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Collagen biosynthesis is a complex process that begins within fibroblasts and continues in the extracellular space. Which of the following processes occurs outside of the fibroblasts during collagen synthesis?

A. C-terminal propeptide removal
B. Lysine residue glycosylation
C. Proline residue hydroxylation
D. Terminal disulfide bond formation
E. Triple helix formation
F. Cleavage of hydrophobic N-terminal signal peptides

An: AAA

why not FFF? Where and when does FFF happen? Thanks.

because that process requires golgi apparatus

"F" occur in Endo. Reticulum

and also that has nothing to do with collagen synthesis as the question stem is describing

A---From Soluble Procollagen, cleaved to insoluble Tropocollagen.
Covalent lysine-hydrolysine cross-linkage also occur outside fibroblast.

Just note one word in F, signal peptide.
They are amino acids that direct the transport of protein to either the endoplasmic reticulum thru secretory pathway, and they are cleave after transport of protein; it has nothing to o with the real synthesis.

Thank you for all the clarification.

I feel its more like the word "HYDROPHOBIC"
as both N and C terminals are actually "HYDROPHILIC" in nature, hence to make collagen (hydrophobic) both C and N (hydrophilic) need to be cleaved

since F says "Hydrophobic" N, that makes the statement wrong in itself.


Also, if N and C terminal not properly cleaved that makes collagen water soluble and hence defective.

usmle8484, I see your point. Thanks.