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D-Amino acids are used in racemic crystallography to create centrosymmetric crystals, which, depending on the protein, may allow for easier and more robust protein structure determination. [9] Gramicidin is a polypeptide made up from mixture of D- and L-amino acids. [10] Other compounds containing D-amino acids are tyrocidine and valinomycin.
Amino acids are the building blocks of peptides and enzymes while sugar-peptide chains are the backbone of RNA and DNA. [5] [6] In biological organisms, amino acids appear almost exclusively in the left-handed form (L-amino acids) and sugars in the right-handed form (R-sugars).
In organic chemistry, an amino sugar is a sugar molecule in which a hydroxyl group has been replaced with an amine group. More than 60 amino sugars are known, with one of the most abundant being N -acetyl- D -glucosamine (a 2-amino-2-deoxysugar ), which is the main component of chitin .
For example, the essential amino acid L-threonine contains two chiral stereocenters and is written (2S,3S)-threonine. There is no strict relationship between the R/S, the D/L, and (+)/(−) designations, although some correlations exist. For example, of the naturally occurring amino acids, all are L, and most are (S).
The commercial production of amino acids usually relies on mutant bacteria that overproduce individual amino acids using glucose as a carbon source. Some amino acids are produced by enzymatic conversions of synthetic intermediates. 2-Aminothiazoline-4-carboxylic acid is an intermediate in one industrial synthesis of L-cysteine for example.
Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like layer (sacculus) that surrounds the bacterial cytoplasmic membrane. [1] The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
L-forms of amino acids tend to be tasteless, whereas D-forms tend to taste sweet. [13] Spearmint leaves contain the L-enantiomer of the chemical carvone or R-(−)-carvone and caraway seeds contain the D-enantiomer or S-(+)-carvone. [9] The two smell different to most people because our olfactory receptors are chiral.
Glutamine can exist in either of two enantiomeric forms, L-glutamine and D-glutamine. The L-form is found in nature. Glutamine contains an α-amino group which is in the protonated −NH 3 + form under biological conditions and a carboxylic acid group which is in the deprotonated −COO − form, known as carboxylate, under physiological ...