BIOC 385 Exam 3
How is excess intracellular ammonia removed from a. muscle tissue? b. liver tissue? C. all other tissues?
(a) Ammonia is removed from muscle tissue by the alanine-glucose cycle, which converts pyruvate to alanine using glutamate as the nitrogen donor. (b) Ammonia is removed from liver tissue by the production of urea in the urea cycle using glutamate and glutamine as nitrogen donors. (c) Ammonia is removed from all other tissue by export of glutamine produced by glutamine synthetase.
Glyphosate (Roundup) is a very effective herbicide that is toxic to almost all types of plants. a. Why is glyphosate considered an animal-safe herbicide? b. Why does it take up to 7 days before there is any noticeable herbicidal effect of glyphosate? c. Why don't Roundup Ready soybean plants die when they are sprayed with glyphosate?
(a) glyphosate inhibits 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase, which converts shikimate-3-phosphate to EPSP in chorismate biosynthesis. Animal cells do not synthesize chorismate, and therefore enzyme inhibitors of this pathway are considered animal-safe. (b) It takes 7 days to see the effects of glyphosate because because the plant has to use up all available phenylalanine to become dependent on phenylalanine biosynthesis. (c) Roundup Ready soybeans contain a bacterial gene coding for the enzyme CP4 EPSP synthase, which does not bind glyphosate and thereby provides glyphosate resistance to the plant.
Type 1 and Type 2 diabetes are diagnosed with a clinical test following a 12 hour fast. Identify each of the parameters in the graph below by choosing the correct labels for letters A-F. A) Drink glucose A) Inject insulin B) Type 1 diabetes B) Type 2 diabetes C) Percent activity C) Serum glucose D) Time (hours) D) Time (days) E) Type 1 diabetes E) Normal F) Type 2 diabetes F) Normal
A) Inject insulin B) Type 2 diabetes C) Serum glucose D) Time (hours) E) Type 1 diabetes F) Normal
Select the options that are true A. insulin stimulates glucose uptake in muscle cells B. insulin stimulates glucose release from liver cells C. glucagon stimulates glucose uptake in liver cells D. glucagon stimulates glucose release from muscle cells E. glucagon increases blood glucose levels in between meals
A. insulin stimulates glucose uptake in muscle cells E. glucagon increases blood glucose levels in between meals
Other than the proteasome, there is a second organelle mechanism of protein degradation within the eukaryotic cell. Which of the following organelles is also involved in protein degradation? A. lysosome B. nucleosome C. centrosome D. peroxisome
A. lysosome
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. A. phosphopentomutase; phosphoribosyl transferase; kinase; PRPP synthetase B. phosphopentomutase; PRRP synthetase; phosphoribosyl transferase C. PRPP synthetase; phosphoribosyl transferase; phosphopentomutase; kinase; kinase D. PRPP synthetase; phosphopentomutase; kinase; kinase; phosphoribosyl transferase
B. phosphopentomutase; PRRP synthetase; phosphoribosyl transferase
Long term starvation (>30 days) leads to _______________. A. decreased release of fatty acids from adipose tissue B. protein degradation in skeletal muscle C. decreased gluconeogenesis in liver and kidney cells D. decreased ketogenesis in liver cells
B. protein degradation in skeletal muscle
Consider a cell that is using protein as a primary carbon/energy source. Which of the following amino acids would be most relevant for this cell in terms of glycogen synthesis? A. lysine B. serine C. leucine
B. serine
Dihydropyrimidine dehydrogenase deficiencies can lead to toxic side effects from high doses of 5-fluorouracil because 5-fluorouracil __________ dihydropyrimidine dehydrogenase. A. is inhibited by B. denatured by C. is activated by D. is degraded by
D. is degraded by
The disease ADA-SCID is due to __________ than normal activity of the enzyme __________. A. higher; xanthine oxidase B. higher; adenosine deaminase C. lower; HGPRT D. lower; ribonucleotide reductase
D. 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 _________. A. higher; xanthine oxidase B. lower; ribonucleotide reductase C. higher; ribonucleotide reductase D. lower; hypoxanthine-guanine phosphoribosyl transferase
B. lower; ribonucleotide reductase
Arginine, leucine, and lysine are all essential amino acids. This means that they are____________. A. the main intermediates to the urea cycle. B. only available from dietary sources. C. produced from other intermediates. D. not needed for a body to function.
B. only available from dietary sources.
In what four biochemical processes can you find the purine nucleotide adenine? A. gene mutations, signal transduction, acid-base catalysis, energy conversion B. signal transduction, coenzyme function, energy conversion, genetic information C. energy conversion, genetic information, ubiquitination, coenzyme function D. coenzyme function, signal transduction, energy conversion, passive transport
B. signal transduction, coenzyme function, energy conversion, genetic information
What cellular condition(s) would cause the upregulation of AMPK activity? A.high ATP content in muscle cells B.phosphorylation of Thr172 in the α subunit C.presence of staurosporine bound to the active site D.low energy charge in muscle cells
B.phosphorylation of Thr172 in the α subunit D.low energy charge in muscle cells
What is the mechanism by which glyphosate, the active ingredient in RoundUp, kills plants? A. glyphosate inhibits the production of aspartate, alanine, and glycine B. glyphosate is an allosteric activator to plant EPSP synthase C. glyphosate binds to tyrosine and prevents incorporation into proteins D. glyphosate is a competitive inhibitor of the plant EPSP synthase
D. glyphosate is a competitive inhibitor of the plant EPSP synthase
In order for a cancer cell to be resistant to the drug methotrexate, a mutation in the dihydrofolate reductase enzyme must be able to _____________. A. bind to methotrexate, but not convert dihydrofolate to tetrahydrofolate B. bind to methotrexate and form an inhibitory covalent intermediate C. not bind methotrexate, but still convert dUMP to dTMP D. maintain enzyme activity without being inhibited by methotrexate
D. maintain enzyme activity without being inhibited by methotrexate
Aspartate is a(n) _____________ amino acid, so if a person had a diet that contained no aspartate then _____________. A. nonessential; they would be unable to synthesize proteins B. essential; they would be unable to synthesize proteins C. essential; aspartate could be synthesized from other intermediates D. nonessential; aspartate could be synthesized from other intermediates
D. nonessential; aspartate could be synthesized from other intermediates
A person who has alkaptonuria is easily diagnosed from their black urine. What causes the black odor? A. reduction of acetoacetyl-CoA B. oxidation of phenylalanine C. phenylpyruvate and phenylacetate D. oxidation of homogentisate
D. oxidation of homogentisate
What is the difference between a glucogenic and ketogenic amino acid? Which amino acids fit the description of both a glucogenic and ketogenic amino acid?
Glucogenic amino acids are metabolized to form pyruvate or citrate cycle intermediates, precursors for gluconeogenesis. Ketogenic amino acids are converted into acetyl-CoA or acetoacetyl-CoA, which give rise to ketone bones. Isoleucine, phenylalanine, threonine, tryptophan and tyrosine are both glucogenic and ketogenic
All 20 amino acids are found in the bloodstream, but alanine and glutamine are by far the most abundant. Explain this observation.
Glutamine carries nitrogen from most tissues to the liver for disposal after transamination reactions, whereas alanine carries nitrogen from muscle to the liver. The alanine-glucose cycle is responsible for removing excess muscle nitrogen that is due to protein degradation.
The human genome contains 11 E1 genes, 26 E2 genes and Over 500 E3 genes. What does this tell you about the biochemistry of the ubiquidation process?
The recognition of distinct target proteins destined for ubiquitination requires specific E3 proteins that bind to target proteins and recruit them to the E2 ubiquitinating complex. Therefore, a large number of E3 genes need to be encoded in the genome to specify the large number of E3 proteins required.
Match the atoms in the pyrimidine ring with their precursors
green: Aspartate blue: glutamine orange: bicarbonate
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
What two pathways provide the ATP needed to phosphorylate creatine during muscle contraction?
oxidative phosphorylation and glycolysis
Which of the following is a starting material for the synthesis of heme? A. Glycine B. Histidine C. Phenylalanine D. Alanine
A. Glycine
Choose the correct answers below that describe the difference between metabolic disease resulting from the build up of a substrate. Phenylketonuria is caused by a defect in the enzyme (1) phenylalanine hydroxylase/(2) phenylalanine aminotransferase. The symptoms of the disorder are caused by (3) substrate accumulation/(4) lack of product and can be treated by diets that limit (5) phenylalanine/(6) tyrosine. Albinism is characterized by white skin and hair loss due to (7) allosteric activation/(8) gene mutation in the enzyme tyrosinase and is characterized by a (9) substrate accumulation/(10) lack of product mechanism.
1, 3, 5, 8, and 10
Put the following steps in the correct order for the ribonucleotide reductase reaction mechanism. Step 1 of the six step reaction mechanism is shown above to help you get started. Cation on C-2' is reduced by C462 creating the deoxynucleotide and the radical at C-3' is reduced by C439 A thiyl free radical removes a hydrogen atom from the C-3' position of the ribose ring to generate a radical The hydroxyl group on C-2' of the ribose ring gains a proton from the C225 residue of the enzyme A free radical at Y122 abstracts a hydrogen atom from C439 to form a cysteine thiyl radical A water molecule is removed in the reaction leaving behind a cation on C-2' that is stabilized by the radical on C-3' Deoxynucleoside diphosphate is released from the enzyme and C225-C462 disulfide bond is reduced by thioredoxin
1. A free radical at Y122 abstracts a hydrogen atom from C439 to form a cysteine thiyl radical 2. A thiyl free radical removes a hydrogen atom from the C-3' position of the ribose ring to generate a radical 3. The hydroxyl group on C-2' of the ribose ring gains a proton from the C225 residue of the enzyme 4. A water molecule is removed in the reaction leaving behind a cation on C-2' that is stabilized by the radical on C-3' 5. Cation on C-2' is reduced by C462 creating the deoxynucleotide and the radical at C-3' is reduced by C439 6. Deoxynucleoside diphosphate is released from the enzyme and C225-C462 disulfide bond is reduced by thioredoxin
In purines, __________ nitrogen atoms and __________ carbon atoms originate from glycine. A. 1; 2 B. 1; 1 C. 2; 1 D. 0; 2
A. 1; 2
All _____ amino acids are derived from just ______ metabolic intermediates, which are found in three metabolic pathways _________, _________, and _______. A. 20, 7, glycolysis, pentose phosphate, citrate cycle B. 15, 5, glycolysis, pentose phosphate, citrate cycle C. 20, 7, glycolysis, fatty acid synthesis, citrate cycle D. 20, 9, glycolysis, pentose phosphate, urea cycle
A. 20, 7, glycolysis, pentose phosphate, citrate cycle
The conversion of hypoxanthine to IMP is catalyzed by __________, which is deficient in __________. A. HGPRT; Lesch-Nyhan syndrome B. xanthine oxidase; Lesch-Nyhan syndrome C. adenosine deaminase; ADA-SCID D. purine nucleoside phosphorylase; ADA-SCID
A. HGPRT; Lesch-Nyhan syndrome
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. A. Supplying humans with the enzyme urate oxidase theoretically could be effective in reducing uric acid levels. B. 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. C. If gout is caused by insensitivity of glutamine-PRPP aminotransferase to feedback inhibition, raising the levels of 5-phosphoribosylamine could be effective in reducing uric acid levels. D. 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. E. 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.
A. Supplying humans with the enzyme urate oxidase theoretically could be effective in reducing uric acid levels. B. 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.
A steep drop in blood glucose concentration occurs after consumption of high glycemic index foods because of a(n) A. insulin spike. B. catecholamine spike. C. insulin drop. D. glucagon spike.
A. insulin spike.
When AMPK is bound by AMP and is phosphorylated at Thr172, _________ activity will _________. A. acetyl-CoA carboxylase; decrease B. phosphofruktokinase-2; decrease C. glycogen synthase; increase D. hormone-sensitive lipase; decrease
A. acetyl-CoA carboxylase; decrease
Which of the following biomolecules is secreted by visceral fat? A. adipokines B. glucagon C. somatostatin D. phosphocreatine
A. adipokines
What are the sources for the two nitrogens in urea? A. aspartate and carbamoyl phosphate B. glutamate and glutamine C. asparagine and glutamine D. NH4+ and carbamoyl phosphate
A. aspartate and carbamoyl phosphate
Thrifty genes are __________ during times of starvation and __________ when physical activity is low. A. beneficial; detrimental B. detrimental; beneficial C. beneficial; beneficial D. detrimental; detrimental
A. beneficial; detrimental
15N-labeled aspartate is provided to bacteria during the biosynthesis of pyrimidine trinucleotides. The radiolabeled nitrogen would ultimately be found in____________. A. both UTP and CTP. B. UTP but not CTP. C. neither UTP or CTP. D. CTP but not UTP.
A. both UTP and CTP.
In the duodenum, enteropeptidase _______________. A. cleaves trypsinogen to form trypsin B. neutralizes the pH of the duodenum to a pH of 7 C. generates peptides and amino acids D. cleaves chymotrypsinogen to form chymotrypsin
A. cleaves trypsinogen to form trypsin
Which of the following reactions utilize tetrahydrofolate? A. conversion of homocysteine to methionine B. conversion of glycine to serine C. conversion of pyruvate to alanine D. conversion of proline to glutamate
A. conversion of homocysteine to methionine B. conversion of glycine to serine
Partial inhibition of lipoprotein lipase would______________. A. decrease the level of ketone bodies in the blood. B. increase rates of glycogen breakdown in heart muscle cells. C. prevent neurons in the brain from using free fatty acids as an energy source. D. decrease liver lactate dehydrogenase activity.
A. decrease the level of ketone bodies in the blood.
Alanine, cysteine, glycine, and serine are all considered __________ amino acids. A. glucogenic B. ketogenic C. urea D. essential
A. glucogenic
Binding of ATP to the ______ subunit shifts ATCase to the ______ state, whereas ______ binding to the regulatory subunit stabilizes the ______ state. A. regulatory; R; CTP; T B. regulatory; T; CTP; R C. catalytic; R; CTP; T D. catalytic; R; GTP; T
A. regulatory; R; CTP; T
A negative nitrogen balance in a person would be an indicator of_____________. A. starvation. B. a diet heavy in protein. C. accumulation of nitrogen in the body. D. overall good health.
A. starvation.
Compared to purine biosynthesis, where the common intermediate IMP is synthesized attached to ribose-5-phosphate, pyrimidine biosynthesis: Choose one or more: A.is different in that all the pyrimidines are synthesized sequentially from UMP. B.is different in that the pyrimidine base is synthesized and then attached to ribose-5-phosphate. C.is the same in that carbamoyl phosphate is an early product of both purine and pyrimidine biosynthesis. D.is similar in that a common intermediate is synthesized and modified to make each unique pyrimidine base. E.is different in that bicarbonate (HCO3-) is not part of the pyrimidine ring synthesis but is part of the purine ring synthesis.
A.is different in that all the pyrimidines are synthesized sequentially from UMP. B.is different in that the pyrimidine base is synthesized and then attached to ribose-5-phosphate.
A newborn infant with highly elevated levels of blood ammonia was diagnosed to have a urea cycle enzyme defect in either carbamoyl phosphate synthetase or arginase. The clinical lab was able to measure the concentrations of alanine, glutamine and arginine in the blood, but enzyme assays were not available. How would knowledge of abnormal levels of alanine, glutamine or arginine in the blood be useful to distinguish between an enzyme defect in carbamoyl phosphate synthetase or arginase?
An enzyme defect in carbamoyl phosphate synthetase would block the urea cycle at the the first step of citrulline production from ornithine and carbamoyl phosphate. This would cause higher than normal alanine and glutamine concentrations because they cannot be metabolized and lower than normal arginine concentration because the urea cycle is not functioning (no arginine produced or argininosuccinase). However, a defective arginase would cause arginine to accumulate , and alanine and glutamine concentrations would be closer to normal, assuming excess nitrogen is excreted as argininosuccinate and arginine.
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. (check all that apply) A. ATP is an allosteric inhibitor of ATCase activity B. ATP is an allosteric activator of ATCase activity C. CTP is an allosteric activator of ATCase activity D. Aspartate is an allosteric inhibitor of ATCase activity E. Aspartate is an allosteric activator of ATCase activity F. CTP is an allosteric inhibitor of ATCase activity
B. ATP is an allosteric activator of ATCase activity F. CTP is an allosteric inhibitor of ATCase activity
Which enzyme deficiency is responsible for Lesch-Nyhan syndrome? A. Xanthine oxidase B. HGPRT C. PRPP synthetase D. Adenosine deaminase
B. HGPRT
Why do individuals with both type 1 and type 2 diabetes have elevated blood glucose levels but respond differently to the same dose of injected insulin? A. Individuals with type 2 diabetes are insulin deficient and their intracellular insulin signaling pathways are inhibited, whereas individuals with type 1 diabetes have normal insulin signaling pathways. B. Individuals with type 1 diabetics are insulin deficient, but the intracellular insulin signaling pathways are inhibited in individuals with type 2 diabetes. C. The intracellular signaling pathways are inhibited in individuals with both type 1 and type 2 diabetes, but individuals with type 2 diabetes would require a higher dose of insulin to lower blood glucose levels. D. Individuals with both type 1 and type 2 diabetes are insulin deficient, but those with type 2 diabetes would require a higher dose of insulin to lower blood glucose levels.
B. Individuals with type 1 diabetics are insulin deficient, but the intracellular insulin signaling pathways are inhibited in individuals with type 2 diabetes.
Which amino acid in a target protein for proteasomal degradation is tagged by ubiquitin? A. Serine B. Lysine C. Tyrosine D. Arginine
B. Lysine
Which of the following is correct concerning ribonucleotide reductase? A. Prokaryotes other than E. coli rely on amino acids from the R1 and R2 subunits and a dinuclear Fe3+ iron center. B. Ribonucleotide reductase in most eukaryotes contains a dinuclear Fe3+ center in the R2 subunit. C. Eukaryotic ribonucleotide reductase contains a 4 Fe-4 S center. D. E. coli ribonucleotide reductase contains a cobalt reactive center.
B. Ribonucleotide reductase in most eukaryotes contains a dinuclear Fe3+ center in the R2 subunit.
Ketogenesis stimulated during starvation because it leads to______________. A. increased protein synthesis and increased glycolysis. B. increased gluconeogenesis and increased fatty acid oxidation. C. decreased fatty acid oxidation and increased acetyl-CoA oxidation. D. increased liver glycolysis and increased adipocyte fatty acid synthesis. E. increased acetyl-CoA oxidation and increased fatty acid synthesis.
B. increased gluconeogenesis and increased fatty acid oxidation.
AMPK is a serine/threonine kinase that is highly conserved in eukaryotes. The AMP nucleotide associates with the regulatory subunit of the protein, and another subunit that has multiple α helices and β sheets is the catalytic subunit. In the molecular structure, the kinase inhibitor staurosporine is bound to the active site in the catalytic α subunit. What is staurosporine, shown in blue? A. an allosteric noncompetitive inhibitor that blocks the active site access to ATP and/or a target protein serine/threonine residue B. a competitive inhibitor that blocks the active site access to ATP and/or a target protein serine/threonine residue C. a competitive inhibitor that alters the shape of the protein and distorts the shape of the active site, thereby restricting access to ATP and/or a target protein serine/threonine residue D. an allosteric noncompetitive inhibitor that alters the shape of the protein and distorts the shape of the active site, thereby restricting access to ATP and/or a target protein serine/threonine residue
B. a competitive inhibitor that blocks the active site access to ATP and/or a target protein serine/threonine residue
THF derivatives are interconverted to generate transferable C1 groups that differ by the level of oxidation. In addition to methylene (-CH2-), formyl (-CHO), and formimino (-CH=NH) groups, the other transferable groups are which two of the following? A. a carbonyl group (-C=O) B. a methyl group (-CH3) C. a carboxylic acid (-C=OOH) D. a methenyl group (-CH=) E. a phosphate group (-PO4) F. an aldehyde (-C=OH)
B. a methyl group (-CH3) D. a methenyl group (-CH=)
Which of the following chemical moieties compose tetrahydrofolate (THF)? A .indole B. a pterin C. glutamate D. serine
B. a pterin C. glutamate
Which metabolite listed below serves as the biochemical link between the urea cycle and the citrate cycle? A. malate B. fumarate C. arginine D. ornithine
B. fumarate
Compared with a normal patient, a person with type 1 diabetes would display __________ during a glucose tolerance test. A. more rapid rise in blood glucose levels after drinking the glucose solution B. higher starting blood glucose level C. reduction in blood glucose levels after drinking the glucose solution D. more rapid recovery to normal blood glucose levels after drinking the glucose solution
B. higher starting blood glucose level
Which cellular change(s) would not encourage the Krebs bicycle and thus the probability of the urea cycle taking place to completion? A. increased import of ornithine into the mitochondria B. increased aspartate charging to mitochondrial tRNAs C. increased conversion of oxaloacetate into citrate D. increased citrulline being transported into the cytoplasm
B. increased aspartate charging to mitochondrial tRNAs C. increased conversion of oxaloacetate into citrate
Individuals with enzyme deficiencies in the urea cycle have elevated blood ammonia levels, which can be life threatening. One useful therapy is to feed these individuals benzoic acid, which reacts with glycine to form hippuric acid. This compound can be excreted in urine. Why does benzoic acid therapy lower blood ammonia levels in these individuals?
Benzoic acid lowers blood ammonia levels by depleting cells of glycine, which reacts with benzoic acid to form hippuric acid. Because cells are depleted of glycine as a result of benzoic acid treatment, free ammonia is used in the glycine synthesis pathway. The net result is lower levels of free ammonia.
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. Dieters usually over-estimate how much weight they actually lose on a diet and the data are likely flawed. C. Amino acid degradation results in urea production to remove excess NH4+, so mostly water weight loss. D. 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.
Which of the following is the net reaction of the urea cycle? A. NH+ + HCO3 + fumerate + 3ATP urea + aspartate + 2 ADP + 2Pi + AMP + PPi B. NH+ + HCO3 + aspartate + 2 ADP + 2Pi + AMP + PPi urea + fumerate + 3ATP C. NH+ + HCO3 + aspartate + 3ATP urea + fumerate + 2 ADP + 2Pi + AMP + PPi D. Urea + Fumerate + 2 ADP + 2Pi + AMP + PPi NH+ + HCO3- + aspartate + 3ATP
C. NH+ + HCO3 + aspartate + 3ATP urea + fumerate + 2 ADP + 2Pi + AMP + PPi
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? A. GLP-1 stimulates glucagon release by pancreatic alpha cells to lower blood glucose levels. B. GLP-1 increases the rate of apoptosis in pancreatic alpha cells to reduce glucagon and lower blood glucose levels. C. GLP-1 stimulates insulin release by pancreatic beta cells to lower blood glucose levels. D. GLP-1 decreases GLUT4 synthesis in muscle cells to decrease glucose uptake and lower blood glucose levels.
C. GLP-1 stimulates insulin release by pancreatic beta cells to lower blood glucose levels.
Which of the following amino acids are required in the first step of heme biosynthesis? A. Alanine B. Alanine C. Glycine D. Histidine E. Phenylalanine
C. Glycine
What biochemical marker differentiates insulin-sensitive and insulin-resistant muscle cells? A. High levels of tyrosine phosphorylated IRS-1 in insulin-resistant muscle cells. B. High levels of serine phosphorylated IRS-1 in insulin-sensitive muscle cells. C. High levels of tyrosine phosphorylated IRS-1 in insulin-sensitive muscle cells. D. Low levels of TNF-alpha receptor activation in insulin-resistant muscle cells.
C. High levels of tyrosine phosphorylated IRS-1 in insulin-sensitive muscle cells.
Why don't brain and muscle respond to glucagon that is released from the pancreas in response to low blood glucose levels? A. There are no glucagon membrane transporters in these cell types. B. The glucagon intracellular signaling cascade is tissue specific. C. Skeletal muscle and brain cells do not contain glucagon receptors. D. The insulin receptors in these cell types inhibit glucagon receptor signaling.
C. Skeletal muscle and brain cells do not contain glucagon receptors.
In the figure, the change in the concentrations of the three biomolecules is different, with two showing a similar pattern while the third increases rapidly as starvation conditions continue. What is the explantion for this biological phenomenon? Label the graph in Part 1 and base your answer to this question on your placement of those labels. A. Oxidation of fatty acids by the skeletal muscle and heart during the initial days of starvation leads to a rapid release of ketone bodies as a by-product. B. Most organs do not use ketone bodies for fuel until after a singificant amount of time has passed, so initial production outpaces use. C. The rapid increase in gluconeogenic flux early in starvation leads to a corresponding increase in ketone body synthesis. D. An increase in the catabolism of amino acids in the first few days of starvation leads to a release of ketone bodies.
C. The rapid increase in gluconeogenic flux early in starvation leads to a corresponding increase in ketone body synthesis.
Which of the following statements is correct concerning diabetes? A. Type 1 diabetes is characterized by insulin resistance. B. Type 2 diabetics show similar blood glucose responses as healthy individuals when given an insulin injection. C. Type 1 and Type 2 diabetics show similar blood glucose responses when given a glucose tolerance test. D. Type 2 diabetics suffer from insufficient insulin production.
C. Type 1 and Type 2 diabetics show similar blood glucose responses when given a glucose tolerance test.
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? A. When thymidine kinase is not present, protein phosphatase dephosphorylates BrdU preventing its incorporation into RNA B. Without thymidine kinase, the BrdU is phosphorylated by Dihydrofolate Reductase and inactivated. C. When thymidine kinase is lacking, BrdU does not become phosphorylated and hence cannot be incorporated into DNA. D. Thymidine kinase is required for the thymidylate synthase reaction to work.
C. When thymidine kinase is lacking, BrdU does not become phosphorylated and hence cannot be incorporated into DNA.
It is important that proteolytic enzymes in the lysosome are optimized to work at low pH because low pH_____________. A. enhances the degradation of ubiquitinated proteins. B. makes it easier for ATP to be converted to ADP + Pi. C. enhances protein denaturing. D. deactivates cysteine proteases.
C. enhances protein denaturing.
Tyr122 is important in the mechanism of the E. coli ribonucleotide reductase. The function of this amino acid in the mechanism is to ________________. A. carry out a nucleophilic attack on the substrate B. coordinate water in the active site C. generate the Cys439 radical species D. hydrogen-bond to the phosphates of the substrate
C. generate the Cys439 radical species
In the human disease called severe combined immunodeficiency (ADA-SCID), ribonucleotide reductase activity is __________ because of an overabundance of __________. A. inhibited; cAMP B. activated; cAMP C. inhibited; dATP D. activated; dATP
C. inhibited; dATP
What type of enzyme (dashed box) is responsible for the conversion in the nucleotide salvage pathway shown? A. nucleotidases B. phosphodiesterases C. kinases D. phosphorylases
C. kinases
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. A. aminopterin; fluorodeoxyuridine--monophosphate B. methotrexate; raltitrexed C. methotrexate; aminopterin D. aminopterin; raltitrexed
C. methotrexate; aminopterin
When the ____________ second-order neurons are activated, appetite increases and basal metabolic rates are decreased. A. POMC B. anorexigenic C. orexigenic D. ghrelin
C. orexigenic
A person who has phenylketonuria will have an excess amount of ___________ in the cell. A. pyruvate B. tyrosine C. phenylalanine D. alanine
C. phenylalanine
Diseases affecting heme biosynthesis as a result of deficiencies in the heme biosynthetic pathway are called______________. A. albinism. B. alkaptonuria. C. porphyrias. D. shikimate.
C. porphyrias.
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? A. the mouse with leptin will be thinner than the mouse without leptin B. the mouse with leptin will be fatter than the mouse whiteout leptin C. the mouse with leptin will be as fat as the mouse without leptin D. the mouse without leptin will be fatter than the mouse with leptin
C. the mouse with leptin will be as fat as the mouse without leptin
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? A. 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. B. 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. C. 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. D. 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.
D. 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.
Which of the three proteins in the ubiquination pathway is the most responsible for recognizing the ubiquinated target protein? A. all three of the proteins recognize the target protein B. E2 C. E1 D. E3
D. E3
Which metabolite listed below is considered central to human physiology based on its link to multiple biochemical pathways? A. Glucose B. 6-phosphogluconolactone C. Fructose-6P D. Glucose-6-phosphate
D. Glucose-6-phosphate
What clinical test distinguishes between Type 1 and Type 2 diabetes? A. Drink glucose and measure blood glucose levels over time. B. Drink water and measure urine production over time. C. Measure levels of glycosylated hemoglobin over 3 month period. D. Inject insulin and measure blood glucose levels over time.
D. Inject insulin and measure blood glucose levels over time.
Considering the physiology of thymidylate synthase, why is Tomudex an effective anticancer drug? A. The drug is an enzyme activator that binds to thymidylate synthase and increases enzymatic activity. This causes an excess of dNTPs that are available for DNA replication. B. The drug is a nucleotide analog that binds to thymidylate synthase and decreases enzymatic activity because the drug is converted by the enzyme into an unusable dNTP. C. The drug is a competitive inhibitor that binds to thymidylate synthase and decreases enzymatic activity. This causes an imbalance in the quantities of dNTPs that are available for DNA replication. D. The drug is a noncompetitive inhibitor that binds to thymidylate synthase and decreases enzymatic activity. This causes an imbalance in the quantities of dNTPs that are available for DNA replication.
D. The drug is a noncompetitive inhibitor that binds to thymidylate synthase and decreases enzymatic activity. This causes an imbalance in the quantities of dNTPs that are available for DNA replication.
Which of the following is correct and most accurately describes the complete urea cycle of the eukaryotic cell? A. The urea cycle occurs completely within the cytoplasm of the eukaryotic cell. B. The urea cycle occurs between the inner mitochondrial membrane and the matrix of the eukaryotic cell. C. The urea cycle occurs completely within the mitochondrial matrix of the eukaryotic cell. D. The urea cycle occurs between the mitochondrial matrix and the cytoplasm of the eukaryotic cell.
D. The urea cycle occurs between the mitochondrial matrix and the cytoplasm of the eukaryotic cell.
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. A. X = glucose; Y = fatty acids; Z = ketone bodies B. X = fatty acids; Y = glucose; Z = ketone bodies C. X = ketone bodies; Y = fatty acids; Z = glucose D. X = ketone bodies; Y = glucose; Z = fatty acids
D. X = ketone bodies; Y = glucose; Z = fatty acids
Which of the following best describes the nucleotide in this image? A. uracil B. thymine C. cytosine D. adenine E. guanine
D. adenine
What is the regulatory mechanism by which arginine stimulates flux through the urea cycle? A. arginine stimulates flux through the urea cycle by inhibiting the enzyme nitrogenase B. arginine stimulates the production of N-acetylglutamate which activates arginase C. arginine stimulates the activity of carbamoyl phosphate synthetase I D. arginine stimulates the production of the allosteric activator N-acetylglutamate
D. arginine stimulates the production of the allosteric activator N-acetylglutamate
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. A. PRPP synthetase; phosphopentomutase; kinase; kinase; phosphoriboxyl transferase B. PRPP synthetase; phosphoriboxyl transferase; phosphopentomutase; kinase; kinase C. phosphopentomutase; phosphoriboxyl transferase; kinase; PRPP synthetase; kinase D. phosphopentomutase; PRPP synthetase; phosphoriboxyl transferase; kinase; kinase
D. phosphopentomutase; PRPP synthetase; phosphoriboxyl transferase; kinase; kinase
Disease affecting heme biosynthesis as a result of deficiencies in the heme biosynthetic pathway are called A. albinism B. alkaptonuria C. phenylketonuria D. porphyria
D. porphyria
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? A. glutaredoxin B. thioredoxin C. glutathione reductase D. ribonucleotide reductase
D. ribonucleotide reductase
Albinism is caused by______________. A. overproduction of NADPH B. inefficient production of dopamine C. low levels of ATP available in the cell D. the enzyme tyrosinase working inefficiently
D. the enzyme tyrosinase working inefficiently
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 essential until reaching puberty, and then after that, it is non-essential because of hormones. B. Tyrosine is not essential because it can be synthesized from tryptophan, and tryptophan is essential. C. There are other pathways to synthesize tyrosine from shikimate-3P, so EPSP synthase is not required. D. Most animals do actually contain the enzyme EPSP synthase it is just not expressed all of the time. 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.
Angina patients sometimes carry nitroglycerine pills with them___________ A. to inhibit acetylcholine release from neurons B. as a source of ammonia for muscle relaxation C. to increase heart rate during a heart attack. D. to inhibit cGMP phosphodiesterase E. as a rapid source of NO for blood vessel dilation
E. as a rapid source of NO for blood vessel dilation
Five nucleotide bases are found in nucleic acids. Choose a pyrimidine/purine pair from the list below. A. guanine/adenine B. guanine/cytosine C. thiamine/cysteine D. adenine/uracil E. thymine/adenine
E. thymine/adenine
Describe the function of the E1, E2, and E3 enzymes in the ubiquitinating system. Why are there ~500 E3 genes in the human genome but only two E1 genes?
E1 enzymes attached ubiquitin to E2 enzymes, E2 enzymes conjugate ubiquitin to target proteins, and E3 enzymes recognize target proteins and facilitate ubiquitination by interacting directly with E2-ubiquitin and the target protein. E3 proteins must recognize a large number of target proteins, and thus there are hundreds of different E3 genes. In contrast, E1 needs to recognize only ubiquitin and E2 and therefore fewer genes are needed.
What is the functional definition of essential and nonessential amino acids in the human diet? How might this functional definition be explained in evolutionary terms?
Essential amino acids: must be obtained in our diet because we lack necessary enzymes for their synthesis.Nonessential amino acids: we can synthesize and do not necessarily need in our diets.As plants and bacteria must be able to synthesize all 20 amino acids for survival, but humans eat diverse foods that provide many amino acid requirements, an evolutionary explanation is humans have lost the amino acid biosynthetic pathways that require multiple steps and are the most complex and energy demanding; that is, pathways for the 10 essential amino acids
What is meant by the term "inborn errors of metabolism"? Give three examples of inborn errors that are directly related to the metabolism of phenylalanine and tyrosine
Inborn errors of metabolism was first used to describe alkaptonuria, a genetically inherited defect in the homogentisate 1,2-dioxygenase. Homogentisate is a metabolite of tyrosine degradation that accumulates in alkaptonuria and is responsible for the name black urine disease. Two other genetic diseases related to phenylalanine degradation are phenylketonuria, a defect in phenylalanine hydroxylase, and albinism, a defect in tyrosinase.
Match the effect that glucagon has to the appropriate tissue type (Liver, Adipose, or Muscle) A. Lacks appreciable levels of glucagon receptors and considered to be glucagon insensitive B. activates triacylglycerol hydrolysis and fatty acid export C. activates protein kinase A-mediated phosphorylation of perilipin D. stimulates glucose export E. increases rate of gluconeogenesis and glycogen degradation F. down-regulates glycogen synthase activity
Liver E. increases rate of gluconeogenesis and glycogen degradation D. stimulates glucose export F. down-regulates glycogen synthase activity Adipose B. activates triacylglycerol hydrolysis and fatty acid export C. activates protein kinase A-mediated phosphorylation of perilipin Muscle A. Lacks appreciable levels of glucagon receptors and considered to be glucagon insensitive
In the reaction of nitric oxide synthase shown below, sort the molecules into those oxidized and those that get reduced. L-Arginine NADPH O2
Oxidized: L-Arginine NADPH Reduced: O2
The amidation reaction during CTP synthesis uses glutamine as the source of nitrogen in most species; however, bacteria use...
NH4+
What explains the observation that some forms of porphyria are associated with jaundice while others are not?
Porphyrias are genetically inherited diseases caused by defects in enzymes for heme biosynthesis. Acute intermittent porphyria is a genetic defect in porphobilinogen deaminase causing a buildup of bilirubin, which leads to yellow skin, or jaundice. Because some of the heme biosynthesis intermediates are chemically related to heme degradation products, defects in heme biosynthesis can lead to a buildup of substrates converted to bilirubin to cause jaundice. Not all porphyrias lead to an accumulation of bilirubin, therefore not all porphyrias are associated with jaundice.
Why does it make metabolic sense that tadpoles (which live in water) have low levels of the enzyme arginase, but after their metamorphosis into frogs (which spend extended periods of time on land) their arginase levels increase dramatically?
Tadpoles can excrete ammonia directly into the water, but frogs that live on land need to converse water and excrete ammonia as urea. Arginase is essential for the production of urea from arginine.
What is the metabolic function of the "Krebs bicycle" in nitrogen metabolism?
The Krebs bicycle is a set of reactions that link the urea cycle and citrate cycle through fumarate. This shunt pathway recycles the carbon backbone of aspartate, which donates one of the two nitrogen to urea. Fumarate produced by the urea cycle is used by the citrate cycle to generate oxaloacetate for the aspartate aminotransferase reaction. In this way, the amino group of glutamate is transferred to urea via aspartate and fumarate.
Animals cannot synthesize tyrosine from shikimate-3P because they lack EPSP synthase, yet tyrosine is categorized as a non-essential amino acid in most cases. Why?
Tyrosine can be synthesized from phenylalanine (an essential amino acid) by the enzyme phenylalanine hydroxylase.
High-protein and low-carbohydrate diets involving daily ingestion of large amounts of protein hydrolysate (a mixture of amino acids and small oligopeptides) can be dangerous, although body weight often decreases quickly. Explain why most of the rapid weight loss in a high-protein diet is due to water loss rather than increased rates of fatty acid oxidation.
Using amino acids as the only source of carbon causes increased urea production. Urea is used to remove ammonia resulting from amino acid deamination to generate pyruvate, oxaloacetate, and α-ketoglutarate for energy generation. Because a large volume of water is required to excrete urea, individuals become dehydrated and weigh less in the short term if they do not drink large amounts of water to compensate.
When 15N-labeled aspartate is fed to animals, many 15N-labeled amino acids appear in protein within a short time. a) explain this observation and include in your answers the most likely enzyme reactions responsible for this finding b) What is the enzyme cofactor in this reaction, and what type of chemical bond must be formed for the reaction to proceed?
a) Aspartate is a common amino group donor for transamination such as:Aspartate + a-keto acid >> Oxaloacetate + a amino acidBecause the a-keto acid in the equation can come from any amino acid, the 15N from aspartate is rapidly transferred to other amino acidsb) The cofactor is pyridoxal phosphate, which forms a Schiff base between the cofactor carbonyl carbon and an amino group from either a lysine of the enzyme or a free amino acid
Cats were fasted overnight and then given a single meal containing all amino acids except arginine. Within 2 hours, blood ammonia levels rose by 800%. A control group of cats were fasted and then fed the same meal but with arginine included, and showed no change in blood ammonia levels. a) Fasting was required to obtain this difference in blood ammonia levels. Why? b) What caused the ammonia levels to rise in the experimental group compared to the control group?
a) Fasting lowered blood glucose, so that the fed amino acids are deaminated to form substrates for gluconeogenesis b) Arginine is required for the urea cycle thus the experimental animals were unable to remove ammonia via the urea cycle
Kwashiorkor is a dietary deficiency disease characterized by decreased pigment in the skin and hair a) which major food group is likely missing from the diet? b) what would you conclude if adding the missing food group to the diet had no effect on the skin and hair condition?
a) Kwashiorkor is caused by a lack of protein in the diet. The decreased pigmentation is caused by a deficiency in tyrosine, which is the precursor to melanin pigments. Moreover, because phenylalanine is converted to tyrosine by phenylalanine hydroxylase, phenylalanine deficiency also contributes to the skin and hair condition. b) In this case, the individual may have a defect in an enzyme required to convert tyrosine to melanin.
Individuals with the disease phenylketonuria lack the enzyme phenylalanine hydroxylase, which is required to convert phenylalanine to tyrosine. Albinism is a disease characterized by lack of skin pigments due to a deficiency in the enzyme tyrosine. a) explain why patients with PKU can be spared from many of the deleterious effects of the disease, whereas there is no feasible treatment for albinism? b) Explain why individuals with PKU are not complete albinos, even though they cannot synthesize tyrosine from phenylalanine.
a) The level of phenylalanine in the body can be controlled by diet. There is no safe way to continually add pigments to the cells through diet or drugs. b) Individuals with PKU have tyrosinase and obtain tyrosine in their diet.