13.2 Protein

Proteins are highly complicated nitrogenous compounds made up of amino acids. Proteins consist of carbon, hydrogen, oxygen, nitrogen and sulphur. They are polymers of amino acids. Amino acids are linked with each other through peptide

Protein has more than 10,000 amino acids. All proteins yield amino acids upon hydrolysis.

Proteins are present in all living organisms. They make up bulk of the non- bony structure of the animal bodies. They are major component of all cells and tissues of animals. About $50\%$ of the dry weight of cell is made up of proteins. They are found in muscles, skin, hair, nails, wool, feathers, etc.

Amino acids

Amino acids are organic compounds consisting of both amino and carboxyl groups. They have the general formula:

Side chain 'R' is different for different amino acids. There are 20 amino acids. Ten out of twenty amino acids can be synthesized by human body. These amino acids are called non- essential amino acids. While the other ten which cannot be synthesized by our bodies are called essential amino acids. Essential amino acids are required by our bodies and must be supplied through diet.

13.2.1 Amino acids are Building Blocks of Proteins:

Two amino acids link through peptide linkage. Peptide linkage (bond) is formed by the elimination of water molecule between the amino group of one amino acid and carboxyl acid group of another, such as: