Describe the term D- and L- configuration used for amino acids with examples.

Every amino acid except glycine occurs in D- and L- forms. Most naturally occurring amino acids are present in L- forms. D/L configuration is determined by analogy with the structure of glyceraldehyde. One example of an amino acid having D and L isomers is the chiral amino acid alanine, which has two optical isomers, and they are labeled according to which isomer of glyceraldehyde they come from.

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