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The incorporation of these nonstandard amino acids is rare. For example, 25 human proteins include selenocysteine in their primary structure, [64] and the structurally characterized enzymes (selenoenzymes) employ selenocysteine as the catalytic moiety in their active sites. [65] Pyrrolysine and selenocysteine are encoded via variant codons.
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 ...
An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life forms, the nine amino acids humans cannot synthesize are valine , isoleucine , leucine , methionine ...
A branched-chain amino acid (BCAA) is an amino acid having an aliphatic side-chain with a branch (a central carbon atom bound to three or more carbon atoms). Among the proteinogenic amino acids, there are three BCAAs: leucine, isoleucine, and valine. [1] Non-proteinogenic BCAAs include 2-aminoisobutyric acid and alloisoleucine. Leucine ...
Leucine ball and stick model spinning. Leucine (symbol Leu or L) [3] is an essential amino acid that is used in the biosynthesis of proteins.Leucine is an α-amino acid, meaning it contains an α-amino group (which is in the protonated −NH 3 + form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −COO − form under biological conditions), and a side ...
A dipeptide is an organic compound derived from two amino acids. The constituent amino acids can be the same or different. When different, two isomers of the dipeptide are possible, depending on the sequence. Several dipeptides are physiologically important, and some are both physiologically and commercially significant.
Glutamine ball and stick model spinning. Glutamine (symbol Gln or Q) [3] is an α-amino acid that is used in the biosynthesis of proteins.Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide.
M phase See mitosis. macromolecule Any very large molecule composed of dozens, hundreds, or thousands of covalently bonded atoms, especially one with biological significance. . Many important biomolecules, such as nucleic acids and proteins, are polymers consisting of a repeated series of smaller monomers; others such as lipids and carbohydrates may not be polymeric but are nevertheless large ...