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In chemistry, the force holding two neighboring atoms in place and resisting their separation; a b. is electrovalent if it consists of the attraction between oppositely charged groups, or covalent if it results from the sharing of one, two, or three pairs of electrons by the bonded atoms.
acylmercaptan b. -CO-S-;a "high energy" b. formed by the condensation of a carboxyl group (-COOH) and a mercaptan (or thiol) group (-SH); widely formed in the course of intermediary metabolism, notably in the oxidation of fats, where the -SH is part of coenzyme A and the -COOH is part of the fatty acid being oxidized.
apolar b. See hydrophobic interaction.
conjugated double b.'s two or more double b.'s separated by each single b.
coordinate covalent b. semipolar b
disulfide b. a single bond between two sulfurs; specifically, the -S-S- link binding two peptide chains (or different parts of one peptide chain); also occurs as part of the molecule of the amino acid, cystine, and is important as a structural determinant in many protein molecules, notably keratin, insulin, and oxytocin. A symmetric disulfide is R-S-S-R; R´-S-S-R is a mixed disulfide.
double b. a covalent b. resulting from the sharing of two pairs of electrons; e.g., H2C=CH2 (ethylene).
electrostatic b. b. between atoms or groups carrying opposite charges (or, in some cases, partial charges).heteropolar b., salt bridge;
energy-rich b. See high energy compounds, under compound.
eupeptide b. a peptide b. between the a-carboxyl group of one amino acid and the a-amino group of another amino acid. Cf. peptide b., isopeptide b.
heteropolar b. electrostatic b
high energy phosphate b. See high energy phosphates, under phosphate.
hydrogen b. a b. arising from the sharing of a hydrogen atom, covalently bound to an electronegative element (e.g., N or O), with another electronegative element (e.g., N, O, or a halogen). In substances of biological importance, the most common hydrogen b.'s are those in which H links N to O or N; such b.'s link purines on one strand to pyrimidines on the other strand of nucleic acids, thus maintaining double-stranded structures as in the Watson-Crick helix.
hydrophobic b. See hydrophobic interaction.
isopeptide b. an amide linkage between a carboxyl group of one amino acid and an amino group of another amino acid in which at least one of these groups is not on the a-carbon of one of the amino acids; for example, the bond between the glutamyl residue and the cysteinyl residue of glutathione. Cf. peptide b., eupeptide b.
noncovalent b. b. in which electrons are not shared between atoms; e.g., electrostatic b., hydrogen b.
peptide b. the common link (-CO-NH-) between amino acids in proteins, actually a substituted amide, formed by elimination of H2O between the -COOH of one amino acid and the H2N- of another. Cf. eupeptide b., isopeptide b.
semipolar b. a b. in which the two electrons shared by a pair of atoms belonged originally to only one of the atoms; often represented by a small arrow pointing toward the electron receiver; e.g., nitric acid, O(OH)N->O; phosphoric acid, (OH)3P->O.coordinate covalent b;
single b. a covalent b. resulting from the sharing of one pair of electrons; e.g., H3C-CH3 (ethane).
triple b. a covalent b. resulting from the sharing of three pairs of electrons; e.g., HC=CH (acetylene).
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