| order | <zoology> A taxonomic classification between class and family. (09 Oct 1997) |
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| ordered | A scheme for substrate binding and product release for multisubstrate enzymes; for a two-substrate two-product enzyme with an ordered mechanism, one particular substrate has to bind to the enzyme first followed by the other substrate; chemistry then occurs, products are formed and are released from the enzyme in a distinct order. More complex ordered schemes exist for enzymes having more than two substrates. Some of the dehydrogenases have such a mechanism. Synonym: ordered. (05 Mar 2000) |
| ordered mechanism | A scheme for substrate binding and product release for multisubstrate enzymes; for a two-substrate two-product enzyme with an ordered mechanism, one particular substrate has to bind to the enzyme first followed by the other substrate; chemistry then occurs, products are formed and are released from the enzyme in a distinct order. More complex ordered schemes exist for enzymes having more than two substrates. Some of the dehydrogenases have such a mechanism. Synonym: ordered. (05 Mar 2000) |
| ordered on-random off mechanism | A scheme for substrate binding and product release for multisubstrate enzymes; for a two-substrate two-product enzyme with this mechanism, the individuals have to bind to the enzyme in a distinct order; however, once the products are formed they may dissociate from the enzyme in either order. It has been suggested that pyruvate kinase has such a mechanism. The random on-ordered off mechanism is simply the reverse of this mechanism. (05 Mar 2000) |
| orderly | An attendant in a hospital unit who assists in the care of patients. (05 Mar 2000) |
| birth order | The sequence in which children are born into the family. (12 Dec 1998) |
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| higher order conditioning | The use of a previously conditioned stimulus to condition further responses, in much the same way unconditioned stimuli are used. (05 Mar 2000) |
| second-order conditioning | The use of a previously successfully conditioned stimulus as the unconditioned stimulus for further conditioning. (05 Mar 2000) |
| second-order kinetics | A term describing the reaction rate of a chemical reaction in which the rate is proportional to the product of the concentrations (in moles) of two of the reactants (also called bimolecular kinetics), or to the square of the molar concentration of the reactant if there is only one. Such a reaction might have an equation like rate = k[A][B] or rate = k[A]2, where k is the reaction rate constant, [A] is the concentration of reactant A, and [B] is the concentration of reactant B. (09 Oct 1997) |
| third-order kinetics | <pharmacology> A term describing the reaction rate of a chemical reaction in which the rate is proportional to the product of the concentrations (in moles) of three of the reactants, the product of the molar concentration of one reactant and the square of the molar concentration of another reactant, or the cube of the molar concentration of one of the reactants. Such a reaction might have an equation like rate = k[A][B][C] or rate = [A][B]2 or rate = [A]3, where k is the reaction rate constant, [A] is the concentration of reactant A, [B] is the concentration of reactant B, and [C] is the concentration of reactant C. (09 Oct 1997) |
| zero-order reaction | A reaction that proceeds at a particular rate independently of the concentration of the reactant or reactants. (05 Mar 2000) |
| first-order kinetics | A term describing the reaction rate of a chemical reaction in which the rate is proportional to the concentration (in moles) of only one of the reactants. Such a reaction might have an equation like rate = k[A], where k is the reaction rate constant and [A] is the concentration of a reactant A. (09 Oct 1997) |
| first-order reaction | A reaction the rate of which is proportional to the concentration of the single substance undergoing change; radioactive decay is a first-order process, defined by the equation -(dN/dt)=kN, where N is the number of atoms subject to decay (reaction), t is time, and k is the first-order decay (reaction) constant, i.e., the fraction of all atoms decaying per unit of time. See: decay constant, order. (05 Mar 2000) |