- Twenty-two amino acids are naturally incorporated into polypeptides and are called proteinogenic or natural amino acids. Of these, 20 are encoded by the universal genetic code. The remaining 2, selenocysteine and pyrrolysine, are incorporated into proteins by unique synthetic mechanisms.

- There is an N-terminal and C-terminal present in all the proteins.

- The solubility of a protein in water depends on the 3D shape of it. Usually, globular proteins are soluble, while fibrous ones are not. 

- A peptide bond is a type of covalent bond or amide C-N bond formation between the carboxyl group of one amino acid and the amino group of another amino acid.