Enzyme Catalysis and Reaction Kinetics

Flashcards covering key vocabulary related to enzyme catalysis, reaction kinetics, and thermodynamic principles from the lecture notes.

Enzyme Catalyst

A substance that reduces the energy required to reach the transition state, thereby changing the rate of a reaction without altering the overall delta G.

Transition State Energy (Ea / ΔG‡)

The amount of free energy required to get from the reactant state to the transition state, also known as the thermodynamic barrier or energy of activation. Enzymes lower this energy.

Overall Delta G (ΔG)

The difference in free energy between the ground state of reactants and products; enzyme catalysts do not change this value for a reaction.

Arrhenius Equation

An equation that connects a rate constant (k) to the transition state energy (Ea or ΔG‡) and temperature (T).

Rate Constant (k)

A numerical value that quantifies the rate of a chemical reaction, influenced by factors such as transition state energy and temperature.

Absolute Zero (0 Kelvin)

The theoretical lowest possible temperature where there is no thermal motion, meaning no bonds are vibrating. Temperature in kinetic equations is always in Kelvin and cannot be negative.

First Order Reaction

A reaction whose rate depends linearly on the concentration of a single reactant component.

Second Order Reaction (Overall)

A reaction whose overall rate depends on the concentrations of two reactants, where each is first order, or on the square of one reactant's concentration.

Rate Law

An equation that expresses the rate of a chemical reaction in terms of the concentrations of its reactants.

Derivative (in Reaction Kinetics)

Represents the instantaneous rate of change, such as the change in concentration of a reactant or product with respect to time (e.g., d[A]/dt).

In Vitro

Refers to experimental conditions or reactions performed outside of a living organism, typically 'in glass' (e.g., in a test tube).

Initial Velocity

The approximate rate of an enzyme-catalyzed reaction measured at the very beginning when product concentration is low, often determined by fitting early time points to a straight line.

Michaelis-Menten Kinetics

A prevalent model used to describe the kinetics of enzyme-catalyzed reactions, especially under steady-state approximation.

Steady-State Approximation

An assumption in enzyme kinetics that, after an initial pre-steady state phase, the concentration of enzyme-intermediate complexes (like EA complex) remains relatively constant over time.

Pre-Steady State

The very rapid initial phase of an enzyme-catalyzed reaction where the enzyme-substrate complex (EA complex) is quickly formed before the steady-state conditions are established.

Product Inhibition

A phenomenon in enzyme kinetics where a high concentration of the product starts to drive the reverse reaction, effectively slowing down the net forward reaction rate as the system approaches equilibrium.

Equilibrium (Reaction Kinetics)

The state in a reversible reaction where the rates of the forward and reverse reactions are equal, resulting in no net change in the concentrations of reactants and products.

EA Complex (Enzyme-Substrate Complex)

The intermediate molecular complex formed when an enzyme binds to its specific substrate(s) during an enzyme-catalyzed reaction.