Question

"An amino acid residue in a protein differs from a free amino acid in having ...

(a) one less H.
(b) one less OH.
(c) one less H and one less OH.
(d) Either (a) or (b).
(e) Could be any of the above."

Answer 1

An amino acid residue in a protein is missing one hydrogen and one hydroxyl group compared to a free amino acid, because these are lost during the formation of a peptide bond and water molecule removal.

Step-by-step explanation:

An amino acid residue in a protein differs from a free amino acid in that it has one less hydrogen (H) and one less hydroxyl (OH) group. This is because during peptide bond formation (a link between two amino acid molecules), a molecule of water is removed, which includes these atoms—one hydrogen from the amino group of one amino acid and the hydroxyl group from the carboxylic acid of another. Therefore, an amino acid residue embedded in a peptide or protein chain lacks these components compared to its free, unconjugated form.