Principles of Biochemistry (2+1)

Proteins are the most abundant substances in all cells forming about  50% of a cell's over all mass. A protein is an unbranched polymer of amino acids.

Functions: Proteins supply the required  amino acids as building blocks for protein biosynthesis. Amino acids are precursors of other nitrogen containing substances such as enzymes, hormones, porphyrins, and many other biomolecules.Oxidation of the carbon skeletons of amino acids also furnishes significant fraction of the total daily energy requirement. They also contribute to the flavour of food and are precursors of aroma compounds and colours formed during thermal or enzymatic reactions in production, processing and storage of food.  

Sources: Meat, fish, milk, egg, pulses, beans and peas are important sources of protein.