Purines and Pyrimidines Quiz
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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.
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Involve(s) reduction and cleavage of the nitrogen-containing ring
- A. Catabolism of guanine
- B. Catabolism of uracil
- 1. A only
- 2. B only
- 3. Both A and B
- 4. Neither A or B
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Orotic acid would be an intermediate.
- A. Catabolism of guanine
- B. Catabolism of uracil
- 1. A only
- 2. B only
- 3. Both A and B
- 4. Neither A or B
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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.
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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. 3, 2, 1, 4
- E. 3, 1, 2, 4
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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.
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In the catabolism of CTP:
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- 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. hpoxanthine will be an intermediate.
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The formation of dATP for DNA synthesis occurs primarily by:
- A. de novo synthesis beginning with dPRPP.
- B. salvaging adenine 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.
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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.
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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
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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
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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
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If a cell has an adequate supply of adenine nucleotides but 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
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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
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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.
- D. maintenances of the adenine nucleotide pool by a salvage mechanism.
- E. the synthesis of most proteins.
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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 in hypoxanthine in the blood.
- D. increased levels of PRPP.
- E. increased xanthine in the blood.
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Last modified 1/5/95