Key Terms

activation energy
energy necessary for reactions to occur
active site
specific region of the enzyme to which the substrate binds
allosteric inhibition
inhibition by a binding event at a site different from the active site, which induces a conformational change and reduces the affinity of the enzyme for its substrate
anabolic
(also, anabolism) pathways that require an input of energy to synthesize complex molecules from simpler ones
ATP
adenosine triphosphate, the cell’s energy currency
bioenergetics
study of energy flowing through living systems
catabolic
(also, catabolism) pathways in which complex molecules are broken down into simpler ones
chemical energy
potential energy in chemical bonds that is released when those bonds are broken
coenzyme
small organic molecule, such as a vitamin or its derivative, which is required to enhance the activity of an enzyme
cofactor
inorganic ion, such as iron and magnesium ions, required for optimal regulation of enzyme activity
competitive inhibition
type of inhibition in which the inhibitor competes with the substrate molecule by binding to the active site of the enzyme
denature
process that changes the natural properties of a substance
endergonic
describes chemical reactions that require energy input
enthalpy
total energy of a system
entropy (S)
measure of randomness or disorder within a system
exergonic
describes chemical reactions that release free energy
feedback inhibition
effect of a product of a reaction sequence to decrease its further production by inhibiting the activity of the first enzyme in the pathway that produces it
free energy
Gibbs free energy is the usable energy, or energy that is available to do work.
heat
energy energy transferred from one system to another that is not work—energy of the motion of molecules or particles
heat energy
total bond energy of reactants or products in a chemical reaction
induced fit
dynamic fit between the enzyme and its substrate, in which both components modify their structures to allow for ideal binding
kinetic energy
type of energy associated with objects or particles in motion
metabolism
all the chemical reactions that take place inside cells, including anabolism and catabolism
phosphoanhydride bond
bond that connects phosphates in an ATP molecule
potential energy
type of energy that has the potential to do work; stored energy
substrate
molecule on which the enzyme acts
thermodynamics
study of energy and energy transfer involving physical matter
transition state
high-energy, unstable state—an intermediate form between the substrate and the product—occurring during a chemical reaction