Significance of Stereoisomers in Protein Synthesis and Function

Of the standard α-amino acids, all but glycine can exist in either of two_____

optical isomers

Of the standard α-amino acids, all but glycine can exist in either of two stereoisomeric forms, L or D. This is because of the chiral center at the α-carbon atom, bonded to four different groups (an amino group, a carboxyl group, a hydrogen atom, and a side chain R). The L and D forms are mirror images of each other and are non-superimposable, just like our left and right hands. The L form is the one that is biologically active and is used by cells to synthesize proteins. The D form is relatively rare in nature and is found in some bacterial cell walls and antibiotics. The ability of amino acids to exist as stereoisomers is important in protein structure and function, as the way in which amino acid residues are arranged in a protein determines its three-dimensional structure and ultimately its function.

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