Section B - Amino acids and proteins

All proteins are made up from the same set of 20 standard amino acids. A typical amino acid has a primary amino group, a carboxyl group, a hydrogen atom and a side-chain (R group) attached to a central a-carbon atom (Ca). Proline is the exception to the rule in that it has a secondary amino group. 

All of the 20 standard amino acids, except for glycine, have four different groups arranged tetrahedrally around the Ca atom and thus can exist in either the d or l configuration. These two enantiomers are nonsuperim-posable mirror images that can only be distinguished on the basis of their different rotation of plane-polarized light. Only the l isomer is found in proteins. 

Amino acids Amino acids are the building blocks of proteins (see Topic B3). Proteins of all 

Instant Notes in Biochemistry 2nd Edition, B.D. Hames N.M. Hooper, (c) 2000 BIOS Scientific Publishers Ltd, Oxford. 

Enantiomers All of the amino acids, except for glycine (Gly or G see Fig. 2), have four 

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