. Proteins Proteins are most abundant biomolecules in all living organisms. The term protein is derived from Greek word ‘ Proteious ’ meaning primary or holding first place. They are main functional units for the living things.
They are involved in every function of the cell including respiration. Proteins are polymers of α -amino acids. . .
Amino acids Amino acids are compounds which contain an amino group and a carboxylic acid group. The protein molecules are made up α -amino acids which can be represented by the following general formula. R C * COOH NH There are α -amino acids commonly found in the protein molecules. Each amino acid is given a trivial name, a three letter code and a one letter code.
In writing the amino acid sequence of a protein, generally either one letter or three letter codes are used. . . Classification of α -amino acids The amino acids are classified based on the nature of their R groups commonly known as side chain.
They can be classified as acidic, basic and neutral amino acids. They can also be classified as polar and non-polar (hydrophobic) amino acids. XII XII - - - - Figure . Structure of amino acids XII XII - - - - Amino acids can also be classified as essential and non-essential amino acids based on the ability to be synthesise by the human.
The amino acids that can be synthesised by us are called non-essential amino acids (Gly, Ala, Glu, Asp, Gln, Asn, Ser, Cys, Tyr & Pro) and those needs to be obtained through diet are called essential amino acids (Phe, Val, Thr, Trp, Ile, Met, His, Arg, Leu and Lys). These ten essential amino acids can be memorised by mnemonic called PVT TIM HALL. Although the vast majority of plant and animal proteins are formed by these α - amino acids, many other amino acids are also found in the cells. These amino acids are called as non–protein amino acids.
Example: ornithine and citrulline (components of urea cycle where