As a Physician Volunteer in a Free Clinic, You Are

As a physician volunteer in a free clinic, you are examining a 52-year-old homeless man. You note that he has numerous petechiae and suspect impaired collagen production. Given his poor dietary habits, you determine that he lacks adequate intake of vitamin C. For which of the following steps of collagen synthesis is ascorbic acid required?

A) cross-linking lysine and hydroxylysine residues
B) glycosylation of hydroxylysine residues
C) hydroxylation of proline residues
D) removal of the signal peptide from preprocollagen
E) translocation of collagen peptides into the endoplasmic reticulum