Understanding the biological role of amino acids is essential for B. Pharm students preparing for pharmacology, biochemistry, and therapeutics. This SEO-focused guide on Biological role of amino acids MCQs With Answer explains how amino acids act as protein building blocks, neurotransmitter precursors, metabolic intermediates, and regulators of drug metabolism. Topics covered include essential versus non-essential amino acids, nitrogen balance, urea cycle, gluconeogenesis, ketogenesis, post-translational modifications, and clinical correlations relevant to pharmacy practice. Each question emphasizes mechanism, pathway, and therapeutic relevance to deepen conceptual understanding and exam readiness. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which of the following is the primary biological role of amino acids?
- Acting solely as energy storage molecules
- Serving as building blocks for proteins and precursors for key metabolites
- Forming the lipid bilayer of cell membranes
- Transporting oxygen in the blood
Correct Answer: Serving as building blocks for proteins and precursors for key metabolites
Q2. Which amino acid is a direct precursor for the neurotransmitter serotonin?
- Tyrosine
- Tryptophan
- Glutamate
- Histidine
Correct Answer: Tryptophan
Q3. Which amino acid is essential for adults and must be obtained from the diet?
- Alanine
- Leucine
- Glycine
- Glutamine
Correct Answer: Leucine
Q4. Which amino acid serves as the primary nitrogen donor in transamination reactions?
- Lysine
- Glutamate
- Phenylalanine
- Isoleucine
Correct Answer: Glutamate
Q5. Phenylketonuria (PKU) is caused by a defect in the metabolism of which amino acid?
- Methionine
- Phenylalanine
- Tryptophan
- Arginine
Correct Answer: Phenylalanine
Q6. Which amino acid is the precursor for nitric oxide synthesis?
- Arginine
- Proline
- Serine
- Cysteine
Correct Answer: Arginine
Q7. Which amino acid contributes to disulfide bond formation critical for protein tertiary structure?
- Serine
- Cysteine
- Asparagine
- Valine
Correct Answer: Cysteine
Q8. In gluconeogenesis, which amino acids are considered glucogenic?
- Amino acids that can be converted to acetyl-CoA only
- Amino acids that can be converted to glucose precursors such as pyruvate or TCA intermediates
- Amino acids that form ketogenic bodies exclusively
- Amino acids that are only used for protein synthesis
Correct Answer: Amino acids that can be converted to glucose precursors such as pyruvate or TCA intermediates
Q9. Which pair of amino acids are strictly ketogenic (cannot form glucose)?
- Leucine and lysine
- Alanine and serine
- Valine and isoleucine
- Glutamate and glutamine
Correct Answer: Leucine and lysine
Q10. Which amino acid is the major carrier of nitrogen in the blood from peripheral tissues to liver?
- Alanine
- Glycine
- Histidine
- Methionine
Correct Answer: Alanine
Q11. Which amino acid is methyl donor via S-adenosylmethionine (SAM) pathway?
- Tryptophan
- Methionine
- Threonine
- Proline
Correct Answer: Methionine
Q12. Tyrosine is a precursor for which of the following groups of molecules?
- Purines and pyrimidines
- Catecholamines (dopamine, norepinephrine, epinephrine) and thyroid hormones
- Fatty acids and cholesterol
- Histamine and serotonin
Correct Answer: Catecholamines (dopamine, norepinephrine, epinephrine) and thyroid hormones
Q13. Which cofactor is required for transamination reactions catalyzed by aminotransferases?
- FAD
- Pyridoxal phosphate (PLP)
- Biotin
- NAD+
Correct Answer: Pyridoxal phosphate (PLP)
Q14. Which amino acid is the precursor for the antioxidant glutathione?
- Leucine
- Glutamate (as part of synthesis involving cysteine and glycine)
- Phenylalanine
- Asparagine
Correct Answer: Glutamate (as part of synthesis involving cysteine and glycine)
Q15. Which amino acid is hydroxylated by prolyl hydroxylase during collagen maturation?
- Proline
- Tyrosine
- Histidine
- Alanine
Correct Answer: Proline
Q16. Which amino acid side chain has an imidazole group and contributes to enzyme active site acid–base catalysis?
- Histidine
- Lysine
- Aspartate
- Valine
Correct Answer: Histidine
Q17. The urea cycle primarily disposes of which element derived from amino acid catabolism?
- Carbon
- Nitrogen (ammonia)
- Phosphorus
- Sulfur
Correct Answer: Nitrogen (ammonia)
Q18. Which enzyme deficiency leads to hyperammonemia type I by impairing the first step of the urea cycle?
- Ornithine transcarbamylase
- Carbamoyl phosphate synthetase I
- Arginase
- Argininosuccinate lyase
Correct Answer: Carbamoyl phosphate synthetase I
Q19. Which amino acid is involved in one-carbon metabolism and is a precursor for purine synthesis?
- Glycine
- Leucine
- Isoleucine
- Tyrosine
Correct Answer: Glycine
Q20. Which amino acid contains a sulfur atom and participates in methyl group transfers after conversion to SAM?
- Cysteine
- Methionine
- Serine
- Threonine
Correct Answer: Methionine
Q21. Which transport mechanism moves amino acids across cell membranes using sodium cotransport in the intestine?
- Simple diffusion
- Sodium-dependent secondary active transporters
- ABC ATP-dependent transporters
- Endocytosis
Correct Answer: Sodium-dependent secondary active transporters
Q22. Which amino acid is a direct precursor for histamine?
- Glutamate
- Histidine
- Tryptophan
- Arginine
Correct Answer: Histidine
Q23. In amino acid catabolism, transamination transfers an amino group to which keto acid to form glutamate?
- Oxaloacetate
- Alpha-ketoglutarate
- Pyruvate
- Succinyl-CoA
Correct Answer: Alpha-ketoglutarate
Q24. Cysteine is semi-essential because it can be synthesized from which essential amino acid?
- Methionine
- Phenylalanine
- Valine
- Threonine
Correct Answer: Methionine
Q25. Which amino acid side chain is positively charged at physiological pH and often binds negatively charged substrates?
- Aspartate
- Lysine
- Phenylalanine
- Proline
Correct Answer: Lysine
Q26. Which amino acid is converted to acetyl-CoA and can contribute to ketone body formation?
- Leucine
- Alanine
- Asparagine
- Glutamine
Correct Answer: Leucine
Q27. Which amino acid is most commonly phosphorylated during signal transduction on proteins?
- Glycine
- Serine
- Proline
- Valine
Correct Answer: Serine
Q28. Which amino acid derivative acts as a neurotransmitter and is synthesized from glutamate?
- GABA (gamma-aminobutyric acid)
- Serotonin
- Dopamine
- Acetylcholine
Correct Answer: GABA (gamma-aminobutyric acid)
Q29. Which amino acid is a precursor for creatine synthesis important in muscle energy metabolism?
- Glycine and arginine (with methionine providing methyl groups)
- Phenylalanine alone
- Leucine and isoleucine
- Threonine and valine
Correct Answer: Glycine and arginine (with methionine providing methyl groups)
Q30. The isoelectric point (pI) of an amino acid is defined as:
- The pH at which the amino acid is fully protonated
- The pH at which the amino acid carries no net electrical charge
- The pH at which the amino acid is completely deprotonated
- The pH where solubility is maximal
Correct Answer: The pH at which the amino acid carries no net electrical charge
Q31. Which amino acid modification is critical for anchoring some proteins to membranes via glycosylphosphatidylinositol (GPI) anchors?
- Ubiquitination of lysine residues
- Addition of a GPI anchor to a C-terminus glycine
- Phosphorylation of serine residues
- Nitration of tyrosine residues
Correct Answer: Addition of a GPI anchor to a C-terminus glycine
Q32. Which amino acid is directly involved in bile acid conjugation (taurine conjugation)?
- Arginine
- Taurine (derived from cysteine)
- Leucine
- Phenylalanine
Correct Answer: Taurine (derived from cysteine)
Q33. Which amino acid is required for synthesis of porphyrins and thus heme?
- Glycine (with succinyl-CoA)
- Methionine
- Valine
- Threonine
Correct Answer: Glycine (with succinyl-CoA)
Q34. Which enzyme catalyzes the deamination of glutamate to release ammonia for urea cycle entry?
- Glutamate dehydrogenase
- Glutamine synthetase
- Alanine aminotransferase
- Phenylalanine hydroxylase
Correct Answer: Glutamate dehydrogenase
Q35. Branched-chain amino acids (BCAAs) are primarily metabolized in which tissue?
- Liver
- Muscle
- Adipose tissue
- Kidney
Correct Answer: Muscle
Q36. Which amino acid contributes sulfur for synthesis of coenzyme A and lipoic acid indirectly through methionine?
- Leucine
- Methionine
- Tyrosine
- Alanine
Correct Answer: Methionine
Q37. Which amino acid residue often undergoes N-linked glycosylation in secreted proteins?
- Asparagine (N-linked)
- Serine
- Tyrosine
- Proline
Correct Answer: Asparagine (N-linked)
Q38. Which amino acid is a precursor for melatonin synthesis in the pineal gland?
- Tyrosine
- Tryptophan
- Histidine
- Arginine
Correct Answer: Tryptophan
Q39. Which metabolic fate describes amino acids that give rise to both glucose and ketone precursors?
- Exclusively glucogenic
- Exclusively ketogenic
- Both glucogenic and ketogenic
- Neither glucogenic nor ketogenic
Correct Answer: Both glucogenic and ketogenic
Q40. Which amino acid is oxidized to produce fumarate in the TCA cycle intermediates list?
- Phenylalanine and tyrosine (via fumarate)
- Leucine only
- Glycine only
- Lysine only
Correct Answer: Phenylalanine and tyrosine (via fumarate)
Q41. In drug development, why is knowledge of amino acid transporters important?
- They are irrelevant to drug absorption and targeting
- They influence oral absorption, BBB penetration, and targeted delivery of peptide-like drugs
- They only transport lipids
- They solely regulate hormonal secretion
Correct Answer: They influence oral absorption, BBB penetration, and targeted delivery of peptide-like drugs
Q42. Which amino acid side chain is aromatic and can participate in stacking interactions in proteins?
- Alanine
- Phenylalanine
- Serine
- Arginine
Correct Answer: Phenylalanine
Q43. Which inherited disorder results from defective homogentisate oxidase leading to accumulation of homogentisic acid from tyrosine degradation?
- Alkaptonuria
- Phenylketonuria
- Maple syrup urine disease
- Homocystinuria
Correct Answer: Alkaptonuria
Q44. Which amino acid can be phosphorylated on a protein and also serve as a precursor for glycine and serine interconversion?
- Threonine
- Serine
- Valine
- Tyrosine
Correct Answer: Serine
Q45. Which enzyme converts phenylalanine to tyrosine and requires tetrahydrobiopterin (BH4)?
- Tyrosine hydroxylase
- Phenylalanine hydroxylase
- Phenylalanine ammonia-lyase
- Tyrosinase
Correct Answer: Phenylalanine hydroxylase
Q46. Which amino acid is critically involved in metal ion binding in metalloproteins via its thiol group?
- Cysteine
- Glycine
- Asparagine
- Glutamate
Correct Answer: Cysteine
Q47. Homocystinuria is most commonly associated with a defect in which metabolic process?
- Branched-chain amino acid catabolism
- Methionine metabolism and remethylation/transsulfuration pathways
- Tryptophan to serotonin conversion
- Glycine cleavage system
Correct Answer: Methionine metabolism and remethylation/transsulfuration pathways
Q48. Which amino acid is often involved in helix-breaking due to its rigid cyclic structure?
- Proline
- Glutamine
- Leucine
- Threonine
Correct Answer: Proline
Q49. Which amino acid generally increases during starvation to provide substrate for gluconeogenesis in the liver?
- Branched-chain amino acids (e.g., alanine from muscle transamination)
- Histidine only
- Phenylalanine only
- Methionine only
Correct Answer: Branched-chain amino acids (e.g., alanine from muscle transamination)
Q50. Why is pyridoxal phosphate (PLP) an important pharmacologically relevant cofactor in amino acid metabolism?
- It functions as an electron carrier in the ETC
- It is required for transamination, decarboxylation, and racemization reactions affecting neurotransmitter and amino acid drug metabolism
- It stores methyl groups for DNA methylation
- It transports amino acids across membranes
Correct Answer: It is required for transamination, decarboxylation, and racemization reactions affecting neurotransmitter and amino acid drug metabolism
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