Question

Why only only l amino acids are constituent of proteins.

Answer 1

Only L-amino acids are manufactured in cells and incorporated into proteins. Some D-amino acids are found in the cell walls of bacteria, but not in bacterial proteins. Glycine, the simplest amino acid, has no enantiomers because it has two hydrogen atoms attached to the central carbon atom.

Answer 2

because, it is produced inside cells of the living beings,which contains proteins.