Question

Why is glycine not in alpha helix?

Answer 1

Glycine:

1. An alpha helix is a right-handed coil made up of amino acid residues that typically range from $4$ to $40$ residues on a polypeptide chain
2. The alpha helix becomes unstable when an amino acid's R group is either too large (tryptophan or tyrosine) or too small (glycine).
3. The molecular formula for glycine is ${\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NO}}_2$. It is the smallest amino acid and is made up of a hydrogen molecule and a side chain.
4. Due to its small size, glycine can produce chain bends that result in extremely high structural mobility.

Therefore, due to its small size glycine is not in the alpha helix.