In the generalized form of amino acid, one central carbon atom is present. This central carbon is known as the alpha carbon. Apart from this alpha carbon atom also an amino group and a carboxyl group is present in the structure. These two groups are attached with the central carbon atom. Thus two bonds out of four bonds are occupied. Rest two are occupied by one hydrogen atom and one R group. The R group denotes the alkyl group. This is what the generalized structure of amino acid looks like.