Question

Which of the following is not correct about the α-Helices?

(a) An α-helix has a main chain backbone conformation that resembles a corkscrew

(b) Nearly all known α-helices are right handed, exhibiting a leftward spiral form

(c) Nearly all known α-helices are right handed, exhibiting a rightward spiral form

(d) In right handed helix, there are 3.6 amino acids per helical turn

I have been asked this question during an internship interview.

My question is from Protein Structure Basics topic in section Structural Bioinformatics of Bioinformatics

Answer 1

Correct choice is (b) Nearly all known α-helices are right handed, exhibiting a leftward spiral form

Easiest explanation: The structure is stabilized by hydrogen bonds formed between the main chain atoms of residues i and i + 4. The hydrogen bonds are nearly parallel with the helical axis. The average φ and ψ angles are 60◦ and 45◦, respectively, and are distributed in a narrowly defined region in the lower left region of a Ramachandran plot.