Biochem Chapter 6

Front 1

induced fit

Back 1

a change in the conformation of an enzyme in response to substrate binding that renders the enzyme catalytically active; also used to denote changes in the conformation of any macromolecule in response to ligand binding such that the binding site of the macromolecule better conforms to the shape of the ligand

Front 2

specificity

Back 2

the ability of an enzyme or receptor to discriminate among competing substrates or ligands

Front 3

binding energy ∆G'(b)

Back 3

the energy derived from noncovalent interactions between enzyme and substrate or receptor and ligand

Front 4

rate constant

Back 4

the proportionality constant that relates the velocity of a chemical reaction to the concentration of the reactants

Front 5

equilibrium constant K{eq}

Back 5

a constant, characteristic for each chemical reaction; relates the specific concentrations of all reactants and products at equilibrium at a given temp and pressure

Front 6

rate limiting step

Back 6

1) generally, the step in an enzymatic reaction with the greatest activation energy or the transistion state of highest free energy
2) The slowest step in a metabolic pathway

Front 7

reaction intermediate

Back 7

any chemical species in a reaction pathway that has a finite chemical lifetime

Front 8

activation energy

Back 8

the amount of energy in Joules required to convert all the molecules in 1 mole of a reacting substance from the ground state to the transistion state

Front 9

transistion state

Back 9

an activated form of a molecule in which the molecule has undergone a partial chemical reaction; the highest point on the reaction coordinate

Front 10

standard free energy change

Back 10

the free energy change for a reaction occurring under a set of standard conditions; temp=298K; pressure=1 atm or 101.3 kPa; and all solutes at 1 M concentration

Front 11

ground state

Back 11

the normal, stable form of an atom or molecule; as distinct from the excited state

Front 12

substrate

Back 12

the specific compound acted upon by an enzyme

Front 13

active site

Back 13

the region of an enzyme surface that binds the substrate molecule and catalytically transforms it; also known as the catalytic site

Front 14

apoprotein

Back 14

the protein portion of a protein, exclusive of any organic or inorganic cofactors or prosthetic groups that might be required for activity

Front 15

apoenzyme

Back 15

the protein portion of an enzyme, exclusive of any organic or inorganic cofactors or prosthetic groups that might be required for catalytic activity

Front 16

holoenzyme

Back 16

a catalytically active enzyme including all necessary subunits, prosthetic groups, and cofactors

Front 17

prosthetic group

Back 17

a metal ion or an organic compound (other than an amino acid) that is covalently bound to a protein and is essential to its activity

Front 18

coenzyme

Back 18

an organic cofactor required for the action of certain enzymes; often contains a vitamin as a component

Front 19

cofactor

Back 19

an inorganic ion or a coenzyme required for enzyme activity

Front 20

enzyme

Back 20

a biomolecule, either protein or RNA, that catalyzes a specific chemical reaction. It does not affect the equilibrium of the catalyzed reaction; it enhances the rate of a reaction by providing a reaction path with a lower activation energy

Front 21

protein kinases

Back 21

enzymes that transfer the terminal phosphoryl group of ATP or another nucleoside tiphosphate to a Ser, Thr, Asp, or His side chain in a target protein, thereby regulating the activity or other properties of that protein

Front 22

allosteric enzyme

Back 22

a regulatory enzyme, with catalytic activity modulated by the noncovalent binding of a specific metabolite at a site other than the active site

Front 23

turnover number

Back 23

the number of times an enzyme molecule transforms a substrate molecule per unit time, under conditions giving maximal activity at substrate concentrations that are saturating

Front 24

Lineweaver-Burk equation

Back 24

an algebraic transform of the Michaelis-Menten equation, allowing determination of V{max} and K{m} by extrapolation of [S] to infinity

Front 25

Michaelis-Menten equation

Back 25

the equation describing the hyperbolic dependence of the initial reaction velocity, V{0}, on substrate concentration, [S], in many enzyme catalyzed reactions

At V = 1/2 V{max}, the substrate concentration [S] is equal to the K{m}

Front 26

Michaelis constant K{m}

Back 26

the substrate concentration at which an enzyme catalyzed reaction proceeds at one-half its maximum velocity

Front 27

V{max}

Back 27

the maximum velocity of an enzymatic reaction when the binding site is saturated with substrate