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 ".

Cysteine is unusual since it has a sulfur atom at the second position in its side-chain, which has a larger atomic mass than the groups attached to the first carbon, which is attached to the α-carbon in the other standard amino acids, thus the ( R ) instead of ( S ).

The primary structure of a protein simply consists of its linear sequence of amino acids ; for instance, " alanine-glycine-tryptophan-serine-glutamate-asparagine-glycine-lysine -…".

It is first hydrolyzed into its component amino acids.

The convention for a polypeptide is to list its constituent amino acid residues as they occur from the amino terminus to the carboxylic acid terminus.

The amino acid composition of collagen is atypical for proteins, particularly with respect to its high hydroxyproline content.

The amino terminus of calreticulin interacts with the DNA-binding domain of the glucocorticoid receptor and prevents the receptor from binding to its specific glucocorticoid response element.

For example, the putative primary role of Buchnera is to synthesize essential amino acids that the aphid cannot acquire from its natural diet of plant sap.

A change to the DNA in a gene can change a protein's amino acids, changing its shape and function: this can have a dramatic effect in the cell and on the organism as a whole.

As a central metabolic control mechanism, its status is also used as a control signal to other body systems ( such as amino acid uptake by body cells ).

Dihydrobiopterin Reductase activity is to replenish quinonoid-Dihydrobiopterin back into its Tetrahydrobiopterin form, which is an important cofactor in many metabolic reactions in amino acid metabolism.

The side chains of the standard amino acids, detailed in the list of standard amino acids, have a great variety of chemical structures and properties ; it is the combined effect of all of the amino acid side chains in a protein that ultimately determines its three-dimensional structure and its chemical reactivity.

Each protein has its own unique amino acid sequence that is specified by the nucleotide sequence of the gene encoding this protein.

The mRNA is loaded onto the ribosome and is read three nucleotides at a time by matching each codon to its base pairing anticodon located on a transfer RNA molecule, which carries the amino acid corresponding to the codon it recognizes.

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 ).

The amino acids that an organism cannot synthesize on its own are referred to as essential amino acids.

Generic amino acids ( 1 ) in neutral form, ( 2 ) as they exist physiologically, and ( 3 ) joined together as a dipeptide.

These amino acids contain an aromatic ring in their sidechain that fits into a ' hydrophobic pocket ' ( the S < sub > 1 </ sub > position ) of the enzyme.

If amino acids were randomly assigned to triplet codons, then there would be 1. 5 x 10 < sup > 84 </ sup > possible genetic codes to choose from.

The approximate amino acid composition of gelatin is: glycine 21 %, proline 12 %, hydroxyproline 12 %, glutamic acid 10 %, alanine 9 %, arginine 8 %, aspartic acid 6 %, lysine 4 %, serine 4 %, leucine 3 %, valine 2 %, phenylalanine 2 %, threonine 2 %, isoleucine 1 %, hydroxylysine 1 %, methionine and histidine < 1 % and tyrosine < 0. 5 %.

However, amino acid content is almost negligible in honey, accounting for only 0. 05 – 0. 1 % of the composition.

The amino terminal ( NH < sub > 2 </ sub >) end ( JH4-JH7 ) of Jaks is called a FERM domain ( short for band 4. 1 ezrin, radixin and moesin ); this domain is also found in the focal adhesion kinase ( FAK ) family and is involved in association of JAKs with cytokine receptors and / or other kinases.

with 1 and 4 being aliphatic amino acids, 2 and 5 always and 3 sometimes being proline.

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 ).

The CFTR gene, found at the q31. 2 locus of chromosome 7, is 230, 000 base pairs long, and creates a protein that is 1, 480 amino acids long.

The 1, 024 amino acids of E. coli

These indels consist of a 4 amino acid insertion in transcription repair coupling factor Mfd, a 10 amino acid insertion in ribosomal protein L19, a 1 amino acid insertion in FtsZ, a 1 amino acid insertion in major sigma factor 70, and a 1 amino acid deletion in exonuclease VII.

The prototype of a protein disulfide bond is the two-amino-acid peptide cystine, which is composed of two cysteine amino acids joined by a disulfide bond ( shown in Figure 2 in its unionized form ).

At pH values greater than the pKa of the carboxylic acid group ( mean for the 20 common amino acids is about 2. 2, see the table of amino acid structures above ), the negative carboxylate ion predominates.

One is an amino group, — NH < sub > 2 </ sub >, and one is a carboxylic acid group, — COOH ( although these exist as — NH < sub > 3 </ sub >< sup >+</ sup > and — COO < sup >−</ sup > under physiologic conditions ).

With four different nucleotides, a code of 2 nucleotides would allow for only a maximum of 4 < sup > 2 </ sup > or 16 amino acids.

The main action of these aldehyde fixatives is to cross-link amino groups in proteins through the formation of CH < sub > 2 </ sub > ( methylene ) linkage, in the case of formaldehyde, or by a C5H10 cross-links in the case of glutaraldehyde.

It encodes 37 genes: 13 for subunits of respiratory complexes I, III, IV and V, 22 for mitochondrial tRNA ( for the 20 standard amino acids, plus an extra gene for leucine and serine ), and 2 for rRNA.

However, Bada noted that in current models of early Earth conditions, carbon dioxide and nitrogen ( N < sub > 2 </ sub >) create nitrites, which destroy amino acids as fast as they form.

A Peptide bond ( amide bond ) is a covalent chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, causing the release of a molecule of water ( H < sub > 2 </ sub > O ), hence the process is a dehydration synthesis reaction

Peroxisome targeting signal 2 ( PTS2 ): a nonapeptide located near the N-terminus with a consensus sequence ( R / K )-( L / V / I )- XXXXX -( H / Q )-( L / A / F ) ( where X can be any amino acid ).

The five membered ring also possesses a keto group ( in the 8 position ), flanked by two secondary amino groups ( in the 7 and 9 positions ), and deprotonation of one of these at high pH could explain the pK < sub > 2 </ sub > and behavior as a diprotic acid.