Question 17:
4-hydroxyproline is an example of:
4-Hydroxyproline is a modified amino acid found primarily in collagen. The correct classification is option (A).
Correct Answer
(A) Nonstandard amino acid
4-Hydroxyproline forms via post-translational hydroxylation of proline residues in collagen, making it nonstandard as it’s not one of the 20 proteinogenic amino acids directly encoded by DNA.
Key Facts
This imino acid stabilizes collagen’s triple helix through hydrogen bonding. Its presence (~10% of collagen residues) distinguishes it from standard amino acids used in general protein synthesis.
Option Analysis
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(A) Nonstandard amino acid: Correct; derived from proline modification, absent from genetic code but vital for connective tissue.
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(B) Hormone: Incorrect; hormones are signaling molecules like insulin or steroids, not modified amino acids.
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(C) Antibiotic: Incorrect; antibiotics like penicillin target bacteria, unrelated to hydroxyproline’s structural role.
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(D) Antibody: Incorrect; antibodies are immunoglobulins produced by B-cells for antigen recognition.
| Option | Category | Role/Example | Status |
|---|---|---|---|
| A | Nonstandard AA | Collagen stabilizer | Correct |
| B | Hormone | e.g., adrenaline | Wrong |
| C | Antibiotic | e.g., tetracycline | Wrong |
| D | Antibody | Immune defense protein | Wrong |
Exam Preparation Tips
Remember: standard amino acids = 20 canonical; nonstandard include hydroxyproline, selenocysteine. Link to scurvy (vitamin C deficiency impairs hydroxylation).
