Question

Why proline and glycine are exception in ramachandran plot?

Answer 1

Hey mate please follow

In contrast to all other amino acids, Gly has only a hydrogen as "side chain". Its van der Waals radius is smaller and is thus less restricted. Proline, on the other hand has a 5-membered ring as a side chain. Therefore it is much more restricted than the other amino acids and allows for only a limited number of ψ and φ.

Gly is the only amino acid that has no chiral center. Pro is the only amino acid that has a 5-membered aliphatic ring structure.

Hope this helps.