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activation energy

The amount of energy that reactants must absorb before a chemical reaction will start; also called free energy of activation.

active site

The specific portion of an enzyme that binds the substrate by means of multiple weak interactions and that forms the pocket in which catalysis occurs.

Adenosine triphosphate

An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.

allosteric regulation

The binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site.


The study of energy transformations that occur in a collection of matter.

second law of thermodynamics

The principle stating that every energy transfer or transformation increases the entropy of the universe. Ordered forms of energy are at least partly converted to heat.


The reactant on which an enzyme works.

potential energy

energy that matter possesses because of its location or structure


referring to a molecule that is covalently bonded to a phosphate group

noncompetitive inhibitor

A substance that reduces the activity of an enzyme by binding to a location remote from the active site, changing the enzyme's shape so that the active site no longer functions effectively.


The totality of an organism's chemical reactions, consisting of catabolic and anabolic pathways, which manage the material and energy resources of the organism.

metabolic pathway

A series of chemical reactions that either builds a complex molecule (anabolic pathway) or breaks down a complex molecule into simpler compounds (catabolic pathway).

kinetic energy

the energy associated with the relative motion of objects. Moving matter can perform work by imparting motion to other matter.

induced fit

the change in shape of the active site of an enzyme so that it binds more snugly to the substrate


An iron-containing protein in red blood cells that reversibly binds oxygen.


The total amount of kinetic energy due to molecular motion in a body of matter; also called thermal energy

free energy

The portion of a system's energy that can perform work when temperature is uniform throughout the system.

free energy formula

ΔG= ΔH-TΔS where H is enthalpy, T is absolute temperature, S is entropy

first law of thermodynamics

The principle of conservation of energy. Energy can be transferred and transformed, but it cannot be created or destroyed.

feedback inhibition

A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.

exergonic reaction

A spontaneous chemical reaction in which there is a net release of free energy.

enzyme-substrate complex

A temporary complex formed when an enzymes binds to its substrate molecules


A macromolecule serving as a catalyst, a chemical agent that changes the rate of a reaction without being consumed by the reaction.


A measure of disorder or randomness

energy coupling

In cellular metabolism, the use of energy released from an exergonic reaction to drive an endergonic reaction.

endergonic reaction

A nonspontaneous chemical reaction in which free energy is absorbed from the surroundings

competitive inhibitor

A substance that reduces the activity of an enzyme by entering the active site in place of the substrate whose structure it mimics.


A chemical agent that changes the rate of a reaction without being consumed by the reaction.

catabolic pathway

A metabolic pathway that releases energy by breaking down complex molecules to simpler compounds.

anabolic pathway

A metabolic pathway that consumes energy to synthesize a complex molecule from simpler compounds.

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