This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which of the following are intracellular events occurring in fibroblast during synthesis of collagen- 
Select and explain. 
A. Hydrolysis of procollagen to collagen, B. Glycosylation of proline, C. Formation of triple helix, D. Formation of covalent cross link b/w fibrils
C: Formation of triple helix
Answer: C: Formation of triple helix 
Explanation: Formation of triple helix (of pre-a-chains) takes place intracellularly in RER.
Formation of a cross-link between fibrils (i.e. self-assembly of tropocollagen monomers into mature collagen fiber) occurs extracellularly after secretion from fibroblasts.
Glycosylation also occurs intracellularly, but its glycosylation of hydroxylysine (not of proline).