Purines and Pyrimidines Quiz

Question 1 of 16

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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.

Question 2 of 13

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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

Question 3 of 16

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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

Question 4 of 16

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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.

Question 5 of 16

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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

Question 6 of 16

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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.

Question 7 of 16

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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. hpoxanthine will be an intermediate.

Question 8 of 16

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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.

Question 9 of 16

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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.

Question 10 of 16

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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

Question 11 of 16

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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

Question 12 of 16

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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

Question 13 of 16

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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

Question 14 of 16

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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

Question 15 of 16

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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.

Question 16 of 16

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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