in the liver C. Conversion to fatty acids for storage of energy D. Generation of energy in the tissues E. Generation of energy in red blood cells
D
An elevation of homocysteine and a decrease in cysteine would most likely be present due to which of the following deficiencies? A. Cobalamin deficiency B. Loss of function of methionine synthase C. Tetrahydrobiopterin (BH4) deficiency D. Loss of function of cystathionine-β synthase
D
An increase in the ratio of insulin to glucagon leads to which of the following metabolic shifts? A. Hormone-sensitive lipase will become dephosphorylated and active B. VLDL synthesis will decrease C. Cytosolic levels of malonyl-CoA will decrease D. Acetyl-CoA carboxylase will become dephosphorylated and active
D
An increase in the ratio of insulin to glucagon will increase the activity of which of the following enzymes (+ indicates activity is increased; - indicates activity is not increased by insulin)? 1. Hormone-sensitive lipase 2. Acetyl-CoA carboxylase 3. Phosphofructokinase 2 (PFK2) 4. Glycogen synthase 1, 2, 3, 4 A. +, +, +, - B. +, +, -, - C. +, -, -, - D. -, +, +, +
D
HDL particles interact with VLDL particles to exchange cholesterol ester for triacylglycerols. Which of the following enzymes is responsible for this process? A. Phosphatidylcholine:cholesterol acyltransferase (PCAT, aka LCAT) B. HMG-CoA reductase C. ABCA1 transporter D. Cholesteryl ester transfer protein (CETP)
D
In pyrimidine synthesis, uridine triphosphate (UTP) can feedback and inhibit which of the following enzymes? A. Dihydrooratase B. Thymidylate synthase C. Aspartate transcarbamylase D. Carbamoyl phosphate synthase II
D
In the event of a deficiency in ApoCII on VLDLs, which of the following processes would be impaired? A. Transfer of triacylglycerols from HDL to chylomicrons B. Uptake of chylomicrons by peripheral tissues using the LDL receptor C. Reuptake of chylomicron remnants by the liver D. Interaction of VLDL with lipoprotein lipase
D
Ketogenesis is regulated by: A. Activity of lipolysis. B. Cytosolic levels of malonyl-CoA which inhibit CPTI. C. Flux through the TCA depending on NADH levels and concentration of intermediates, specifically OAA. D. All of the above.
D
Purines: A. Adenine will pair with thymine (DNA) or uracil (RNA) B. Base has a double ring structure C. Base is difficult to break → it is recycled. D. All of the above.
D
Pyrimidines: A. Base has a single ring structures B. Thymine base pairs with adenine C. Cytosine base pairs with guanine D. All of the above
D
Select the choice that correctly indicates the proper sequence of the three stages of urea biosynthesis leading to the urea cycle. A. oxidative deamination of glutamate → ammonia transport → transamination B. transamination → ammonia transport → oxidative deamination of glutamate C. ammonia transport → oxidative deamination of glutamate → transamination D. transamination → oxidative deamination of glutamate → ammonia transport
D
Supplementation of which of the following cofactors/coenzymes may assist the activity of branched-chain ketoacid dehydrogenase? A. Folate B. Pyridoxal phosphate (PLP) C. Cobalamin D. Thiamine E. Tetrahydrobiopterin (BH4)
D
The processes of β-oxidation and fatty acid synthesis are regulated in such a manner that neither process is active at the same time. Which of the following enzymes required for fatty acid synthesis is paired with the correct activator? A. Citrate synthase; acetyl-CoA B. Hormone-sensitive lipase; free fatty acids C. Carnitine palmitoyl transferase I (CPTI); malonyl-CoA D. Acetyl-CoA carboxylase; citrate
D
The transamination of all amino acids requires which of the following cofactors? A. Thiamine B. Folate C. N-acetyl glutamate D. Pyridoxal phosphate (PLP)
D
The urea cycle takes place in which of the following subcellular locations? A. The cytosol only B. The mitochondria only C. The nucleus and mitochondria D. The cytosol and the mitochondria
D
VLDL particles have which of the following combinations of apoproteins in their mature form? A. ApoCII and ApoE B. ApoA, ApoCII, ApoE C. ApoB48, ApoCII, ApoE D. ApoB100, ApoCII, ApoE
D
When Apo CII on chylomicrons interact with Lipoprotein lipase (LPL): A. This hydrolyses TAGs → FFA B. FAA are taken up by muscle (directly oxidized) or adipose (stored as TAGs) C. Insulin enhances the activity of LPL D. All of the above
D
Which of the following cellular processes can increase uptake of LDL? A. Increased activity by HMG-CoA reductase B. Increase in intracellular cholesterol pools C. Enhanced PSK9 mediated degradation of LDL-receptor D. Enhanced transcription of the LDL-receptor
D
Which of the following compounds contributes both the sugar and phosphate groups to the nucleotide bases? A. 5- methyl thymidine B. Inosine monophosphate C. Glucose 6-phosphate D. PRPP (5- phosphoribosylpyrophosphate)
D
Which of the following enzymes is regulated by N-acetyl glutamate (NAG)? A. Ornithine transcarbamylase B. Argininosuccinate lyase C. Carbamoyl phosphate synthetase II (CPS II) D. Carbamoyl phosphate synthetase I (CPS I)
D
Which of the following enzymes is the regulatory step in the urea cycle? A. Argininosuccinate lyase B. Ornithine transcarbamylase C. Arginase D. Carbamoyl phosphate synthetase I (CPS I)
D
Which of the following is not required for the transport of newly synthesized fatty acids to the adipose? A. Synthesis of triacylglycerol using glycerol 3-phosphate B. Transport of triacylglycerols from the liver using VLDLs C. Interaction of ApoCII with lipoprotein lipase D. Carnitine to shuttle the fatty acids out of the mitochondria
D
Which one of the following is NOT a phospholipid? A. Sphingomyelin B. Plasmalogen C. Cardiolipin D. Galactosylceramide E. Lysolecithin
D
Which one of the following statements concerning fatty acid molecules is CORRECT? A. They consist of a carboxylic acid head group attached to a carbohydrate chain. B. They are called polyunsaturated when they contain one or more carbon-carbon double bonds. C. Their melting points increase with increasing unsaturation. D. They almost always have their double bonds in the cis configuration when they occur naturally. E. They occur in the body mainly in the form of free (nonesterified) fatty acids.
D
β- oxidation of long-chain fatty acids is inhibited by: A. Carnitine B. Pantothenic Acid (vitamin B5) C. Fatty acids D. Malonyl-CoA
D
Which one of the following statements concerning chylomicrons is CORRECT? A. Chylomicrons are made inside intestinal cells and secreted into lymph, where they acquire apolipoproteins B and C. B. The core of chylomicrons contains triacylglycerol and phospholipids. C. The enzyme hormone-sensitive lipase acts on chylomicrons to release fatty acids from triacylglycerol when they are bound to the surface of endothelial cells in blood capillaries. D. Chylomicron remnants differ from chylomicrons in that they are smaller and contain a lower proportion of triacylglycerol and a higher proportion of cholesterol. E. Chylomicrons are taken up by the liver.
D (Explanation: Chylomicrons are metabolized by lipoprotein lipase when bound to the surface of endothelial cells. This process releases fatty acids from triacylglycerol which are then taken up by the tissues. The resulting smaller, cholesterol-enriched chylomicron remnant particles are released into the circulation and cleared by the liver.)
Inactivation of acetyl-CoA carboxylase is favored WHEN: A. Cytosolic citrate levels are high. B. It is in a polymeric form. C. Palmitoyl-CoA levels are low. D. The tricarboxylate transporter is inhibited. E. It is dephosphorylated.
D (Explanation: Inhibition of the tricarboxylic acid transporter causes levels of citrate in the cytosol to decrease and favors inactivation of the enzyme.)
Carnitine is needed for fatty acid oxidation BECAUSE: A. It is a cofactor for acyl-CoA synthetase, which activates fatty acids for breakdown. B. Long-chain acyl-CoA ("activated fatty acids") need to enter the mitochondrial matrix to be oxidized, but cannot cross the outer mitochondrial membrane. Transfer of the acyl group from CoA to carnitine enables translocation to occur. C. Acylcarnitine, formed when long-chain acyl groups are transferred from CoA to carnitine is the substrate for the first step in the β-oxidation pathway. D. Long-chain acyl-CoA ("activated fatty acids") need to enter the mitochondrial intermembrane space to be oxidized, but cannot cross the inner mitochondrial membrane. Transfer of the acyl group from CoA to carnitine enables translocation to occur. E. It prevents the breakdown of long-chain fatty acyl-CoA in the mitochondrial intermembrane space.
D (Explanation: Long chain fatty acids are activated by coupling to CoA, but fatty acyl CoA cannot cross the inner mitochondrial membrane. After transfer of the acyl group from CoA to carnitine by carnitine palmitoyl transferase (CPT)-I, acylcarnitine is carried across by carnitine-acylcarnitine translocase in exchange for a carnitine. Inside the matrix, CPT-II transfers the acyl group back to CoA and carnitine is taken back into the intermembrane space by the translocase enzyme.)
Select the one of the following statements that is NOT CORRECT: A. Δ1-Pyrroline-5-carboxylate is an intermediate both in the biosynthesis and in the catabolism of L-proline. B. Human tissues can form dietarily nonessential amino acids from amphibolic intermediates or from dietarily essential amino acids. C. Human liver tissue can form serine from the glycolytic intermediate 3-phosphoglycerate. D. The reaction catalyzed by phenylalanine hydroxylase interconverts phenylalanine and tyrosine. E. The reducing power of tetrahydrobiopterin derives ultimately from NADPH.
D (Explanation: Phenylalanine hydroxylase catalyzes a functionally irreversible reaction, and thus cannot convert tyrosine to phenylalanine.)
A 62-year-old female presented at clinic with intense jaundice, steadily increasing over the preceding 3 months. She gave a history of severe upper abdominal pain. radiating to the back. and had lost considerable weight. She had noted that her stools had been very pale for some time. Lab tests revealed a very high level of direct bilirubin. and also elevated urinary bilirubin. The plasma level of alanine aminotransferase (ALT) was only slightly elevated, whereas the level of alkaline phosphatase was markedly elevated. Abdominal ultrasonography revealed no evidence of gallstones. Of the following, which is the most likely diagnosis? A. Gilbert syndrome B. Hemolytic anemia C. Type 1 Crigler-Najjar syndrome D. Carcinoma of the pancreas E. Infectious hepatitis
D (Explanation: The severe jaundice, upper abdominal pain, and weight loss plus the lab results indicating an obstructive type of jaundice are consistent with cancer of the pancreas.)
Which of the plasma lipoproteins is best described as follows: formed in the circulation by removal of triacylglycerol from very-low-density lipoprotein, contains apo B-100, delivers cholesterol to extrahepatic tissues? A. Chylomicrons B. High-density lipoprotein C. Intermediate-density lipoprotein D. Low-density lipoprotein E. Very-low-density lipoprotein
D. (Explanation: Very low density lipoprotein secreted by the liver is converted to intermediate density lipoprotein and then to low density lipoprotein (LDL) by the action of lipases and the transfer of cholesterol and proteins from high density lipoprotein. LDL delivers cholesterol to extrahepatic tissues and is also cleared by the liver.)
Which of the following statements about β,γ-methylene and β,γ-imino derivatives of purine and pyrimidine triphosphates is CORRECT? A. They are potential anticancer drugs. B. They are precursors of B vitamins. C. They readily undergo hydrolytic removal of the terminal phosphate. D. They can be used to implicate involvement of nucleotide triphosphates by effects other than phosphoryl transfer. E. They serve as polynucleotide precursors.
D. (Explanation: β,γ-Methylene and β,γ-imino purine pyrimidine triphosphates do not readily release the terminal phosphate by hydrolysis or by phosphoryl group transfer.)
An 11-year-old female is brought to the emergency department by her parent. They report she has recently been very thirsty and needs to make frequent trips to the bathroom. Physical examination revealed a thin girl in the 30th percentile for height and weight. A rapid dipstick test revealed glucose in her urine. Evaluation of this girl's blood would reveal decreased levels of which of the following compounds or hormones? A. Ketones B. Glucose C. Glutamine D. Fatty acids E. Insulin
E
Cholesterol is used as a substrate for the synthesis of: A. Steroid hormones B. Sex hormones C. Bile acids D. Vitamin D E. All of the above.
E
Which one of the following is the major product of fatty acid synthase? A. Acetyl-CoA B. Oleate C. Palmitoyl-CoA D. Acetoacetate E. Palmitate
E
Which of the following is NOT a hemoprotein? A. Myoglobin B. Cytochrome c C. Catalase D. Cytochrome P450 E. Albumin
E (Explanation: Albumin is not a hemoprotein. In cases of hemolytic anemia, albumin can bind some metheme, but unlike the other proteins listed, albumin is not a hemoprotein.)
Which of the following will be elevated in the bloodstream about 4 hours after eating a high-fat meal? A. Low-density lipoprotein B. High-density lipoprotein C. Ketone bodies D. Nonesterified fatty acids E. Very-low-density lipoprotein
E (Explanation: Chylomicrons and their remnants are cleared from the circulation rapidly after a meal, and the secretion of very low density lipoprotein by the liver then increases. Ketone bodies and nonesterified fatty acids are elevated in the fasting state.)
Select the one of the following statements that is NOT CORRECT: A. One metabolic function of glutamine is to sequester nitrogen in a nontoxic form. B. Liver glutamate dehydrogenase is allosterically inhibited by ATP and activated by ADP. C. Urea is formed both from absorbed ammonia produced by enteric bacteria and from ammonia generated by tissue metabolic activity. D. The concerted action of glutamate dehydrogenase and glutamate aminotransferase may be termed transdeamination. E. Fumarate generated during biosynthesis of argininosuccinate ultimately forms oxaloacetate in reactions in mitochondria catalyzed successively by fumarase and malate dehydrogenase.
E (Explanation: Cytosolic fumarase and cytosolic malate dehydrogenase convert fumarase to oxaloacetate following a cytosolic reaction of the urea cycle. The mitochondrial fumarase and malate dehydrogenase function in the TCA cycle, not urea biosynthesis.)
Select the one of the following statements that is NOT CORRECT: A. Excreted creatinine is a function of muscle mass, and can be used to determine whether a patient has provided a complete 24-hour urine specimen. B. Many drugs and drug catabolites are excreted in urine as glycine conjugates. C. The major nonprotein metabolic fate of methionine is conversion to S-adenosylmethionine. D. The concentration of histamine in brain hypothalamus exhibits a circadian rhythm. E. Decarboxylation of glutamine forms the inhibitory neurotransmitter GABA (γ-aminobutyrate).
E (Explanation: Decarboxylation of glutamate, not glutamine forms GABA.)
Hormone-sensitive lipase, the enzyme which mobilizes fatty acids from triacylglycerol stores in adipose tissue is inhibited by: A. Glucagon B. ACTH C. Epinephrine D. Vasopressin E. Prostaglandin E
E (Explanation: Glucagon, ACTH, epinephrine and vasopressin promote activation of the enzyme.)
Identify the metabolite that does NOT serve as a precursor of a dietarily essential amino acid: A. α-Ketoglutarate B. 3-Phosphoglycerate C. Glutamate D. Aspartate E. Histamine
E (Explanation: Histamine is a catabolite, not a precursor, of histidine.)
Which of the following statements about purine nucleotide metabolism is NOT CORRECT? A. An early step in purine biosynthesis is the formation of PRPP (phosphoribosyl 1-pyrophosphate). B. Inosine monophosphate (IMP) is a precursor of both AMP and GMP. C. Orotic acid is an intermediate in pyrimidine nucleotide biosynthesis. D. Humans catabolize uridine and pseudouridine by analogous reactions. E. Ribonucleotide reductase converts nucleoside diphosphates to the corresponding deoxyribonucleoside diphosphates.
E (Explanation: Ribonucleotide reductase converts RIBOnucleoside diphosphates to the corresponding deoxyribonucleoside diphosphates.)
Which of the plasma lipoproteins is best described as follows: synthesized in the liver, contains a high concentration of triacylglycerol, and is mainly cleared from the circulation by adipose tissue and muscle? A. Chylomicrons B. High-density lipoprotein C. Intermediate-density lipoprotein D. Low-density lipoprotein E. Very-low-density lipoprotein
E. (Explanation: VLDL is synthesized and secreted by the liver, and adipose tissue and muscle take up the fatty acids released by the action of lipoprotein lipase.)
Fatty acids are broken down by repeated removal of two carbon fragments as acetyl-CoA in the β-oxidation cycle, and synthesized by repeated condensation of acetyl-CoAs until a long-chain saturated fatty acid with an even number of carbons is formed. Since fatty acids need to be broken down when energy is short supply and synthesized when it is plentiful, there are important differences between the two processes which help cells to regulate them efficiently. Which one of the following statements concerning these differences is INCORRECT? A. Fatty acid breakdown takes place inside mitochondria, while synthesis occurs in the cytosol. B. Fatty acid breakdown uses NAD+ and produces NADH, while synthesis uses NADPH and produces NADP. C. Fatty acyl groups are activated for breakdown using CoA and for synthesis using acyl carrier protein. D. Transport across the mitochondrial membrane of fatty acyl groups is required for fatty acid breakdown, but not for synthesis. E. Glucagon promotes fatty acid synthesis and inhibits fatty acid breakdown.
E. (Explanation: Glucagon is released when blood glucose levels are low. In this situation, fatty acids are broken down for energy and fatty acid synthesis is inhibited.)
