The generic structure of an alpha amino acid in its unionized form

Amino acids (,, or ) are biologically important molecules made from amine (- NH < sub > 2 </ sub >) and carboxylic acid (- COOH ) functional groups, along with a side-chain specific to each amino acid.

The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen.

Structurally they can be classified according to the functional groups ' locations as alpha-( α -), beta-( β -), gamma-( γ -) or delta-( δ -) amino acids ; other categories relate to polarity, acid / base / neutral, and side chain group type ( including: aliphatic, acyclic, hydroxyl or sulphur-containing, aromatic ).

It lacks the NH < sub > 2 </ sub > group because of the cyclization of the side-chain and is known as an imino acid ; it falls under the category of special structured amino acids .</ ref > where R is an organic substituent known as a " side-chain "); often the term " amino acid " is used to refer specifically to these.

For example the standard glutamic acid ( glutamate ) and the non-standard gamma-amino acid gamma-amino-butyric acid ( GABA ) are respectively the brain's main excitatory and inhibitory neurotransmitters, hydroxyproline-a major component of the connective tissue collagen-is synthesised from proline, the standard amino acid glycine is used to synthesise porphyrins used in red blood cells, and the non-standard carnitine is used in lipid transport.

In 1806, the French chemists Louis-Nicolas Vauquelin and Pierre Jean Robiquet isolated a compound in asparagus that was subsequently named asparagine, the first amino acid to be discovered.

Another amino acid that was discovered in the early 19th century was cystine, in 1810, although its monomer, cysteine, was discovered much later, in 1884.

The side-chain can make an amino acid a weak acid or a weak base, and a hydrophile if the side-chain is polar or a hydrophobe if it is nonpolar.

Proline is the only proteinogenic amino acid whose side-group links to the α-amino group and, thus, is also the only proteinogenic amino acid containing a secondary amine at this position.

In chemical terms, proline is, therefore, an imino acid, since it lacks a primary amino group, although it is still classed as an amino acid in the current biochemical nomenclature, and may also be called an " N-alkylated alpha-amino acid ".

Bufotenin, an alkaloid from some toads, contains an indole core and is produced in living organisms from the amino acid tryptophan.

As an example, the important blood serum protein albumin contains 585 amino acid residues.

The alpha chain of hemoglobin contains 146 amino acid residues ; substitution of the glutamate residue at position 6 with a valine residue changes the behavior of hemoglobin so much that it results in sickle-cell disease.

This is DNA which contains units named genes that can produce proteins through a code ( genetic code ) in which a series of triplets ( codons ) of four possible nucleotides are translated into one of twenty possible amino acids.

Cervical mucus also contains electrolytes ( calcium, sodium and potassium ), organic components such as glucose, amino acids and soluble proteins.

In adult humans, the most common hemoglobin type is a tetramer ( which contains 4 subunit proteins ) called hemoglobin A, consisting of two α and two β subunits non-covalently bound, each made of 141 and 146 amino acid residues, respectively.

Honey contains many kinds of acids, both organic and amino.

Breast milk contains proteins and amino acids vital to a child's growth.

Maple syrup also contains trace amounts of amino acids, which may contribute to the " buddy " flavour of syrup produced late in the season, as the amino acid content of sap increases at this time.

The human body contains chemical compounds, such as water, carbohydrates ( sugar, starch, and fiber ), amino acids ( in proteins ), fatty acids ( in lipids ), and nucleic acids ( DNA and RNA ).

A diet that contains adequate amounts of amino acids ( especially those that are essential ) is particularly important in some situations: during early development and maturation, pregnancy, lactation, or injury ( a burn, for instance ).

A complete protein source contains all the essential amino acids ; an incomplete protein source lacks one or more of the essential amino acids.

The sweetener aspartame, present in many diet foods and soft drinks, must also be avoided, as aspartame contains two amino acids: phenylalanine and aspartic acid.

Because DNA contains four nucleotides, the total number of possible codons is 64 ; hence, there is some redundancy in the genetic code, with some amino acids specified by more than one codon.

The size of a synthesized protein can be measured by the number of amino acids it contains and by its total molecular mass, which is normally reported in units of daltons ( synonymous with atomic mass units ), or the derivative unit kilodalton ( kDa ).

Pasta is considered to be a good source for vegetarians because it contains extensive amounts of protein, proteins that consist of the six essential amino acids.

aminoacyl-tRNA contains a complementary anticodon on one end and the appropriate amino acid on the other.

Schematic diagram of the amino acid sequence ( amino terminus to the left and carboxylic acid terminus to the right ) of a prototypical transcription factor that contains ( 1 ) a DNA-binding domain ( DBD ), ( 2 ) signal-sensing domain ( SSD ), and a transactivation domain ( TAD ).

Since 2004, it has been marketed as a healthful drink ; its manufacturers claim it contains high concentrations of amino acids.

Catalase is a tetramer of four polypeptide chains, each over 500 amino acids long .< ref name = Boon_a > It contains four porphyrin heme ( iron ) groups that allow the enzyme to react with the hydrogen peroxide.

Finger millet is especially valuable as it contains the amino acid methionine, which is lacking in the diets of hundreds of millions of the poor who live on starchy staples such as cassava, plantain, polished rice, or maize meal.

Exons can include both sequences that code for amino acids ( red ) and untranslated sequences ( grey ).

For example, the most common hemoglobin sequences in humans and chimpanzees are nearly identical, differing by only one amino acid in both the alpha and the beta globin protein chains.

They made this proposal based on the structural similarity that exists between the two macromolecules, that is, both protein and DNA are linear sequences of amino acids and nucleotides respectively.

In addition to the amino acids, many other compounds that contain both acidic and basic centres tautomerize to the zwitterionic form.

Peptide bonds to proline, and to other N-substituted amino acids ( such as sarcosine ), are able to populate both the cis and trans isomers.

By contrast, the cis and trans isomers of the X-Pro peptide bond ( where X represents any amino acid ) both experience steric clashes with the neighboring substitution and are nearly equal energetically.

The essential fact of folding, however, remains that the amino acid sequence of each protein contains the information that specifies both the native structure and the pathway to attain that state.

* Imazapic, a selective herbicide for both the pre-and postemergent control of some annual and perennial grasses and some broadleaf weeds, kills plants by inhibiting the production of branched chain amino acids ( valine, leucine, and isoleucine ), which are necessary for protein synthesis and cell growth.

While taurine is sometimes called an amino acid, and indeed is an acid containing an amino group, it is not an amino acid in the usual biochemical meaning of the term, which refers to compounds containing both an amino and a carboxyl group.

Similarly, several proteins ( including prestin ) that are implicated in high frequency hearing in mammals have undergone numerous parallel amino acid replacements in bats and dolphins, both of which have evolved ultrasonic hearing for echolocation.

Similarly, both humans and chimpanzees have the identical molecule, while rhesus monkeys share all but one of the amino acids: the 66th amino acid is isoleucine in the former and threonine in the latter.

This view is based in part on the degenerate genetic code, in which sequences of three nucleotides ( codons ) may differ and yet encode the same amino acid ( GCC and GCA both encode alanine, for example ).

A key feature of these models included the idea that the antigen binding domains of antibodies ( Fab ) include amino acids from both the light and heavy protein subunits.

This beta subunit contains an amino acid sequence that exhibits large homologies with that of the beta subunit of hCG and both stimulate the same receptor.

< li > Some amino acids are catabolized into both glucogenic and ketogenic products.

They both are promoted by heating, but the Maillard reaction involves amino acids, as discussed above, whereas caramelization is simply the pyrolysis of certain sugars.

MTs have the capacity to bind both physiological ( such as zinc, copper, selenium ) and xenobiotic ( such as cadmium, mercury, silver, arsenic ) heavy metals through the thiol group of its cysteine residues, which represents nearly the 30 % of its amino acidic residues.

The approach is both more sensitive and more accurate than that of Chou and Fasman because amino acid structural propensities are only strong for a small number of amino acids such as proline and glycine.