Properties of amino acids

The amino acids are the fundamentals units of protein structure.  Amino acids are all characterized by the presence of an amino (NH2) group with basic properties and a carboxyl (COOH) group with acidic properties attached to the same carbon atom.

Most naturally occurring amino acids are of the L-configurations, although D-amino acids are not uncommon in some microorganisms.

In the formation of a protein, amino acids are linked together by the peptide linkage in which the basic (amino) group of one amino acid is linked to the carboxyl group of another, with the elimination of a molecule of water.

Amino acid crystals are generally white. All crystalline amino acid, except for glutamine and cysteine have a high melting point of more than 200 ° C. Glutamine and cysteine have melting point of 185 ° C and 178 °C respectively.

In solution, at physiologic pH, the free amino acids exist as zwitterions, ions in which the amino group is positively charged and the carboxylate group is negatively charged.
Properties of amino acids