Question

Biochemistry: Why do eight AA’s of every alpha helix have only one H-bond per AA, while the rest of AA’s in a helix have 2 H-bonds per residue?

Answer 1

Alpha helix flexibility (easy rotation) is mainly due to the presence of single hydrogen bonds

Then... this is given due to numbers of simple hydrogen bonds, the rotation could be compared to the amino acids with 2 hydrogen bonds.

If the alpha helix has 80% amino acids with two hydrogen bonds then the flexibility will lost (which is similar to this specifc case)

Therefore, the alpha helix has eight amino acids with one hydrogen bond and two amino acids with two hydrogen bonds