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In aqueous solution at pH close to neutrality, amino acids exist as zwitterions, i.e. as dipolar ions with both NH + 3 and CO − 2 in charged states, so the overall structure is NH + 3 −CHR−CO − 2. At physiological pH the so-called "neutral forms" −NH 2 −CHR−CO 2 H are not present to any measurable degree. [36]
Hydrophobicity scales. Hydrophobicity scales are values that define the relative hydrophobicity or hydrophilicity of amino acid residues. The more positive the value, the more hydrophobic are the amino acids located in that region of the protein. These scales are commonly used to predict the transmembrane alpha-helices of membrane proteins.
Like other amino acids, tryptophan is a zwitterion at physiological pH where the amino group is protonated (– NH + 3; pK a = 9.39) and the carboxylic acid is deprotonated ( –COO −; pK a = 2.38). [5] Humans and many animals cannot synthesize tryptophan: they need to obtain it through their diet, making it an essential amino acid.
The pH-dependence of the activity displayed by enzymes and the pH-dependence of protein stability, for example, are properties that are determined by the pK a values of amino acid side chains. The p K a values of an amino acid side chain in solution is typically inferred from the p K a values of model compounds (compounds that are similar to ...
Infobox references. Phenylalanine (symbol Phe or F) [ 3] is an essential α- amino acid with the formula C. 9H. 11NO. 2. It can be viewed as a benzyl group substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of alanine.
Amino acid replacement. Amino acid replacement is a change from one amino acid to a different amino acid in a protein due to point mutation in the corresponding DNA sequence. It is caused by nonsynonymous missense mutation which changes the codon sequence to code other amino acid instead of the original. Notable mutations.
Arginine is the amino acid with the formula (H 2 N)(HN)CN(H)(CH 2) 3 CH(NH 2)CO 2 H. The molecule features a guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO 2 −) and both the amino and guanidino groups are protonated, resulting in a cation.
Isoleucine (symbol Ile or I) [1] is an α-amino acid that is used in the biosynthesis of proteins.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 hydrocarbon side chain with a branch (a central carbon atom bound to three other ...