AP Biology: Enzymes

Activation Energy

The energy barrier that blocks the tendency for a set of chemical substances to react.

Active Site

The region on the surface of an enzyme where the substrate binds, and where catalysis occurs.

Allostery

Regulation of the activity of a protein by the binding of an effector molecule at a site other than the active site.

Anabolism

Using energy to build substances.

Catabolism

Break down substance to use as energy.

ATP (adenosine triphosphate)

An energy-storage compound containing adenine, ribose, and three phosphate groups. When it is formed from ADP, useful energy is stored; when it is broken down (to ADP or AMP), energy is released to drive endergonic reactions.

catalyst

A chemical substance that accelerates a reaction without itself being consumed in the overall course of the reaction. Catalysts lower the activation energy of a reaction. Enzymes are biological catalysts.

catalytic subunit

The polypeptide in an enzyme protein with quaternary structure that contains the active site for the enzyme.

chemical equilibrium

A state reached in a reversible chemical reaction when the forward and reverse reactions balance each other and there is no net change.

Coenzyme

A nonprotein organic molecule that plays a role in catalysis by an enzyme.

competitive inhibitor

A nonsubstrate that binds to the active site of an enzyme and thereby inhibits binding of substrate and reaction from part of the environment.

endergonic reaction

A chemical reaction that requires the input of energy in order to proceed.

Feedback (end product) inhibition

A control capacity of some metabolic pathways in which the final product produced inhibits an early enzyme in the pathway.

Energy

The capacity to do work or move matter against an opposing force. The capacity to accomplish change.

Enthalpy

The sum of the internal energy of a system; the product of the volume multiplied by the pressure.

entropy

A measure of the degree of disorder in any system. Spontaneous reactions in a closed system are always accompanied by an increase in disorder and entropy.

enzyme

A protein, on the surface of which are chemical groups so arranged as to make the enzyme a catalyst for a chemical reaction.

Enzyme substrate complex

The complex that forms when an enzyme binds to its substrate(s).

exergonic reaction

A reaction in which free energy is released.

end product inhibition

A control capacity of some metabolic pathways in which the final product produced inhibits an early enzyme in the pathway.

free energy

That energy which is available for doing useful work, after allowance has been made for the increase or decrease of disorder.

induced fit

A change in enzyme conformation upon binding to substrate with an increase in the rate of catalysis.

Inhibitor

A substance that binds to the surface of an enzyme and interferes with its action on its substrates.

Isozymes

Enzymes that have somewhat different amino acid sequences but catalyze the same reaction.

kinetic energy

The energy associated with movement.

Metabolism

The sum total of the chemical reactions that occur in an organism, or some subset of that total (as in respiratory metabolism).

Noncompetitive inhibitor

An inhibitor that binds the enzyme at a site other than the active site.

Potential Energy

"Stored" energy not doing work, such as the energy in chemical bonds.

Regulatory Subunit

The polypeptide in an enzyme protein with quaternary structure that does not contain the active site, but instead binds non-substrate molecules and changes its structure, in turn changing the structure and function of the active site.

Substrate

The molecule or molecules on which an enzyme exerts catalytic action.

Lock & Key Hypothesis

The substrate and active site are complementary to one another.