Nucleic Acid Metabolism MCQs (1) PDF

Image **Section A: Purine Anabolism (Synthesis)** 1. **Which of the following is the first committed step in purine nucleotide biosynthesis?**\ a) Conversion of IMP to AMP\ b) Formation of 5-phosphoribosylamine\ c) Formation of PRPP\ d) Conversion of GMP to XMP\ **Answer**...

Image **Section A: Purine Anabolism (Synthesis)** 1. **Which of the following is the first committed step in purine nucleotide biosynthesis?**\ a) Conversion of IMP to AMP\ b) Formation of 5-phosphoribosylamine\ c) Formation of PRPP\ d) Conversion of GMP to XMP\ **Answer**: b 2. **Which enzyme catalyzes the formation of 5-phosphoribosylamine in purine biosynthesis?**\ a) PRPP synthetase\ b) Amidophosphoribosyltransferase\ c) IMP dehydrogenase\ d) Adenylosuccinate synthetase\ **Answer**: b 3. **Which molecule serves as the precursor for the ribose sugar in purine biosynthesis?**\ a) Ribose-5-phosphate\ b) Fructose-6-phosphate\ c) PRPP\ d) XMP\ **Answer**: a 4. **What is the source of the nitrogen in the formation of 5-phosphoribosylamine?**\ a) Ammonia\ b) Glutamine\ c) Glycine\ d) Aspartate\ **Answer**: b 5. **Which purine base is formed first during de novo synthesis?**\ a) AMP\ b) GMP\ c) Hypoxanthine\ d) IMP\ **Answer**: d 6. **What is the function of PRPP in purine biosynthesis?**\ a) It acts as an energy donor.\ b) It serves as the sugar-phosphate donor.\ c) It catalyzes the addition of nitrogen to form purine bases.\ d) It breaks down purine nucleotides.\ **Answer**: b 7. **Which amino acid contributes both nitrogen and carbon atoms to the purine ring?**\ a) Glycine\ b) Aspartate\ c) Glutamine\ d) Alanine\ **Answer**: a 8. **The enzyme IMP dehydrogenase is responsible for the conversion of IMP to which compound?**\ a) XMP\ b) AMP\ c) GMP\ d) Uric acid\ **Answer**: a 9. **GMP is synthesized from which intermediate in the purine biosynthesis pathway?**\ a) AMP\ b) XMP\ c) IMP\ d) PRPP\ **Answer**: b **Section B: Purine Catabolism (Breakdown)** 10. **Which enzyme catalyzes the conversion of adenosine to inosine in purine catabolism?**\ a) Adenosine deaminase\ b) Xanthine oxidase\ c) Guanine deaminase\ d) Purine nucleoside phosphorylase\ **Answer**: a 11. **What is the final product of purine catabolism in humans?**\ a) Urea\ b) Uric acid\ c) Ammonia\ d) Allantoin\ **Answer**: b 12. **Xanthine oxidase is involved in the conversion of xanthine to which compound?**\ a) Uric acid\ b) Hypoxanthine\ c) IMP\ d) GMP\ **Answer**: a 13. **What is the major clinical condition associated with excess uric acid production?**\ a) Gout\ b) Hyperammonemia\ c) Uremia\ d) Phenylketonuria\ **Answer**: a 14. **The conversion of AMP to IMP during purine degradation is catalyzed by which enzyme?**\ a) AMP deaminase\ b) IMP dehydrogenase\ c) Adenylosuccinate synthetase\ d) Purine nucleoside phosphorylase\ **Answer**: a 15. **Which compound is a substrate for the enzyme purine nucleoside phosphorylase?**\ a) Adenosine\ b) Inosine\ c) Hypoxanthine\ d) Uric acid\ **Answer**: b 16. **Hypoxanthine is converted to xanthine by which enzyme?**\ a) Xanthine oxidase\ b) Hypoxanthine-guanine phosphoribosyltransferase\ c) Adenosine deaminase\ d) AMP deaminase\ **Answer**: a 17. **Which of the following is NOT an intermediate in purine catabolism?**\ a) Hypoxanthine\ b) Xanthine\ c) Urea\ d) Uric acid\ **Answer**: c **Section C: Regulation and Disorders** 18. **Which molecule acts as a feedback inhibitor of PRPP synthetase?**\ a) ATP\ b) GMP\ c) IMP\ d) All of the above\ **Answer**: d 19. **What is the salvage pathway for purine nucleotides?**\ a) Synthesis of purines from PRPP and free bases\ b) Conversion of purines into uric acid\ c) Conversion of AMP to IMP\ d) All of the above\ **Answer**: a 20. **A key feature of purine nucleotide synthesis is that it occurs mainly in:**\ a) Liver\ b) Kidney\ c) Muscle\ d) Brain\ **Answer**: a 21. **The purine ring is assembled on which molecule?**\ a) PRPP\ b) Ribose-5-phosphate\ c) XMP\ d) ATP\ **Answer**: a 22. **Which of the following is true about purine catabolism in humans?**\ a) Urea is the final product.\ b) Purines are excreted as uric acid.\ c) Ammonia is the major end product.\ d) Guanine is directly excreted.\ **Answer**: b **[Other questions:]** 23. **Purine nucleotides consist of which nitrogenous bases?**\ a) Adenine and Cytosine\ b) Adenine and Guanine\ c) Guanine and Uracil\ d) Thymine and Adenine\ **Answer**: b 24. **What does PRPP stand for in purine metabolism?**\ a) Phosphoribosyl pyrophosphate\ b) Purine ribose phosphate pyrophosphate\ c) Phosphoribosyl phosphate pathway\ d) Purine ribose phosphate\ **Answer**: a 25. **Which amino acid is the primary nitrogen donor in purine biosynthesis?**\ a) Glycine\ b) Glutamine\ c) Alanine\ d) Serine\ **Answer**: b 26. **The purine ring structure is built on which sugar molecule?**\ a) Glucose\ b) Ribose\ c) Fructose\ d) Galactose\ **Answer**: b 27. **Which of the following is a precursor for both purine and pyrimidine synthesis?**\ a) PRPP\ b) XMP\ c) Uric acid\ d) Hypoxanthine\ **Answer**: a 28. **Which of the following is NOT involved in purine biosynthesis?**\ a) Glycine\ b) Aspartate\ c) Tyrosine\ d) Glutamine\ **Answer**: c 29. **Which organ in humans is primarily responsible for purine synthesis?**\ a) Brain\ b) Liver\ c) Kidney\ d) Muscle\ **Answer**: b 30. **What is the main purpose of the salvage pathway in purine metabolism?**\ a) To synthesize purines from scratch\ b) To recycle free purine bases into nucleotides\ c) To convert purines into uric acid\ d) To produce ATP from purine bases\ **Answer**: b