Life Sciences Multiple Choice Questions on “Nucleotide Metabolism”.
1. Salvage pathway is used in the synthesis of ___________
A. Amino acid
B. Carbohydrate
C. Nucleotide
D. Fatty acid
Answer: C
Clarification: Nucleotide synthesis takes place by two pathways: salvage pathways and de novo pathways. In de novo pathway pyrimidine base is assembled first and then attached to ribose while in the salvage pathway preformed base is recovered and reconnected to a ribose sugar.
2. All deoxyribonucleotide is synthesized by the ribonucleotides.
A. True
B. False
Answer: A
Clarification: Deoxyribonucleotide cannot be synthesized directly from de novo and salvage pathway but it is generated by the reduction of ribose from the corresponding ribonucleotide.
3. Name the precursor of RNA?
A. Glutamine
B. Cytidine
C. Orotidylate
D. Uridylate
Answer: D
Clarification: Uridylate or UMP is a major pyrimidine nucleotide formed by the decarboxylation of orotidylate (OMP) during pyrimidine synthesis. UMP further gets converted to a ribonucleotide, and act as a precursor of RNA.
4. The activity of which of the following enzyme is inhibited by the chemotherapeutic agent during deoxyribonucleotide synthesis?
A. Dihydrofolate reductase
B. Ribonucleotide reductase
C. Thymidylate synthase
D. CTP synthetase
Answer: A
Clarification: Methotrexate and aminopterin are two anticancer drugs which inhibits the activity of dihydrofolate reductase. This will stop the formation of deoxyribonucleotide or DNA and the growth of the cell stops.
5. Which of the following is not the precursor of a purine ring?
A. Glutamine
B. Lysine
C. Glycine
D. Aspartate
Answer: B
Clarification: Purine ring is derived from various precursors like glutamine (N2 and N9), glycine (C4, C5, and N7), aspartate (N1), Co2 (C6), folate (C2 and C8). Except for lysine, all are the precursor of purine ring.
6. During purine synthesis the activity of amidotransferase enzyme is inhibited by the antitumor agent, mark the correct one.
A. Aminopterin
B. Methotrexate
C. Texol
D. Azaserine
Answer: D
Clarification: Azaserine is the structural analog of glutamine and works as an antitumor agent by preventing the activity of enzyme amidotransferase which in turn block purine synthesis.
7. What is the final product of purine degradation in mammals?
A. Guanine
B. Inosine
C. Uric acid
D. Hypoxanthine
Answer: C
Clarification: Punine nucleotides are sequentially degraded from inosine to hypoxanthine and guanine and finally to the uric acid which is excreted with the urine in the human being while in some other animals it is further degraded to urea and ammonia.
8. Name the deficiency in which T and B lymphocyte do not develop properly?
A. XLA
B. CVID
C. SCID
D. Multiple myeloma
Answer: C
Clarification: Severe combined immunodeficiency syndrome (SCID. is caused by the deficiency of adenosine deaminase which leads to increase in the cellular concentration of dATP. High level of dATP reduces dNTPs in T-lymphocytes.
9. Which of the following disorder is caused due to the high serum level of urate?
A. Gout
B. Galectosemia
C. Cystic fibrosis
D. Maple syrup urine disease
Answer: A
Clarification: Gout is caused due to the high amount of uric acid, which is the product of purine degradation. It involves precipitation of sodium urate crystals in the joints and causes inflammation.
10. Name the genetic disorder which is caused by the deficiency of enzyme HGPRT?
A. SCID
B. Lesch-Nyhan syndrome
C. Cystic fibrosis
D. Down syndrome
Answer: B
Clarification: This genetic disorder is caused by the deficiency of enzyme hypoxanthine-guanine phosphoribosyl-transferase (HGPRT). This results in increase rate of purine biosynthesis by de novo pathway and overproduction of urate.
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