15 to 30% of collagen residues are 4-hydroxyproline residues (Hyp). When rats are fed with ¹⁴C labeled Hyp, the collagen produced by them is not…
15 to 30% of collagen residues are 4-hydroxyproline residues (Hyp). When rats are fed with ¹⁴C labeled Hyp, the collagen produced by them is not radioactive, but when they are fed with ¹⁴C labeled Proline, the collagen produced is radioactive. What is the most plausible reason?
Select an option to attempt
Correct Answer: Option C
Explanation
4-Hydroxyproline (Hyp) and collagen biosynthesis:Key experimental observations:1. Feeding ¹⁴C-Hyp → collagen produced is NOT radioactive.2. Feeding ¹⁴C-Pro → collagen IS radioactive (contains labelled hydroxyproline).Explanation:• Free hydroxyproline (Hyp) CANNOT be directly charged onto tRNA and incorporated into proteins by ribosomes. There is no tRNA for Hyp; the genetic code only specifies proline.• Proline is incorporated into collagen polypeptide normally. AFTER translation, prolyl hydroxylase (a vitamin C-dependent enzyme) hydroxylates specific proline residues in the -X-Pro-Gly- sequence.• When free ¹⁴C-Hyp is ingested, it is degraded as a regular metabolite and NOT salvaged back into collagen.This also explains why vitamin C deficiency causes scurvy (defective collagen, as prolyl hydroxylase requires ascorbate as a cofactor).Answer: Proline residues are hydroxylated once incorporated into collagen (Option 3).