91Ó°ÊÓ

Proteins are complex molecules made up of amino acids. Proteins are formed when amino acids make peptide bonds with one another. Peptide linkages connect hundreds or even thousands of amino acids to form the structure of proteins.

Fibrous proteins and globular proteins are two forms of protein molecules. Fibrous and globular proteins can have one or more of four different protein structures: primary, secondary, tertiary, and quaternary.

The protein sequence can evolve due to their mutations and vary between different species. However, the polypeptide backbone of those proteins shows similarity in their structures.

The structures of those domains persist because of the following reasons:

(a) They form stable folding patterns.

(b) They support essential biological functions.

(c) They can survive the evolutionary changes by tolerating the substitutions, insertions, or deletions of amino acids.

Due to these reasons, the protein domains do not evolve as fast as their sequences.