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This amino acid displays a free amino group in the peptide ALA-GLN-ARG-SER-HIS

Dear OTA,
I have 2 multiple questions as attached. I have done those but have some doubts. The questions are in red and my answer is in black.

Need to get explanation why the option B in #61 is wrong (heavy references) and why option A in #53 is wrong (also references)
Basically I need to know why only 1 option is good for each question.


Solution Preview

For the first question, the correct answer is alanine.

Gln doesn't have a free amino group. It has an amide group.
Arg doesn't have a free amino group either. It has a very complex functional group.
Ser has no NH2 group at all. The only NH2 group it has will be bound up in the peptide linkage.
His ...