Q1: Peptide formation is FROM the amino group TO the carbonyl group (N --> C). So, the best answer is A because that is where peptide bond formation originates. In other words, the amino group is the nucleophile.

Q13: Here are the different protein structures:

PRIMARY - linear sequence of amino acid residues

SECONDARY - formation of H-bonds between atoms in the backbone, which folds into (either) α-helices or β-sheets

TERTIARY - secondary structures (helices and sheets) fold into one another to form a 3D structure that generates the geometric shape of the protein. The 3D structure is determined by the interactions and bonding of the amino acid sidee chains in the protein.

QUATERNARY - results from further interactions of side chains in the tertiary structure to give rise to a functional protein

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