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BIOC 385 Exam 3

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Albinism is caused by a defect in the enzyme tyrosinase (1)/ phenylalanine hydroxylase (2). The symptoms of the disorder are caused by substrate accumulation (3) /lack of product (4) and unlike phenylketonuria (5)/ Lesch-Nyhan (6), albinism cannot be treated by altering the diet. The biochemical basis for albinism relates to defects in the melatonin (7) /melanin (8) metabolic pathway and is associated with an increased (9) / decreased (10) survival rate in the nature for animals with this defective enzyme.

1,4,5,8,10

Which two amino acids are required for the synthesis of all five nucleotide bases? A. glutamine, aspartate B. glycine, alanine C. glutamine, asparagine D. asparagine, valine E. glutamine, glutamate

A. glutamine, aspartate

The synthesis of tetrahydrofolate is chemically coupled to which of the following?

A. reduction of NADP+ to NADPH B. oxidation of NADH to NAD+ C. reduction of NAD+ to NADH D. oxidation of NADPH to NADP+ E. reduction of NADPH to NAD+

A nutritional deficiency in Vitamin D causes rickets and is best described as: A. Genes B. Environment C. GenesàEnvironment D. EnvironmentàGenes E. Bad luck

B. Environment

A deficiency in the enzyme G6PD causes favism and is best described as: A. Genes effect. B. Environment effect. C. Genes à Environment effect. D. Environment à Genes effect. E. A matter of being unlucky.

C. Genes à Environment effect.

Which of the following represent the reactants of the net equation of the urea cycle? A. NH4 + , urea, aspartate, and HCO3 - B. NH4 + , ATP, fumarate, and HCO3 - C. NH4 + , ATP, aspartate, and HCO3 - D. NH4 + , AMP, aspartate, and urea E. NH2 + , ADP, asparagine, and urea

C. NH4 + , ATP, aspartate, and HCO3 -

Five nucleotide bases are found in nucleic acids. Name a purine/pyrimidine in that order. A. guanine/adenine B. thiamine/cytosol C. adenine/uracil D. thymidine/adenine E. cytosine/guanine

C. adenine/uracil

Which of the following amino acids is a starting material for the synthesis of heme? A. proline B. alanine C. glycine D. phenylalanine E. glutamine

C. glycine

Which reaction explains why animals fed 15N-Asp will accumulate 15N-labeled proteins? A. Oxaloacetate + aspartate ® a-keto acid + a-amino acid B. Aspartate + a -ketoglutarate ® oxaloacetate + glutamate C. Glutamine + a -ketoglutarate ® glutamate + glutamate D. Aspartate + a -keto acid ® oxaloacetate + a -amino acid E. Glutamate + NH4+ ® glutamine + aspartate

D. Aspartate + a -keto acid ® oxaloacetate + a -amino acid

Five nucleotide bases are found in nucleic acids. Name a pyrimidine/purine in that order. A. guanine/adenine B. thiamine/cysteine C. adenine/uridine D. thymidine/adenine E. guanine/cytosine

D. thymidine/adenine

People with argininosuccinase deficiency have decreased ability to convert argininosuccinate into arginine in the urea cycle. Why is supplementing with L-arginine the best treatment for this disorder? A. Urea is produced from arginine, allowing for excretion of nitrogenous waste obtained from L-arginine. B. L-arginine activates argininosuccinase, thereby increasing production of arginine endogenously. C. L-arginine activates the Krebs Bicycle, thereby increase nitrogen flux through the citrate cycle. D. L-arginine is a transcription factor that upregulates gene expression of the arginosuccinase enzyme E. Ornithine is produced from arginine, allowing for nitrogen to be excreted in the form of argininosuccinate.

E. Ornithine is produced from arginine, allowing for nitrogen to be excreted in the form of argininosuccinate.

The ribose sugar in ribonucleosides and in deoxyribonucleosides is derived from which pathway? A. Glycogen synthesis pathway B. Krebs bicycle pathway C. Glycogen degradation pathway D. Ketogenic pathway E. Pentose Phosphate pathway

E. Pentose Phosphate pathway

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? A. Tyrosine is not essential because it can be synthesized from tryptophan, and tryptophan is essential. B. Most animals do actually contain the enzyme EPSP synthase it is just not expressed all of the time. C. Tyrosine is essential until reaching puberty, and then after that, it is non-essential because of hormones. D. There are other pathways to synthesize tyrosine from shikimate-3P, so EPSP synthase is not required. E. Tyrosine can be synthesized from phenylalanine, and since phenylalanine is essential, tyrosine is not.

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

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. Choose the best underline word or phrase that correctly completes the sentence and record the numbers.

2, 4, 5, 8, 10

What three biochemical mechanisms determine glucose-6P flux through metabolic pathways. 1. Configuration of C-C bonds in glucose-6P (cis or trans) 2. Bioavailability of glucose-6P (concentration) when used as a substrate 3. Levels of acetyl-CoA in liver cells before breakfast 4. Activity level of enzymes (allosteric control) for which glucose-6P is a substrate 5. Level of DNA and RNA synthesis under low atmospheric pressure 6. Bioavailability of enzymes (cell localization) for which glucose-6P is a substrate 7. Ratio of NADPH to NAD+ in the cell under conditions of oxidative stress

2, 4, 6

Put the following steps in the correct order for the ribonucleotide reductase reaction mechanism. Beginning with "a" at the top of the list, and "e" at the bottom of the list. a. Step ___ The hydroxyl group on C-2' of the ribose ring gains a proton from C225 residue. b. Step ___ A free radical at Y122 abstracts a hydrogen atom from C439 to form a cysteine thiyl radical. c. Step ___A thiyl free radical removes a hydrogen atom from the C-3' position of the ribose ring. d. Step ___ Deoxynucleoside diphosphate is released and a disulfide bond is reduced by thioredoxin. e. Step ___ Cation on C-2' is reduced by C462 creating the deoxynucleotide

3,1,2,5,4

How is pyrimidine biosynthesis allosterically-regulated? A.ATP binds to the regulatory subunit which shifts ATCase to the T state B.CTP binds to the regulatory subunit which inhibits ATCase C.ATP and CTP bind to the active site to accomplish their functions D. The binding of ATP and CTP help ATCase change the equilibrium of the reaction E. ATP slows down the enzyme activity

B.CTP binds to the regulatory subunit which inhibits ATCase

Which of the following is true about the urea cycle? A.It solely occurs in the cytosol B.Carbamoyl phosphate synthetase I catalyzes the rate -limiting reaction C.It produces an abundance of NH4+. D.The urea cycle helps dispose our body of excess fatty acids E.The urea cycle would not work without excess storage of histidine and tryptophan

B.Carbamoyl phosphate synthetase I catalyzes the rate -limiting reaction

Which of the following diets relies on high fiber and is often called the Mediterranean diet? A. Atkins diet B. Ornish diet C. Zone diet D. Weight Watchers diet E. RLM cashew die

ornish diet

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

1, 4, 2, 5,3

1,4,2,5,3

Put the following steps in the correct order for the ribonucleotide reductase reaction mechanism. Beginning with "a" at the top of the list, and "e" at the bottom of the list, which numbered sequence in the answers given below correctly puts Steps 1-5 in order. Step 4 is provided for you. a. Step __ A free radical at Y122 abstracts a hydrogen atom from C439 to form a cysteine thiyl radical. b. Step __ Cation on C-2' is reduced by C462 creating the deoxynucleotide. c. Step __ Deoxynucleoside diphosphate is released and a disulfide bond is reduced by thioredoxin. d. Step __ The hydroxyl group on C-2' of the ribose ring gains a proton from C225 residue. e. Step __ A thiyl free radical removes a hydrogen atom from the C-3' position of the ribose ring.

1,4,5,3,2

Put the following steps in the correct order for the ribonucleotide reductase reaction mechanism. Step 1 of the six step reaction mechanism is shown at the right to help you get started. _____ Deoxynucleoside diphosphate is released from the enzyme and C225- C462 disulfide bond is reduced by thioredoxin ____ Cation on C-2' is reduced by C462 creating the deoxynucleotide and the radical at C-3' is reduced by C439 _____ A water molecule is removed in the reaction leaving behind a cation on C-2' that is stabilized by the radical on C-3' _____ The hydroxyl group on C-2' of the ribose ring gains a proton from the C225 residue of the enzyme ____ A thiyl free radical removes a hydrogen atom from the C-3' position of the ribose ring to generate a radical ____ A free radical at Y122 abstracts a hydrogen atom from C439 to form a cysteine thiyl radical

6,5,4,3,2,1

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

9,2,6,3

Which of the following neuronal signaling pathways leads to decreased fat storage? A. Activation of anorexigenic second-order neurons and inhibition of orexigenic second-order neurons. B. Inhibition of POMC first-order neurons, which leads to activation of orexigenic second-order neurons. C. Inhibition of anorexigenic second-order neurons and activation of orexigenic second-order neurons. D. Activation of NPY/AGRP first-order neurons, which inhibits orexigenic second-order neurons. E. Increased secretion of ghrelin in the stomach and decreased secretion of leptin from fat tissue

A. Activation of anorexigenic second-order neurons and inhibition of orexigenic second-order neurons.

Based on the function of PYY3-36, why should you eat quickly if you are trying to gain weight? A. Because PYY3-36 signals food is in small intestine, so need to fill up quickly before feeling too full. B. Gherlin signals that you are hungry and PYY3-36 signals that you have already eaten, so drink water. C. Because PYY3-36 signals food is in small intestine, so need to eat slowly so that you feel full sooner. D. PYY3-36 is produced in the stomach and ghrelin is produced in the small intestine, so better eat slowly. E. Food is addictive and the quicker you eat, the more likely your neurons will be turned off by calcium.

A. Because PYY3-36 signals food is in small intestine, so need to fill up quickly before feeling too full.

Why does it makes sense that ghrelin stimulates orexigenic neurons (eat more/metabolize less)? A. Because ghrelin is released from stomach cells when your stomach is empty. B. Because ghrelin is released from the brain when you exercise intensely. C. Because leptin stimulates anorexigenic neurons when you have extra fat. D. Because orexigenic neurons are the neurons that tell your brain to close your mouth. E. Because ghrelin is released from the intestines when your stomach is full of food.

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

A deficiency in the enzyme tyrosinase causes albinism and is best described as: A. Genes effect. B. Environment effect. C. Genes à Environment effect. D. Environment à Genes effect. E. A matter of being unlucky.

A. Genes effect.

Normal blood glucose concentration is considered to be 4.5 mM. Changes in blood glucose can lead to changes such that the level of insulin is greater than the level of glucagon (insulin>glucagon) or the level of insulin is less than that of glucagon (insulin<glucagon).Which statement correctly describes the ratio of insulin to glucagon release by the pancreas and how this ratio is affected by changes in serum glucose? A. Insulin and glucagon are secreted continuously at different levels; insulin>glucagon when glucose in the blood exceeds 4.5 mM, whereas insulin<glucagon if this concentration drops below 4.5 mM. B. Insulin and glucagon are released continuously at different levels; insulin>glucagon when glucose in the blood is below 4.5 mM, whereas insulin<glucagon if this concentration increases above 4.5 mM. C. Insulin is only released when blood glucose is less than 4.5 mM, whereas glucagon is only released if this concentration increases above 4.5 mM. Insulin and glucagon are not present at the same time. D. Insulin is released when blood glucose levels exceed 4.5 mM, whereas glucagon is released if this concentration drops below 4.5 mM. These two hormones are always present at the same levels. E. Insulin is released when blood glucose levels fall below 4.5 mM and glucagon is release when blood glucose levels fall below 4.5 mM. These two hormones are always present in the blood at high levels.

A. Insulin and glucagon are secreted continuously at different levels; insulin>glucagon when glucose in the blood exceeds 4.5 mM, whereas insulin<glucagon if this concentration drops below 4.5 mM.

How does the herbicide, glyphosate, work? A. It inhibits the shikimate pathway, preventing production of phenylalanine, tyrosine, and tryptophan. 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 kills off Rhizobacteria in the soil, thereby disrupting beneficial nitrogen fixation. E. It coats plants in a waxy substance that prevents water absorption during rainfall.

A. It inhibits the shikimate pathway, preventing production of phenylalanine, tyrosine, and tryptophan.

Why does benzoic acid therapy lower blood ammonia levels in patients with deficiencies in the urea cycle considering that benzoic acid reacts with glycine to form hippuric acid, which is rapidly excreted? A. Loss of glycine by hippuric acid excretion, drives more NH4 + into glycine biosynthesis to replace it. B. Benzoic acid increases the rate at which NH4 + is converted to glucose through acetylation. C. Benzoic acid increases the excretion of glutamate and glutamine directly in urine. D. Hippuric acid is a scavenger of NH4 + in plant root nodules, which are present in vegetarian diets. E. No one really knows how benzoic acid therapy works, but it is used as an alternative to surgery.

A. Loss of glycine by hippuric acid excretion, drives more NH4 + into glycine biosynthesis to replace it.

Why does it make sense that tadpoles (aquatic) have low levels of the enzyme arginase, but after metamorphosis into frogs (terrestrial), their arginase levels increase? A. Tadpoles living in water can excrete ammonia directly, but once on land, they need to excrete urea. B. The volume of water in a pond is so large that tadpoles can excrete ammonia directly and not die. C. Arginase is the enzyme that converts glutamine to glutamate and therefore required for urea cycle. D. Tadpoles develop into frogs when ammonia levels in the pond gets too high and they crawl on land. E. Frogs are able to walk around and excrete urea in lots of places, but tadpoles are confined to a pond.

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

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? A. Tadpoles living in water can excrete ammonia directly, but once on land, they need to excrete urea. B. The volume of water in a pond is so large that tadpoles can excrete ammonia directly and not die. C. Arginase is the enzyme that converts glutamine to glutamate and therefore required for urea cycle. D. Tadpoles develop into frogs when ammonia levels in the pond gets too high and they crawl on land. E. Frogs are able to walk around and excrete urea in lots of places, but tadpoles are confined to a pond.

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

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. The cause of the gout is excess production of uric acid because glycine is a precursor to purines.

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.

B. 1, 3, 5, 8, 10

How does metabolic flux change during starvation? A. An increase of fatty acid mobilization, glycolysis, ketogenesis, and uric acid production. B. An increase of fatty acid mobilization, gluconeogenesis, ketogenesis, and protein degradation. C. An increase of fatty acid mobilization, glycolysis, uric acid production, and protein degradation D. A decrease of fatty acid mobilization, gluconeogenesis, and protein synthesis E. There is very little change in metabolic flux as a result of starvation.

B. An increase of fatty acid mobilization, gluconeogenesis, ketogenesis, and protein degradation

How is excess intracellular ammonia removed from skeletal muscles a result of protein turnover? A. By production of urea in the urea cycle using glutamate and glutamine as nitrogen donors. B. By the Glucose-Alanine Cycle, which converts pyruvate to alanine using glutamate as the nitrogen donor. C. By the Cori Cycle, which converts glucose to pyruvate and alanine as a product of aminotransferase. D. By exporting glutamine produced by glutamine synthetase, which is converted to alanine in the liver. E. By the Glucose-Glutamine Cycle, which converts pyruvate to alanine using urea as the nitrogen donor

B. By the Glucose-Alanine Cycle, which converts pyruvate to alanine using glutamate as the nitrogen donor.

What is the biochemical mechanism by which proteins are digested in the small intestine? A. Proteins are not digested in the small intestine due to the increase in pH B. Enteropeptidase cleaves trypsin, which initiates a proteolytic cascade C. By releasing ghrelin to initiate a phosphorylation cascade leading to trypsin activation. D. Duodenum secretes trypsin which activates and cleaves other proteins E. Pepsin activation leads to the breakdown of proteins in the small intestine

B. Enteropeptidase cleaves trypsin, which initiates a proteolytic cascade

Extreme weight loss and liver failure owing to ingesting dinitrophenol (DNP) is best described as: A.Genes B.Environment C. Genes à Environment D. Environment à Genes E. Bad luck

B. Environment

A nutritional deficiency in Vitamin D causes rickets and is best described as: A. Genes effect. B. Environment effect. C. Genes à Environment effect. D. Environment à Genes effect. E. A matter of being unlucky.

B. Environment effect.

AMP-dependent protein kinase (AMPK) is activated by low energy charge in the cell, which is the result of direct AMP binding to the g 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? A. Phosphofructokinase-2 and glycogen synthase B. Glycogen synthase and acetyl-CoA carboxylase C. Hormone-sensitive lipase and phosphofructokinase-2 D. Acetyl-CoA carboxylase and phosphofructokinase-2 E. PGC1-alpha and cAMP response element binding protein

B. Glycogen synthase and acetyl-CoA carboxylase

Why might have nucleotide salvage pathways evolved? A. Pyrimidines cannot be synthesized de novo, so salvage pathways needed to evolve. B. It is energetically expensive for the cell to solely rely on de novo biosynthetic pathways. C. Purines cannot be synthesized de novo, so salvage pathways needed to evolve. D. Cells relying on de novo nucleotide synthesis grow fast and salvage pathways regulate growth rate. E. The DNA world gave rise to the RNA world, and during that process, salvage pathways evolved

B. It is energetically expensive for the cell to solely rely on de novo biosynthetic pathways.

What are two problems that have been identified owing to overuse of glyphosate in agriculture? A. Cows and goats develop skin rashes and fish often have mutations in their fins and gills. B. Native plants become glyphosate-resistance and increased human health problems, including cancer. C. Soybeans and carrots grow slower after being sprayed with glyphosate, but corn grows faster. D. Processed foods made from RoundUp-Ready crops turn yellow quickly and milk tastes like metal. E. Bacteria become resistant to glyphosate causing microbiome mutations and plants grow too fast.

B. Native plants become glyphosate-resistance and increased human health problems, including cancer.

Which of the following diets relies on high fiber to slow down digestion? A. Atkins diet B. Ornish diet C. Zone diet D. Weight Watchers diet E. RLM cashew diet

B. Ornish diet

The human genome encodes three types of enzymes in the ubiquitinating pathway, all with multiple variant gene copies; 11 E1 variant genes, 26 E2 variant genes and over 500 E3 variant genes. What does this tell you about the biochemistry of the ubiquitination process? A. That four E3 enzymes are needed to attached at least four ubiquitin subunits to a single target protein. B. That recognition of distinct target proteins requires specific E3 sequences; therefore many E3 proteins. C. That E1, E2, and E3 proteins are part of an evolving gene family such that E1 > E2 > E3. D. That the E3 enzyme requires ATP and therefore many more genes are needed to catalyze the reaction. E. It doesn't tell you anything other than ubiquitination is complicated.

B. That recognition of distinct target proteins requires specific E3 sequences; therefore many E3 proteins.

What is the biochemical basis for gout; b) what is the most common symptom of gout? A. a) Gout is caused by too much dATP, which inhibits the enzyme ribonucleotide reductase; b) blindness. B. a) Gout is caused by a buildup of uric acid owing to at least three factors; b) pain in the big toe. C. a) Gout is caused by low levels of phenylacetate and phenyllactate; b) pain in the big toe D. a) Gout is caused by too much uric acid accumulating in hair follicles; b) hair loss and skin cancer E. a) Gout is caused by too much homogentisate in the urine; b) oxidization of yellow urine to black urine.

B. a) Gout is caused by a buildup of uric acid owing to at least three factors; b) pain in the big toe.

Normal blood glucose concentration is considered to be 4.5 mM. Changes in blood glucose can lead to changes such that the level of insulin is greater than the level of glucagon or the level of insulin is less than that of glucagon. Which statement correctly describes the ratio of insulin to glucagon release by the pancreas and how this ratio is affected by changes in serum glucose? A. Insulin and glucagon are released simultaneously; insulin>glucagon when glucose in the blood is below 4.5 mM, whereas insulinglucagon when glucose in the blood exceeds 4.5 mM, whereas insulin B. Insulin is released when glucose in the blood exceeds 4.5 mM, whereas glucagon is released if this concentration drops below 4.5 mM. These two hormones are never present at the same time. C. Insulin and glucagon are released simultaneously; insulin>glucagon when glucose in the blood exceeds 4.5 mM, whereas insulin< glucagon if this concentration drops below 4.5mM.

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

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

What is the biochemical explanation for why rapid weight loss is reported with protein-rich diets? A. A protein-rich diet is a high energy regimen that leads to nervous energy and a strong desire to exercise. B. The rapid weight loss is due to ketogenesis and the "melting" of fat away from the thighs and upper body. C. Amino acid degradation results in urea production to remove excess NH4+, so mostly water weight loss. D. Dieters usually over-estimate how much weight they actually lose on a diet and the data are likely flawed. E. None of these answers are correct.

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

What explains dramatic weight loss in people who ingest dinitrophenol (DNP) as a diet strategy? A. Weight loss is due to excess water loss owing to increase rates of dehydration and perspiration. B. DNP induces a mental state in which the individual imagines they can lose weight and they do. C. DNP depletes ATP levels in the liver leading to increased rates of fatty acids derived from fat cells. D. Increased rates of glycogen synthesis stimulates beta oxidation owing to effect of DNP on cytochromes. E. dTTP bound to substrate specificity site; ATP bound to regulatory site of ribonucleotide reductase.

C. DNP depletes ATP levels in the liver leading to increased rates of fatty acids derived from fat 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. A. 5-FU is an activator of DPD, and DPD is an activator of cancer cell death, so DPD deficiency is toxic. B. DPD converts 5-FU to fluorodihydrouracil, which is needed to kill cancer cells, so without it, too toxic. C. DPD degrades 5-FU so high doses need to be given, if DPD is deficient, then high 5-FU doses are toxic. D. Toxicity occurs when the 5-FU is converted to methotrexate by a DPD deficiency, leading to cell death E. None of these answers are correct.

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

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

Glucagon circulates throughout the body, but has no signaling effect in brain and muscle. Why? A. The available glucagon is bound by the numerous receptors in liver and muscle, and therefore there is not enough left to bind to the smaller number of receptor in the brain and muscle. B. Glucagon signaling only works aerobically, and since these tissues primarily work anaerobically, glucagon signaling has no effect. C. Energy produced in muscle and brain is only utilized by these tissues themselves, and is never exported, so there is no need for these tissues to express glucagon receptors. D. Response to blood sugar levels in brain and muscle is controlled only by allosteric regulation of enzyme activity, so hormonal signaling has no effect. E. In response to insulin signaling, brain and muscle produce glucose for use by other tissues, since glucose is in excess.

C. Energy produced in muscle and brain is only utilized by these tissues themselves, and is never exported, so there is no need for these tissues to express glucagon receptors.

A deficiency in the enzyme G6PD causes favism and is best described as: A. Genes B. Environment C. Genes à Environment D. Environment à Genes E. Bad luck

C. Genes à Environment

What is the biochemical mechanism of Viagra? A. It upregulates acetylcholine receptors on the endothelial cell membrane. B. It allosterically activates endothelial nitric oxide synthase, leading to increased production of nitric oxide. C. It prevents degradation of cGMP, thereby maintaining high levels of cGMP in smooth muscle cells. D. It increases cardiac output, resulting in greater blood flow. E. It transports nitric oxide from the endothelium to the smooth muscle.

C. It prevents degradation of cGMP, thereby maintaining high levels of cGMP in smooth muscle cells.

Explain why glyphosate works faster in the summer after rain than after two weeks without rain. A. It works faster after it rains because the leaves are not wilted and the glyphosate spray sticks better. B. It does not work faster after it rains, it actually works worse because the glyphosate is oil based. C. It works faster after it rains because the plants grow faster and run out of amino acids quicker. D. It works faster after it rains because the roots take up the glyphosate that is sprayed on the dirt. E. It works faster after it rains because the plants may need more aspartate and glutamate.

C. It works faster after it rains because the plants grow faster and run out of amino acids quicker.

What is the name of the syndrome characterized by a decreased amount of pigment in hair, skin, and eyes; if a change in diet leads to increased pigmentation, what was missing from the diet? A. Kwashiorkor; phenylalanine B. Albinism; tyrosine C. Kwashiorkor; tyrosine D. Albinism; protein and lipid E. Gout; purines and pyrimidines

C. Kwashiorkor; tyrosine

Which of these three diets provides the most complete nutrition and why? Diet 1: carbohydrate + protein Diet 2: carbohydrate + fats Diet 3: protein + fats A. Diet 2; because it contains the most energy available since carbohydrates and fats store energy. B. Diet 3; because it contains the most diversity available since protein has nitrogen and fats are energy. C. Diet 3; because it contains essential amino acids and carbohydrates are synthesized from fats. D. Diet 1; because it contains essential amino acids and fats are synthesized from carbohydrates. E. Diet 2; because it contains carbohydrates and lipids for glycoprotein and glycolipid synthesis

D. Diet 1; because it contains essential amino acids and fats are synthesized from carbohydrates.

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

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

Which of these three diets provides the least complete 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 carbon skeleton backbones required during starvation. B. Diet 3; because it lacks carbohydrates, which are essential for glycoproteins in the immune system. C. Diet 1; because lipids can be used to generate glucose by gluconeogenesis, but carbohydrates cannot. D. Diet 1; because it lacks protein, which provides 10 essential amino acids required for protein synthesis. E. Diet 2; because it lacks lipids, which are required to synthesize glucose for the glycolytic pathway.

D. Diet 1; because it lacks protein, which provides 10 essential amino acids required for protein synthesis.

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. HGPRT deficiency prevents purine salvage, leading to increased purine biosynthesis to make up for it.

What explains the smell of acetone on the breath of dieters following the Atkins diet? A. Eating large amounts of bacon and high amounts of starch, but no protein, elevates fatty acid synthesis. B. High fat diets lead to a dangerously high level of ammonia, which sometimes smells like acetone. C. High levels of fats in the diet combined with high levels of fructose syrup leads to intestinal fermentation. D. Insufficient carbohydrates to maintain flux through the citrate cycle leads to increased ketogenesis. E. None of these answers are correct.

D. Insufficient carbohydrates to maintain flux through the citrate cycle leads to increased ketogenesis.

What are three mechanisms by which cancer cells become resistant to the drug methotrexate? A. Inactivation of the cell death pathway, blocking oncogenic kinase inhibitor, DHFR gene amplification B. DHFR gene amplification, thymidylate synthase mutation, mutation in membrane receptor binding C. Deletion of all copies of DHFR gene, DHFR mutation blocking drug binding, DHFR transporter mutation D. Overexpression of drug transporter, DHFR mutation blocking drug binding, DHFR gene amplification E. MDR inhibition of DHFR by DPD deficiency, Raltitrexed drug amplification, DHFR gene mutation.

D. Overexpression of drug transporter, DHFR mutation blocking drug binding, DHFR gene amplification

Five nucleotide bases are found in nucleic acids. Of the two choices below in each pair, choose the correct answer in which a pyrimidine is listed first and a purine is listed second. Pair is not a base pair. A. guanine:adenine B. thiamine:guanine C. adenine:uracil D. thymine:adenine E. cytosine:uraci

D. thymine:adenine

How does a defect in adenosine deaminase \ lead to inhibition of DNA synthesis? A. Most cells have regulatory proteins that control the level of dNTPs produced by ADA, so without it, no DNA synthesis. B. Inhibition of DNA synthesis is due to a buildup of 2'- deoxyribose-5P, which can be toxic at high levels in cells. C. ADA-SCID is an immune disease caused by mutations in the ribonucleotide reductase R1 subunit, so no DNA synthesis. D. ADA is the only enzyme that can lead to the production of ribose-5P, so without ribose-5P, there is no DNA synthesis. E. An ADA deficiency increases dATP levels, which inhibits ribonucleotide reductase and DNA synthesis.

E. . An ADA deficiency increases dATP levels, which inhibits ribonucleotide reductase and DNA synthesis.

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.

How does a defect in adenosine deaminase (ADA) lead to inhibition of DNA synthesis? A. Most cells have regulatory proteins that control the level of dNTPs produced by ADA, so without it, no DNA synthesis. B. Inhibition of DNA synthesis is due to a buildup of 2'- deoxyribose-5P, which can be toxic at high levels in cells. C. ADA-SCID is an immune disease caused by mutations in the ribonucleotide reductase R1 subunit, so no DNA synthesis. D. ADA is the only enzyme that can lead to the production of ribose-5P, so without ribose-5P, there is no DNA synthesis. E. An ADA deficiency increases dATP levels, which inhibits ribonucleotide reductase and DNA synthesis.

E. An ADA deficiency increases dATP levels, which inhibits ribonucleotide reductase and DNA synthesis.

Nucleotides 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.

What are three mechanisms by which cancer cells become resistant to the drug methotrexate? A. Deletion of all copies of DHFR gene, DHFR mutation blocking drug binding, DHFR transporter mutation B. DHFR gene amplification, thymidylate synthase mutation, mutation in membrane receptor binding C. Inactivation of the cell death pathway, blocking oncogenic kinase inhibitor, DHFR gene amplification D. MDR inhibition of DHFR by DPD deficiency, Raltitrexed drug amplification, DHFR gene mutation. E. DHFR mutation blocking drug binding, Overexpression of drug transporter, DHFR gene amplification

E. DHFR mutation blocking drug binding, Overexpression of drug transporter, DHFR gene amplification

Which of the following best explains why nucleotide salvage pathways evolved? A. Pyrimidines cannot be synthesized de novo, so salvage pathways needed to evolve. B. Cells relying on de novo nucleotide synthesis grow fast and salvage pathways regulate growth rate. C. Purines cannot be synthesized de novo, so salvage pathways needed to evolve. D. The DNA world gave rise to the RNA world, and during that process, salvage pathways evolved E. It is energetically expensive for the cell to solely rely on de novo biosynthetic pathways.

E. It is energetically expensive for the cell to solely rely on de novo biosynthetic pathways.

Undiagnosed phenylketonuria (PKU) can lead to severe neuronal damage and mental incapacity, which is avoidable if the disease is diagnosed at birth. In contrast, albinism is easily diagnosed at birth, but there is no treatment, which leads to an increased risk of skin cancer in these patients. Choose the statement that best explains the reasons for these differences. A. PKU is the result of product deficiency, which can be treated by removing tyrosine from the diet. Albinism is due to a missing product, which cannot be replaced through injections or dietary regimens. B. Defects in the enzyme tyrosinase can be treated using gene therapy to replace this enzyme in the skin cells of adult PKU patients, which reverses neuronal defects in the brain. In contrast, defects in the enzyme phenylalanine hydroxylase can be ameliorated by restricting certain amino acids in the diet. C. It is easy to treat PKU because phenylalanine can be metabolized by other pathways to avoid neuronal damage, whereas albinos would need to eat excess tyrosine to produce pigments and not too many foods contain tyrosine. D. Phenylketonuria is caused by insufficient tyrosine, which is why PKU individuals have light skin at birth. In contrast, albinism is cause by too many white pigments that accumulate when the enzyme tyrosinase is mutated. E. Phenylalanine is found in many types of food, and therefore by avoiding foods with high amounts of phenylalanine, the build-up pyruvate metabolites can be controlled. In contrast, skin pigments must be made from tyrosine and there is no way to do this if tyrosine metabolism is compromised.

E. Phenylalanine is found in many types of food, and therefore by avoiding foods with high amounts of phenylalanine, the build-up pyruvate metabolites can be controlled. In contrast, skin pigments must be made from tyrosine and there is no way to do this if tyrosine metabolism is compromised.

Glucose-6P is critical in metabolic homeostasis, which mechanism controls metabolic flux? A. proton force B. free energy change C. reduction potential D. equilibrium constant E. enzyme levels

E. enzyme levels

Extreme weight loss and liver failure owing to ingesting dinitrophenol (DNP) is best described as: A. Genes B. Environment C. GenesàEnvironment D. EnvironmentàGenes E. GenesàGenes

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