Question 1

Which of the following best describes the difference between de novo nucleotide synthesis and salvage pathways?

Accepted Answer

De novo synthesis builds nucleotides from simple molecules, while salvage pathways recycle bases and nucleosides from degradation.

Question 2

A patient presents with severe joint pain and swelling in the big toe. Laboratory tests reveal elevated uric acid levels. Which metabolic disorder is most likely responsible for these symptoms?

Accepted Answer

Gout

Question 3

Which enzyme catalyzes the conversion of dUMP to dTMP, a reaction targeted by some chemotherapeutic agents?

Accepted Answer

Thymidylate synthase

Question 4

Which of the following is a correct equation for the reaction catalyzed by adenylate kinase?

Accepted Answer

$$AMP + ATP \rightarrow 2\ ADP$$

Question 5

A deficiency in hypoxanthine-guanine phosphoribosyltransferase (HGPRT) leads to which of the following disorders, characterized by self-mutilation and neurological symptoms?

Accepted Answer

Lesch-Nyhan syndrome

Question 6

Which of the following statements about purine and pyrimidine rings is correct?

Accepted Answer

Purines have a double-ring structure, while pyrimidines have a single-ring structure.

Question 7

Which of the following best explains why uric acid crystals precipitate in joints, leading to gout?

Accepted Answer

Uric acid has poor solubility in aqueous solutions, especially at lower temperatures found in extremities.

Question 8

Which of the following is NOT a function of nucleotides in the cell?

Accepted Answer

Serving as structural components of cell membranes

Question 9

Which of the following reactions is catalyzed by ribonucleotide reductase?

Accepted Answer

$$NDP \rightarrow dNDP$$

Question 10

A chemotherapeutic drug inhibits thymidylate synthase. What is the most direct effect of this inhibition on DNA synthesis?

Accepted Answer

Decreased production of dTMP, leading to impaired DNA synthesis

Question 11

Which of the following best describes the role of PRPP (phosphoribosyl pyrophosphate) in nucleotide metabolism?

Accepted Answer

It acts as a ribose-phosphate donor in both purine and pyrimidine nucleotide synthesis.

Question 12

Which of the following is a correct equation for the reaction catalyzed by nucleoside diphosphate kinase?

Accepted Answer

$$GDP + ATP \rightarrow GTP + ADP$$

Question 13

Which of the following best explains why rapidly dividing cancer cells are particularly sensitive to inhibitors of nucleotide synthesis?

Accepted Answer

They require large amounts of nucleotides for DNA replication.

Question 14

Which of the following is a pyrimidine base found in DNA but not in RNA?

Accepted Answer

Thymine

Question 15

A patient with Lesch-Nyhan syndrome is found to have increased de novo purine synthesis. Which of the following best explains this observation?

Accepted Answer

Deficiency of HGPRT leads to decreased purine salvage, increasing PRPP and stimulating de novo synthesis.

Question 16

Which of the following best describes the role of ATP in metabolism?

Accepted Answer

ATP acts as the primary energy currency, coupling exergonic and endergonic reactions.

Question 17

Which of the following is a correct description of the relationship between dUDP, dUMP, and dTMP in pyrimidine metabolism?

Accepted Answer

dUDP is converted to dUMP, which is then methylated by thymidylate synthase to form dTMP.

Question 18

Which of the following best explains why inhibition of ribonucleotide reductase would impair DNA synthesis but not RNA synthesis?

Accepted Answer

Ribonucleotide reductase converts ribonucleotides to deoxyribonucleotides, which are required for DNA but not RNA synthesis.

Question 19

Which of the following best describes the fate of purines during catabolism in humans?

Accepted Answer

Purines are degraded to uric acid, which is excreted in the urine.

Question 20

A researcher is studying the regulation of ribonucleotide reductase. Which of the following best describes how dATP regulates this enzyme?

Accepted Answer

dATP acts as an allosteric inhibitor, decreasing the activity of ribonucleotide reductase.

Nucleotide Metabolism: Structure, Synthesis, and Disorders

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