- Amino acids are
molecules containing an amine group, a carboxylic acid group and a
side-chain that varies between different amino acids.
- The key elements of an
amino acid are carbon, hydrogen, oxygen, and nitrogen. They are
particularly important in biochemistry, where the term usually
refers to alpha-amino acids.
- Amino acids are
critical to life, and have many functions in metabolism. One
particularly important function is to serve as the building blocks
of proteins, which are linear chains of amino acids. Amino acids can
be linked together in varying sequences to form a vast variety of
- Twenty-two amino acids
are naturally incorporated into polypeptides and are called
proteinogenic or standard amino acids. Of these, 20 are encoded by
the universal genetic code. Nine standard amino acids are called
"essential" for humans because they cannot be created from other
compounds by the human body, and so must be taken in as food.
- When taken up into the
human body from the diet, the 22 standard amino acids either are
used to synthesize proteins and other biomolecules or are oxidized
to urea and carbon dioxide as a source of energy.
- The oxidation pathway
starts with the removal of the amino group by a transaminase, the
amino group is then fed into the urea cycle. The other product of
transamidation is a keto acid that enters the citric acid cycle.
- Amino acids are used
for a variety of applications in industry, but their main use is as
additives to animal feed. This is necessary, since many of the bulk
components of these feeds, such as soybeans, either have low levels
or lack some of the essential amino acids: Lysine, methionine,
threonine, and tryptophan are most important in the production of
- In this industry,
amino acids are also used to chelate metal cations in order to
improve the absorption of minerals from supplements, which may be
required to improve the health or production of these animals.
- Degradation of an
amino acid often involves deamination by moving its amino group to
alpha-ketoglutarate, forming glutamate. This process involves
transaminases, often the same as those used in amination during
- In many vertebrates,
the amino group is then removed through the urea cycle and is
excreted in the form of urea. However, amino acid degradation can
produce uric acid or ammonia instead. For example, serine
dehydratase converts serine to pyruvate and ammonia.
- Some amino acids have
special properties such as cysteine, that can form covalent
disulfide bonds to other cysteine residues, proline that forms a
cycle to the polypeptide backbone, and glycine that is more flexible
than other amino acids.
- Many proteins undergo
a range of posttranslational modifications, when additional chemical
groups are attached to the amino acids in proteins. Some
modifications can produce hydrophobic lipoproteins, or hydrophilic
- These type of
modification allow the reversible targeting of a protein to a
membrane. For example, the addition and removal of the fatty acid
palmitic acid to cysteine residues in some signaling proteins causes
the proteins to attach and then detach from cell membranes.
- The kinds of amino
acids determine the shape of the proteins formed. Commonly
recognized amino acids include glutamine, glycine, phenylalanine,
tryptophan, and valine. Three of those — phenylalanine, tryptophan,
and valine — are essential amino acids for humans; the others are
isoleucine, leucine, lysine, methionine, and threonine. The
essential amino acids cannot be synthesized by the body; instead,
they must be ingested through food.
- One of the best-known
essential amino acids is tryptophan, which performs several critical
functions for people. Tryptophan helps induce normal sleep. It helps
reduce anxiety, depression, and artery spasm risk and helps produce
a stronger immune system.
- Tryptophan is perhaps
most well-known for its role in producing serotonin, which is what
gets all the press at Thanksgiving time for putting you to sleep
after the big holiday feast.
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