1 or 3 Codons Equal One Amino Acid

1 or 3 Codons Equal One Amino Acid

Organic compounds containing amine and carboxylic groups

Structure of a generic L-amino acid in the “neutral” form needed for defining a systematic proper noun, without implying that this form really exists in detectable amounts either in aqueous solution or in the solid state.

Amino acids
are organic compounds that contain amino[a]

) and carboxylic acrid (−CO2H) functional groups, forth with a side concatenation (R grouping) specific to each amino acid.[1]
The elements present in every amino acrid are carbon (C), hydrogen (H), oxygen (O), and nitrogen (Northward) (CHON); in improver sulfur (Due south) is present in the side chains of cysteine and methionine, and selenium (Se) in the less common amino acid selenocysteine. More than 500 naturally occurring amino acids are known to institute monomer units of peptides, including proteins, as of 2020[update]
although only 22 announced in the genetic code, 20 of which have their own designated codons and two of which have special coding mechanisms: Selenocysteine which is present in all eukaryotes and pyrrolysine which is present in some prokaryotes.[three]

Amino acids are formally named by the IUPAC-IUBMB Joint Commission on Biochemical Nomenclature[5]
in terms of the fictitious “neutral” construction shown in the analogy. For example, the systematic name of alanine is 2-aminopropanoic acid, based on the formula
CHiii−CH(NHtwo)−COOH. The Commission justified this approach as follows:

The systematic names and formulas given refer to hypothetical forms in which amino groups are unprotonated and carboxyl groups are undissociated. This convention is useful to avoid various nomenclatural bug but should non be taken to imply that these structures correspond an observable fraction of the amino-acid molecules.

They can be classified according to the locations of the cadre structural functional groups, every bit alpha-
(α-), beta-
(β-), gamma-
or delta-
amino acids; other categories chronicle to polarity, ionization, and side chain group type (aliphatic, acyclic, effluvious, containing hydroxyl or sulfur, etc.). In the form of proteins, amino acrid
grade the second-largest component (h2o being the largest) of man muscles and other tissues.[half-dozen]
Across their part as residues in proteins, amino acids participate in a number of processes such every bit neurotransmitter transport and biosynthesis.



The first few amino acids were discovered in the early 1800s.[7]
In 1806, French chemists Louis-Nicolas Vauquelin and Pierre Jean Robiquet isolated a chemical compound from asparagus that was later named asparagine, the first amino acrid to be discovered.[9]
Cystine was discovered in 1810,[11]
although its monomer, cysteine, remained undiscovered until 1884.[12]
Glycine and leucine were discovered in 1820.[thirteen]
The last of the 20 common amino acids to exist discovered was threonine in 1935 by William Cumming Rose, who also determined the essential amino acids and established the minimum daily requirements of all amino acids for optimal growth.[14]

The unity of the chemical category was recognized by Wurtz in 1865, but he gave no particular name to information technology.[16]
The start employ of the term “amino acid” in the English linguistic communication dates from 1898,[17]
while the German term,

, was used before.[18]
Proteins were found to yield amino acids subsequently enzymatic digestion or acid hydrolysis. In 1902, Emil Fischer and Franz Hofmeister independently proposed that proteins are formed from many amino acids, whereby bonds are formed between the amino grouping of i amino acid with the carboxyl grouping of another, resulting in a linear structure that Fischer termed “peptide”.[19]

Full general construction


In the structure shown at the top of the page R represents a side chain specific to each amino acid. The carbon atom adjacent to the carboxyl group is called the α–carbon. Amino acids containing an amino group bonded directly to the α-carbon are referred to as
α-amino acids.[20]
These include proline and hydroxyproline,[c]
which are secondary amines. In the past they were oftentimes chosen
imino acids, a misnomer because they do not contain an imine grouping
The obsolete term remains frequent.



The common natural forms of amino acids have the structure


in the example of proline) and


functional groups attached to the aforementioned C atom, and are thus α-amino acids. With the exception of achiral glycine, natural amino acids have the
and are the only ones plant in proteins during translation in the ribosome.

convention for amino acid configuration refers not to the optical activity of the amino acrid itself merely rather to the optical activity of the isomer of glyceraldehyde from which that amino acid can, in theory, be synthesized (D-glyceraldehyde is dextrorotatory;
L-glyceraldehyde is levorotatory).

An culling convention is to apply the (S) and (R) designators to specify the
absolute configuration.[23]
Almost all of the amino acids in proteins are (S) at the α carbon, with cysteine being (R) and glycine non-chiral.[24]
Cysteine has its side concatenation in the aforementioned geometric location every bit the other amino acids, simply the
terminology is reversed because sulfur has higher atomic number compared to the carboxyl oxygen which gives the side concatenation a higher priority by the
Cahn-Ingold-Prelog sequence rules, whereas the atoms in most other side chains give them lower priority compared to the carboxyl group.[23]

D-amino acid residues are institute in some proteins, but they are rare.

Side bondage


Amino acids are designated as α- when the amino nitrogen cantlet is fastened to the α-carbon, the carbon atom adjacent to the carboxylate group.

In all cases below in this department the




{\displaystyle \mathrm {p} K_{\mathrm {a} }}

values (if whatsoever) refer to the ionization of the groups as amino acrid residues in proteins. They are not




{\displaystyle \mathrm {p} K_{\mathrm {a} }}

values for the free amino acids (which are of little biochemical importance).

Aliphatic side-chains


Several side-chains comprise only H and C, and do not ionize. These are as follows (with iii- and ane-letter symbols in parentheses):

  • Glycine (Gly, G):
  • Alanine (Ala, A):
  • Valine (Val, 5):
  • Leucine (Leu, 50):
  • Isoleucine (Ile, I):
  • Proline (Pro, P):
    cyclized onto the amine

Polar neutral side-chains


Two aminoacids comprise alcohol side-bondage. These practice not ionize in normal conditions, though 1, serine, becomes deprotonated during the catalysis by serine proteases: this is an case of severe perturbation, and is not characteristic of serine residues in general.

Threonine has two chiral centers, not only the
(twoS) chiral heart at the α-carbon shared by all amino acids apart from achiral glycine, only also (iiiR) at the β-carbon. The full stereochemical specification is
L-threonine (2Due south,3R).

Amide side-chains


Two amino acids have amide side-bondage, equally follows:

  • Asparagine (Asn, Northward):
  • Glutamine (Gln, Q):

These side-chains practise not ionize in the normal range of pH.

Sulfur-containing side-chains


Two side-chains comprise sulfur atoms, of which 1 ionizes in the normal range (with




{\displaystyle \mathrm {p} K_{\mathrm {a} }}

indicated) and the other does not:

Aromatic side-chains


Side-chains of phenylalanine (left), tyrosine (middle) and tryptophan (right)

Three amino acids have aromatic ring structures equally side-chains, as illustrated. Of these, tyrosine ionizes in the normal range; the other two do not).

Anionic side-chains


2 amino acids take side-chains that are anions at ordinary pH. These amino acids are oft referred to every bit if carboxylic acids but are more correctly called carboxylates, as they are deprotonated at most relevant pH values. The anionic carboxylate groups bear as Brønsted bases in all circumstances except for enzymes like pepsin that act in environments of very low pH similar the mammalian tummy.

Cationic side-bondage


Side-chains of histidine (left), lysine (centre) and arginine (correct)

There are three amino acids with side-bondage that are cations at neutral pH (though in ane, histidine, cationic and neutral forms both exist). They are commonly called
basic amino acids, but this term is misleading: histidine can human activity both every bit a Brønsted acid and as a Brønsted base at neutral pH, lysine acts as a Brønsted acrid, and arginine has a fixed positive charge and does not ionize in neutral conditions. The names
histidinium, lysinium
would be more than accurate names for the structures, but have substantially no currency.

β- and γ-amino acids


Amino acids with the construction


, such as β-alanine, a component of carnosine and a few other peptides, are β-amino acids. Ones with the construction


are γ-amino acids, and so on, where X and Y are ii substituents (ane of which is normally H).[5]



Ionization and Brønsted character of N-final amino, C-final carboxylate, and side bondage of amino acid residues

In aqueous solution amino acids at moderate pH exist as zwitterions, i.e. every bit dipolar ions with both



in charged states, so the overall construction is


. At physiological pH the so-called “neutral forms”
are not nowadays to whatever measurable degree.[25]
Although the two charges in the real structure add up to zero it is misleading and wrong to phone call a species with a net accuse of null “uncharged”.

At very low pH (below 3), the carboxylate group becomes protonated and the structure becomes an ammonio carboxylic acid,
. This is relevant for enzymes like pepsin that are active in acidic environments such as the mammalian stomach and lysosomes, but does not significantly employ to intracellular enzymes. At very high pH (greater than 10, non normally seen in physiological weather condition), the ammonio group is deprotonated to give



Although various definitions of acids and bases are used in chemistry, the only i that is useful for chemical science in aqueous solution is that of Brønsted:[26]
an acid is a species that can donate a proton to another species, and a base is one that can accept a proton. This criterion is used to characterization the groups in the above analogy. Discover that aspartate and glutamate are the principal groups that act equally Brønsted bases, and the common references to these as
acidic amino acids
(together with the C final) is completely wrong and misleading. Too the then-called
basic amino acids
include ane (histidine) that acts as both a Brønsted acrid and a base of operations, one (lysine) that acts primarily as a Brønsted acrid, and one (arginine) that is unremarkably irrelevant to acid-base of operations beliefs equally it has a fixed positive accuse. In addition, tyrosine and cysteine, which act primarily as acids at neutral pH, are commonly forgotten in the usual classification.

Isoelectric point


Blended of titration curves of twenty proteinogenic amino acids grouped past side chain category

For amino acids with uncharged side-bondage the zwitterion predominates at pH values between the two pK
values, just coexists in equilibrium with small amounts of internet negative and cyberspace positive ions. At the midpoint betwixt the two pK
values, the trace corporeality of net negative and trace of net positive ions balance, so that average net charge of all forms present is zero.[27]
This pH is known as the isoelectric bespeak pI, then pI

+ pK

For amino acids with charged side chains, the pChiliad
of the side chain is involved. Thus for aspartate or glutamate with negative side bondage, the terminal amino grouping is essentially entirely in the charged class

, merely this positive charge needs to exist balanced by the country with only ane C-last carboxylate grouping is negatively charged. This occurs halfway between the two carboxylate pThousand
values: pI

+ pYard
a(R)), where pM
is the side chain pM

Like considerations utilise to other amino acids with ionizable side-chains, including not only glutamate (similar to aspartate), only too cysteine, histidine, lysine, tyrosine and arginine with positive side chains

Amino acids accept zero mobility in electrophoresis at their isoelectric indicate, although this behaviour is more than usually exploited for peptides and proteins than single amino acids. Zwitterions have minimum solubility at their isoelectric point, and some amino acids (in particular, with nonpolar side chains) tin can be isolated by precipitation from water by adjusting the pH to the required isoelectric betoken.

Physicochemical properties of amino acids


The ca. 20 canonical amino acids tin can be classified according to their properties. Important factors are charge, hydrophilicity or hydrophobicity, size, and functional groups.[22]
These properties influence protein construction and protein–protein interactions. The h2o-soluble proteins tend to accept their hydrophobic residues (Leu, Ile, Val, Phe, and Trp) buried in the centre of the protein, whereas hydrophilic side chains are exposed to the aqueous solvent. (Note that in biochemistry, a residue refers to a specific monomer within the polymeric concatenation of a polysaccharide, poly peptide or nucleic acid.) The integral membrane proteins tend to have outer rings of exposed hydrophobic amino acids that anchor them into the lipid bilayer. Some peripheral membrane proteins have a patch of hydrophobic amino acids on their surface that locks onto the membrane. In like fashion, proteins that have to bind to positively charged molecules have surfaces rich with negatively charged amino acids like glutamate and aspartate, while proteins binding to negatively charged molecules have surfaces rich with positively charged chains like lysine and arginine. For example, lysine and arginine are highly enriched in low-complication regions of nucleic-acid binding proteins.[28]
At that place are various hydrophobicity scales of amino acid residues.[29]

Some amino acids accept special properties such equally cysteine, that can course covalent disulfide bonds to other cysteine residues, proline that forms a wheel to the polypeptide backbone, and glycine that is more flexible than other amino acids.

Furthermore, glycine and proline are highly enriched inside low complexity regions of eukaryotic and prokaryotic proteins, whereas the opposite (under-represented) has been observed for highly reactive, or complex, or hydrophobic amino acids, such as cysteine, phenylalanine, tryptophan, methionine, valine, leucine, isoleucine.[28]

Many proteins undergo a range of posttranslational modifications, whereby additional chemical groups are fastened to the amino acid side bondage. Some modifications can produce hydrophobic lipoproteins,[32]
or hydrophilic glycoproteins.[33]
These type of modification allow the reversible targeting of a protein to a membrane. For case, the add-on and removal of the fatty acid palmitic acid to cysteine residues in some signaling proteins causes the proteins to attach and so detach from prison cell membranes.[34]

Table of standard amino acid abbreviations and properties


Although one-letter symbols are included in the table, IUPAC–IUBMB recommend[5]
that “Employ of the i-letter symbols should be restricted to the comparing of long sequences”.

Amino acid 3- and 1-letter symbols Side chain Hydropathy

Molar absorptivity[36] Molecular mass Abundance in
proteins (%)[37]
Standard genetic coding,
IUPAC notation
3 1 Class Polarity[38] Net charge
at pH 7.4[38]

Alanine Ala A Aliphatic Nonpolar Neutral 1.eight 89.094 8.76 GCN
Arginine Arg R Stock-still cation Basic polar Positive −four.5 174.203 5.78 MGR, CGY[39]
Asparagine Asn Northward Amide Polar Neutral −3.5 132.119 3.93 AAY
Aspartate Asp D Anion Brønsted base of operations Negative −3.5 133.104 5.49 GAY
Cysteine Cys C Thiol Brønsted acid Neutral ii.5 250 0.iii 121.154 1.38 UGY
Glutamine Gln Q Amide Polar Neutral −3.five 146.146 3.nine Automobile
Glutamate Glu E Anion Brønsted base Negative −three.5 147.131 6.32 GAR
Glycine Gly Chiliad Aliphatic Nonpolar Neutral −0.4 75.067 7.03 GGN
Histidine His H Effluvious cation Brønsted acid and base Positive, x%
Neutral, 90%
−3.2 211 5.9 155.156 two.26 CAY
Isoleucine Ile I Aliphatic Nonpolar Neutral 4.5 131.175 5.49 AUH
Leucine Leu Fifty Aliphatic Nonpolar Neutral 3.8 131.175 9.68 YUR, CUY[40]
Lysine Lys K Cation Brønsted acid Positive −3.9 146.189 v.xix AAR
Methionine Met M Thioether Nonpolar Neutral 1.9 149.208 2.32 AUG
Phenylalanine Phe F Effluvious Nonpolar Neutral 2.8 257, 206, 188 0.two, nine.3, 60.0 165.192 3.87 UUY
Proline Pro P Cyclic Nonpolar Neutral −i.half dozen 115.132 v.02 CCN
Serine Ser S Hydroxylic Polar Neutral −0.8 105.093 7.14 UCN, AGY
Threonine Thr T Hydroxylic Polar Neutral −0.7 119.119 5.53 ACN
Tryptophan Trp Due west Aromatic Nonpolar Neutral −0.9 280, 219 5.6, 47.0 204.228 ane.25 UGG
Tyrosine Tyr Y Effluvious Brønsted acrid Neutral −1.3 274, 222, 193 1.4, eight.0, 48.0 181.191 2.91 UAY
Valine Val Five Aliphatic Nonpolar Neutral 4.ii 117.148 vi.73 GUN
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Two additional amino acids are in some species coded for by codons that are ordinarily interpreted as stop codons:

21st and 22nd amino acids 3-letter i-alphabetic character Molecular mass
Selenocysteine Sec U 168.064
Pyrrolysine Pyl O 255.313

In addition to the specific amino acid codes, placeholders are used in cases where chemical or crystallographic assay of a peptide or poly peptide cannot conclusively decide the identity of a residue. They are as well used to summarise conserved protein sequence motifs. The use of single letters to indicate sets of similar residues is like to the apply of abbreviation codes for degenerate bases.[41]

Ambiguous amino acids iii-letter of the alphabet 1-letter Amino acids included Codons included
Whatever / unknown Xaa Ten All NNN
Asparagine or aspartate Asx B D, N RAY
Glutamine or glutamate Glx Z E, Q SAR
Leucine or isoleucine Xle J I, Fifty YTR, ATH, CTY[43]
Hydrophobic Φ V, I, Fifty, F, West, Y, Thousand NTN, TAY, TGG
Effluvious Ω F, Westward, Y, H YWY, TTY, TGG[44]
Aliphatic (non-effluvious) Ψ V, I, L, 1000 VTN, TTR[45]
Small π P, G, A, Due south BCN, RGY, GGR
Hydrophilic ζ S, T, H, N, Q, E, D, One thousand, R VAN, WCN, CGN, AGY[46]
Positively-charged + Grand, R, H ARR, CRY, CGR
Negatively-charged D, East GAN

is sometimes used instead of
Xaa, only is less standard.

(from termination) is used in notation for mutations in proteins when a stop codon occurs. Information technology represent to no amino acrid at all.[47]

In addition, many nonstandard amino acids take a specific code. For example, several peptide drugs, such equally Bortezomib and MG132, are artificially synthesized and retain their protecting groups, which have specific codes. Bortezomib is Pyz–Phe–boroLeu, and MG132 is Z–Leu–Leu–Leu–al. To aid in the analysis of poly peptide structure, photo-reactive amino acid analogs are available. These include photoleucine (pLeu) and photomethionine (pMet).[48]

Occurrence and functions in biochemistry


Diagrammatic comparison of the structures of β-alanine and α-alanine

β-Alanine and its α-alanine isomer

A diagram showing the structure of selenocysteine

Amino acids which have the amine group fastened to the (alpha-) carbon cantlet side by side to the carboxyl group have main importance in living organisms since they participate in protein synthesis.[49]
They are known as
blastoff-, or
α-amino acids
(generic formula
in most cases,[d]
where R is an organic substituent known as a “side concatenation”);[50]
often the term “amino acid” is used to refer specifically to these. They include the 22 proteinogenic (“protein-building”) amino acids,[51]
which combine into peptide bondage (“polypeptides”) to form the building blocks of a vast array of proteins.[49]
These are all
Fifty-stereoisomers (“left-handed” enantiomers), although a few
D-amino acids (“correct-handed”) occur in bacterial envelopes, as a neuromodulator (D-serine), and in some antibiotics.[54]

Many proteinogenic and not-proteinogenic amino acids have biological functions. For case, in the human brain, glutamate (standard glutamic acid) and gamma-aminobutyric acid (“GABA”, nonstandard gamma-amino acrid) are, respectively, the chief excitatory and inhibitory neurotransmitters.[55]
Hydroxyproline, a major component of the connective tissue collagen, is synthesised from proline. Glycine is a biosynthetic precursor to porphyrins used in cherry-red blood cells. Carnitine is used in lipid transport. Nine proteinogenic amino acids are called “essential” for humans considering they cannot be produced from other compounds by the human being body and so must exist taken in as food. Others may be conditionally essential for certain ages or medical conditions. Essential amino acids may also vary from species to species.[e]
Because of their biological significance, amino acids are important in nutrition and are commonly used in nutritional supplements, fertilizers, feed, and food technology. Industrial uses include the product of drugs, biodegradable plastics, and chiral catalysts.

Proteinogenic amino acids


Amino acids are the precursors to proteins. They join by condensation reactions to form short polymer chains called peptides or longer chains called either polypeptides or proteins. These chains are linear and unbranched, with each amino acid residue within the concatenation fastened to 2 neighboring amino acids. In Nature, the procedure of making proteins encoded past Deoxyribonucleic acid/RNA genetic material is called
and involves the footstep-by-step addition of amino acids to a growing protein chain by a ribozyme that is called a ribosome.[56]
The society in which the amino acids are added is read through the genetic lawmaking from an mRNA template, which is an RNA copy of one of the organism’south genes.

Twenty-two amino acids are naturally incorporated into polypeptides and are called proteinogenic or natural amino acids.[22]
Of these, 20 are encoded by the universal genetic code. The remaining 2, selenocysteine and pyrrolysine, are incorporated into proteins by unique synthetic mechanisms. Selenocysteine is incorporated when the mRNA being translated includes a SECIS chemical element, which causes the UGA codon to encode selenocysteine instead of a finish codon.[57]
Pyrrolysine is used by some methanogenic archaea in enzymes that they apply to produce methyl hydride. It is coded for with the codon UAG, which is ordinarily a finish codon in other organisms.[58]
This UAG codon is followed past a PYLIS downstream sequence.[59]

Several independent evolutionary studies have suggested that Gly, Ala, Asp, Val, Ser, Pro, Glu, Leu, Thr may belong to a group of amino acids that constituted the early on genetic code, whereas Cys, Met, Tyr, Trp, His, Phe may belong to a grouping of amino acids that constituted later additions of the genetic code.[threescore]

Standard vs nonstandard amino acids


The twenty amino acids that are encoded directly by the codons of the universal genetic code are called
amino acids. A modified form of methionine (North-formylmethionine) is often incorporated in place of methionine every bit the initial amino acrid of proteins in bacteria, mitochondria and chloroplasts. Other amino acids are chosen
non-approved. Most of the nonstandard amino acids are besides non-proteinogenic (i.e. they cannot be incorporated into proteins during translation), only ii of them are proteinogenic, as they tin can be incorporated translationally into proteins past exploiting information non encoded in the universal genetic lawmaking.

The two nonstandard proteinogenic amino acids are selenocysteine (nowadays in many non-eukaryotes too as almost eukaryotes, but not coded directly by DNA) and pyrrolysine (found only in some archaea and at least one bacterium). The incorporation of these nonstandard amino acids is rare. For example, 25 human proteins include selenocysteine in their chief structure,[63]
and the structurally characterized enzymes (selenoenzymes) employ selenocysteine as the catalytic moiety in their agile sites.[64]
Pyrrolysine and selenocysteine are encoded via variant codons. For instance, selenocysteine is encoded past stop codon and SECIS element.[65]

Northward-formylmethionine (which is often the initial amino acid of proteins in bacteria, mitochondria, and chloroplasts) is mostly considered as a form of methionine rather than every bit a separate proteinogenic amino acid. Codon–tRNA combinations not found in nature tin can also exist used to “expand” the genetic code and class novel proteins known as alloproteins incorporating non-proteinogenic amino acids.[68]

Non-proteinogenic amino acids


Aside from the 22 proteinogenic amino acids, many
amino acids are known. Those either are not found in proteins (for example carnitine, GABA, levothyroxine) or are not produced straight and in isolation by standard cellular mechanism (for example, hydroxyproline and selenomethionine).

Non-proteinogenic amino acids that are found in proteins are formed by post-translational modification, which is modification later on translation during protein synthesis. These modifications are often essential for the function or regulation of a protein. For case, the carboxylation of glutamate allows for amend binding of calcium cations,[71]
and collagen contains hydroxyproline, generated by hydroxylation of proline.[72]
Another example is the formation of hypusine in the translation initiation factor EIF5A, through modification of a lysine residual.[73]
Such modifications can also determine the localization of the protein, e.g., the addition of long hydrophobic groups tin can cause a protein to bind to a phospholipid membrane.[74]

Some non-proteinogenic amino acids are not constitute in proteins. Examples include two-aminoisobutyric acid and the neurotransmitter gamma-aminobutyric acid. Non-proteinogenic amino acids often occur equally intermediates in the metabolic pathways for standard amino acids – for example, ornithine and citrulline occur in the urea cycle, function of amino acid catabolism (come across below).[75]
A rare exception to the dominance of α-amino acids in biology is the β-amino acid beta alanine (3-aminopropanoic acrid), which is used in plants and microorganisms in the synthesis of pantothenic acrid (vitamin B5), a component of coenzyme A.[76]

In human being nutrition


Diagram showing the relative occurrence of amino acids in blood serum as obtained from diverse diets.

Share of amino acid in diverse human diets and the resulting mix of amino acids in homo claret serum. Glutamate and glutamine are the near frequent in nutrient at over 10%, while alanine, glutamine, and glycine are the virtually common in blood.

When taken up into the human torso from the diet, the xx standard amino acids either are used to synthesize proteins, other biomolecules, or are oxidized to urea and carbon dioxide as a source of energy.[77]
The oxidation pathway starts with the removal of the amino group by a transaminase; the amino group is and then fed into the urea cycle. The other product of transamidation is a keto acid that enters the citric acid cycle.[78]
Glucogenic amino acids can besides exist converted into glucose, through gluconeogenesis.[79]
Of the 20 standard amino acids, nine (His, Ile, Leu, Lys, Met, Phe, Thr, Trp and Val) are chosen essential amino acids because the human trunk cannot synthesize them from other compounds at the level needed for normal growth, so they must exist obtained from food.[80]
In addition, cysteine, tyrosine, and arginine are considered semiessential amino acids, and taurine a semiessential aminosulfonic acid in children. The metabolic pathways that synthesize these monomers are non fully adult.[83]
The amounts required besides depend on the age and wellness of the individual, so it is hard to make general statements about the dietary requirement for some amino acids. Dietary exposure to the nonstandard amino acid BMAA has been linked to homo neurodegenerative diseases, including ALS.[85]

Signaling cascade diagram

Graph of muscle protein synthesis vs time

Resistance training stimulates muscle poly peptide synthesis (MPS) for a menses of upwardly to 48 hours post-obit exercise (shown by lighter dotted line).[89]
Ingestion of a poly peptide-rich meal at any betoken during this period volition augment the practice-induced increase in muscle poly peptide synthesis (shown by solid lines).[89]

Non-protein functions


In humans, non-protein amino acids also have important roles every bit metabolic intermediates, such as in the biosynthesis of the neurotransmitter gamma-aminobutyric acid (GABA). Many amino acids are used to synthesize other molecules, for example:

  • Tryptophan is a forerunner of the neurotransmitter serotonin.[93]
  • Tyrosine (and its forerunner phenylalanine) are precursors of the catecholamine neurotransmitters dopamine, epinephrine and norepinephrine and various trace amines.
  • Phenylalanine is a precursor of phenethylamine and tyrosine in humans. In plants, information technology is a precursor of various phenylpropanoids, which are important in plant metabolism.
  • Glycine is a precursor of porphyrins such as heme.[94]
  • Arginine is a precursor of nitric oxide.[95]
  • Ornithine and
    S-adenosylmethionine are precursors of polyamines.[96]
  • Aspartate, glycine, and glutamine are precursors of nucleotides.[97]
    However, not all of the functions of other arable nonstandard amino acids are known.

Some nonstandard amino acids are used as defenses confronting herbivores in plants.[98]
For example, canavanine is an counterpart of arginine that is found in many legumes,[99]
and in particularly big amounts in
Canavalia gladiata
(sword edible bean).[100]
This amino acid protects the plants from predators such equally insects and can cause disease in people if some types of legumes are eaten without processing.[101]
The non-poly peptide amino acid mimosine is found in other species of legume, in particular
Leucaena leucocephala.[102]
This compound is an analogue of tyrosine and tin can toxicant animals that graze on these plants.

Uses in industry


Amino acids are used for a variety of applications in industry, but their primary utilize is every bit additives to animal feed. This is necessary, since many of the majority components of these feeds, such as soybeans, either take low levels or lack some of the essential amino acids: lysine, methionine, threonine, and tryptophan are virtually important in the product of these feeds.[103]
In this manufacture, amino acids are as well used to chelate metal cations in gild to ameliorate the absorption of minerals from supplements, which may exist required to improve the health or productivity of these animals.[104]

The nutrient industry is also a major consumer of amino acids, in item, glutamic acid, which is used as a flavor enhancer,[105]
and aspartame (aspartylphenylalanine 1-methyl ester) every bit a depression-calorie bogus sweetener.[106]
Similar technology to that used for animate being nutrition is employed in the human diet industry to alleviate symptoms of mineral deficiencies, such as anemia, by improving mineral absorption and reducing negative side effects from inorganic mineral supplementation.[107]

The chelating ability of amino acids has been used in fertilizers for agriculture to facilitate the delivery of minerals to plants in lodge to right mineral deficiencies, such as iron chlorosis. These fertilizers are as well used to preclude deficiencies from occurring and to improve the overall health of the plants.[108]
The remaining production of amino acids is used in the synthesis of drugs and cosmetics.[103]

Similarly, some amino acids derivatives are used in pharmaceutical industry. They include 5-HTP (5-hydroxytryptophan) used for experimental treatment of low,[109]
Fifty-DOPA (L-dihydroxyphenylalanine) for Parkinson’s handling,[110]
and eflornithine drug that inhibits ornithine decarboxylase and used in the handling of sleeping sickness.[111]

Expanded genetic code


Since 2001, forty not-natural amino acids have been added into protein by creating a unique codon (recoding) and a respective transfer-RNA:aminoacyl – tRNA-synthetase pair to encode information technology with diverse physicochemical and biological properties in club to be used as a tool to exploring protein structure and role or to create novel or enhanced proteins.[68]

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Nullomers are codons that in theory lawmaking for an amino acid, even so, in nature there is a selective bias against using this codon in favor of some other, for example bacteria prefer to use CGA instead of AGA to code for arginine.[112]
This creates some sequences that do not appear in the genome. This characteristic can be taken advantage of and used to create new selective cancer-fighting drugs[113]
and to prevent cross-contamination of Dna samples from crime-scene investigations.[114]

Chemical edifice blocks


Amino acids are important as low-price feedstocks. These compounds are used in chiral pool synthesis as enantiomerically pure building blocks.[115]

Amino acids take been investigated as precursors chiral catalysts, such as for disproportionate hydrogenation reactions, although no commercial applications exist.[116]

Biodegradable plastics


Amino acids have been considered as components of biodegradable polymers, which have applications as environmentally friendly packaging and in medicine in drug delivery and the structure of prosthetic implants.[117]
An interesting example of such materials is polyaspartate, a water-soluble biodegradable polymer that may have applications in disposable diapers and agriculture.[118]
Due to its solubility and ability to chelate metal ions, polyaspartate is besides existence used equally a biodegradable antiscaling agent and a corrosion inhibitor.[119]
In add-on, the aromatic amino acid tyrosine has been considered every bit a possible replacement for phenols such as bisphenol A in the manufacture of polycarbonates.[121]



For the steps in the reaction, see the text.

The Strecker amino acid synthesis

Chemic synthesis


The commercial production of amino acids commonly relies on mutant bacteria that overproduce individual amino acids using glucose as a carbon source. Some amino acids are produced by enzymatic conversions of synthetic intermediates. ii-Aminothiazoline-4-carboxylic acrid is an intermediate in one industrial synthesis of
L-cysteine for example. Aspartic acid is produced by the addition of ammonia to fumarate using a lyase.[122]



In plants, nitrogen is first assimilated into organic compounds in the form of glutamate, formed from alpha-ketoglutarate and ammonia in the mitochondrion. For other amino acids, plants employ transaminases to motion the amino group from glutamate to another alpha-keto acrid. For instance, aspartate aminotransferase converts glutamate and oxaloacetate to blastoff-ketoglutarate and aspartate.[123]
Other organisms use transaminases for amino acid synthesis, too.

Nonstandard amino acids are commonly formed through modifications to standard amino acids. For case, homocysteine is formed through the transsulfuration pathway or past the demethylation of methionine via the intermediate metabolite
while hydroxyproline is made by a mail translational modification of proline.[125]

Microorganisms and plants synthesize many uncommon amino acids. For example, some microbes make 2-aminoisobutyric acid and lanthionine, which is a sulfide-bridged derivative of alanine. Both of these amino acids are establish in peptidic lantibiotics such equally alamethicin.[126]
However, in plants, 1-aminocyclopropane-1-carboxylic acid is a pocket-size disubstituted circadian amino acid that is an intermediate in the production of the plant hormone ethylene.[127]



Amino acids undergo the reactions expected of the elective functional groups.[128]

Peptide bond formation


Two amino acids are shown next to each other. One loses a hydrogen and oxygen from its carboxyl group (COOH) and the other loses a hydrogen from its amino group (NH2). This reaction produces a molecule of water (H2O) and two amino acids joined by a peptide bond (–CO–NH–). The two joined amino acids are called a dipeptide.

The condensation of ii amino acids to class a dipeptide. The two amino acrid
are linked through a
peptide bond

As both the amine and carboxylic acrid groups of amino acids can react to form amide bonds, one amino acrid molecule can react with another and go 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 h2o. In cells, this reaction does non occur directly; instead, the amino acrid is commencement activated by attachment to a transfer RNA molecule through an ester bond. This aminoacyl-tRNA is produced in an ATP-dependent reaction carried out past an aminoacyl tRNA synthetase.[130]
This aminoacyl-tRNA is then a substrate for the ribosome, which catalyzes the set on of the amino group of the elongating poly peptide chain on the ester bail.[131]
As a issue of this mechanism, all proteins made by ribosomes are synthesized starting at their
N-terminus and moving toward their

Nevertheless, not all peptide bonds are formed in this way. In a few cases, peptides are synthesized past specific enzymes. For example, the tripeptide glutathione is an essential part of the defenses of cells confronting oxidative stress. This peptide is synthesized in two steps from costless amino acids.[132]
In the first stride, gamma-glutamylcysteine synthetase condenses cysteine and glutamate through a peptide bond formed between the side chain carboxyl of the glutamate (the gamma carbon of this side concatenation) and the amino group of the cysteine. This dipeptide is then condensed with glycine by glutathione synthetase to class glutathione.[133]

In chemistry, peptides are synthesized by a variety of reactions. One of the almost-used in solid-stage peptide synthesis uses the effluvious oxime derivatives of amino acids as activated units. These are added in sequence onto the growing peptide chain, which is attached to a solid resin support.[134]
Libraries of peptides are used in drug discovery through high-throughput screening.[135]

The combination of functional groups allow amino acids to be effective polydentate ligands for metal–amino acid chelates.[136]
The multiple side chains of amino acids tin also undergo chemical reactions.



Catabolism of proteinogenic amino acids. Amino acids tin can be classified according to the properties of their principal degradation products:[137]

Glucogenic, with the products having the ability to form glucose by gluconeogenesis

Ketogenic, with the products not having the ability to course glucose. These products may still be used for ketogenesis or lipid synthesis.

* Amino acids catabolized into both glucogenic and ketogenic products.

Degradation of an amino acid often involves deamination by moving its amino group to alpha-ketoglutarate, forming glutamate. This process involves transaminases, often the aforementioned as those used in amination during synthesis. In many vertebrates, the amino group is so removed through the urea bicycle and is excreted in the class of urea. Nevertheless, amino acid deposition tin can produce uric acid or ammonia instead. For instance, serine dehydratase converts serine to pyruvate and ammonia.[97]
Subsequently removal of one or more amino groups, the remainder of the molecule tin sometimes be used to synthesize new amino acids, or it tin be used for free energy by entering glycolysis or the citric acrid bike, equally detailed in paradigm at right.



Amino acids are bidentate ligands, forming transition metal amino acid complexes.[138]


Chemic assay


The total nitrogen content of organic matter is mainly formed by the amino groups in proteins. The Full Kjeldahl Nitrogen (TKN) is a measure of nitrogen widely used in the assay of (waste product) water, soil, food, feed and organic thing in full general. As the name suggests, the Kjeldahl method is practical. More sensitive methods are available.[139]

See likewise


  • Amino acid dating
  • Beta-peptide
  • Degron
  • Erepsin
  • Homochirality
  • Hyperaminoacidemia
  • Leucines
  • Miller–Urey experiment
  • Nucleic acrid sequence
  • RNA codon table



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    The tardily discovery is explained past the fact that cysteine becomes oxidized to cystine in air.

  3. ^

    Hydroxyproline is present in very few proteins, most notably collagen.

  4. ^

    Proline is an exception to this full general formula. It lacks the

    grouping because of the cyclization of the side chain and is known as an imino acrid; information technology falls under the category of special structured amino acids.

  5. ^

    For example, ruminants such every bit cows obtain a number of amino acids via microbes in the first ii stomach chambers.



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Further reading


  • Tymoczko JL (2012). “Protein Composition and Structure”.

    . New York: Due west. H. Freeman and company. pp. 28–31. ISBN9781429229364.

  • Doolittle RF (1989). “Redundancies in protein sequences”. In Fasman GD (ed.).
    Predictions of Poly peptide Construction and the Principles of Protein Conformation. New York: Plenum Press. pp. 599–623. ISBN978-0-306-43131-ix. LCCN 89008555.

  • Nelson DL, Cox MM (2000).

    Lehninger Principles of Biochemistry

    (third ed.). Worth Publishers. ISBN978-one-57259-153-0. LCCN 99049137.

  • Meierhenrich U (2008).
    Amino acids and the asymmetry of life
    (PDF). Berlin: Springer Verlag. ISBN978-3-540-76885-2. LCCN 2008930865. Archived from the original on 12 January 2012.

    {{cite book}}: CS1 maint: bot: original URL status unknown (link)
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External links


  • Media related to Amino acrid at Wikimedia Commons

1 or 3 Codons Equal One Amino Acid

Source: https://en.wikipedia.org/wiki/Amino_acid

Originally posted 2022-08-01 01:16:12.

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