Purines and Pyrimidines Quiz answers PDF

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1/14/2018 Purine and Pyrimidine Question 1 Question 1 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. In tissues that do not carry out active de novo synthesis, maintenance of an adequate supply of adenine nucleotides: A. occurs primarily by adenine salvage...

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1/14/2018

Purine and Pyrimidine Question 1

Question 1 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. In tissues that do not carry out active de novo synthesis, maintenance of an adequate supply of adenine nucleotides: A. occurs primarily by adenine salvage using A-PRT. B. requires ATP uptake from the blood. C. depends upon the action of nucleoside phosphorylase D. is accomplished entirely by the action of adenylate kinase. E. involves hypoxanthine salvage using HG-PRT. The correct answer is (E). Comments: A. A-PRT is not considered to be the major enzyme because we produce very little free adenine. B. Phosphorylated compounds generally don't cross the plasma membrane. C. This enzyme is primarily for the salvage of pyrimidines. D. Adenylate kinase equilibrates ATP, AMP and ADP E. Correct. The IMP formed is converted to AMP by amination with aspartate. Return to Question Document cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq1.htm#Q1d

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Purines and Pyrimidines Question 2

Question 2 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. Involve(s) reduction and cleavage of the nitrogen-containing ring. A. Catabolism of guanine B. Catabolism of uracil A. A only B. B only C. Both A and B D. Neither A or B The correct answer is (B). Comments: Guanine is a purine and the purine ring is excreted as uric acid. Only the pyrimidine ring is cleaved. Return to Question Document cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq2.htm#Q2a

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Purines and Pyrimidines Question 3

Question 3 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. Orotic acid would be an intermediate A. Catabolism of guanine B. Catabolism of uracil A. A only B. B only C. Both A and B D. Neither A or B The correct answer is (D). Comments: Orotic acid is an intermediate in the synthesis of the pyrimidines. Return to Question Document cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq3.htm#Q3a

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1/14/2018

https://library.med.utah.edu/NetBiochem/pupyr/ppq4.htm#Q4a

Question 4 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. Thioredoxin is involved in the: A. conversion of AMP to ATP. B. conversion of dUMP to dTMP. C. conversion of a ribonucleotide to a deoxyribonucleotide. D. inhibition of xanthine oxidase as a treatment for gout. E. degradation of nucleoprotein. The correct answer is (C). Comments: A. Adenylate kinase does this. B. This is a methylation by thymidylate synthetase. C. Correct. Thioredoxin fluctuates between the sulfhydryl and disulfide forms. D. This is allopurinol. E. A variety of enzymes are involved here, but not thioredoxin. Return to Question Document cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq4.htm#Q4a

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1/14/2018

Purines and Pyrimidines Question 5

Question 5 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. The following enzymes are involved in the catabolism of AMP to uric acid. The correct order of their use is: 1. A deaminase 2. A nucleoside phosphorylase 3. A nucleotidase 4. Xanthine oxidase A. 1, 2, 3, 4. B. 1, 3, 2, 4 C. 1, 4, 2, 3 D. i3, 2, 1, 4 E. 3, 1, 2, 4 The correct answer is (B). Comments: AMP is first deaminated to IMP. Then it loses the phosphate and the sugar to form the free base, hypoxanthine. Both hypoxanthine and xanthine are oxidized by xantine oxidase. Return to Question Document cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq5.htm#Q5b

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1/14/2018

Purines and Pyrimidines Question 6

Question 6 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. The major control of de novo pyrimidine nucleotide synthesis in man is: A. feedback inhibition of glutamine-PRPP amidotransferase. B. feedback inhibition of aspartate transcarbamylase.< C. availability of N-acetyl glutamate. D. substrate availability. E. competitive inhibition of carbamoyl phosphate synthetase II. The correct answer is (E). Comments: A. This is the control for purine nucleotide synthesis. B. This is true in bacteria but not in man. C. This is the control of CPS I which leads to urea synthesis but NAG is not an activator of CPS II. D. Although this is true for some pathways, eg. degradation of purines, it is not true for this one. E. Correct. UTP is competitive with ATP in this reaction. Return to Question Document cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq6.htm#Q6e

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Purines and Pyrimidines Question 7

Question 7 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. In the catabolism of CTP: A. uric acid is an end product.. B. nitrogen will be released in the form of ammonia (ammonium ion). C. the nitrogen-containing ring will be oxidized. D. the final product will have the same type of nitrogen-containing ring as CTP. E. hypoxanthine will be an intermediate. The correct answer is (B). Comments: A. CTP is a pyrimidine, not a purine nucleotide. B. Correct. Both the side-chain and ring nitrogens are released as ammonia. C. Actually the ring has to be reduced by NADPH in order to be cleaved. D. The characteristic of pyrimidine catabolism is that the ring is cleaved. E. Not for a pyrimidine. Return to Question Document cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq7.htm#Q7b

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Purines and Pyrimidines Question 8

Question 8 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. IThe formation of dATP for DNA synthesis occurs primarily by: A. de novo synthsis beginning with dPRPP. B. salvaging using A-PRT. C. salvaging adenine using a nucleoside phosphorylase and dR 1-P. D. converting ADP to dADP using thioredoxin. E. converting dIMP to dAMP using 5,10-methylene THF. The correct answer is (D). Comments: A. De novo synthesis occurs with PRPP only. B. Very little adenine is salvaged. C. See above. What adenine is salvaged would be by PRT since the phosphorylase is used primarily for pyrimidines. D. Correct. The resulting dADP would be converted to the triphophate by a nucleoside diphosphate kinase. E. That pathway converts dUMP to dTMP. Return to Question Document cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq8.htm#Q8d

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Purines and Pyrimidines Question 9

Question 9 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. Which of the following would NOT be expected to contribute to hyperuricemia (gout)? A. Unusually high levels of PRPP B. Inhibition of xanthine oxidase C. Unusually high turnover of nucleic acids D. High activity of adenosine deaminase E. Deficiency of HG-PRT The correct answer is (B). Comments: Since the only control on uric acid synthesis is the availablility of substrates, anything which contributes to an increase in substrate concentration could lead to hyperuricemia. PRPP overcomes the normal feedback inhibition of synthesis. Both C and D would lead to more substrates. Since HG-PRT is an active consumer of PRPP and also the main salvage mechanism for both the guanine and adenine nucleotides, a deficiency would lead to high synthesis of nucleotides and, therefore, uric acid. An inhibitor of xanthine oxidase would specifically lower uric acid levels. Return to Question Document cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq9.htm#Q9d

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Purine and Pyrimidine Question 10

Question 10 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. Direct sources of purine ring atoms in the de novo synthesis of IMP include: 1. glutamine. 2. a component of the tetrahydrofolate one-carbon pool. 3. aspartate. 4. glycine. A. 1, 2 and 3 B. 1 and 3 C. 2 and 4 D. 4 only E. All four The correct answer is (E). Comments: 1. Nitrogens 3 and 9 2. Carbons 2 and 8 3. Nitrogen 1 4. Atoms 4, 5, and 7 Return to Question Document cna Last modified 1/6/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq10.htm#Q10e

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Purine and Pyrimidine Question 11

Question 11 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. A nucleoside phosphorylase: 1. cleaves a nucleoside with the production of ribose 1-phosphate. 2. is necessary for the major salvage pathway for pyrimidines. 3. is used in the degradation of purine nucleotides. 4. is responsible for the equilibration of nucleoside monophosphates and nucleoside diphosphate. A. 1, 2 and 3 B. 1 and 3 C. 2 and 4 D. 4 only E. All four The correct answer is (A). Comments: 1. As the name implies, the reaction is a phosphorolysis. 2. The pyrimidine salvage is a two-step pathway. The next step is catalyzed by a kinase. 3. This is true for the degradation of both purine and pyrimidine nucleosides 4. This equilibration is catalyzed by nucleoside monophosphate kinases. Return to Question Document cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq11.htm#Q11a

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Purine and Pyrimidine Question 12

Question 12 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. Methotrexate is an inhibitor of dihydrofolate reductase. Administration of methotrexate would inhibit: 1. de novo synthesis of UMP. 2. conversion of dUMP to dTMP. 3. conversion of IMP to GMP. 4. de novo synthesis of IMP. A. 1, 2 and 3 B. 1 and 3 C. 2 and 4 D. 4 only E. All four The correct answer is (C). Comments: 1. Pyrimidine synthesis doesn't involve the one-carbon pool. 2. The methyl group that appears in dTMP is synthesized during the transfer of the methylene group from the one-carbon pool. 3. This conversion involves an oxidation and an amination but no additional carbons. 4. Purine synthesis requires two components of the one-carbon pool. In the absence of this enzyme, dietary folate could not be reduced to the tetrahydro form necessary for carbon carriage. Return to Question Document cna Last modified 1/5/95

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Purine and Pyrimidine Question 13

Question 13 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. If a cell has an adequate supply of adenine nucleotides byt requires more guanine nucleotides for protein synthesis: 1. Glutamine-PRPP amidotransferase will not be fully inhibited. 2. AMP will be a feedback inhibitor of the condensation of IMP with aspartate. 3. ATP will stimulate the production of GMP from IMP. 4. ATP will inhibit nucleoside diphosphate reductase.. A. 1, 2 and 3 B. 1 and 3 C. 2 and 4 D. 4 only E. All four The correct answer is (A). Comments: 1. The synergistic effect of both AMP and GMP is needed for complete inhibition. 2. This assures that the limited amount of IMP formed will be channeled to the production of the guanine nucleotides. 3. ATP provides the energy for this branch. 4. The formation of dATP is not applicable in this situation. Return to Question Document cna Last modified 1/5/95

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Purine and Pyrimidine Question 14

Question 14 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. Major controls of de novo AMP synthesis include: 1. allosteric inhibition by GMP. 2. allosteric inhibition by AMP. 3. availability of PRPP. 4. stimulation by GTP.. A. 1, 2 and 3 B. 1 and 3 C. 2 and 4 D. 4 only E. All four The correct answer is (E). Comments: 1 and 2. Both of these are inhibitors of gln-PRPP amidotransferase and their effect is synergistic. 3. Since the kinetics of gln-PRPP amidotransferase are sygmoidal with respect to PRPP, and the concentrations are in the steep part of the curve, [PRPP] can significantly influence the rate. 4. GTP provides the energy for the branch from IMP to AMP. Return to Question Document cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq14.htm#Q14a

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Purines and Pyrimidines Question 15

Question 15 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. Aspartate plays a role in all of the following EXCEPT: A. conversion of UTP to CTP. B. de novo synthesis of AMP. C. de novo synthesis of orotic acid./a> D. maintenance of the adenine nucleotide pool by a salvage mechanism. E. the synthesis of most proteins. The correct answer is (A). Comments: A. UTP to CTP does involve an amination but the amino group used is the amide of glutamine. B. Aspartate provides nitrogen 1 of the purine ring. C. The whole aspartate molecule (at least the carbons and nitrogen) becomes part of the pyrimidine ring. D. Maintenance of the adenine nucleotide pool involves salvaging hypoxanthine and then converting IMP to AMP using aspartate. E. Most, probably all, proteins include aspartate. Return to Question Document cna Last modified 1/5/95

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Purines and Pyrimidines Question 16

Question 16 of 16 The answer you chose is highlighted in reverse video. The correct answer is in bold. Allopurinol is an inhibitor of xanthine oxidase. Administration of allopurinol to a patient with gout and normal HG-PRT levels would be expected to lead to all of the following EXCEPT: A. decreased de novo synthesis of IMP. B. decreased urate in the urine. C. an increase of hypoxanthine in the blood./a> D. increased levels of PRPP . E. tincreased xanthine in the blood. The correct answer is (D). Comments: A. As long as HG-PRT is available, the increased xanthine and hypoxanthine will be salvaged to GMP and IMP, both of which inhibit the rate limiting step of the synthesis.. B. Allopurinol directly inhibits the production of urate. C. Hypoxanthine is a substrate for the inhibited enzyme and, therefore, increases. D. As long as HG-PRT is available, the increasing xanthine and hypoxanthine will consume PRPP. Contrast this to the situation with the Lesch-Nyhan syndrome. E. Xanthine is a substrate for the inhibited enzyme. Return to Question Document Return to Topics cna Last modified 1/5/95

https://library.med.utah.edu/NetBiochem/pupyr/ppq16.htm#Q16d

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