Ch 5: Enzymes: Core Concepts and Kinetics

What determines whether or not a reaction can happen?

The energy differences between reactants and products

What determines the rate of a reaction?

the energy required to initiate the conversion of reactants into products

What is ΔG?

Actual free energy change of a reaction | The dynamic energy change happening at any moment that depends on the actual concentrations of reactants and products present in the environment

What is ΔG°?

Standard free energy change | A fixed reference constant for a specific reaction that represents the energy difference under hypothetical controlled conditions where the concentration of both the reactants and products is 1 M.

What is ΔG° used for?

It is a baseline measurement so we can compare the inherent energy of different reactions

What do enzymes not alter in a reaction?

reaction equilibrium

How do enzymes accelerate reactions?

By facilitating the formation of the transition state

What is a transition state (X^‡)?

A chemical species that has the highest free energy and the lowest concentration of those on the pathway from a substrate to a product.

What is ΔG^‡?

Gibbs free energy of activation (activation energy) | The energy required to form the transition state from the substrate of a reaction when considered from a particular direction.

What is the first step in enzymatic catalysis? Why?

The formation of an enzyme–substrate complex. This is when the structure of the substrate is altered by the enzyme after binding

What is an active site?

A specific region of an enzyme that binds the enzyme’s substrate and carries out catalysis.

What is the shape of an active site and how is it formed?

The active site is a three-dimensional cleft, or crevice, formed by groups that come from different parts of the amino acid sequence.

What is induced fit?

The modification of the shape of an active site in an enzyme, toward a structure complementary to the transition state, after the substrate has been bound.

What is binding energy?

The free energy released in the formation of the noncovalent interactions between enzyme and substrate that facilitate the formation of the transition state.

What is kinetics?

The study of the rates of chemical reactions

What are first-order reactions?

Reactions that are directly proportional to the reactant concentration

What are Bimolecular or Second-order reactions?

reactions that include two reactants

What are zero order reactions?

reactions where rate is independent of reactant concentrations

What is the Michaelis constant?

The concentration of substrate at which an enzyme is operating at one-half maximum velocity.

What is the maximal rate (V_Max)?

The theoretical maximum velocity of an enzyme catalyzed reaction at infinite substrate concentration

When is the maximal rate attained?

When [ES]=[E]_T

K_M is equal to what?

the substrate concentration at which the reaction rate is half its maximal value

What does the Michaelis–Menten equation predict?

how the speed of an enzyme-catalyzed reaction changes depending on how much substrate is available