Which one of these characteristics is not true for the a helix?
A) There are 3.6 amino acids per turn.
B) There is a requirement for glycine every third amino acid residue.
C) A hydrogen bond forms between the carbonyl oxygen of the nth amino acid residue and the NH group of the (n + 4)th amino acid residue.
D) Proline is typically not found in the a helix.
E) It is right-handed.
