$$\text{Guanine} + \text{PRPP} \longrightarrow \text{GMP} + \text{PP}_i$$

Question 1

Which of the following is required for both purine and pyrimidine biosynthesis?

Accepted Answer

5-phosphoribosyl 1-pyrophosphate (PRPP)

Question 2

A patient presents with high levels of orotic acid in the urine and megaloblastic anemia. Which enzyme deficiency is most likely responsible?

Accepted Answer

UMP synthase

Question 3

Which of the following drugs acts as a suicide inhibitor of thymidylate synthase, blocking dTMP synthesis in cancer cells?

Accepted Answer

FdUMP (Fluorouracil)

Question 4

What is the base of inosine monophosphate (IMP) called?

Accepted Answer

Hypoxanthine

Question 5

Which enzyme catalyzes the conversion of ribonucleotides (NDPs) to deoxyribonucleotides (dNDPs)?

Accepted Answer

Ribonucleotide reductase

Question 6

A defect in which enzyme leads to Lesch-Nyhan syndrome, characterized by self-mutilation and excess uric acid?

Accepted Answer

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)

Question 7

Which of the following is a product of purine nucleotide degradation in humans?

Accepted Answer

Uric acid

Question 8

Which molecule is used to salvage adenine to form AMP in mammals?

Accepted Answer

PRPP (5-phosphoribosyl 1-pyrophosphate)

Question 9

Which of the following is a key regulatory molecule that activates pyrimidine biosynthesis?

Accepted Answer

PRPP

Question 10

Which enzyme is inhibited by methotrexate, leading to decreased dTMP synthesis?

Accepted Answer

Dihydrofolate reductase (DHFR)

Question 11

Which of the following is the correct reaction for the salvage of guanine?

Accepted Answer

$$	ext{Guanine} + 	ext{PRPP} \longrightarrow 	ext{GMP} + 	ext{PP}_i$$

Question 12

Which of the following is a symptom of gout?

Accepted Answer

Inflamed and painful joints due to uric acid crystal deposition

Question 13

Which of the following is NOT a precursor for purine ring biosynthesis?

Accepted Answer

Malonyl-CoA

Question 14

Which enzyme is responsible for converting dihydrofolate back to tetrahydrofolate?

Accepted Answer

Dihydrofolate reductase

Question 15

Which of the following statements about purine biosynthesis regulation is correct?

Accepted Answer

High levels of AMP, GMP, IMP, and ADP inhibit purine biosynthesis

Question 16

Which of the following is a direct product of the action of ribonucleotide reductase on UDP?

Accepted Answer

$$	ext{dUDP}$$

Question 17

Which of the following is a function of allopurinol in the treatment of gout?

Accepted Answer

Inhibits xanthine oxidase, reducing uric acid production

Question 18

Which of the following is true regarding the difference between purine and pyrimidine degradation?

Accepted Answer

Purine degradation produces uric acid, while pyrimidine degradation produces malonyl-CoA

Question 19

Which of the following is a correct step in the formation of dTMP from dUMP?

Accepted Answer

dUMP is methylated by thymidylate synthase using N$$^5$$,N$$^{10}-$$methylene tetrahydrofolate as a cofactor

Nucleotide Metabolism: Biosynthesis, Regulation, and Clinical Relevance

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