Amino Acids: Difference between revisions
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D-form | D-form | ||
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ALA<br>MET<br>SER | ALA<br>MET<br>PHE<br>SER | ||
</td><td> | </td><td> | ||
DAL<br>MED<br>DSN | DAL<br>MED<br>DPN<br>DSN | ||
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The asymmetric α-carbon in 19 of the standard amino acids (all except glycine) is a chiral center<ref name='chirality' />. Thus, each amino acid can exist in either of two optical isomers or enantiomers (mirror images), designated the L-form and D-form. Nearly all naturally-occuring amino acids are L-amino acids, so named because they are derived from the L-form of glyceraldehyde<ref name='chirality'>See [http://en.wikipedia.org/wiki/Chirality_(chemistry) Chirality in Wikipedia]].</ref>. (Not all L-amino acids are levorotatory; some rotate polarized light clockwise<ref name='chirality' />). | The asymmetric α-carbon in 19 of the standard amino acids (all except glycine) is a chiral center<ref name='chirality' />. Thus, each amino acid can exist in either of two optical isomers or enantiomers (mirror images), designated the L-form and D-form. Nearly all naturally-occuring amino acids are L-amino acids, so named because they are derived from the L-form of glyceraldehyde<ref name='chirality'>See [http://en.wikipedia.org/wiki/Chirality_(chemistry) Chirality in Wikipedia]].</ref>. (Not all L-amino acids are levorotatory; some rotate polarized light clockwise<ref name='chirality' />). | ||
Although D-amino acids are rare in nature, they do occur (see [http://en.wikipedia.org/wiki/Chirality_(chemistry)#D-Amino_Acid_Natural_Abundance natural abundance in Wikipedia]). D-alanine (DAL) occurs in over 100 entries in the [[PDB]], D-serine (DSN) in over 50, and D-methionine (MED) in over 10. | Although D-amino acids are rare in nature, they do occur (see [http://en.wikipedia.org/wiki/Chirality_(chemistry)#D-Amino_Acid_Natural_Abundance natural abundance in Wikipedia]). D-alanine (DAL) occurs in over 100 entries in the [[PDB]], D-phenylalanine and D-serine (DSN) each occur in over 50, and D-methionine (MED) in over 10. | ||
==Unusual Amino Acids== | ==Unusual Amino Acids== | ||
