General reactions of amino acid metabolism MCQs With Answer

Introduction:

Mastering general reactions of amino acid metabolism is essential for B. Pharm students preparing for pharmacology, biochemistry, and clinical coursework. This focused guide covers transamination, deamination, oxidative deamination, PLP-dependent reactions, urea cycle regulation, and connections to gluconeogenesis and ketogenesis. Key concepts include aminotransferases (ALT/AST), glutamate dehydrogenase, carbamoyl phosphate synthetase I, and one-carbon transfers via SAM and folate pathways. Practical clinical links—hyperammonemia, phenylketonuria, maple syrup urine disease, and diagnostic enzyme markers—are emphasized to aid application in therapeutics. Clear MCQs reinforce mechanism-focused learning and exam readiness. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which reaction best describes transamination in amino acid metabolism?

• Removal of amino group as free ammonia
• Transfer of amino group to alpha-ketoglutarate
• Oxidative decarboxylation of amino acids
• Formation of urea from two ammonia molecules

Correct Answer: Transfer of amino group to alpha-ketoglutarate

Q2. Which cofactor is essential for aminotransferase (transaminase) activity?

• Flavin adenine dinucleotide (FAD)
• Nicotinamide adenine dinucleotide (NAD+)
• Pyridoxal phosphate (PLP)
• Coenzyme A (CoA)

Correct Answer: Pyridoxal phosphate (PLP)

Q3. Oxidative deamination of glutamate primarily produces which pair of products?

• Glutamine and carbon dioxide
• Alpha-ketoglutarate and ammonium ion
• Ornithine and urea
• Aspartate and fumarate

Correct Answer: Alpha-ketoglutarate and ammonium ion

Q4. Which enzyme catalyzes the oxidative deamination of glutamate?

• Alanine aminotransferase (ALT)
• Aspartate aminotransferase (AST)
• Glutamate dehydrogenase
• Glutamine synthetase

Correct Answer: Glutamate dehydrogenase

Q5. Which amino acid is the primary nitrogen donor for most transamination reactions?

• Glycine
• Alanine
• Glutamate
• Serine

Correct Answer: Glutamate

Q6. Which pair of enzymes are commonly used as clinical markers of liver damage?

• Glutamine synthetase and carbamoyl phosphate synthetase I
• Alanine aminotransferase (ALT) and aspartate aminotransferase (AST)
• Phenylalanine hydroxylase and tyrosine aminotransferase
• Ornithine transcarbamylase and arginase

Correct Answer: Alanine aminotransferase (ALT) and aspartate aminotransferase (AST)

Q7. In the glucose-alanine cycle, alanine carries nitrogen from muscle to liver and is converted to which compound in the liver?

• Pyruvate
• Oxaloacetate
• Fumarate
• Acetoacetate

Correct Answer: Pyruvate

Q8. Which enzyme initiates the urea cycle by synthesizing carbamoyl phosphate?

• Ornithine transcarbamylase
• Arginase
• Carbamoyl phosphate synthetase I (CPS I)
• Argininosuccinate synthetase

Correct Answer: Carbamoyl phosphate synthetase I (CPS I)

Q9. What is the allosteric activator required for carbamoyl phosphate synthetase I activity?

• ATP
• Arginine
• N-acetylglutamate (NAG)
• Fumarate

Correct Answer: N-acetylglutamate (NAG)

Q10. Which amino acid is exclusively ketogenic (cannot be converted to glucose)?

• Leucine
• Isoleucine
• Phenylalanine
• Alanine

Correct Answer: Leucine

Q11. Phenylalanine is hydroxylated to tyrosine by which enzyme?

• Phenylalanine hydroxylase
• Tyrosine aminotransferase
• Phenylalanine decarboxylase
• Monoamine oxidase

Correct Answer: Phenylalanine hydroxylase

Q12. A deficiency of phenylalanine hydroxylase leads to accumulation of which metabolite?

• Tyramine
• Phenylpyruvate (phenyl ketones)
• Homogentisate
• Succinyl-CoA

Correct Answer: Phenylpyruvate (phenyl ketones)

Q13. Which disorder results from branched-chain α-ketoacid dehydrogenase deficiency?

• Phenylketonuria (PKU)
• Maple syrup urine disease (MSUD)
• Alkaptonuria
• Homocystinuria

Correct Answer: Maple syrup urine disease (MSUD)

Q14. The trans-sulfuration pathway converts homocysteine to which amino acid?

• Methionine
• Cysteine
• Serine
• Glycine

Correct Answer: Cysteine

Q15. S-adenosylmethionine (SAM) functions primarily as which type of donor in metabolism?

• Acetyl donor
• Methyl donor
• Phosphate donor
• Ammonia donor

Correct Answer: Methyl donor

Q16. Which amino acid provides the one-carbon units for folate-dependent reactions after conversion to N5,N10-methylene-THF?

• Alanine
• Glycine
• Serine
• Tryptophan

Correct Answer: Serine

Q17. Which enzyme converts glutamine to glutamate and free ammonia in peripheral tissues?

• Glutamate dehydrogenase
• Glutamine synthetase
• Glutaminase
• Glutamate decarboxylase

Correct Answer: Glutaminase

Q18. Which amino acid is the immediate precursor for nitric oxide synthesis?

• Arginine
• Ornithine
• Citrulline
• Glutamate

Correct Answer: Arginine

Q19. In the urea cycle, ornithine combines with carbamoyl phosphate to form which product?

• Arginine
• Ornithine transcarbamylate
• Ornithine carbamate
• Citrulline

Correct Answer: Citrulline

Q20. Which reaction type removes an amino group as free ammonia rather than transferring it?

• Transamination
• Reductive amination
• Deamination
• Amidation

Correct Answer: Deamination

Q21. Which amino acid is the major carrier of ammonia in the bloodstream to the liver?

• Alanine
• Glutamate
• Glutamine
• Leucine

Correct Answer: Glutamine

Q22. Which cofactor is required by serine hydroxymethyltransferase for one-carbon metabolism?

• PLP (pyridoxal phosphate)
• Biotin
• FAD
• Thiamine pyrophosphate

Correct Answer: PLP (pyridoxal phosphate)

Q23. Which product from tyrosine catabolism accumulates in alkaptonuria?

• Homogentisic acid
• Fumarylacetoacetate
• Melanin
• S-adenosylmethionine

Correct Answer: Homogentisic acid

Q24. Which enzyme converts phenylalanine to phenylpyruvate in untreated phenylketonuria?

• Phenylalanine hydroxylase
• Transaminase (aminotransferase)
• Phenylalanine decarboxylase
• Tyrosine aminotransferase

Correct Answer: Transaminase (aminotransferase)

Q25. The aminotransferase reaction mechanism involves formation of which intermediate between PLP and amino acid?

• Thioester
• Schiff base (aldimine)
• Carbamate
• Enamine

Correct Answer: Schiff base (aldimine)

Q26. Which amino acids yield acetyl-CoA or acetoacetate and are therefore ketogenic?

• Leucine and lysine
• Glutamate and aspartate
• Alanine and serine
• Glycine and proline

Correct Answer: Leucine and lysine

Q27. Which TCA cycle intermediate is directly formed from the catabolism of aspartate?

• Alpha-ketoglutarate
• Oxaloacetate
• Succinyl-CoA
• Fumarate

Correct Answer: Oxaloacetate

Q28. Which enzyme converts ammonia and glutamate to glutamine, consuming ATP?

• Glutaminase
• Glutamine synthetase
• Glutamate dehydrogenase
• Carbamoyl phosphate synthetase I

Correct Answer: Glutamine synthetase

Q29. Which amino acid is the primary precursor for creatine synthesis?

• Arginine
• Glycine
• Methionine (as SAM)
• All of the above

Correct Answer: All of the above

Q30. In hyperammonemia, which enzyme deficiency causes an X-linked disorder with high orotic acid levels?

• Carbamoyl phosphate synthetase I deficiency
• Ornithine transcarbamylase deficiency
• Arginase deficiency
• Argininosuccinate lyase deficiency

Correct Answer: Ornithine transcarbamylase deficiency

Q31. Which amino acid is converted to pyruvate by serine dehydratase?

• Serine
• Threonine
• Glycine
• Alanine

Correct Answer: Serine

Q32. Which enzyme catalyzes the last step of the urea cycle to release urea?

• Argininosuccinate synthetase
• Argininosuccinate lyase
• Arginase
• Ornithine transcarbamylase

Correct Answer: Arginase

Q33. Which amino acid serves as the nitrogen donor for asparagine synthesis in most tissues?

• Glutamine
• Glutamate
• Ammonia
• Asparagine synthase uses aspartate and glutamine

Correct Answer: Asparagine synthase uses aspartate and glutamine

Q34. Which reaction links amino acid catabolism to gluconeogenesis by producing oxaloacetate?

• Transamination of alanine to pyruvate
• Transamination of aspartate to oxaloacetate
• Oxidative deamination of glutamate to alpha-ketoglutarate
• Decarboxylation of leucine

Correct Answer: Transamination of aspartate to oxaloacetate

Q35. The branched-chain amino acids (leucine, isoleucine, valine) are primarily metabolized in which tissue?

• Liver
• Kidney
• Muscle
• Brain

Correct Answer: Muscle

Q36. Which cofactor is required for branched-chain α-ketoacid dehydrogenase complex activity?

• Biotin
• Thiamine pyrophosphate (TPP)
• PLP
• Folate

Correct Answer: Thiamine pyrophosphate (TPP)

Q37. Which amino acid catabolic product enters the TCA cycle as succinyl-CoA?

• Methionine via propionyl-CoA
• Phenylalanine directly as fumarate
• Leucine as acetyl-CoA
• Alanine as pyruvate

Correct Answer: Methionine via propionyl-CoA

Q38. Which enzyme deficiency leads to elevated homocysteine and risk of vascular disease?

• Cystathionine β-synthase deficiency (homocystinuria)
• Phenylalanine hydroxylase deficiency
• Arginase deficiency
• Ornithine transcarbamylase deficiency

Correct Answer: Cystathionine β-synthase deficiency (homocystinuria)

Q39. Which amino acid is both gluconeogenic and a precursor for heme synthesis?

• Glycine
• Leucine
• Lysine
• Tyrosine

Correct Answer: Glycine

Q40. The enzyme alanine aminotransferase (ALT) catalyzes the reversible transfer between alanine and which keto acid?

• Oxaloacetate
• Alpha-ketoglutarate
• Pyruvate
• Succinyl-CoA

Correct Answer: Pyruvate

Q41. Which amino acid degradation yields fumarate as an intermediate?

• Phenylalanine and tyrosine
• Leucine and lysine
• Methionine and threonine
• Alanine and glycine

Correct Answer: Phenylalanine and tyrosine

Q42. During fasting, increased proteolysis supplies amino acids for gluconeogenesis primarily through which mechanism?

• Direct conversion of amino acids to ketone bodies
• Transamination to form TCA cycle intermediates and pyruvate
• Storage as glycogen
• Conversion to triglycerides for energy

Correct Answer: Transamination to form TCA cycle intermediates and pyruvate

Q43. Which enzyme catalyzes the reversible interconversion of glutamate and glutamine?

• Glutamate dehydrogenase and glutamine synthetase/glutaminase pair
• Alanine aminotransferase only
• Carbamoyl phosphate synthetase I
• Arginase

Correct Answer: Glutamate dehydrogenase and glutamine synthetase/glutaminase pair

Q44. Nitrogen from aspartate enters the urea cycle at which intermediate?

• Carbamoyl phosphate
• Arginase
• Argininosuccinate
• Ornithine

Correct Answer: Argininosuccinate

Q45. Which reaction in amino acid metabolism requires biotin as a cofactor?

• Carboxylation of pyruvate to oxaloacetate
• Transamination of alanine
• Methylation by SAM
• Oxidative deamination of glutamate

Correct Answer: Carboxylation of pyruvate to oxaloacetate

Q46. In liver mitochondria, which amino acid-derived intermediate provides nitrogen for urea synthesis via transamination to glutamate?

• Alanine to pyruvate
• Aspartate to oxaloacetate
• Branched-chain amino acids to branched-chain keto acids
• None; only free ammonia is used

Correct Answer: Aspartate to oxaloacetate

Q47. Which enzyme deficiency causes accumulation of fumarylacetoacetate leading to liver failure and dark urine?

• Homogentisate oxidase deficiency (alkaptonuria)
• Fumarylacetoacetate hydrolase deficiency (tyrosinemia type I)
• Tyrosine aminotransferase deficiency
• Phenylalanine hydroxylase deficiency

Correct Answer: Fumarylacetoacetate hydrolase deficiency (tyrosinemia type I)

Q48. Which amino acid is the precursor for porphyrin (heme) synthesis along with succinyl-CoA?

• Glycine
• Glutamate
• Cysteine
• Proline

Correct Answer: Glycine

Q49. Which pathway regenerates tetrahydrofolate derivatives used for nucleotide and amino acid metabolism?

• Folate cycle (one-carbon metabolism)
• Urea cycle
• Glycolysis
• Fatty acid β-oxidation

Correct Answer: Folate cycle (one-carbon metabolism)

Q50. Which amino acid is converted to oxaloacetate via transamination and can be used for gluconeogenesis?

• Alanine
• Aspartate
• Leucine
• Lysine

Correct Answer: Aspartate

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com