BIOC 385 Exam 3

The conversion of ribose-1-phosphate to guanosine-5'-triphosphate via the salvage pathway would require the activity of several enzymes. Choose the answer that lists them in the order that they would act in this pathway.

(1) phosphopentomutase; PRPP synthetase; phosphoribosyl transferase

When AMPK is bound by AMP and is phosphorylated at Thr172, _________ activity will _________.

acetyl-Coa carboxylase; decrease AMPK leads to increased ATP - glycolysis - fatty A oxi - oxi phos increase fluc acetyl-coa carboxylase - enzyme in fatty acid synth

Which of the following biomolecules is secreted by visceral fat? phosphocreatine adipokines somatostatin glucagon

adipokines

What nitrogen source is used to produce carbamoyl phosphate? urea alanine ammonia glutamine

ammonia

NO is generated from ______

arginie reaction needs O2 input and NADPH

Angina patients sometimes carry nitroglycerine pills with them___________ as a rapid source of NO for blood vessel dilation to increase heart rate during a heart attack. to inhibit cGMP phosphodiesterase as a source of ammonia for muscle relaxation to inhibit acetylcholine release from neurons

as a rapid source of NO for blood vessel dilation

Oxaloacetate precursor to

aspartate asparagine lysine threonine methoionine

GLUCOSE-6-PHOS

at least four fates 1. ) most used to synth glycogen in liver after it is converted to glucose - 1 - phos by phosphoglucomutase 2. ) Pentose phos path to gen NADPH for FA synthesis 3. ) Fructose-6-phos for glycolysis 4.) to make glucose for blood transport delivery mostly to brain

Thrifty genes are ________ during times of starvation and ________ when physical activity is low.

beneficial ; detrimental

Weight watchers

calorie restriction

stomach

chyme

The shikimate pathway involves the ________________. synthesis of essential amino acids from oxaloacetate. condensation of oxaloacetate and shikimate. condensation of phosphoenolpyruvate and erythrose-4-phosphate. synthesis of essential amino acids from pyruvate.

condensation of phosphoenolpyruvate and erythrose-4-phosphate.

Thymidylate synthase

converts dUMP to dTMP - C1 transfer of N5N10-methylenetetrahydrofolate - produces duhydrofolate DHFR to form tetrahydrofolate - reaction using serine to reg. N5N10

Partial inhibition of lipoprotein lipase would______________. decrease the level of ketone bodies in the blood. increase rates of glycogen breakdown in heart muscle cells. decrease liver lactate dehydrogenase activity. prevent neurons in the brain from using free fatty acids as an energy source.

decrease the level of ketone bodies in the blood.

methotrexate and aminopterin bind to _______ and prevent ______

dihydrofolate reductase ; regeneration of N5N10 -methyltertrahydrofolate slowing rate/met flux of thymidylate synthase reaction

It is important that proteolytic enzymes in the lysosome are optimized to work at low pH because low pH_____________. enhances the degradation of ubiquitinated proteins. deactivates cysteine proteases. makes it easier for ATP to be converted to ADP + Pi. enhances protein denaturing.

enhances protein denaturing.

Tyrosine is a precursor to _________

epinephrine

TYROSINE

gen from phenylalanine - phenylalanine essential

Tyr122 is important in the mechanism of the E. coli ribonucleotide reductase. The function of this amino acid in the mechanism is to ________________.

generate Cys439 radical species

Ketogenesis stimulated during starvation because it leads to______________. increased protein synthesis and increased glycolysis. increased liver glycolysis and increased adipocyte fatty acid synthesis. decreased fatty acid oxidation and increased acetyl-CoA oxidation. increased gluconeogenesis and increased fatty acid oxidation. increased acetyl-CoA oxidation and increased fatty acid synthesis.

increased gluconeogenesis and increased fatty acid oxidation.

In the human disease called severe combined immunodeficiency (ADA-SCID), ribonucleotide reductase activity is __________ because of an overabundance of __________. activated; dATP inhibited; dATP inhibited; cAMP activated; cAMP

inhibited; dATP

Orlistat and olestra can both lead to undigested lipids in the colon, yet they do so by contrasting mechanisms. Orlistat ________, whereas olestra ________.

inhibits panreatic lipase; is a fat substiture that is not a substrate for pancreatic lipase

Dihydropyrimidine dehydrogenase deficiencies can lead to toxic side effects from high doses of 5-fluorouracil because 5-fluorouracil __________ dihydropyrimidine dehydrogenase.

is degraded by

Pyruvate precursor to

isoleucine valine leucine

Atkins diet

low carb diet

Ornish diet

low fat vegetarian diet

The disease ADA-SCID is due to __________ than normal activity of the enzyme __________. higher; xanthine oxidase lower; HGPRT higher; adenosine deaminase lower; ribonucleotide reductase

lower; ribonucleotide reductase

The lack of an immune system in patients born with a defect in the enzyme adenosine deaminase results in the disease ADA-SCID, which is caused by _________ than normal activity of _________.

lower; ribonucleotide reductase

In order for a cancer cell to be resistant to the drug methotrexate, a mutation in the dihydrofolate reductase enzyme must be able to _____________.

maintain enzyme activity without being inhibited by methotrexate

A compound is added to a cell and dihydrofolate reductase activity is reduced. If this compound is __________, it can be predicted that a similar result would be seen if __________ were added instead. methotrexate; raltitrexed aminopterin; fluorodeoxyuridine--monophosphate aminopterin; raltitrexed methotrexate; aminopterin

methotrexate; aminopterin

Nitrogen in biological compounds ultimately comes from ___________. nitrate hemoglobin nucleotides ammonia nitrogen gas

nitrogen gas

Aspartate is a(n) ________ amino acid, so if a person had a diet that contained no aspartate then ________.

nonessential ; aspartate could be synthesized from other intermediates

Metabolic homeostasis relies on maintaining___________________. maximum ATP synthase activity. optimal metabolite concentrations. maximum flux through the citric acid cycle. minimal inhibition of gluconeogenesis.

optimal metabolite concentrations.

What two pathways provide the ATP needed to phosphorylate creatine during muscle contraction?

oxidative phos and glycolysis

A person who has phenylketonuria will have an excess amount of ___________ in the cell. tyrosine phenylalanine pyruvate alanine

phenylalanine

Insulin signaling increases the catalytic activity of ___________ in liver cells. fructose-1,6-bisphosphatase phosphofructokinase-1 glycogen phosphorylase phosphorylase kinase

phosphofructokinase-1

The conversion of ribose-1-phosphate to ATP via the salvage pathway would require the activity of several enzymes. Choose the answer that lists them in the order that they would act in this pathway. phosphopentomutase; phosphoriboxyl transferase; kinase; PRPP synthetase; kinase phosphopentomutase; PRPP synthetase; phosphoriboxyl transferase; kinase; kinase PRPP synthetase; phosphoriboxyl transferase; phosphopentomutase; kinase; kinase PRPP synthetase; phosphopentomutase; kinase; kinase; phosphoriboxyl transferase

phosphopentomutase; PRPP synthetase; phosphoriboxyl transferase; kinase; kinase

Diseases affecting heme biosynthesis as a result of deficiencies in the heme biosynthetic pathway are called______________. porphyrias. albinism. alkaptonuria. shikimate.

porphyrias.

Long term starvation (>30 days) leads to _______________. decreased gluconeogenesis in liver and kidney cells decreased release of fatty acids from adipose tissue protein degradation in skeletal muscle decreased ketogenesis in liver cells

protein degradation in skeletal muscle

Insulin signaling in liver cells activates the enzyme __________, which in turn activates the enzyme __________.

protein phosphatase 2A; acetyl-CoA carboxylase

If the genomes of 100 different species were analyzed, gene sequences for which enzyme required for deoxyribonucleotide biosynthesis would most likely to be found in all of them? ribonucleotide reductase thioredoxin glutathione reductase glutaredoxin

ribonucleotide reductase

Nonessential amino acids are more ________

simple alanine serine aspartate

A negative nitrogen balance in a person would be an indicator of_____________. a diet heavy in protein. overall good health. accumulation of nitrogen in the body. starvation.

starvation.

EPHEDRINE

stimulates adrenergic receptor

Regulation of protein ubiquitination is most often mediated by modification of_____________. target proteins and E3 ligases. E1 ubiquitin ligase complex. E1 and E2 ligases. the E2-ubiquitin-E3 complex. target proteins and E1 ligases.

target proteins and E3 ligases.

Fluorodeoxyuridine--monophosphate is an inhibitor of the enzyme____________. ribonucleotide reductase thymidine kinase dihydrofolate reductase serine hydroxymethyltransferase thymidylate synthase

thymidylate synthase

nonessential amino acids

we can synthesize ALANINE ASPARAGINE ASPARTATE CYSTEINE GLUTAMINE GLUTAMATE GLYCINE PROLINE SERINE TYROSINE+

Olestra

zero-calorie food additive FA attached to sucrose

Phenylketonuria is caused by a defect in the enzyme phenylalanine hydroxylase (1) / phenylalanine aminotransferase (2). The symptoms of the disorder are caused by substrate accumulation (3) / lack of product (4) and can be treated by diet which limits phenylalanine (5) / tyrosine (6). Albinism is characterized by white skin and hair due to a defect in the enzyme arginase (7) / tyrosinase (8) and is characterized by a substrate accumulation (9) / lack of product (10) mechanism.

1, 3, 5, 8, 10

Which FIVE of the following gene variants are good candidates to function as Thrifty Genes? 1) Acetyl-CoA carboxylase with high affinity for citrate 2) Glucokinase with increased affinity for glucose 3) Decreased catalytic activity of fatty acyl-CoA synthetase 4) Fructokinase with increased affinity for fructose 5) Acetyl-CoA carboxylase with low affinity for palmitoyl-CoA 6) Gherlin mutant with a low affinity for the ghrelin receptor 7) Decreased catalytic activity of fatty acid synthase 8) High basal level expression of Uncoupling Protein 1 9) Low activity lipoprotein lipase on the membrane of adipocytes

1. WOULD INCREASE FATTY ACID SYNTH 4. Fructokinase with increased affinity for fructose - fast energy usuage and breakdown for stores 2. Glucokinase increased affinity for glucose (controls rate of glucose entry into glycolysis) 5. ACETYL-COA carboxylase with low affinity for palmitoyl-CoA (decreased fatty acid synthesis) 3. Decreased catalytic activity of fatty acyl-coa synthetase (decreased fatty acid degradtion; inturn increase fat stores)

Three sources of dUMP

1. dephosphorylation of dUTP by dUTP diphosphohydrolyase 2. deamination of dCTP by dCTP deaminase to gen dUTP - which is diphosphorylated by dUTP disphos 3. Phosphorylation of deoxyuridine by the enzyme thymidine kinase to yield dUMP

3 mechanisms of methotrexate resistance:

1. point mutations in dihydrofolate reductase coding seq Leu--> Arg on L22R decreasing methotrexate binding affinity 2. dihydrofolate reductase gene amplification ; lots in call so it can maintain tetrafolate levels to support thymidylate synthase reaction 3. overexpression of membrane transport - multidrug resistance protein - P-glycoprotein

How does AMPK and PGC-1alpha increase signaling in skeletal muscle?

1. stimulating flux through glycolysis (phos phosphofructokinase 2 and cAMP protein to activate hexokinase; inactivation of glycogen synthase) 2. stimulating FA oxidation (inactivate acetyl-coa carboxylase; phos hormone sentive lipase; PPARy) 3. increased oxidative phosphorylation

In purines, __________ nitrogen atoms and __________ carbon atoms originate from glycine. 1; 1 0; 2 2; 1 1; 2

1; 2

Phenylketonuria (1) / Albinism (2) is characterized by white skin due to a defect in the enzyme tyrosinase, which leads to a block in the pathway needed to synthesize adrenaline (3) / melanin (4). Animals with this condition have an increased risk of skin cancer (5) / mental illness (6). The genetic disease albinism (7) / phenylketonuria (8) is caused by a defect in the enzyme phenylalanine hydroxylase, which leads to the accumulation of tyrosine (9) / phenylalanine (10) derivatives that are toxic metabolites

2, 4, 5, 8, 10

Two healthy kidneys filter 6 L of human blood up to 30 times each day and remove 2 L of water containing concentrated levels of urea, NH4+, ketone bodies, and other soluble metabolites. How much water should one drink to sustain kidney?

2-3 L

An oncologist has a patient with dihydropyrimidine dehydrogenase deficiency. Which of the following is a chemotherapy agent that the doctor should be cautious about using with this patient because of serious side effects? 5-fluorouracil BETA-alanine primaquine 5-dihydrothymine

5-fluorouracil

A tyrosine deficiency leads to muscle wasting and Kwashiorkor disease. What is the treatment? A. high protein diet B. high fat diet C. low fat diet D. ketogenic diet E. low phenylalanine diet

A

Alkaptonuria is easily diagnosed by the presence black urine. What causes the black color? A. homogentisate oxidation B. serine reduction C. high uric acid D. low ketones E. acetyl-CoA oxidation

A

Individuals with type 2 diabetes are often prescribed the drug, Metformin, which activates AMPK signaling. Why would Metformin be an effective treatment for obese individuals with type 2 diabetes? A. AMPK increases glycolytic flux and increases fatty acid oxidation, resulting in burning of fat stores as well as increased cellular glucose uptake. B. AMPK decreases glycolytic flux, while increasing fatty acid oxidation, resulting in increased fat stores as well as increasing blood glucose levels. C. AMPK increases gluconeogenesis, as well as fatty acid synthesis, resulting in increased storage of fat decreased cellular glucose uptake D. AMPK decreases the pentose phosphate pathway and inhibits amino acid oxidation, ultimately resulting in decreased cellular glucose uptake. E. AMPK has no impact on glycolytic flux or fatty acid oxidation, and is only thought to work by decreasing oxidative phosphorylation, which decreases glucose uptake.

A

Uric acid is derived from both purine biosynthesis and by diet. What accounts for high levels of 15N in excreted urine after feeding a patient 15N-glycine to diagnose the cause of gout? Explain. A. The cause of the gout is excess production of uric acid because glycine is a precursor to purines. B. The cause of the gout is due to inability to produce uric acid because a key enzyme is missing. C. The cause of the gout is inability to break down uric acid because missing a key enzyme needed. D. The cause of the gout is overproduction of arginine because glycine is the precursor to tyrosine. E. The cause of gout is due to incorporation of uracil into DNA and thymine into RNA.

A

What explains the smell of acetone on the breath of dieters following the Atkins diet? A. Insufficient carbohydrates to maintain flux through the citrate cycle leads to increased ketogenesis. B. Eating lots of bacon and high amounts of starch, but no protein, elevates fatty acid synthesis. C. High levels of fats in the diet combined with high levels of fructose syrup leads to intestinal fermentation. D. High fat diets lead to a dangerously high level of ammonia, which sometimes smells like acetone. E. High levels of Acetyl CoA which were formed by alpha-oxidation in the pancreas.

A

Which of these three diets below is the most incomplete with regard to nutrition and why? Diet 1: carbohydrate + lipid Diet 2: protein + carbohydrates Diet 3: amino acids + fatty acids A. Diet 1; because it lacks protein, which provides 10 essential amino acids required for protein synthesis. B. Diet 3; because it lacks carbohydrates, which are essential for glycoproteins in the immune system. C. Diet 1; because it lacks protein, which provides carbon skeleton backbones required during starvation. D. Diet 2; because it lacks lipids, which are required to synthesize glucose for the glycolytic pathway. E. Diet 1; because lipids can be used to generate glucose by gluconeogenesis, but carbohydrates cannot.

A

SMALL INTESTINE

Absorption enteroli

What molecule signals the endothelial cell to produce nitric oxide, and what is the enzymatic reaction?

Acetylcholine ; L-arginine + 1.5 NADPH + H+ + 2O2 ---> Citrulline + NO + 1.5 NADP+

AMPK

Activated by AMP Increases ATP production - mediated through phosphorylation of transcription factor PGC1-alpha

What is the biochemical explanation for why rapid weight loss is reported with protein-rich diets? The rapid weight loss is due to ketogenesis and the "melting" of fat away from the thighs and upper body. A protein-rich diet is a high energy regimen that leads to nervous energy and a strong desire to exercise. Dieters usually over-estimate how much weight they actually lose on a diet and the data are likely flawed. Amino acid degradation results in urea production to remove excess NH4+, so mostly water weight loss.

Amino acid degradation results in urea production to remove excess NH4+, so mostly water weight loss.

Defects in nucleotide metabolism that lead to a buildup of uric acid cause the disease gout. Select the TWO true statements below regarding potential treatments for gout. If gout is caused by insensitivity of glutamine-PRPP amidotransferase to feedback inhibition, raising the levels of 5-phosphoribosylamine could be effective in reducing uric acid levels. An inhibitor of xanthine oxidase, such as allopurinol, will limit the conversion of hypoxanthine to uric acid, and could be effective in reducing uric acid levels. If gout is caused by HGPRT deficiency, increasing the amount of guanine available would shunt more hypoxanthine to GMP production, and could be effective in reducing uric acid levels. If gout is caused by increased levels of PRPP synthetase, increasing the activity of other enzymes in the uric acid production pathway could be effective in reducing uric acid levels. Supplying humans with the enzyme urate oxidase theoretically could be effective in reducing uric acid levels.

An inhibitor of xanthine oxidase, such as allopurinol, will limit the conversion of hypoxanthine to uric acid, and could be effective in reducing uric acid levels. Supplying humans with the enzyme urate oxidase theoretically could be effective in reducing uric acid levels.

Which of the following THREE statements are true regarding neuropeptides and appetite control? Ghrelin stimulates orexigenic signaling by binding to NPY/POMC neurons. Orexigenic neurons decrease appetite. PYY3-36 binding to NPY/AGRP neurons stimulates orexigenic signaling. Anorexigenic neurons are responsible for increasing fat stores. Orexigenic neurons increase energy expenditure. Anorexigenic neurons send out signals that increase energy expenditure. Leptin and insulin in the fed state inhibit both POMC and NPY/AGRP neurons. Orexigenic neurons increase fat stores. Anorexigenic neurons send out signals that increase appetite.

Anorexigenic neurons send out signals that increase energy expenditure. Ghrelin stimulates orexigenic signaling by binding to NPY/POMC neurons. Orexigenic neurons increase fat stores.

Why is ingesting large amounts of L-arginine a viable treatment for argininosuccinase deficiency?

Arginine is converted to ornithine, which provides urea cycle intermediates needed for nitrogen removal

Why is ingesting large amounts of L-arginine a viable treatment for argininosuccinase deficiency? Arginine is converted to ornithine, which provides urea cycle intermediates needed for nitrogen removal. The aspartate-argininosuccinate shunt requires arginine to carry the nitrogen to the urea cycle. Secreting fumarate would also work, but fumarate is an acid and it causes stomach bleeding. Citrulline can be excreted in the urine, which provides a way to remove excess dietary nitrogen. By ingesting large amounts of L-arginine, the patient is able to excrete large amounts of urea.

Arginine is converted to ornithine, which provides urea cycle intermediates needed for nitrogen removal.

What is the regulatory mechanism by which arginine stimulates flux through the urea cycle?

Arginine stimulates the production of the allosteric activator N-aceylglutamate

SHIKIMATE PATH MAKES

Aromatic compounds - tryptophan - tyrosine - phenylalanine C10 - CHORISMATE intermediate

Hemodialysis

Artifical kidney function - based on osmosis

Pyrimidine Thymine (DNA only) Uracil (RNA only) Cytosine

Aspartate (C-1, C-4, C-5, C-6) Carbamoyl phosphate (which is composed from glutamine N-3 and HCO3- C-2) UMP intermediate Thymine is made from dUMP ATPcase reaction 2

Starting with the process of nitrogen fixation by bacteria, explain how atmospheric nitrogen is incorporated into the amino acid aspartate.

Atmospheric nitrogen (N2) is converted into ammonia (NH3) as a nitrogen source for plants by three distinct processes: (1) biological fixation by soil bacteria, (2) industrial fixation by the Haber process, and (3) atmospheric fixation as a result of lightning. All organisms require nitrogen for the synthesis of numerous biomolecules, the most abundant of which are amino acids and nucleotides. Biological fixation is carried out by two types of soil bacteria: free-living bacteria and symbiotic bacteria. Both of these bacteria use an ATP-dependent reaction mechanism catalyzed by the enzyme nitrogenase to reduce N2 to NH3 (which becomes ammonium ion, NH4+). Much of the NH4+ present in the soil is oxidized to nitrate (NO3−) and nitrite (NO2−) by nitrifying bacteria, so plants have nitrate and nitrite reductase enzymes to convert these compounds back into NH4+. Atmospheric nitrogen (N2) is converted into ammonia (NH3) as a nitrogen source for plants by three distinct processes: (1) biological fixation by soil bacteria, (2) industrial fixation by the Haber process, and (3) atmospheric fixation as a result of lightning. All organisms require nitrogen for the synthesis of numerous biomolecules, the most abundant of which are amino acids and nucleotides. Biological fixation is carried out by two types of soil bacteria: free-living bacteria and symbiotic bacteria. Both of these bacteria use an ATP-dependent reaction mechanism catalyzed by the enzyme nitrogenase to reduce N2 to NH3 (which becomes ammonium ion, NH4+). Much of the NH4+ present in the soil is oxidized to nitrate (NO3−) and nitrite (NO2−) by nitrifying bacteria, so plants have nitrate and nitrite reductase enzymes to convert these compounds back into NH4+.

Aspartate transcarbamoylase (ACTase) is a rate-limiting enzyme in the pyrimidine biosynthetic pathway of bacteria. How is ACTase allosterically-regulated in bacterial cells? A. UTP shifts ATCase to the R state B. CTP shifts ATCase to the T state C. ATP shifts ATCase to the T state D. CTP shifts ATCase to the R state E. UTP shifts ATCase to the T state

B

Glucagon-like peptide-1 (GLP-1) is a hormone secreted by intestinal cells in response to nutrient detection in the small intestine. The resulting physiological response is the lowering of blood glucose levels. Which of the following is a potential mechanism for how GLP-1 signaling leads to lower blood glucose? A.increase in the rate of cell death in pancreatic beta cells B. stimulation of insulin release by pancreatic beta cells C. downregulation of the glucose transporter Glut 4 D. stimulation of glucagon release by pancreatic alpha cells E. activation of glycogen phosphorylase activity

B

Nitric Oxide (NO) is a soluble gas and regulator of intracellular pathways causing vasodilation. What is the mechanism by which NO reduces blood pressure by stimulating vasodilation? A. NO is produced in smooth muscles cells in response to sildenafil, which leads to vasodilation. B. NO binds to guanylate cyclase to stimulate cyclic GMP production, which leads to vasodilation. C. NO activates uridylylate cyclase by stimulating protein kinase A to induce muscle relaxation. D. NO mediates phosphorylation of adenylate cyclase, which increases cAMP production and vasodilation E. NO stimulates acetylcholine release to activate muscarinic receptors and vasodilation

B

Tobacco smoking, which is associated with a high risk of lung cancer, is described as: A. Genes B. Environment C. GenesàEnvironment D. EnvironmentàGenes E. Bad luck

B

Which symptom is the best indication of Phenylketonuria disease in a patient A. self-mutilation B. elevated phenylpyruvate C. nervous and fidgety D. black urine E. abdominal pain

B

Why does glucagon signaling stimulate glucose and fatty acid release from liver and adipose tissue, but has no effect on muscle cells even though muscle cells contain glycogen? A. Liver and adipose tissue contain glucagon transporter proteins, but muscle cells lack these transporters B. Muscle lacks glucose-6-phosphatase, contains insulin receptors, and lacks glucagon receptors D. Glucagon signaling in liver and adipose tissue is stimulated by leptin, but muscle lacks leptin receptors C. Muscle contains glucose-6-phosphate, lacks leptin receptors, but has glucagon receptors E. Liver cells lack glucose-6-phosphatase, whereas muscle cells lack glucose-6-phophate receptors

B

Cells cannot store excess amino acids such as aspartate and glutamate, which accumulate as a result of protein degradation. Once the nitrogen is removed from aspartate and glutamate, what happens to the alpha-keto acids oxaloacetate and alpha-ketoglutarate, respectively? A. These two alpha-keto acids are metabolized in the urea cycle. B. These two alpha-keto acids are metabolized in the citrate cycle. C. These two alpha-keto acids are used to synthesize nucleotides. D. These two alpha-keto acids are metabolized in the Calvin-Benson cycle. E. These two alpha-keto acids are used to synthesize phenylalanine and tyrosine

B. These two alpha-keto acids are metabolized in the citrate cycle.

Which metabolite is an intermediate in both pyrimidine biosynthesis and the urea cycle? A. fumarate B. carbamoyl phosphate C. glutamine D. ornithine E. ribose-5P

B. carbamoyl phodphate

Why does it makes sense that ghrelin stimulates orexigenic neurons? Because ghrelin is released from the intestines when your stomach is full of food. Because orexigenic neurons are the neurons that tell your brain to close your mouth. Because leptin stimulates anorexigenic neurons when you have extra fat. Because ghrelin is released from stomach cells when your stomach is empty. Because ghrelin is released from the brain when you exercise intensely.

Because ghrelin is released from stomach cells when your stomach is empty.

15N-labeled aspartate is provided to bacteria during the biosynthesis of pyrimidine trinucleotides. The radiolabeled nitrogen would ultimately be found in____________.

Both UTP and CTP

Muscle glycogen vs. the liver

But unlike the liver, which contains 10% glycogen by weight, individual muscle groups contain only ∼1% glycogen by weight. Therefore, glycogen stores in the most active muscle groups become depleted after an hour of continual use, whereas liver glycogen maintains safe blood glucose levels for 12-18 hours. As muscle glycogen levels decline with continual use, muscle cells depend more on fatty acids released from adipose tissue and on ketone bodies produced in the liver to maintain the high rates of ATP synthesis needed for contraction.

A deficiency in the enzyme dihydropyrimidine dehydrogenase (DPD) is best described as: A. Genes B. Environment C. GenesàEnvironment D. EnvironmentàGenes E. Bad luck

C

If HCO3 that is radioactively labeled with 13C is available, which carbon atom in the molecule below would ultimately be expected to be radioactive? D A C B

C

Which symptom is the best indication of Lesch-Nyhan disease in a patient? A. black urine B. red blood cell lysis C. male infant with gout D. vomiting E. undeveloped bones

C. male infant with gout

Regulation of aspartate transcarbamoylase (ATCase) by nucleotides controls flux through the pyrimidine biosynthetic pathway in bacteria. Choose the two true statements below that describe this regulation.

CTP allosteric inhibitor of ATCase ATP allosteric activator of ATCase

In the duodenum, enteropeptidase _______________.

Cleaves trypsinogen to form trypsin

What is the mechanism by which glyphosate kills plants

Competitive inhibitor or plant EPSP synthases

AMP-dependent protein kinase (AMPK) is activated by low energy charge (higher AMP) and phosphorylates downstream target proteins, some of which are inhibited by phosphorylation. Inhibition of which two enzymes by AMPK phosphorylation will result in an increased energy charge (higher ATP)? A. Phosphofructokinase-2 and glycogen synthase B. Hormone-sensitive lipase and phosphofructokinase-2 C. Acetyl-CoA carboxylase and phosphofructokinase-2 D. Glycogen synthase and acetyl-CoA carboxylase E. PGC1-alpha and cAMP response element binding protein

D

Explain how a deficiency in the enzyme dihydropyrimidine dehydrogenase (DPD) could lead to severe side effects in cancer treatments using 5-fluorouracil (5-FU) as a chemotherapeutic agent. A. Toxicity occurs when the 5-FU is converted to methotrexate by a DPD deficiency, leading to cell death. B. DPD converts 5-FU to fluorodihydrouracil, which is needed to kill cancer cells, so without it, too toxic. C. 5-FU is an activator of DPD, and DPD is an activator of cancer cell death, so DPD deficiency is toxic. D. DPD degrades 5-FU so high doses need to be given, if DPD is deficient, then high 5-FU doses are toxic. E. Toxicity occurs when the 5-FU is accidently converted to cytidine and adenine by the salvage pathways

D

How does the herbicide, glyphosate, work? A. It coats plants in a waxy substance that prevents water absorption during rainfall. B. It disrupts photosystem II, thereby preventing electron flow through the photosynthetic pathway. C. It inhibits plant EPSP synthase, which causes an increase in reactive oxygen species, damaging cells. D. It inhibits the shikimate pathway, preventing production of phenylalanine, tyrosine, and tryptophan. E. It kills off Rhizobacteria in the soil, thereby disrupting beneficial nitrogen fixation.

D

Leptin secretion from adipocytes is associated with too much stored fat. Leptin binding to POMC neurons causes which of the following effects? A. Activation of orexigenic neurons, resulting in increased appetite and decreased energy expenditures. Fat storage is upregulated. B. Activation of orexigenic neurons, resulting in increased appetite and increased energy expenditures. Fat storage is inhibited. C. Inhibition of anorexigenic neurons, resulting in increased appetite and increased energy storage. Fat storage is upregulated. D. Activation of anorexigenic neurons, resulting in decreased appetite and increased energy expenditure. Fat storage is inhibited. E. Activation of NPY and AGRP neurons, resulting in increased appetite and decreased energy expenditure. Fat storage is upregulated.

D

Why is de novo biosynthesis of purines markedly elevated in patients with a deficiency in hypoxanthine-guanine phosphoribosyl transferase (HGPRT)? A. HGPRT increases pyrimidine salvage and thereby increases purine biosynthesis as a result. B. The activation of ribonucleotide reductase activity by dATP increases purine biosynthesis. C. 5-Fluoruracil is converted to methotrexate by a DPD deficiency, leading to increased purine biosynthesis. D. HGPRT deficiency prevents purine salvage, leading to increased purine biosynthesis to make up for it. E. Increased purine biosynthesis is the result of ATP hydrolysis during the production of cyclic AMP.

D

Why is it a bad idea to eat a Fun Size bag of Skittles (205 grams) 10 minutes before a half marathon (13.1 miles)? Note the ingredients in a bag of Skittles shown in the box to the right: A. Protein will cause an increase in insulin and inhibit fatty acid oxidation later in the race, which will decrease available metabolic energy. B. Cholesterol will cause an decrease in insulin and inhibit fatty acid oxidation later in the race, which will decrease available metabolic energy. C. Carbohydrate will cause an decrease in glucagon and inhibit fatty acid synthesis later in the race, which will increase available metabolic energy. D. Carbohydrate will cause an increase in insulin and inhibit fatty acid oxidation later in the race, which will decrease available metabolic energy. E. Dietary fiber will cause an increase in insulin and stimulate fatty acid oxidation later in the race, which will decrease available water for the race.

D increased insulin would inhibit fatty acid oxidation later in the race since insulin upregulates fatty acid synthesis and glucose up take in cells

Explain how a deficiency in the enzyme dihydropyrimidine dehydrogenase (DPD) could lead to severe side effects in cancer treatments using 5-fluorouracil (5-FU) as a chemotherapeutic agent. Toxicity occurs when the 5-FU is converted to methotrexate by a DPD deficiency, leading to cell death DPD converts 5-FU to fluorodihydrouracil, which is needed to kill cancer cells, so without it, too toxic. DPD degrades 5-FU so high doses need to be given, if DPD is deficient, then high 5-FU doses are toxic. 5-FU is an activator of DPD, and DPD is an activator of cancer cell death, so DPD deficiency is toxic.

DPD degrades 5-FU so high doses need to be given, if DPD is deficient, then high 5-FU doses are toxic.

The pyrimidine thymine is only found in DNA, whereas the pyrimidine uracil is only found in RNA. What is the one BEST explanation for this observation? Deamination of cytosine generates uracil, which will result in a G-C to A-T mutation in DNA if uracil is allowed to persist. Evolution solved this problem by selecting for enzymes that constantly remove uracil from DNA. Uracil base pairs with adenine and thymine base pairs with adenine, therefore if both thymine and uracil were in DNA, then there would be no difference beween an A-T base pair and an U-A base pair. Deamination reactions cause pyrimidines to be converted to purines, which means that a G-C base pair will become an A-T base pair after two rounds of replication. Therefore thymine is in DNA and uracil is in RNA. RNA is easily hydrolyzed into single strands that break, but DNA is a double helix and it cannot break. Therefore, if thymine was incorporated into RNA and uracil was incorporated into DNA, then DNA would be hydrolyzed and genetic information would be lost.

Deamination of cytosine generates uracil, which will result in a G-C to A-T mutation in DNA if uracil is allowed to persist. Evolution solved this problem by selecting for enzymes that constantly remove uracil from DNA.

P450 MONOOXYGENASE ENZYME system -

Detoxifies

What is the explanation for why leptin injections cause weight loss in the strain of ob/ob mutant mice, but leptin injections has no effect in the majority of people? A. ob/ob mice lack insulin receptors and are diabetic with symptoms of metabolic syndrome, however the leptin injections stimulate insulin receptor expression and cures diabetes. Obese humans also have high insulin receptor levels, so injecting leptin has no physiological effect. B. ob/ob mutant mice lack leptin receptors, whereas db/db mice lack leptin hormone, nevertheless injection of leptin into ob/ob mice stimulates leptin hormone secretion, which binds insulin receptors. In contrast, obese humans have chronically high leptin levels but lack leptin receptors and therefore do not respond. C. ob/ob mice are insulin sensitive but leptin insensitive, and therefore the leptin injections stimulate insulin signaling, and increases metabolism. Obese humans are also insulin sensitive, but because they have the ob gene, do not respond via insulin signaling. D. Leptin injections cause weight loss in ob/ob mice because they stimulate the increased expression of leptin receptors. Obese humans, in contrast, are producing too much leptin receptor and therefore leptin injections have no effect. E. ob/ob mutant mice lack leptin, and by providing it through injection, they are able to better maintain energy balance and metabolic homeostasis. In contrast, obese humans have chronically high leptin levels and are often leptin-insensitive

E

Nucleotides such as ATP shown at the right have four key roles in biochemical processes. Name TWO of the possible four. A. Bile acid production and coenzyme-dependent reactions. B. Signal transduction and protein degradation. C. Genetic information and nitrogen balance. D. Energy conversion and glucose homeostasis. E. Coenzyme-dependent reactions and energy conversion.

E coenzyme dependent reactions and energy conversion (NAD(P)H; ATP energy currency)

ADA-SCID is caused by mutations in the enzyme adenosine deaminase leading to accumulation of deoxyadenosine (dA). Excess dA increases production of dATP and inhibition of DNA replication in developing immune cells, causing the SCID immunodeficiency phenotype. Which combination of allosteric effectors bound to the specificity site and the activity site of ribonucleotide reductase provides the BEST biochemical explanation for the ADA-SCID phenotype? A. ATP bound to the specificity site; ATP bound to the activity site of ribonucleotide reductase. B. dATP bound to the specificity site; ATP bound to the activity site of ribonucleotide reductase. C. dGTP bound to the specificity site; ATP bound to the activity site of ribonucleotide reductase. D. dTTP bound to the specificity site; ATP bound to the activity site of ribonucleotide reductase. E. ATP bound to the specificity site; dATP bound to the activity site of ribonucleotide reductase.

E. ATP bound to the specificity site; dATP bound to the activity site of ribonucleotide reductase.

If the efficiency of the urea cycle decreased, there would be a buildup of which amino acid? A. glycine B. phenylalanine C. tyrosine D. serine E. glutamine

E. glutamine

Ubiquitination is most often regulated by biochemical modifications to which two types of proteins (choices at the right): A. E2 ligases and E3 ligases B. proteasomes and E2 ligases C. E2 ligases and target proteins D. E1 ligases and E2 ligases E. target proteins and E3 ligases

E. target proteins and E3 ligases

Which of the three proteins in the ubiquination pathway is the most responsible for recognizing the ubiquintated target protein? E2 E1 all three E3

E3

Adipose tissue

Endocrine organ Adipokines that regulate metabolic homeostasis Key regulators in immunological neurological and developmental functions

Which of the following is a coenzyme that is derived from ATP? FAD heme Fe4-S4 cluster coenzyme Q

FAD

Essential amino acids

From diet ARGINIE+ HISTINE ISOLEUCINE LEUCINE LYSINE METHIONINE PHEYLALANINE THREONINE TRYPTOPHAN VALINE

Glucagon-like peptide-1 (GLP-1) is a hormone peptide secreted by intestinal L cells. It is secreted in response to the nutrient detection in the small intestine. The resulting physiological response is the lowering of blood glucose levels. Which of the following is a potential mechanism for how GLP-1 causes this physiological response? GLP-1 increases the rate of apoptosis in pancreatic alpha cells to reduce glucagon and lower blood glucose levels. GLP-1 decreases GLUT4 synthesis in muscle cells to decrease glucose uptake and lower blood glucose levels. GLP-1 stimulates glucagon release by pancreatic alpha cells to lower blood glucose levels. GLP-1 stimulates insulin release by pancreatic beta cells to lower blood glucose levels.

GLP-1 stimulates insulin release by pancreatic beta cells to lower blood glucose levels.

Alanine, cysteine, glycine and serine

GLUCOgenic AA

Which of the following amino acids are required in the first step of heme biosynthesis? Alanine Alanine Histidine Phenylalanine Glycine

Glycine

AMP-dependent protein kinase (AMPK) is activated by low energy charge in the cell, which is the result of direct AMP binding to the gamma subunit and phosphorylation of Thr172. Name TWO enzymes that are inhibited by AMPK activation and thereby lead to increased ATP synthesis and a higher energy charge? PGC1-alpha and cAMP response element binding protein Glycogen synthase and acetyl-CoA carboxylase Acetyl-CoA carboxylase and phosphofructokinase-2 Phosphofructokinase-2 and glycogen synthase Hormone-sensitive lipase and phosphofructokinase-2

Glycogen synthase and acetyl-CoA carboxylase

The conversion of hypoxanthine to IMP is catalyzed by __________, which is deficient in __________. purine nucleoside phosphorylase; ADA-SCID xanthine oxidase; Lesch-Nyhan syndrome HGPRT; Lesch-Nyhan syndrome adenosine deaminase; ADA-SCID

HGPRT; Lesch-Nyhan syndrome

The conversion of hypoxanthine to IMP is catalyzed by __________, which is deficient in __________.

HGPRT; Lesch-Nylan syndrome

Zone diet

High protein Low carb

Purine metabolism Adenine and Guanine

IMP intermediate build onto PRPP Aspartate (N-1) Glycine (N-7) 2 Glutamines (N-3 and N-9) Glycine (C-4 and C-5) HCO3- (C-6) 2 N10-formyl-tetrafolate (C-2 and C-8) Purinosome Radio labeling of TRIGAFT and F

Orlistat and olestra can both lead to undigested lipids in the colon, yet they do so by contrasting mechanisms. Orlistat ________, whereas olestra ________.

Inhibits pancreatic lipase is a fat substitute that is not a substrate for pancreatic lipase

Explain why glyphosate works faster in the summer after rain than after two weeks without rain. It works faster after it rains because the plants rapidly use up phenylalanine, which becomes limiting in the presence of glyphosate. It works faster after it rains because the leaves are not wilted and the glyphosate spray sticks better. It works faster after it rains because the roots take up the glyphosate that is sprayed on the dirt. It does not work faster after it rains, it actually works less well because the glyphosate is oil based.

It works faster after it rains because the plants rapidly use up phenylalanine, which becomes limiting in the presence of glyphosate.

Which of the following is the reaction for nitric oxide synthase? citrulline + NO + 1.5 NADP+ L-arginine + 1.5 NADPH + H+ + 2O2 L-arginine + 1.5 NADPH + H+ + 2O2 dopamine + NO + 1.5 NADP+ L-arginine + 1.5 NADPH + H+ + 2O2 citrulline + NO + 1.5 NADP+ L-arginine + 1.5 NADP+ + H+ + 2O2 citrulline + NO + 1.5 NADPH

L-arginine + 1.5 NADPH + H+ + 2O2 citrulline + NO + 1.5 NADP+

Based on what is known about neuronal control of energy metabolism in humans, why is it so hard to lose weight by dieting? Choose the three correct answers. Leptin levels decrease when fat deposits decrease, which in turn, decreases the signal to eat less; metabolize more. The net result is that you eat more; metabolize less because your body thinks you are starving. Food can be addictive to some people, much like narcotics. Therefore, the reward they get from binge eating leads to food cravings during diet-induced "withdrawal." Ghrelin levels decrease when your stomach is empty, which is one of the objectives of dieting, yet ghrelin signals to the brain to eat more; metabolize less. The net result is you always feel hungry and eventually give in. PYY3-36 is released when you have no food in your stomach and it inhibits the signal to the brain to eat more; metabolize less. Dieters are often so hungry that they eat so fast that the PYY3-36 inhibitory signal fails. Insulin levels decrease when blood sugar decrease, which is one of the objectives of dieting, therefore it decreases the signal to eat less; metabolize more. The net result is that you eat more; metabolize less because your body thinks you are starving for sugar

Leptin levels decrease when fat deposits decrease, which in turn, decreases the signal to eat less; metabolize more. The net result is that you eat more; metabolize less because your body thinks you are starving. Food can be addictive to some people, much like narcotics. Therefore, the reward they get from binge eating leads to food cravings during diet-induced "withdrawal." Insulin levels decrease when blood sugar decrease, which is one of the objectives of dieting, therefore it decreases the signal to eat less; metabolize more. The net result is that you eat more; metabolize less because your body thinks you are starving for sugar

ARGINIE

Mammals can synthesize arginine from arginosuccinate in the urea cycle - however most is cleaved to form urea and regen orthine so it is unava for protein synthesis

What would happen if purified leptin protein were injected daily into the db/db (diabetes) mouse as compared to a littermate db/db mouse that did not get leptin injections?

Mouse with leptin just as fat as without db/db lack receptors*

How are mucles selfish?

Muscle cells lack fatty acid synthase and glucose-6-phosphatase, which means that they cannot export fatty acids or glucose. Instead, they use these energy-rich compounds for muscle contraction. In this regard, muscle is truly a "selfish" tissue, using energy made available from other parts of the body for its own purpose of mechanical movement.

PANCREAS

One of these organs is the pancreas, a vital organ that secretes the hormones insulin and glucagon in response to changes in blood glucose levels. The pancreas also secretes digestive proteases (trypsin, chymotrypsin, and elastase) that degrade dietary proteins in the small intestine.

A person who has alkaptonuria is easily diagnosed from their black urine. What causes the black color?

Oxidation of homogentisate

A mutation in ____________ would decrease the synthesis of both AMP and GMP. GMP synthase PRPP synthetase adenylosuccinate synthetase IMP dehydrogenase

PRPP synthetase

Orlistate (Xenical)

Pharm drug that inhibits pancreatic lipase - limit dietary fat absorption looks like a diacylglycerol

Diseases affecting heme biosynthesis as a result of deficiencies in the heme biosynthetic pathway are called _________.

Porphyria

MUSCLES

SKELETAL: uses free FA, glu, ketone bodies for metabolic fuel CARDIAC mostly fa AND KETONE BODUES AS MET FUEL FOR STEADY HEART BEAT During resting skeletal uses fatty acids released from adipose tissue as a energy source - FA--> AceCOA then used in CC to gen NADH and FADH2 for oxidative phos ATP is quickly synthesized by creatine kinase using phosphocreatine as phosphoryl donor

Why don't brain and muscle respond to glucagon that is released from the pancreas in response to low blood glucose levels? There are no glucagon membrane transporters in these cell types. Skeletal muscle and brain cells do not contain glucagon receptors. The glucagon intracellular signaling cascade is tissue specific. The insulin receptors in these cell types inhibit glucagon receptor signaling.

Skeletal muscle and brain cells do not contain glucagon receptors.

Why do we see mucle loss in times of starvation?

Skeletal muscle can be used as an energy source for the body during times of starvation by providing amino acid substrates for liver and kidney gluconeogenesis.

Defects in nucleotide metabolism that lead to a buildup of uric acid cause the disease gout. Select the TWO true statements below regarding potential treatments for gout.

Supplying humans with the enzyme urate oxidase theoretically could be effective in reducing uric acid levels. An inhibitor of xanthine oxidase, such as allopurinol, will limit the conversion of hypoxanthine to uric acid, and could be effective in reducing uric acid levels.

Why does it make sense that tadpoles (which live in water) have low levels of the enzyme arginase, but after metamorphosis into frogs (which live on land), their arginase levels increase? The volume of water in a pond is so large that tadpoles can excrete ammonia directly and not die. Arginase is the enzyme that converts glutamine to glutamate and therefore required for urea cycle. Tadpoles living in water can excrete ammonia directly, but once on land, they need to excrete urea. Tadpoles develop into frogs when ammonia levels in the pond gets too high and they crawl on land.

Tadpoles living in water can excrete ammonia directly, but once on land, they need to excrete urea.

Glucose is delivered to brain cells by microcapillaries that are surrounded by glial cells called astrocytes. These cells functionally define the blood-brain barrier (Figure 19.6a). Glucose metabolism by brain cells is the basis for positron emission tomography (PET) imaging, which uses the metabolic radioisotope 2-deoxy-2-(18F)fluoro-D-glucose (18F-deoxyglucose) as an indicator of high glycolytic activity (ATP production) Fatty acids cannot cross the blood-brain barrier because brain astrocytes lack the necessary enzymes to recover fatty acids contained within lipoprotein particles as triacylglycerols. But the energy-rich ketone bodies acetoacetate and D-β-hydroxybutyrate are able to enter the brain through astrocytes during prolonged starvation, when glucose levels are abnormally low. The brain adapts to using ketone bodies to supply the acetyl-CoA needed for ATP synthesis by oxidative phosphorylation.

The brain requires as much as 120 g of glucose each day, which accounts for 60% of the glucose used by the human body under normal conditions

Kidneys

The kidneys are the only major organ system other than the liver that uses the gluconeogenic pathway to synthesize glucose for export to other tissues.

Brain

The steady-state electrical charge across the membrane is maintained by ATP-dependent ion pumps, the most important of which is the Na+−K+ ATPase transporter protein On the basis of studies using ouabain to inhibit the Na+−K+ ATPase transporter, up to half of all the ATP generated in the brain goes toward keeping this critical ion pump fully active.

Nitrogen obtained from dietary proteins is incorporated into the urea cycle_____________.

Through conversion to aspartate

Inhibitors of Thymidylate Synthesis Are Effective Anticancer Drugs

Thymidylate synthesis is required in rapidly dividing cells that need to maintain high rates of DNA synthesis. Because cancer cells generally grow faster than most normal cells in the body, inhibitors of thymidylate synthesis have been developed as anticancer drugs to block DNA synthesis.

Animals cannot synthesize tyrosine from shikimate-3P because they lack EPSP synthase. However, tyrosine is listed as a non-essential amino acid in most tables. What is the explanation? Tyrosine is not essential because it can be synthesized from tryptophan, and tryptophan is essential. Tyrosine is essential until reaching puberty, and then after that, it is non-essential because of hormones. There are other pathways to synthesize tyrosine from shikimate-3P, so EPSP synthase is not required. Tyrosine can be synthesized from phenylalanine, and since phenylalanine is essential, tyrosine is not. Most animals do actually contain the enzyme EPSP synthase it is just not expressed all of the time.

Tyrosine can be synthesized from phenylalanine, and since phenylalanine is essential, tyrosine is not.

Explain why cells with defects in thymidine kinase grow in media containing high amounts of 5-bromodeoxyuridine [BrdU], whereas cells with normal thymidine kinase will die when exposed to BrdU?

When thymidine kinase is lacking, BrdU does not become phosphorylated and hence cannot be incorporated into DNA.

The graph below shows the relative changes in concentration of glucose, fatty acids, and ketone bodies during 40 days of starvation. Choose the answer that correctly labels the data on the graph. X = ketone bodies; Y = glucose; Z = fatty acids X = glucose; Y = fatty acids; Z = ketone bodies X = ketone bodies; Y = fatty acids; Z = glucose X = fatty acids; Y = glucose; Z = ketone bodies

X = ketone bodies; Y = glucose; Z = fatty acids