| high energy bond | <chemistry> Chemical bonds that release more than 25kJ/mol on hydrolysis: their importance is that the energy can be used to transfer the hydrolysed residue to another compound. The risk in using the term is that students may think the bond itself is different in some way, whereas it is the compound that matters. Hydrolysis of creatine phosphate yields 42.7kJ/mol, of phosphoenolpyruvate, 53.2, ATP to ADP, 30.5: the latter is important because it shows that energetically the hydrolysis of creatine phosphate will suffice to reconstitute ATP, hence the use of creatine phosphate in muscle. (18 Nov 1997) |
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| high energy phosphate bond | See: high energy phosphates. (05 Mar 2000) |
| semipolar bond | A bond 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. Synonym: coordinate covalent bond. (05 Mar 2000) |
| hydrogen bond | <chemistry> A weak electrostatic link between an electronegative atom (such asoxygen) and a hydrogen atom which is linked covalently to anotherelectronegative atom, hydrogen bonding is what makes water stick toitself. (09 Oct 1997) |
| hydrophobic bond | See: hydrophobic interaction. (05 Mar 2000) |
| sigma bond | <chemistry> A bond formed from the overlap of either two s-orbitals or two hybrid orbitals such as sp3 or sp2 orbitals. (09 Jan 1998) |
| single bond | A covalent bond resulting from the sharing of one pair of electrons; e.g., H3C-CH3 (ethane). (05 Mar 2000) |
| noncovalent bond | Bond in which electrons are not shared between atoms; e.g., electrostatic bond, hydrogen bond. (05 Mar 2000) |
| sulfur-sulfur bond isomerases | <enzyme> Enzymes that catalyze the transposition of a sulfur-sulfur bond. Registry number: EC 5.3.4 (12 Dec 1998) |
| disulfide bond | 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. (05 Mar 2000) |
| disulphide bond | <chemistry, molecular biology> The S S linkage. A linkage formed between the SH groups of two cysteine moieties either within or between peptide chains. Each cysteine then becomes a half cystine residue. S S linkages stabilise, but do not determine, secondary structure in proteins. They are easily disrupted by SH groups in an exchange reaction and are not present in cytosolic proteins (cytosol has a high concentration of glutathione that has a free SH residue). (18 Nov 1997) |
| double bond | <chemistry> A covalent bond resulting from the sharing of two pairs of electrons; e.g., H2C==CH2 (ethylene). (05 Mar 2000) |
| isopeptide bond | 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. Compare: peptide bond, eupeptide bond. (05 Mar 2000) |
| electrostatic bond | Bond between atoms or groups carrying opposite charges (or, in some cases, partial charges). Synonym: heteropolar bond, salt bridge. (05 Mar 2000) |
| energy-rich bond | See: high energy compounds. (05 Mar 2000) |