Amino information
Chemistry will tell you that an amino acid is any molecule that
has both carboxylic acid and amino functional groups. They are
the basic building units of a protein. In biochemistry, the
shorter and more general term is used to refer to alpha amino
acids. Those are amino acids wherein the amino and carboxylate
functionalities are attached to a common carbon. Amino acids'
residue is what's left of an amino acid once a water molecule
has been lost in the formation of a peptide bond. Peptides are
polymer chains which form the protien in our bodies.
Twenty amino acids will be encoded by the standard genetic code.
These are called proteinogenic or standard Amino acids.
More complicated ones are produced by our bodies, and are called
nonstandard (these are not as common). Proline is the only
proteinogenic amino acid, whose side group links to the a-amino
group and is cyclic. This forms a secondary amino group. Before,
proline was called "imino", which was misleading and was
changed. Protiens contain other amino acids which are usually
formed by post-translational modification (modifications AFTER
translation). These modifications are essential for the function
of protein. At least two amino acids, other than the standard
20, are sometimes incorporated into proteins during the
translation process.
Even though only 20 amino acids are genetically encoded, over
one hundred have been found in nature. Some of these have been
seen in meteorites, especially in a type called carbonaceous
chondrites. Microorganisms and plants can often produce somewhat
uncommon amino acids, which are located in peptidic antibiotics.
Lanthionine is a sulfide-bridged alanine dimer found along with
unsaturated amino acids in "lantibiotics", which are antibiotic
peptides of microbial origin.
As well as protein synthesis, amino acids have some other
biologically important jobs. Glycine, and glutamate, are used as
neurotransmitters as well as standard amino acids in proteins.
Many amino acids take on the role of synthesizing other
molecules, such as tryptophan, which is a precursor of the
neurotransmitter serotonin, and glycine, one of the few
reactants in the synthesis of porphyrins such as heme. Heme is
in "hemoglobin", which is also important in the makeup of
protein. Numerous, non-standard amino acids, are biologically
important: "GABA",another neurotransmitter, carnitine, which is
used in lipid transport within the cell, citrulline, ornithine,
hydroxyproline, hydroxylysine, homocysteine, and sarcosine.