Protein are polymers of amino acids. The name of proteins is derived from the Greek word called proteios. It mean first place. Protein always contain atom of carbon, hydrogen, nitrogen ,oxygen and some times sulfur 50% of dry weight of cell is composed of proteins.

Amino acids are building blocks of proteins. More than 150 types of amino acids are known. But only 20 amino acids take part in the formation of proteins.

Amino acids:       


        They are building blocks of protein:

                Amino acids contain an amino group  (NH2) a carboxyl group (COOH) a hydrogen atom and a functional group R . They all are bonded to a central carbon atom called a carbon.

The alpha carbon is an a symmetric carbon it is attached with four different covalent partners.

 Structure of amino acids is following.


Nature of R group :

The structure of the R group dictates that amino acid’s chemical properties. R group  is called side chain. It may be single hydrogen atom as glycerin. It  may be carbon skeleton with various functional groups like glutamic acids


Amino acids are divided in two groups on the basis of properties of R group:

1. Hydrophobic amino acids:

These amino acids non polar side chain

2. Hydrophilic amino acids

 The amino acids have polar side chain there are two types of hydrophobic amino acids.

(a)Acidic amino acids

Acid amino acids are usually charged with a negative side


(B) basic amino acids:

Their side chain are generally positive in charge.

  •   Neutral amino acids:

Amino acids    have single amino group and single carboxyl group .Such amino acids are called neutral amino acids


  •   Basic amino acids:

It contains additional amino group are called basic amino acids.

For example arginine etc.

  •  Acidic amino acids:

Amino acids contain additional carboxyl group are called acidic amino acids. For example   glutamic acids

  Peptide bond formation (Protein):

                In animal peptide bonds, 20 separate amino acids usually join amino acids in the chain. Peptide bond is covalent bond the peptide bond are covalent bond.

The carboxyl group of one amino acids bonds to the amino group of another in peptide bond. One molecule of water is released.

  •    amino acids bonds to form di-peptide
  •    bonded amino acids form tri-peptide
  • Many amino acids bind together to form polypeptide chain.
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