Amino acids are molecules containing an amine group (NH2), a carboxylic acid (COOH)
group and a side chain that varies. In an alpha amino acid, the amino and carboxylate
groups are attached to the same carbon atom, which is called the α‐carbon. The various
alpha amino acids differ in which (R group) is attached to their alpha carbon.
These side chains can vary in size from just a hydrogen atom in Glycine to a methyl
group in Alanine through to a large heterocyclic group in Tryptophan.
Amino acids are critical to life, and have many functions in metabolism. One particularly
important function is as the building blocks of proteins, which are linear (straight) chains
of amino acids. Every protein is chemically defined by this primary structure, while its
unique sequence of amino acid residues, in turn define the three dimensional structure
of the protein. Amino acids are linked together in varying sequences to form a vast
variety of proteins. Amino acids are also important in many other biological molecules,
and due to this central role in biochemistry, they are very important in nutrition.
Amino acids join together to form short polymer chains called peptides or longer chains
called either polypeptides or proteins. These polymers are linear and unbranched, with
each amino acid within the chain attached to two neighbouring amino acids.
Twenty‐two amino acids are naturally incorporated into polypeptides and are called
proteinogenic or standard amino acids. Of the twenty‐two standard amino acids, eight
are called essential amino acids because the human body cannot synthesize them from
other compounds at the level needed for normal growth, so they must be obtained
from food. However, the situation is quite complicated since cysteine, Taurine, Tyrosine,
Histidine and Arginine are semiessential amino acids in children, because the metabolic
pathways that synthesize these amino acids are not fully developed.
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