Properties Of Amino Acids
The English language consists of thousands of words, created from any of twenty-six letters arranged in a precise order. In an analogous fashion, proteins are made up of twenty common amino acids in a precise order dictating the protein's structure and function. Every amino acid has a common structure, in which a central carbon is covalently bonded to a carboxyl group (COOH), an amino group (NH2), a hydrogen, and a variable "R" group.
The chemical properties of the R group are what give an amino acid its character. The R group can be hydrophilic (attracted to water and other polar molecules) or hydrophobic (attracted to nonpolar molecules and repelled by water or other polar molecules). Hydrophilic R groups can have basic charges, as in the amino acid valine, or acidic, as in glutamic acid, or they may even be an uncharged polar group such as-OH (alcohol) or-NH2 (amino), as in serine. A nonpolar or hydrophobic R group can be a hydro-carbon chain, as in leucine. There are also three special amino acids: cysteine, glycine, and proline. Cysteine has a reactive sulfhydryl R group that forms disulfide bridges (S-S) between regions of the protein chain. These bridges increase toughness and resistance to unfolding of the protein structure. Glycine is the smallest amino acid, with hydrogen as its R group, and it fits into tight places within a protein's structure. Proline has a cyclic ring involving the central carbon, and it causes kinks to occur in a protein chain. Both proline and glycine are common at the corner of turns in the protein foldings.
Medicine EncyclopediaGenetics in Medicine - Part 3Proteins - Properties Of Amino Acids, Primary Structure, Secondary Structure And Motifs, Tertiary Structure And Protein Domains - Molecular Chaperones, Proteomics