Enzymes Flashcards
6 classes of enzymes
oxidoreductases, transferases, isomerases, hydrolases, lyases, ligases
oxidoreductase
catalyzes oxidation-reduction reactions
transferase
catalyzes transfer of C-, N-, or P-containing groups
hydrolase
catalyzes cleavage of bonds by the addition of water
lyase
catalyzes cleavage of C-C, C-S, and certain C-N bonds
ligase
catalyzes formation of bonds between C and O, S, or N coupled to hydrolysis of high-energy phosphate
isomerase
catalyzes racemization of optical or geometric isomers
kcat
turnover number
number of substrate molecules converted to product per enzyme molecule per unit time
free energy of activation
energy difference between a reactant and the high energy intermediate required to create the final product
Km
Michaelis constant, property of enzyme
(k-1 + k2)/k1
concentration of substrate at which the initial rate V-subzero = (1/2)Vmax
point at which half of substrate molecules have enzymes in their active site
lower Km = higher affinity of enzyme for substrate
Vmax
maximum velocity of a reaction, number of substrate molecules converted to product per unit time
Michaelis-Menten equation purpose
describes how initial velocity varies with [S]
[S] vs.v0
applies to enzymes with typical hyperbolic kinetics!
Effect of temperature on enzyme kinetics
increases enzyme velocity (higher kinetic energy, increased number of substrates with sufficient energy to reach transition state)
until high enough to denature enzyme
Effect of pH on enzyme kinetics
optimum pH range for catalytic amino acid side chains in active sites
suited for local environment
extreme pH can denature enzymes
Assumptions of Michaelis-Menten
[E]
