#Question id: 722

The structure of alpha helix is stabilized by hydrogen bonds between the hydrogen atom attached to the electronegative nitrogen atom of a peptide linkage and the electronegative carbonyl oxygen atom of the fourth amino acid on the amino-terminal side of that peptide bonds. Within the helix, every peptide bond (except those close to each end of the helix) participates in such hydrogen bonding. Each successive turn of the helix is held to adjacent turns by three to four hydrogen bonds, conferring significant stability on the overall structure. Which of the following are correct statements regarding these findings?

A. At the ends of a helical segment, there are always three or four amide carbonyl or amino groups that participate in this stabilised helical pattern of hydrogen bonding.

B. Helix ends are exposed to the surrounding solvent, where they hydrogen-bond with water, or other parts of the protein may cap the helix to provide the needed hydrogen-bonding partners.

C. Helix can form in polypeptides consisting of either L- or D-amino acids but a D-amino acid will disrupt a regular structure consisting of L-amino acids, and vice versa.

D. The most stable form of a helix consisting of L-amino acids is left-handed.

E. 310 helix occupies similar place as turns in Ramachandran plot due to its confirmation