Question

Abnormalities in the synthesis or structure of collagen cause dysfunctions in cardiac organs, bone, skin, joints, and cyes. Problems may result from abnormal collagen genes, abnormal posttranslational modifications of collagen, or deficiency of cofactors needed by enzymes responsible for posttranslational modifications. Scurvy, a lack of vitamin \(\mathrm{C},\) is an example of the last type. The formation of covalent cross-links in collagen A. occurs during synthesis of the peptide chain. B. uses hydroxyproline. C. involves glycine residues. D. requires conversion of some \(\varepsilon\) -amino groups of lysine to \(\delta\) -aldchydes. E. all of the above.

Short answer

A. Cross-link formation occurs during the synthesis of the peptide chain. B. Covalent cross-link formation uses hydroxyproline. C. The cross-link formation in collagen involves glycine residues. D. Cross-link formation requires conversion of some ε-amino groups of lysine to δ-aldehydes. E. All of the above statements are correct. Answer: D. Cross-link formation in collagen requires conversion of some ε-amino groups of lysine to δ-aldehydes.

Step-by-step solution

Cross-link formation in collagen

Covalent cross-links in collagen are essential for stability. The formation of these cross-links involves the hydroxylysine and lysine residues present in the polypeptide chains.

Check Option A

Option A says cross-link formation occurs during synthesis of the peptide chain. However, cross-links in collagen happen after the peptide chain is synthesized, via post-translational modifications. Therefore, option A is incorrect.

Check Option B

Option B states that covalent cross-link formation uses hydroxyproline. Although hydroxyproline has an essential role in stabilizing collagen structure, it is not involved directly in the formation of cross-links. Instead, cross-link formation involves hydroxylysine and lysine. So option B is incorrect.

Check Option C

Option C says that the cross-link formation in collagen involves glycine residues. Although glycine makes up a significant portion of collagen's structure, it is not involved in the formation of cross-links. Hence, option C is incorrect.

Check Option D

Option D states that cross-link formation requires conversion of some ε-amino groups of lysine to δ-aldehydes. This statement is correct; cross-links are formed through the lysyl oxidase enzyme, which converts some lysine and hydroxylysine residues to aldehydes that can then react to form cross-links. Therefore, option D is correct.

Check Option E

Option E says that all of the above statements are correct. As we have evaluated the options A, B, and C are incorrect; thus, option E cannot be correct either. The correct answer is D. Cross-link formation in collagen requires conversion of some ε-amino groups of lysine to δ-aldehydes.