An Octapeptide Composed of Four Repeating Glycylalanyl Units Has

Question

An octapeptide composed of four repeating glycylalanyl units has:
A) one free amino group on an alanyl residue.
B) one free amino group on an alanyl residue and one free carboxyl group on a glycyl residue.
C) one free amino group on a glycyl residue and one free carboxyl group on an alanyl residue.
D) two free amino and two free carboxyl groups.
E) two free carboxyl groups, both on glycyl residues.

Accepted Answer

Each glycylalanyl unit has a free amino group on the glycyl residue and a free carboxyl group on the alanyl residue. Since there are four repeating units, there are four free amino groups on glycyl residues and four free carboxyl groups on alanyl residues. Therefore, the correct answer is C, which is the only option with one free amino group on a glycyl residue and one free carboxyl group on an alanyl residue.