PHSC1212 Biochemistry - Lecture 8: Enzyme Kinetics (excl. Michaelis-Menten) pt 1

Enzyme kinetics

the study of the rates of enzyme-catalyzed reactions and the factors that affect these rates

Reaction rate

refers to the change in concentration of reactant (or product) per unit time

Velocity

another name for reaction rate

Rate constant, concentration of reactants, order of reaction

What does the rate (v) of a reaction depend on?

Rate constant

a proportionality factor that relates the concentration of reactants (A) to the rate (v) of a chemical reaction

Enzymes

increase reaction rate (v) by increasing the rate constant (k)

By increasing rate constant and decreasing activation energy

How do enzymes increase the reaction rate

Reaction conditions like temperature and activation energy

What does the rate constant (k) depend on?

Uncatalyzed rate constants

increased by enzyme catalysis

Equilibrium

means the rates of the forward and reverse reactions are equal

Concentrations of reactants and products

In reversible reactions and when a state of equilibrium is reached, what does not change?

Forward and reverse reaction rates are equal

In reversible reactions and when a state of equilibrium is reached, why don't concentrations of reactants and products change?

Not equal

What does equilibrium mean in regard to concentrations of reactants and products?

Equilibrium constant

describes the ratio of product to reactant concentrations when a reaction reaches equilibrium

Products favored, equilibrium to right

What does Keq > 1 mean?

Reactants favored, equilibrium to left

What does Keq < 1 mean?

Equal concentrations of reactants and products

What does Keq = 1 mean?

Keq > 1, spontaneous

What does negative ΔG° mean?

Keq < 1, non spontaneous

What does positive ΔG° mean?

Enzymes stabilize transition state and affect forward and reverse rates equally

Why don't enzymes change reaction equilibrium or ratio of reactants to products?

Order

mathematical term that characterizes the mechanism by which reactants are converted to products; the sum of the exponents on the concentration terms in the rate expression

First order

reaction where rate depends on the first power of the concentration of a single reactant

Second order

reaction depends on the concentration of two reactants

Zero order

rate is independent of the reactant concentration because the reactant concentration is so high that all the enzymes are saturated

Concentration so high all enzymes saturated

Why is zero order rate independent of reactant concentration?

Psuedo first order

if one of the substrates in a second-order reaction is in great excess, the reaction can appear to have first order

Excess water

What generally causes a pseudo first order appearance?

Coenzyme

Second substrate in a biochemical reaction is usually what?

S-adenosylmethionine (SAM)

an example of a coenzyme that serves as a methyl donor

NADH and FADH2

examples of electron donors in oxidation/reduction reactions

Sequential and double displacement

two main types of multisubstrate reactions

Sequential

multi-substrate reaction that cannot proceed until all substrates have bound

Ordered and random

two types of sequential reactions

Double-displacement

multi-substrate reaction where the first product released before second substrate binds

Ordered

sequential reaction where the substrates must bind in a specific order

Random

sequential reaction where either substrate can bind first or second

Ordered sequential

A reaction where substrate A must bind before substrate B and product C must be released before product D is an example of what type of multi-substrate reaction?

Random sequential

A reaction where substrates A and B can bind in either order and products C and D can be released in either order is an example of what type of multi-substrate reaction?