Proteinogenic amino acid

Proteinogenic amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and one of the twenty R-groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H₂NCHRCOOH, where R is an organic substituent...

s are those 22 amino acids that are found in protein

Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...

s and that are coded for in the standard genetic code

Genetic code

The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells. A more precise term for the concept might be "genetic cipher". The code defines a mapping between tri-nucleotide sequences, called codons, and amino acids...

. Proteinogenic literally means protein building. Proteinogenic amino acids are assembled into a polypeptide (the subunit of a protein) through a process known as translation (the second stage of protein biosynthesis, part of the overall process of gene expression).

Non-proteinogenic amino acids are either not found in proteins (like carnitine

Carnitine

Carnitine is a quaternary ammonium compound biosynthesized from the amino acids lysine and methionine. In living cells, it is required for the transport of fatty acids from the cytosol into the mitochondria during the breakdown of lipids for the generation of metabolic energy. It is often sold as...

, GABA

Gamma-aminobutyric acid

γ-Aminobutyric acid is the chief inhibitory neurotransmitter in the mammalian central nervous system. It plays an important role in regulating neuronal excitability throughout the nervous system. In humans, GABA is also directly responsible for the regulation of muscle tone...

, or L-DOPA), or not coded for in the standard genetic code

Genetic code

The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells. A more precise term for the concept might be "genetic cipher". The code defines a mapping between tri-nucleotide sequences, called codons, and amino acids...

 (like hydroxyproline

Hydroxyproline

-4-Hydroxyproline, or L-hydroxyproline , is a common proteinogenic amino acid, abbreviated as HYP, e.g., in Protein Data Bank.-Structure:...

 and selenomethionine

Selenomethionine

Selenomethionine is an amino acid containing selenium. The L-isomer of selenomethionine, known as Se-met and Sem, is a common natural food source of selenium. In vivo, selenomethionine is randomly incorporated instead of methionine and is readily oxidized. Its antioxidant activity arises from its...

).

Proteinogenic amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and one of the twenty R-groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H₂NCHRCOOH, where R is an organic substituent...

s are those 22 amino acids that are found in protein

Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...

s and that are coded for in the standard genetic code

Genetic code

The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells. A more precise term for the concept might be "genetic cipher". The code defines a mapping between tri-nucleotide sequences, called codons, and amino acids...

. Proteinogenic literally means protein building. Proteinogenic amino acids are assembled into a polypeptide (the subunit of a protein) through a process known as translation (the second stage of protein biosynthesis, part of the overall process of gene expression).

Non-proteinogenic amino acids are either not found in proteins (like carnitine

Carnitine

Carnitine is a quaternary ammonium compound biosynthesized from the amino acids lysine and methionine. In living cells, it is required for the transport of fatty acids from the cytosol into the mitochondria during the breakdown of lipids for the generation of metabolic energy. It is often sold as...

, GABA

Gamma-aminobutyric acid

γ-Aminobutyric acid is the chief inhibitory neurotransmitter in the mammalian central nervous system. It plays an important role in regulating neuronal excitability throughout the nervous system. In humans, GABA is also directly responsible for the regulation of muscle tone...

, or L-DOPA), or not coded for in the standard genetic code

Genetic code

The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells. A more precise term for the concept might be "genetic cipher". The code defines a mapping between tri-nucleotide sequences, called codons, and amino acids...

 (like hydroxyproline

Hydroxyproline

-4-Hydroxyproline, or L-hydroxyproline , is a common proteinogenic amino acid, abbreviated as HYP, e.g., in Protein Data Bank.-Structure:...

 and selenomethionine

Selenomethionine

Selenomethionine is an amino acid containing selenium. The L-isomer of selenomethionine, known as Se-met and Sem, is a common natural food source of selenium. In vivo, selenomethionine is randomly incorporated instead of methionine and is readily oxidized. Its antioxidant activity arises from its...

). The latter often result from posttranslational modification

Posttranslational modification

Posttranslational modification is the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis for many proteins....

 of proteins.

There are clear reasons why organisms have not evolved

Evolution

In biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...

 to incorporate certain non-proteinogenic amino acids into proteins: for example, ornithine

Ornithine

Ornithine is an amino acid which plays a role in the urea cycle.-Role in urea cycle:L-Ornithine is one of the products of the action of the enzyme arginase on L-arginine, creating urea. Therefore, ornithine is a central part of the urea cycle, which allows for the...

 and homoserine

Homoserine

Homoserine is an α-amino acid with the chemical formula HO₂CCHCH₂CH₂OH. L-Homoserine is not one of the common amino acids encoded by DNA. It differs from the proteinogenic amino acid serine by insertion of an additional methylene group...

 will cyclize against the peptide backbone and fragment the protein with relatively short half-lives, and others are toxic because they can be mistakenly incorporated into proteins, such as the arginine

Arginine

Arginine is an α-amino acid. The L-form is one of the 20 most common natural amino acids. Its codons are CGU, CGC, CGA, CGG, AGA, and AGG. In mammals, arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health...

 analog canavanine

Canavanine

L---Canavanine is a non-proteinogenic amino acid of certain leguminous plants. It is structurally related to the proteinogenic amino acid, L-arginine. Canavanine is accumulated primarily in the seeds where it serves both as a defensive compound against herbivores and...

.

Non-proteinogenic amino acids are found in Nonribosomal peptide

Nonribosomal peptide

Nonribosomal peptides are a class of peptide secondary metabolites, usually produced by microorganisms like bacteria and fungi. Nonribosomal peptides are also found in higher organisms, such as nudibranchs, but are thought to be made by bacteria inside these organisms...

s, which are not produced by the ribosome during translation.

Structures

Structures and symbols of the 20 amino acids which are directly encoded for protein synthesis by the standard genetic code
IUPAC/IUBMB now also recommends standard abbreviations for the following two amino acids:

Non-specific abbreviations

Sometimes the specific identity of an amino acid cannot be determined unambiguously. Certain protein sequencing

Protein sequencing

Proteins are found in every cell and are essential to every biological process, protein structure is very complex: determining a protein's structure involves first protein sequencing - determining the amino acid sequences of its constituent peptides; and also determining what conformation it adopts...

 techniques do not distinguish among certain pairs. Thus, the following codes are used:

• Asx (B) is "asparagine
  Asparagine
  Asparagine is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side chain's functional group. It is not an essential amino acid...
  
   or aspartic acid
  Aspartic acid
  Aspartic acid is an α-amino acid with the chemical formula HO₂CCHCH₂CO₂H. The carboxylate anion of aspartic acid is known as aspartate...
  
  "
• Glx (Z) is "glutamic acid
  Glutamic acid
  Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid...
  
   or glutamine
  Glutamine
  Glutamine is one of the 20 amino acids encoded by the standard genetic code. Its side chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group. It can therefore be considered the amide of glutamic acid. Its codons are CAA and CAG. Glutamine is...
  
  "
• Xle (J) is "leucine
  Leucine
  Leucine is an α-amino acid with the chemical formula HO₂CCHCH₂CH₂. It is an essential amino acid, which means that humans cannot synthesise it. Its codons are UUA, UUG, CUU, CUC, CUA, and CUG. With a hydrocarbon side chain, leucine is classified as a hydrophobic...
  
   or isoleucine
  Isoleucine
  Isoleucine is an α-amino acid with the chemical formula HO₂CCHCHCH₂CH₃. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested...
  
  "

In addition, the symbol X is used to indicate an amino acid that is completely unidentified.

Chemical properties

Following is a table listing the one-letter symbols, the three-letter symbols, and the chemical properties of the side chains of the standard amino acids. The masses listed are based on weighted averages of the elemental isotope

Isotope

Isotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...

s at their natural abundance

Natural abundance

In chemistry, natural abundance refers to the abundance isotopes of a chemical element as naturally found on a planet. The relative atomic mass of these isotopes is the atomic weight listed for the element in the periodic table...

s. Note that forming a peptide bond

Peptide bond

A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amine group of the other molecule, thereby releasing a molecule of water . This is a dehydration synthesis reaction, and usually occursbetween amino acids...

 results in elimination of a molecule of water, so the mass of an amino acid unit within a protein chain is reduced by 18.01524 Da.

General chemical properties

Amino Acid	Short	Abbrev.	Avg. Mass (Da Atomic mass unit The unified atomic mass unit or atomic mass unit , or dalton or, sometimes, universal mass unit , is a unit of mass used to express atomic and molecular masses... )	pI Isoelectric point The isoelectric point , sometimes abbreviated to IEP, is the pH at which a particular molecule or surface carries no net electrical charge....	pK Dissociation constant In chemistry, biochemistry, and pharmacology, a dissociation constant is a specific type of equilibrium constant that measures the propensity of a larger object to separate reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into... 1 (α-COOH)	pK2 (α-+NH3)
Alanine Alanine Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 proteinogenic amino acids, i.e. the building blocks of proteins. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...	A	Ala	89.09404	6.01	2.35	9.87
Cysteine Cysteine Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is nonpolar and thus cysteine is usually classified as...	C	Cys	121.15404	5.05	1.92	10.70
Aspartic acid Aspartic acid Aspartic acid is an α-amino acid with the chemical formula HO2CCHCH2CO2H. The carboxylate anion of aspartic acid is known as aspartate...	D	Asp	133.10384	2.85	1.99	9.90
Glutamic acid Glutamic acid Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid...	E	Glu	147.13074	3.15	2.10	9.47
Phenylalanine Phenylalanine Phenylalanine is an α-amino acid with the formula HO2CCHCH2C6H5. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. The codons for L-phenylalanine are UUU and UUC...	F	Phe	165.19184	5.49	2.20	9.31
Glycine Glycine Glycine is an organic compound with the formula NH2CH2COOH. With only a hydrogen atom as its side chain, glycine is the smallest of the 20 amino acids commonly found in proteins....	G	Gly	75.06714	6.06	2.35	9.78
Histidine Histidine Histidine is one of the 20 standard amino acids present in proteins. Nutritionally, histidine is considered an essential amino acid in human infants. After reaching several years of age, humans begin to synthesize it and it thus becomes a non-essential amino acid...	H	His	155.15634	7.60	1.80	9.33
Isoleucine Isoleucine Isoleucine is an α-amino acid with the chemical formula HO2CCHCHCH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested...	I	Ile	131.17464	6.05	2.32	9.76
Lysine Lysine Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. This amino acid is an essential amino acid, which means that humans cannot synthesize it. Its codons are AAA and AAG.Lysine is a base, as are arginine and histidine...	K	Lys	146.18934	9.60	2.16	9.06
Leucine Leucine Leucine is an α-amino acid with the chemical formula HO2CCHCH2CH2. It is an essential amino acid, which means that humans cannot synthesise it. Its codons are UUA, UUG, CUU, CUC, CUA, and CUG. With a hydrocarbon side chain, leucine is classified as a hydrophobic...	L	Leu	131.17464	6.01	2.33	9.74
Methionine Methionine Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar.-Function:...	M	Met	149.20784	5.74	2.13	9.28
Asparagine Asparagine Asparagine is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side chain's functional group. It is not an essential amino acid...	N	Asn	132.11904	5.41	2.14	8.72
Pyrrolysine Pyrrolysine Pyrrolysine is a naturally occurring, genetically coded amino acid used by some methanogenic archaea in enzymes that are part of their methane-producing metabolism...	O	Pyl
Proline Proline Proline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that humans can synthesize it...	P	Pro	115.13194	6.30	1.95	10.64
Glutamine Glutamine Glutamine is one of the 20 amino acids encoded by the standard genetic code. Its side chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group. It can therefore be considered the amide of glutamic acid. Its codons are CAA and CAG. Glutamine is...	Q	Gln	146.14594	5.65	2.17	9.13
Arginine Arginine Arginine is an α-amino acid. The L-form is one of the 20 most common natural amino acids. Its codons are CGU, CGC, CGA, CGG, AGA, and AGG. In mammals, arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health...	R	Arg	174.20274	10.76	1.82	8.99
Serine Serine Serine is an organic compound with the formula HO2CCHCH2OH.-Occurrence:...	S	Ser	105.09344	5.68	2.19	9.21
Threonine Threonine Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...	T	Thr	119.12034	5.60	2.09	9.10
Selenocysteine Selenocysteine Selenocysteine is an amino acid that is present in several enzymes .-Nomenclature:...	U	Sec	168.053
Valine Valine Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...	V	Val	117.14784	6.00	2.39	9.74
Tryptophan Tryptophan Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...	W	Trp	204.22844	5.89	2.46	9.41
Tyrosine Tyrosine Tyrosine or 4-hydroxyphenylalanine, is one of the 20 amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group...	Y	Tyr	181.19124	5.64	2.20	9.21

Side chain properties

Amino Acid	Short	Abbrev.	Side chain	Hydro- phobic	pKa Acid dissociation constant An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions...	Polar Chemical polarity In chemistry, polarity refers to a separation of electric charge leading to a molecule having an electric dipole. Polar molecules can bond together due to dipole–dipole intermolecular forces between one molecule with asymmetrical charge distribution and another molecule also with asymmetrical...	pH	Small	Tiny	Aromatic Aromaticity In organic chemistry, the structures of some rings of atoms are unexpectedly stable. Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone... or Aliphatic	van der Waals volume Van der Waals radius The van der Waals radius, r, of an atom is the radius of an imaginary hard sphere which can be used to model the atom for many purposes. It is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics, as he was the first to recognise that atoms had a finite size and to...
Alanine Alanine Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 proteinogenic amino acids, i.e. the building blocks of proteins. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...	A	Ala	-CH3	X	-	-	-	X	X	-	67
Cysteine Cysteine Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is nonpolar and thus cysteine is usually classified as...	C	Cys	-CH2SH Thiol In organic chemistry, a thiol is a compound that contains the functional group composed of a sulfur-hydrogen bond . Being the sulfur analogue of an alcohol group , this functional group is referred to either as a thiol group or a sulfhydryl group...	X	8.18	-	acidic	X	-	-	86
Aspartic acid Aspartic acid Aspartic acid is an α-amino acid with the chemical formula HO2CCHCH2CO2H. The carboxylate anion of aspartic acid is known as aspartate...	D	Asp	-CH2COOH	-	3.90	X	acidic	X	-	-	91
Glutamic acid Glutamic acid Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid...	E	Glu	-CH2CH2COOH	-	4.07	X	acidic	-	-	-	109
Phenylalanine Phenylalanine Phenylalanine is an α-amino acid with the formula HO2CCHCH2C6H5. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. The codons for L-phenylalanine are UUU and UUC...	F	Phe	-CH2C6H5	X	-	-	-	-	-	Aromatic	135
Glycine Glycine Glycine is an organic compound with the formula NH2CH2COOH. With only a hydrogen atom as its side chain, glycine is the smallest of the 20 amino acids commonly found in proteins....	G	Gly	-H	X	-	-	-	X	X	-	48
Histidine Histidine Histidine is one of the 20 standard amino acids present in proteins. Nutritionally, histidine is considered an essential amino acid in human infants. After reaching several years of age, humans begin to synthesize it and it thus becomes a non-essential amino acid...	H	His	-CH2-C3H3N2 Imidazole Imidazole is an organic compound with the formula C3H4N2. This aromatic heterocyclic is classified as an alkaloid. Imidazole refers to the parent compound whereas imidazoles are a class of heterocycles with similar ring structure but varying substituents...	-	6.04	X	weak basic	-	-	Aromatic	118
Isoleucine Isoleucine Isoleucine is an α-amino acid with the chemical formula HO2CCHCHCH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested...	I	Ile	-CH(CH3)CH2CH3	X	-	-	-	-	-	Aliphatic	124
Lysine Lysine Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. This amino acid is an essential amino acid, which means that humans cannot synthesize it. Its codons are AAA and AAG.Lysine is a base, as are arginine and histidine...	K	Lys	-(CH2)4NH2	-	10.54	X	basic	-	-	-	135
Leucine Leucine Leucine is an α-amino acid with the chemical formula HO2CCHCH2CH2. It is an essential amino acid, which means that humans cannot synthesise it. Its codons are UUA, UUG, CUU, CUC, CUA, and CUG. With a hydrocarbon side chain, leucine is classified as a hydrophobic...	L	Leu	-CH2CH(CH3)2	X	-	-	-	-	-	Aliphatic	124
Methionine Methionine Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar.-Function:...	M	Met	-CH2CH2S Sulfur Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur, in its native form, is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals... CH3	X	-	-	-	-	-	-	124
Asparagine Asparagine Asparagine is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side chain's functional group. It is not an essential amino acid...	N	Asn	-CH2CONH2	-	-	X	-	X	-	-	96
Pyrrolysine Pyrrolysine Pyrrolysine is a naturally occurring, genetically coded amino acid used by some methanogenic archaea in enzymes that are part of their methane-producing metabolism...	O	Pyl
Proline Proline Proline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that humans can synthesize it...	P	Pro	-CH2CH2CH2-	X	-	-	-	X	-	-	90
Glutamine Glutamine Glutamine is one of the 20 amino acids encoded by the standard genetic code. Its side chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group. It can therefore be considered the amide of glutamic acid. Its codons are CAA and CAG. Glutamine is...	Q	Gln	-CH2CH2CONH2	-	-	X	-	-	-	-	114
Arginine Arginine Arginine is an α-amino acid. The L-form is one of the 20 most common natural amino acids. Its codons are CGU, CGC, CGA, CGG, AGA, and AGG. In mammals, arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health...	R	Arg	-(CH2)3NH-C(NH)NH2	-	12.48	X	strongly basic	-	-	-	148
Serine Serine Serine is an organic compound with the formula HO2CCHCH2OH.-Occurrence:...	S	Ser	-CH2OH	-	-	X	-	X	X	-	73
Threonine Threonine Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...	T	Thr	-CH(OH)CH3	-	-	X	weak acidic	X	-	-	93
Selenocysteine Selenocysteine Selenocysteine is an amino acid that is present in several enzymes .-Nomenclature:...	U	Sec	-CH2SeH Selenol In organic chemistry, a selenol is a chemical compound that contains the functional group composed of a selenium atom bonded to a hydrogen atom . Volatile molecular weight selenols have highly offensive odors and are easily oxidized to diselenides, compounds containing an Se-Se bond. The essential...	X	5.73	-	-	X	-	-
Valine Valine Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...	V	Val	-CH(CH3)2	X	-	-	-	X	-	Aliphatic	105
Tryptophan Tryptophan Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...	W	Trp	-CH2C8H6N Indole Indole is an aromatic heterocyclic organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. Indole is a popular component of fragrances and the precursor to many pharmaceuticals. Compounds that contain an...	X	-	-	-	-	-	Aromatic	163
Tyrosine Tyrosine Tyrosine or 4-hydroxyphenylalanine, is one of the 20 amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group...	Y	Tyr	-CH2-C6H4OH	-	10.46	X	-	-	-	Aromatic	141

Note: The pKa values of amino acids are typically slightly different when the amino acid is inside a protein. Protein pKa calculations

Protein pKa calculations

In computational biology, protein pKa calculations are used to estimate the pKa values of amino acids as they exist within proteins. These calculations complement the pKa values reported for amino acids in their free state, and are used frequently within the fields of molecular modeling, structural...

 are sometimes used to calculate the change in the pKa value of an amino acid in this situation.

Gene expression and biochemistry

Amino Acid	Short	Abbrev.	Codon(s)	Occurrence in proteins (%)	Essential‡ in humans
Alanine Alanine Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 proteinogenic amino acids, i.e. the building blocks of proteins. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...	A	Ala	GCU, GCC, GCA, GCG	7.8	-
Cysteine Cysteine Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is nonpolar and thus cysteine is usually classified as...	C	Cys	UGU, UGC	1.9	Conditionally
Aspartic acid Aspartic acid Aspartic acid is an α-amino acid with the chemical formula HO2CCHCH2CO2H. The carboxylate anion of aspartic acid is known as aspartate...	D	Asp	GAU, GAC	5.3	-
Glutamic acid Glutamic acid Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid...	E	Glu	GAA, GAG	6.3	Conditionally
Phenylalanine Phenylalanine Phenylalanine is an α-amino acid with the formula HO2CCHCH2C6H5. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. The codons for L-phenylalanine are UUU and UUC...	F	Phe	UUU, UUC	3.9	Yes
Glycine Glycine Glycine is an organic compound with the formula NH2CH2COOH. With only a hydrogen atom as its side chain, glycine is the smallest of the 20 amino acids commonly found in proteins....	G	Gly	GGU, GGC, GGA, GGG	7.2	Conditionally
Histidine Histidine Histidine is one of the 20 standard amino acids present in proteins. Nutritionally, histidine is considered an essential amino acid in human infants. After reaching several years of age, humans begin to synthesize it and it thus becomes a non-essential amino acid...	H	His	CAU, CAC	2.3	Yes
Isoleucine Isoleucine Isoleucine is an α-amino acid with the chemical formula HO2CCHCHCH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested...	I	Ile	AUU, AUC, AUA	5.3	Yes
Lysine Lysine Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. This amino acid is an essential amino acid, which means that humans cannot synthesize it. Its codons are AAA and AAG.Lysine is a base, as are arginine and histidine...	K	Lys	AAA, AAG	5.9	Yes
Leucine Leucine Leucine is an α-amino acid with the chemical formula HO2CCHCH2CH2. It is an essential amino acid, which means that humans cannot synthesise it. Its codons are UUA, UUG, CUU, CUC, CUA, and CUG. With a hydrocarbon side chain, leucine is classified as a hydrophobic...	L	Leu	UUA, UUG, CUU, CUC, CUA, CUG	9.1	Yes
Methionine Methionine Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar.-Function:...	M	Met	AUG	2.3	Yes
Asparagine Asparagine Asparagine is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side chain's functional group. It is not an essential amino acid...	N	Asn	AAU, AAC	4.3	-
Pyrrolysine Pyrrolysine Pyrrolysine is a naturally occurring, genetically coded amino acid used by some methanogenic archaea in enzymes that are part of their methane-producing metabolism...	O	Pyl	UAG*		-
Proline Proline Proline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that humans can synthesize it...	P	Pro	CCU, CCC, CCA, CCG	5.2	-
Glutamine Glutamine Glutamine is one of the 20 amino acids encoded by the standard genetic code. Its side chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group. It can therefore be considered the amide of glutamic acid. Its codons are CAA and CAG. Glutamine is...	Q	Gln	CAA, CAG	4.2	-
Arginine Arginine Arginine is an α-amino acid. The L-form is one of the 20 most common natural amino acids. Its codons are CGU, CGC, CGA, CGG, AGA, and AGG. In mammals, arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health...	R	Arg	CGU, CGC, CGA, CGG, AGA, AGG	5.1	Conditionally
Serine Serine Serine is an organic compound with the formula HO2CCHCH2OH.-Occurrence:...	S	Ser	UCU, UCC, UCA, UCG, AGU, AGC	6.8	-
Threonine Threonine Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...	T	Thr	ACU, ACC, ACA, ACG	5.9	Yes
Selenocysteine Selenocysteine Selenocysteine is an amino acid that is present in several enzymes .-Nomenclature:...	U	Sec	UGA**		-
Valine Valine Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...	V	Val	GUU, GUC, GUA, GUG	6.6	Yes
Tryptophan Tryptophan Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...	W	Trp	UGG	1.4	Yes
Tyrosine Tyrosine Tyrosine or 4-hydroxyphenylalanine, is one of the 20 amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group...	Y	Tyr	UAU, UAC	3.2	Conditionally
Stop codon†	-	Term	UAA, UAG, UGA	-	-

* UAG is normally the amber stop codon, but encodes pyrrolysine if a PYLIS element is present.

** UGA is normally the opal (or umber) stop codon, but encodes selenocysteine if a SECIS element

SECIS element

In biology, the SECIS element is an RNA element around 60 nucleotides in length that adopts a stem-loop structure. This structural motif directs the cell to translate UGA codons as selenocysteines...

 is present.

† The stop codon

Stop codon

In the genetic code, a stop codon is a nucleotide triplet within messenger RNA that signals a termination of translation. Proteins are unique sequences of amino acids, and most codons in messenger RNA correspond to the addition of an amino acid to a growing protein chain — stop codons signal...

 is not an amino acid, but is included for completeness.

‡ An essential amino acid

Essential amino acid

An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs...

 cannot be synthesized in humans and must, therefore, be supplied in the diet. Conditionally essential amino acids are not normally required in the diet, but must be supplied exogenously to specific populations that do not synthesize it in adequate amounts.

Mass spectrometry

In mass spectrometry

Mass spectrometry

Mass spectrometry is an analytical technique for the determination of the elemental composition of a sample or molecule. It is also used for elucidating the chemical structures of molecules, such as peptides and other chemical compounds...

 of peptides and proteins, it is useful to know the masses of the residues. The mass of the peptide or protein is the sum of the residue masses plus the mass of water.

Amino Acid	Short	Abbrev.	Formula	Mon. Mass§ (Da Atomic mass unit The unified atomic mass unit or atomic mass unit , or dalton or, sometimes, universal mass unit , is a unit of mass used to express atomic and molecular masses... )	Avg. Mass (Da Atomic mass unit The unified atomic mass unit or atomic mass unit , or dalton or, sometimes, universal mass unit , is a unit of mass used to express atomic and molecular masses... )
Alanine Alanine Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 proteinogenic amino acids, i.e. the building blocks of proteins. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...	A	Ala	C3H5NO	71.03711	71.0788
Cysteine Cysteine Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is nonpolar and thus cysteine is usually classified as...	C	Cys	C3H5NOS	103.00919	103.1388
Aspartic acid Aspartic acid Aspartic acid is an α-amino acid with the chemical formula HO2CCHCH2CO2H. The carboxylate anion of aspartic acid is known as aspartate...	D	Asp	C4H5NO3	115.02694	115.0886
Glutamic acid Glutamic acid Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid...	E	Glu	C5H7NO3	129.04259	129.1155
Phenylalanine Phenylalanine Phenylalanine is an α-amino acid with the formula HO2CCHCH2C6H5. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. The codons for L-phenylalanine are UUU and UUC...	F	Phe	C9H9NO	147.06841	147.1766
Glycine Glycine Glycine is an organic compound with the formula NH2CH2COOH. With only a hydrogen atom as its side chain, glycine is the smallest of the 20 amino acids commonly found in proteins....	G	Gly	C2H3NO	57.02146	57.0519
Histidine Histidine Histidine is one of the 20 standard amino acids present in proteins. Nutritionally, histidine is considered an essential amino acid in human infants. After reaching several years of age, humans begin to synthesize it and it thus becomes a non-essential amino acid...	H	His	C6H7N3O	137.05891	137.1411
Isoleucine Isoleucine Isoleucine is an α-amino acid with the chemical formula HO2CCHCHCH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested...	I	Ile	C6H11NO	113.08406	113.1594
Lysine Lysine Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. This amino acid is an essential amino acid, which means that humans cannot synthesize it. Its codons are AAA and AAG.Lysine is a base, as are arginine and histidine...	K	Lys	C6H12N2O	128.09496	128.1741
Leucine Leucine Leucine is an α-amino acid with the chemical formula HO2CCHCH2CH2. It is an essential amino acid, which means that humans cannot synthesise it. Its codons are UUA, UUG, CUU, CUC, CUA, and CUG. With a hydrocarbon side chain, leucine is classified as a hydrophobic...	L	Leu	C6H11NO	113.08406	113.1594
Methionine Methionine Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar.-Function:...	M	Met	C5H9NOS	131.04049	131.1986
Asparagine Asparagine Asparagine is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side chain's functional group. It is not an essential amino acid...	N	Asn	C4H6N2O2	114.04293	114.1039
Pyrrolysine Pyrrolysine Pyrrolysine is a naturally occurring, genetically coded amino acid used by some methanogenic archaea in enzymes that are part of their methane-producing metabolism...	O	Pyl	C12H21N3O3	255.15829	255.3172
Proline Proline Proline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that humans can synthesize it...	P	Pro	C5H7NO	97.05276	97.1167
Glutamine Glutamine Glutamine is one of the 20 amino acids encoded by the standard genetic code. Its side chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group. It can therefore be considered the amide of glutamic acid. Its codons are CAA and CAG. Glutamine is...	Q	Gln	C5H8N2O2	128.05858	128.1307
Arginine Arginine Arginine is an α-amino acid. The L-form is one of the 20 most common natural amino acids. Its codons are CGU, CGC, CGA, CGG, AGA, and AGG. In mammals, arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health...	R	Arg	C6H12N4O	156.10111	156.1875
Serine Serine Serine is an organic compound with the formula HO2CCHCH2OH.-Occurrence:...	S	Ser	C3H5NO2	87.03203	87.0782
Threonine Threonine Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...	T	Thr	C4H7NO2	101.04768	101.1051
Selenocysteine Selenocysteine Selenocysteine is an amino acid that is present in several enzymes .-Nomenclature:...	U	Sec	C3H5NOSe	168.9642	168.0541
Valine Valine Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...	V	Val	C5H9NO	99.06841	99.1326
Tryptophan Tryptophan Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...	W	Trp	C11H10N2O	186.07931	186.2132
Tyrosine Tyrosine Tyrosine or 4-hydroxyphenylalanine, is one of the 20 amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group...	Y	Tyr	C9H9NO2	163.06333	163.1760

§ Monoisotopic mass

Monoisotopic mass

The monoisotopic mass is the sum of the masses of the atoms in a molecule using the unbound, ground-state, rest mass of the principal isotope for each element instead of the isotopic average mass. For typical organic compounds, where the monoisotopic mass is most commonly used, this also results...

Remarks

Amino Acid	Abbrev.		Remarks
Alanine Alanine Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 proteinogenic amino acids, i.e. the building blocks of proteins. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...	A	Ala	Very abundant, very versatile. More stiff than glycine, but small enough to pose only small steric limits for the protein conformation. It behaves fairly neutrally, can be located in both hydrophilic regions on the protein outside and the hydrophobic areas inside.
Cysteine Cysteine Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is nonpolar and thus cysteine is usually classified as...	C	Cys	The sulfur atom bonds readily to heavy metal Heavy metals A heavy metal is a member of an ill-defined subset of elements that exhibit metallic properties, which would mainly include the transition metals, some metalloids, lanthanoids, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic...  ions. Under oxidizing conditions, two cysteines can join together in a disulfide bond Disulfide bond In chemistry, a disulfide bond is a covalent bond, usually derived by the coupling of two thiol groups. The linkage is also called an SS-bond or disulfide bridge. The overall connectivity is therefore C-S-S-C. The terminology is widely used in biochemistry...  to form the amino acid cystine Cystine Cystine is a dimeric amino acid formed by the oxidation of two cysteine residues which covalently link to make a disulfide bond. This organosulfur compound has the formula 2. It is a colorless solid, and melts at 247-249 °C... . When cystines are part of a protein, insulin Insulin Insulin is a hormone that has extensive effects on metabolism and other body functions, such as vascular compliance. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle, and stopping use of fat as an energy...  for example, this stabilises tertiary structure Tertiary structure In biochemistry and chemistry, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates.-Relationship to primary structure:...  and makes the protein more resistant to denaturation Denaturation (biochemistry) Denaturation is a process in which proteins or nucleic acids lose their tertiary and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat. If proteins in a living cell are denatured, this... ; disulfide bonds are therefore common in proteins that have to function in harsh environments including digestive enzymes (e.g., pepsin Pepsin Pepsin is an enzyme that is released by the chief cells in the stomach and that degrades food proteins into peptides. Pepsin was discovered in 1836 by Theodor Schwann who also coined this enzyme's name from the Greek word pepsis, meaning digestion...  and chymotrypsin Chymotrypsin Chymotrypsin is a digestive enzyme that can perform proteolysis. Chymotrypsin cleaves peptides at the carboxyl side of tyrosine, tryptophan, and phenylalanine because these three amino acids contain aromatic rings, which fit into a 'hydrophobic pocket' in the enzyme... ) and structural proteins (e.g., keratin Keratin Keratins are a family of fibrous structural proteins; tough and insoluble, they form the hard but un-mineralized structures found in reptiles, birds, amphibians, and mammals... ). Disulfides are also found in peptides too small to hold a stable shape on their own (eg. insulin Insulin Insulin is a hormone that has extensive effects on metabolism and other body functions, such as vascular compliance. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle, and stopping use of fat as an energy... ).
Aspartic acid Aspartic acid Aspartic acid is an α-amino acid with the chemical formula HO2CCHCH2CO2H. The carboxylate anion of aspartic acid is known as aspartate...	D	Asp	Behaves similarly to glutamic acid. Carries a hydrophilic acidic group with strong negative charge. Usually is located on the outer surface of the protein, making it water-soluble. Binds to positively-charged molecules and ions, often used in enzymes to fix the metal ion. When located inside of the protein, aspartate and glutamate are usually paired with arginine and lysine.
Glutamic acid Glutamic acid Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid...	E	Glu	Behaves similar to aspartic acid. Has longer, slightly more flexible side chain.
Phenylalanine Phenylalanine Phenylalanine is an α-amino acid with the formula HO2CCHCH2C6H5. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. The codons for L-phenylalanine are UUU and UUC...	F	Phe	Essential Essential amino acid An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs...  for humans. Phenylalanine, tyrosine, and tryptophan contain large rigid aromatic Aromaticity In organic chemistry, the structures of some rings of atoms are unexpectedly stable. Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone...  group on the side chain. These are the biggest amino acids. Like isoleucine, leucine and valine, these are hydrophobic and tend to orient towards the interior of the folded protein molecule. Phenylalanine can be converted into Tyrosine.
Glycine Glycine Glycine is an organic compound with the formula NH2CH2COOH. With only a hydrogen atom as its side chain, glycine is the smallest of the 20 amino acids commonly found in proteins....	G	Gly	Because of the two hydrogen atoms at the α carbon, glycine is not optically active. It is the smallest amino acid, rotates easily, adds flexibility to the protein chain. It is able to fit into the tightest spaces, e.g., the triple helix of collagen Collagen Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. It is naturally found exclusively in metazoa, including sponges. In muscle tissue it serves as a major component of endomysium... . As too much flexibility is usually not desired, as a structural component it is less common than alanine.
Histidine Histidine Histidine is one of the 20 standard amino acids present in proteins. Nutritionally, histidine is considered an essential amino acid in human infants. After reaching several years of age, humans begin to synthesize it and it thus becomes a non-essential amino acid...	H	His	In even slightly acidic conditions protonation Protonation In chemistry, protonation is the addition of a proton to an atom, molecule, or ion. Protonation is possibly the most fundamental chemical reaction and is a step in many stoichiometric and catalytic processes. Some ions and molecules can undergo more than one protonation and are labeled...  of the nitrogen occurs, changing the properties of histidine and the polypeptide as a whole. It is used by many proteins as a regulatory mechanism, changing the conformation and behavior of the polypeptide in acidic regions such as the late endosome Endosome In biology, an endosome is a membrane-bound compartment inside cells, roughly 500 nm in diameter when fully mature.-Function:Many endocytotic vesicles, derived from the plasma membrane, are either transported to a pre-existing endosome and fuse with it or are acidified via proton pump to become an...  or lysosome Lysosome thumb|350px|Schematic of typical animal cell, showing subcellular components. [[Organelle]]s: [[nucleolus]] [[cell nucleus|nucleus]] [[ribosomes]] [[vesicle |vesicle]] ... , enforcing conformation change in enzymes. However only a few histidines are needed for this, so it is comparatively scarce.
Isoleucine Isoleucine Isoleucine is an α-amino acid with the chemical formula HO2CCHCHCH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested...	I	Ile	Essential Essential amino acid An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs...  for humans. Isoleucine, leucine and valine have large aliphatic hydrophobic side chains. Their molecules are rigid, and their mutual hydrophobic interactions are important for the correct folding of proteins, as these chains tend to be located inside of the protein molecule.
Lysine Lysine Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. This amino acid is an essential amino acid, which means that humans cannot synthesize it. Its codons are AAA and AAG.Lysine is a base, as are arginine and histidine...	K	Lys	Essential Essential amino acid An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs...  for humans. Behaves similarly to arginine. Contains a long flexible side-chain with a positively-charged end. The flexibility of the chain makes lysine and arginine suitable for binding to molecules with many negative charges on their surfaces. E.g., DNA-binding proteins have their active regions rich with arginine and lysine. The strong charge makes these two amino acids prone to be located on the outer hydrophilic surfaces of the proteins; when they are found inside, they are usually paired with a corresponding negatively-charged amino acid, e.g., aspartate or glutamate.
Leucine Leucine Leucine is an α-amino acid with the chemical formula HO2CCHCH2CH2. It is an essential amino acid, which means that humans cannot synthesise it. Its codons are UUA, UUG, CUU, CUC, CUA, and CUG. With a hydrocarbon side chain, leucine is classified as a hydrophobic...	L	Leu	Essential Essential amino acid An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs...  for humans. Behaves similar to isoleucine and valine. See isoleucine.
Methionine Methionine Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar.-Function:...	M	Met	Essential Essential amino acid An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs...  for humans. Always the first amino acid to be incorporated into a protein; sometimes removed after translation. Like cysteine, contains sulfur, but with a methyl group instead of hydrogen. This methyl group can be activated, and is used in many reactions where a new carbon atom is being added to another molecule.
Asparagine Asparagine Asparagine is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side chain's functional group. It is not an essential amino acid...	N	Asn	Similar to aspartic acid. Asn contains an amide Amide In chemistry, an amide is usually an organic compound that contains the functional group consisting of an acyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds...  group where Asp has a carboxyl.
Proline Proline Proline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that humans can synthesize it...	P	Pro	Contains an unusual ring to the N-end amine group, which forces the CO-NH amide sequence into a fixed conformation. Can disrupt protein folding structures like α helix Alpha helix A common motif in the secondary structure of proteins, the alpha helix is a right- or left-handed coiled conformation, resembling a spring, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...  or β sheet Beta sheet The β sheet is the second form of regular secondary structure in proteins consisting of beta strands connected laterally by five or more hydrogen bonds, forming a generally twisted, pleated sheet... , forcing the desired kink in the protein chain. Common in collagen Collagen Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. It is naturally found exclusively in metazoa, including sponges. In muscle tissue it serves as a major component of endomysium... , where it often undergoes a posttranslational modification Posttranslational modification Posttranslational modification is the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis for many proteins....  to hydroxyproline Hydroxyproline -4-Hydroxyproline, or L-hydroxyproline , is a common proteinogenic amino acid, abbreviated as HYP, e.g., in Protein Data Bank.-Structure:... . Uncommon elsewhere.
Glutamine Glutamine Glutamine is one of the 20 amino acids encoded by the standard genetic code. Its side chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group. It can therefore be considered the amide of glutamic acid. Its codons are CAA and CAG. Glutamine is...	Q	Gln	Similar to glutamic acid. Gln contains an amide Amide In chemistry, an amide is usually an organic compound that contains the functional group consisting of an acyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds...  group where Glu has a carboxyl. Used in proteins and as a storage for ammonia Ammonia Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers... . The most abundant Amino Acid in the body.
Arginine Arginine Arginine is an α-amino acid. The L-form is one of the 20 most common natural amino acids. Its codons are CGU, CGC, CGA, CGG, AGA, and AGG. In mammals, arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health...	R	Arg	Functionally similar to lysine.
Serine Serine Serine is an organic compound with the formula HO2CCHCH2OH.-Occurrence:...	S	Ser	Serine and threonine have a short group ended with a hydroxyl Hydroxyl In chemistry, hydroxyl is composed of molecules consisting of an oxygen atom and a hydrogen atom connected by a covalent bond . The neutral form is a hydroxyl radical. The hydroxyl anion is called hydroxide; it is a diatomic ion with a charge of negative one...  group. Its hydrogen is easy to remove, so serine and threonine often act as hydrogen donors in enzymes. Both are very hydrophilic, therefore the outer regions of soluble proteins tend to be rich with them.
Threonine Threonine Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...	T	Thr	Essential Essential amino acid An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs...  for humans. Behaves similarly to serine.
Valine Valine Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...	V	Val	Essential Essential amino acid An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs...  for humans. Behaves similarly to isoleucine and leucine. See isoleucine.
Tryptophan Tryptophan Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...	W	Trp	Essential Essential amino acid An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs...  for humans. Behaves similarly to phenylalanine and tyrosine (see phenylalanine). Precursor of serotonin Serotonin Serotonin is a monoamine neurotransmitter. It is found extensively in the gastrointestinal tract of animals, and about 80 to 90 percent of the human body's total serotonin is located in the enterochromaffin cells in the gut, where it is used to regulate intestinal movements... . Naturally fluorescent.
Tyrosine Tyrosine Tyrosine or 4-hydroxyphenylalanine, is one of the 20 amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group...	Y	Tyr	Behaves similarly to phenylalanine (precursor to Tyrosine) and tryptophan (see phenylalanine). Precursor of melanin Melanin Melanin is a class of compounds found in plants, animals, and protists, where it serves predominantly as a pigment. The class of pigments are derivatives of the amino acid tyrosine. Many melanins are insoluble salts and show affinity to water... , epinephrine Epinephrine Epinephrine is a hormone and neurotransmitter that participates in the "fight or flight" response of the sympathetic nervous system... , and thyroid hormone Thyroid hormone The thyroid hormones, thyroxine and triiodothyronine , are tyrosine-based hormones produced by the thyroid gland. An important component in the synthesis of thyroid hormones is iodine. The major form of thyroid hormone in the blood is thyroxine , which has a longer half life than T3... s. Naturally fluorescent, although fluorescence is usually quenched by energy transfer to tryptophans.