Question

How are proteins classified? Explain formation of peptide linkage in proteins.

Answer 1

Proteins are made up of amino acids. These sequences of amino acids are specific to each protein and its arrangements are controlled by DNA. Each amino acid is linked together by peptide bonds. Proteins perform various functions such as catalysing metabolic reactions, DNA replication, providing structure to cells and organisms, transporting molecules etc.

Complete explanation:
Proteins can be classified based on the structure, composition and functions it performs.
Based on the structure proteins are classified as fibrous, globular and intermediate proteins. Fibrous proteins are elongate, fibre like proteins whereas the globular proteins are spherical or globular in shape.
Based on the composition proteins can be classified as simple or conjugated. Simple proteins are composed of amino acids only. Protamine, histone, albumin and globulin are examples of simple proteins. Complex proteins are made up of amino acids as well as a non-protein moiety to become functional. The non-protein component is called the prosthetic group. Some examples are metalloprotein, chromoprotein and glycoprotein.
Peptide linkage or bond is a chemical bond formed between amino acids of the protein by joining the carboxyl group of one amino acid to the amino group of another amino acid. The hydroxyl molecule of the carboxyl group and the hydrogen molecule of the amino group join together and form water. The water molecule is released and the nitrogen replaces the hydroxyl’s place forming a peptide bond. The peptide bond formed is covalent in nature and since the molecule is eliminated it is considered as a dehydration process.

Note:
Based on the function it performs, proteins are classified as structural proteins, enzymes, hormones, transport proteins, storage proteins and respiratory pigments. Each of them performs various bodily functions. Some of the amino acids in a protein are essential and cannot be produced by the body on its own, that’s why a protein rich diet is necessary to keep the body metabolism stable.