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is one of the standard amino acids.
In chemistry, an
amino acid is a
molecule that contains both
amine and carboxyl functional groups. In
biochemistry, this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent. Proline is an exception to this general formula. It lacks the NH2 group because of the cyclization of the side chain. In the alpha amino acids, the amino and carboxylate groups are attached to the same carbon, which is called the
alpha carbon. The various alpha amino acids differ in which side chain (R group) is attached to their alpha carbon. They can vary in size from just a hydrogen atom in
glycine, through a
methyl group in
alanine, to a large heterocycle in
tryptophan.
Beyond the amino acids that are found in all forms of
life, many non-natural amino acids are also important. The
chelating agents EDTA and Nitrilotriacetic acid are alpha amino acids that are industrially synthesized (sometimes from naturally occurring amino acids).
Overview
Alpha-amino acids are the building blocks of proteins. A protein forms via the condensation of amino acids to form a chain of amino acid "residues" linked by
peptide bonds. Proteins are defined by their unique sequence of amino acid residues; this sequence is the
primary structure of the protein. Just as the letters of the alphabet can be combined to form an almost endless variety of words, amino acids can be linked in varying sequences to form a huge variety of proteins.
Twenty list of standard amino acids are used by cell (biology) in
protein biosynthesis, and these are specified by the general genetic code. These twenty amino acids are
biosynthesis from other molecules, but organisms differ in which ones they can synthesize and which ones must be provided in their diet. The ones that cannot be synthesized by an organism are called
essential amino acids.
Functions in proteins
is a chain of amino acids.Amino acids are the basic structural building units of
proteins. They form short
polymer chains called
peptides or longer chains either called polypeptides or
proteins. The process of such formation from an mRNA template is known as translation (biology) which is part of protein biosynthesis. Twenty amino acids are encoded by the standard
genetic code and are called
proteinogenic or
List of standard amino acids. Other amino acids contained in proteins are usually formed by
post-translational modification, which is modification after translation in protein synthesis. These modifications are often essential for the function (biology) or regulation of a protein; for example, the carboxylation of glutamate allows for better binding of
calcium cations, and the hydroxylation of
proline is critical for maintaining
collagen and responding to hypoxia. Such modifications can also determine the localization of the protein, e.g., the addition of long hydrophobic groups can cause a protein to bind to a phospholipid membrane.
Non-protein functions
The twenty standard amino acids are either used to synthesize proteins and other biomolecules, or 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. Glucogenic amino acids can also be converted into glucose, through
gluconeogenesis.
Hundreds of types of non-protein amino acids have been found in nature and they have multiple functions in living organisms.
Microorganisms and plants can produce uncommon amino acids. In microbes, examples include 2-aminoisobutyric acid and
lanthionine, which is a sulfide-bridged alanine dimer. Both these amino acids are both found in peptidic lantibiotics such as
alamethicin. While in plants,
1-Aminocyclopropane-1-carboxylic acid is a small disubstituted cyclic amino acid that is a key intermediate in the production of the plant
hormone ethylene.
In humans, non-protein amino acids also have biologically-important roles.
Glycine, gamma-aminobutyric acid and
glutamate are
neurotransmitters and many amino acids are used to synthesize other molecules, for example:
Also present are hydroxyproline, hydroxylysine, and
sarcosine. The thyroid hormones are also alpha-amino acids.
Some amino acids have even been detected in
meteorites, especially in a type known as carbonaceous chondrites. This observation has prompted the suggestion that life may have arrived on earth from an Origin of life.
General structure
group on the left and the carboxyl group on the right.
In the structure shown to the right, the
R represents a
side chain specific to each amino acid. The central carbon atom called Cα is a
chirality (chemistry) central carbon atom (with the exception of glycine) to which the two termini and the R-group are attached. Amino acids are usually classified by the chemical property of the side chain into four groups. The side chain can make them behave like a
weak acid acid, a
weak base basic (chemistry), a hydrophile if they are
polar molecule, and hydrophobe if they are nonpolar. The chemical structures of the 20 standard amino acids, along with their chemical properties, are catalogued in the list of standard amino acids.
The phrase "
branched-chain amino acids" or BCAA is sometimes used to refer to the amino acids having
aliphatic side-chains that are non-linear, these are leucine, isoleucine and valine. Proline is the only proteinogenic amino acid whose side group links to the α-amino group, and thus is also the only proteinogenic amino acid containing a secondary amine at this position. Proline has sometimes been termed an imino acid, but this is not correct in the current nomenclature.Claude Liebecq (Ed)
Biochemical Nomenclature and Related Documents, 2nd edition, Portland Press, 1992, pages 39-69 ISBN 978-1855780057
Isomerism
Most amino acids can exist in either of two optical isomerism, called D and L. The L-amino acids represent the vast majority of amino acids found in
proteins. D-amino acids are found in some proteins produced by exotic sea-dwelling organisms, such as
cone snails. They are also abundant components of the
peptidoglycan cell walls of bacterium.
The L and D conventions for amino acid configuration do not refer to the optical activity, but rather to the optical activity of the isomer of
glyceraldehyde having the same stereochemistry as the amino acid.
S-Glyceraldehyde is levorotary, and
R-glyceraldehyde is dexterorotary, and so
S-amino acids are called L- even if they are not levorotary, and
R-amino acids are likewise called D- even if they are not dexterorotary.
There are two exceptions to these general rules of amino acid isomerism. Firstly, glycine, where
R = H, no isomerism is possible because the alpha-carbon bears two identical groups (hydrogen). Secondly, in cysteine, the L =
S and D =
R assignment is reversed to L =
R and D =
S. Cysteine is structured similarly (with respect to glyceraldehyde) to the other amino acids but the
sulfur atom alters the interpretation of the Cahn-Ingold-Prelog priority rule.
Reactions
As amino acids have both a primary amine group and a primary carboxyl group, these chemicals can undergo most of the reactions associated with these functional groups. These include
nucleophilic addition, amide formation and
Alkylimino-de-oxo-bisubstitution for the amine group and
esterification,
amide formation and
decarboxylation for the carboxylic acid group. The multiple side chains of amino acids can also undergo chemical reactions. The types of these reactions are determined by the groups on these side chains and are discussed in the articles dealing with each specific type of amino acid.
Peptide bond formation
.
As both the amine and carboxylic acid groups of amino acids can react to form amide bonds, one amino acid molecule can react with another and become joined through an amide linkage. This
polymerization of amino acids is what creates proteins. This
condensation reaction yields the newly formed peptide bond and a molecule of water. In cells, this reaction does not occur directly, instead the amino acid is activated by attachment to a
transfer RNA molecule through an
ester bond. This aminoacyl-tRNA is produced in an
Adenosine triphosphate-dependent reaction carried out by an aminoacyl tRNA synthetase.
is one of the standard amino acids.
In chemistry, an
amino acid is a molecule that contains both amine and carboxyl
functional groups. In biochemistry, this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent. Proline is an exception to this general formula. It lacks the NH2 group because of the cyclization of the side chain. In the alpha amino acids, the amino and carboxylate groups are attached to the same carbon, which is called the alpha carbon. The various alpha amino acids differ in which
side chain (R group) is attached to their alpha carbon. They can vary in size from just a hydrogen atom in
glycine, through a
methyl group in alanine, to a large
heterocycle in tryptophan.
Beyond the amino acids that are found in all forms of life, many non-natural amino acids are also important. The chelating agents EDTA and Nitrilotriacetic acid are alpha amino acids that are industrially synthesized (sometimes from naturally occurring amino acids).
Overview
Alpha-amino acids are the building blocks of proteins. A protein forms via the condensation of amino acids to form a chain of amino acid "residues" linked by peptide bonds. Proteins are defined by their unique sequence of amino acid residues; this sequence is the primary structure of the protein. Just as the letters of the alphabet can be combined to form an almost endless variety of words, amino acids can be linked in varying sequences to form a huge variety of proteins.
Twenty
list of standard amino acids are used by
cell (biology) in
protein biosynthesis, and these are specified by the general
genetic code. These twenty amino acids are
biosynthesis from other molecules, but organisms differ in which ones they can synthesize and which ones must be provided in their diet. The ones that cannot be synthesized by an organism are called essential amino acids.
Functions in proteins
is a chain of amino acids.Amino acids are the basic structural building units of
proteins. They form short polymer chains called peptides or longer chains either called polypeptides or
proteins. The process of such formation from an
mRNA template is known as
translation (biology) which is part of
protein biosynthesis. Twenty amino acids are encoded by the standard genetic code and are called
proteinogenic or
List of standard amino acids. Other amino acids contained in proteins are usually formed by post-translational modification, which is modification after translation in protein synthesis. These modifications are often essential for the
function (biology) or regulation of a protein; for example, the
carboxylation of
glutamate allows for better binding of
calcium cations, and the hydroxylation of
proline is critical for maintaining
collagen and responding to hypoxia. Such modifications can also determine the localization of the protein, e.g., the addition of long hydrophobic groups can cause a protein to bind to a
phospholipid membrane.
Non-protein functions
The twenty standard amino acids are either used to synthesize proteins and other biomolecules, or 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. Glucogenic amino acids can also be converted into glucose, through
gluconeogenesis.
Hundreds of types of non-protein amino acids have been found in nature and they have multiple functions in living organisms.
Microorganisms and plants can produce uncommon amino acids. In microbes, examples include 2-aminoisobutyric acid and lanthionine, which is a sulfide-bridged alanine dimer. Both these amino acids are both found in peptidic lantibiotics such as alamethicin. While in plants,
1-Aminocyclopropane-1-carboxylic acid is a small disubstituted cyclic amino acid that is a key intermediate in the production of the plant
hormone ethylene.
In humans, non-protein amino acids also have biologically-important roles. Glycine,
gamma-aminobutyric acid and
glutamate are
neurotransmitters and many amino acids are used to synthesize other molecules, for example:
- Tryptophan is a precursor of the neurotransmitter serotonin
- Glycine is a precursor of porphyrins such as heme
- Arginine is a precursor of nitric oxide
- Carnitine is used in lipid transport within a cell (biology),
- Ornithine and S-Adenosyl methionine are precursors of polyamines,
- Homocysteine is an intermediate in S-Adenosyl methionine recycling
Also present are hydroxyproline,
hydroxylysine, and
sarcosine. The thyroid hormones are also alpha-amino acids.
Some amino acids have even been detected in
meteorites, especially in a type known as
carbonaceous chondrites. This observation has prompted the suggestion that life may have arrived on earth from an
Origin of life.
General structure
group on the left and the carboxyl group on the right.
In the structure shown to the right, the
R represents a side chain specific to each amino acid. The central carbon atom called Cα is a chirality (chemistry) central
carbon atom (with the exception of glycine) to which the two termini and the R-group are attached. Amino acids are usually classified by the chemical property of the side chain into four groups. The side chain can make them behave like a
weak acid acid, a weak base basic (chemistry), a hydrophile if they are polar molecule, and
hydrophobe if they are nonpolar. The chemical structures of the 20 standard amino acids, along with their chemical properties, are catalogued in the
list of standard amino acids.
The phrase "
branched-chain amino acids" or BCAA is sometimes used to refer to the amino acids having
aliphatic side-chains that are non-linear, these are
leucine,
isoleucine and valine. Proline is the only proteinogenic amino acid whose side group links to the α-amino group, and thus is also the only proteinogenic amino acid containing a secondary amine at this position. Proline has sometimes been termed an imino acid, but this is not correct in the current nomenclature.Claude Liebecq (Ed)
Biochemical Nomenclature and Related Documents, 2nd edition, Portland Press, 1992, pages 39-69 ISBN 978-1855780057
Isomerism
Most amino acids can exist in either of two
optical isomerism, called D and L. The L-amino acids represent the vast majority of amino acids found in
proteins. D-amino acids are found in some proteins produced by exotic sea-dwelling organisms, such as cone snails. They are also abundant components of the peptidoglycan
cell walls of
bacterium.
The L and D conventions for amino acid configuration do not refer to the optical activity, but rather to the optical activity of the isomer of
glyceraldehyde having the same stereochemistry as the amino acid.
S-Glyceraldehyde is levorotary, and
R-glyceraldehyde is dexterorotary, and so
S-amino acids are called L- even if they are not levorotary, and
R-amino acids are likewise called D- even if they are not dexterorotary.
There are two exceptions to these general rules of amino acid isomerism. Firstly, glycine, where
R = H, no isomerism is possible because the alpha-carbon bears two identical groups (hydrogen). Secondly, in cysteine, the L =
S and D =
R assignment is reversed to L =
R and D =
S. Cysteine is structured similarly (with respect to glyceraldehyde) to the other amino acids but the
sulfur atom alters the interpretation of the
Cahn-Ingold-Prelog priority rule.
Reactions
As amino acids have both a primary
amine group and a primary
carboxyl group, these chemicals can undergo most of the reactions associated with these functional groups. These include nucleophilic addition, amide formation and Alkylimino-de-oxo-bisubstitution for the amine group and esterification,
amide formation and decarboxylation for the carboxylic acid group. The multiple side chains of amino acids can also undergo chemical reactions. The types of these reactions are determined by the groups on these side chains and are discussed in the articles dealing with each specific type of amino acid.
Peptide bond formation
.
As both the amine and carboxylic acid groups of amino acids can react to form amide bonds, one amino acid molecule can react with another and become joined through an amide linkage. This polymerization of amino acids is what creates proteins. This
condensation reaction yields the newly formed peptide bond and a molecule of water. In cells, this reaction does not occur directly, instead the amino acid is activated by attachment to a
transfer RNA molecule through an ester bond. This aminoacyl-tRNA is produced in an Adenosine triphosphate-dependent reaction carried out by an
aminoacyl tRNA synthetase.
Introduction To Amino Acids
Introduction To Amino Acids This is a quick introduction to amino acids. It may be used as a short 'test workout' for anyone intending to undertake the GNA course titled Principles ...
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Amino acid - Wikipedia, the free encyclopedia
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Amino Acids and Peptides Home Page
The full text of the IUPAC and IUBMB nomenclature and symbolism for amino acids and peptides ... and INTERNATIONAL UNION OF BIOCHEMISTRY AND MOLECULAR BIOLOGY. IUPAC-IUB Joint ...
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predicting antidepressant response. ... Predictive value of tryptophan/large neutral amino acids ratio to antidepressant response
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Transaminases (aminotransferases) catalyze the reversible reaction shown at right. There are multiple transaminase enzymes which vary in substrate specificity.
Amino Acids
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