4. Protein Structure

A Ramachandran plot shows:

Why are some regions of a Ramachandran plot shaded while others are unshaded? Circle all true answers.

a) Shaded regions correspond to the most common permissible conformations and bond angles.

b) Unshaded regions correspond to the ΔG values for each combination of phi & psi bond angles.

c) Unshaded regions correspond to restricted bond angles that are non-permissible & less common.

d) Shaded regions can be analyzed to reveal the full primary structure of a peptide.

The predominate structure in α-keratin, a mammalian protein that makes up large portions of hair & nails, is the α-helix. Mark the approximate locations on a Ramachandran plot you might expect to find φ and ψ angles for α-keratin amino acid residues.

The principal component of silk is the protein fibroin, which is a classic example of β-sheet structure. Mark the approximate locations on a Ramachandran plot you might expect to find φ and ψ angles for silk amino acid residues.

Which of the following statements is true for the portion of the peptide shown in the figure below?