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Structure of a typical L-alpha-amino acid in the "neutral" form. Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. [1] Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. [2]
Protein structures range in size from tens to several thousand amino acids. [2] By physical size, proteins are classified as nanoparticles, between 1–100 nm. Very large protein complexes can be formed from protein subunits. For example, many thousands of actin molecules assemble into a microfilament.
Each protein has its own unique amino acid sequence that is specified by the nucleotide sequence of the gene encoding this protein. The genetic code is a set of three-nucleotide sets called codons and each three-nucleotide combination designates an amino acid, for example AUG (adenine–uracil–guanine) is the code for methionine.
Additionally, the protein can undergo a variety of post-translational modifications, which are briefly summarized here. The N-terminal amino group of a polypeptide can be modified covalently, e.g., Fig. 1 N-terminal acetylation. acetylation (=)
Three-dimensional structure [1] of an alpha helix in the protein crambin. An alpha helix (or α-helix) is a sequence of amino acids in a protein that are twisted into a coil (a helix). The alpha helix is the most common structural arrangement in the secondary structure of proteins. It is also the most extreme type of local structure, and it is ...
Alanine (symbol Ala or A), [4] or α-alanine, is an α-amino acid that is used in the biosynthesis of proteins. It contains an amine group and a carboxylic acid group, both attached to the central carbon atom which also carries a methyl group side chain. Consequently it is classified as a nonpolar, aliphatic α-amino acid.
Lysine. Technically, any organic compound with an amine (–NH 2) and a carboxylic acid (–COOH) functional group is an amino acid. The proteinogenic amino acids are a small subset of this group that possess a central carbon atom (α- or 2-) bearing an amino group, a carboxyl group, a side chain and an α-hydrogen levo conformation, with the exception of glycine, which is achiral, and proline ...
At the top level are all alpha proteins (domains consisting of alpha helices), all beta proteins (domains consisting of beta sheets), and mixed alpha helix/beta sheet proteins. While most proteins adopt a single stable fold, a few proteins can rapidly interconvert between one or more folds. These are referred to as metamorphic proteins. [5]