Amino acids are the building blocks of proteins. All proteins consist of a sequence of amino acids,  which  are compounds containing  an  amino group  (-BIB)  and  a carhoxyl  group  (-COOH)  as indicated  in  the  general  structural formula  in  the Figure.  Normally 20 different  2-amino  acids or  a-amino  acids (amino acids having  -NH2  group at carbon 2) are found in proteins, though very recently two more amino acids are also found to be present in some proteins. All the amino acids can be represented by a general structural formula,