Natural polymers (proteins)

Proteins

Proteins are linear (not branched or not ring) polymers of amino acids. The twenty genetically encoded amino acids are the molecules which share the centre core: α  carbon atoms which is bonded to N terminus amino group i.e NH₂ , to a C terminus carboxylic acid group i.e COOH, to a hydrogen atom and a side chain of amino acid group also called the R group as shown in fig. The R group determines the identity of amino acid.

Amino acid.

In an aqueous solution at physiological pH about 6.8 the amino group exist in protonated form i.e NH₃⁺ and the carboxylic acid group exist in deprotonated form i.e COO⁻, thus forming zwitter ion as shown in fig.

Zwitter ion.

Most of proteins are made up of amino acid of L- isomers but there are also some proteins made with amino acid of D-isomers.

The amino acids in proteins are linked via peptide bonds which is a type of amide bond as shown in fig.

Peptide bond.

The proteins with less than 20 amino acids are called peptides or polypeptides. The peptide chain starts from N- terminus to C- terminus.

Proteins like myoglobin store oxygen in muscles, haemoglobin transport oxygen, enzymes catalyze biological process, Elastin gives elasticity to artrial walls and ligaments.Next>>