Carbohydrate H OH H OH OH H CH OH H H HO O - - . . PM . Proteins Proteins are the most diverse of all macromolecule.
Proteins make up / of total dry mass of a cell. The term protein was coined by Gerardus Johannes Mulder and is derived form a greek word proteos which means of the first rank. Amino acids are building blocks of proteins. There are about different amino acids exist naturally.
All amino acids have a basic skeleton consisting of a carbon (a-carbon) linked to a basic amino group. H H N H C R OH O C Amino Group Carboxyl Acid Group Variable Side Chain Figure . : Structure of basic amino acid (NH ), an acidic carboxylic group (COOH) and a hydrogen atom (H) and side chain or variable R group. The amino acid is both an acid and a base and hence is called amphoteric .
A zwitterion also called as dipolar ion , is a molecule with two or more functional groups, of which at least one has a positive and other has a negative electrical charge and the net charge of the entire molecule is zero. The pH at which this happens is known as the isoelectric point (Figure . ). Figure .
: Structure of amino acid . . Classification of Amino acids Based on the R group amino acids are classified as acidic, basic, polar, non-polar. The amino group of one amino acid reacts with carboxyl group of other amino acid, forming a peptide bond .
Two amino acids can react together with the loss of water to form a dipeptide . Long strings of amino acids linked by peptide bonds are called polypeptides . In , Fred Sanger first sequenced the Insulin protein (Figure . a and b).
Figure . (a): Formation of peptide bond Linus Pauling and Robert Corey in proposed the α-helix and β sheet secondary structures of proteins. They were awarded Nobel prize in First protein Insulin was sequenced by Fred Sange. - - .
. PM . . Structure of Protein