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General College Biology I, Chapter 8, Metabolism: Energy and Enzymes Vocabulary: metabolism, metabolic pathway, catabolic pathway, anabolic pathway, chemical energy, potential energy, kinetic energy, heat, thermodynamics, entropy, endergonic, exergonic, activation energy, phosphorylation, enzyme, catalyst, substrate, active site, allosteric site, cofactor, coenzyme, competitive inhibitor, noncompetitive inhibitor, allosteric regulation, feedback inhibition Objectives: After attending lectures…


the totality of an organism's chemical reactions, consisting of catabollic 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 to simpler molecules (catabolic pathway)

catabolic pathway

a metabolic pathway that releases energy by breaking down complex molecules to simpler molecules

anabolic pathway

a metabolic pathway that consumes energy to synthesize a complex molecule from simpler molecules


the overall flow and transformation of energy in an organism; the study of how energy flows through organisms


the capacity to cause change, especially to do work (to move matter against an opposing force).

kinetic energy

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

heat (thermal) energy

that total amount of kinetic energy due to the random motion of atoms or molecules in a body of matter; also called thermal energy; energy in its most random form

potential energy

the energy that matter possesses as a result of its location or spatial arrangement (structure)

chemical energy

energy available in molecules for release in a chemical reaction; a forma of potential energy


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

first law of thermodynamics

the principle of conservation of energy; energy can be transferred and transformed, but it cannot be created or destroyed


a measure of disorder, or randomness

second law of thermodynamics

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

spontaneous process

a process that occurs without an overall input of energy; a process that is energetically favorable

free energy

the portion of a biological system's energy that can perform work when temperature and pressure are uniform throughout the system. The change in free energy of a system is calculated by the equation delta G = delta H - T delta S, where delta H is the change in enthaply (in biological systems, equivalent to total energy), T is the absolute temperature, and delta S is the change in entropy.

exergonic reaction

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

endergonic reaction

a non-spontaneous chemical reaction, in which free energy is absorbed from the surroundings

energy coupling

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

ATP (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.

phosphorylated intermediate

a molecule (often a reactant) with a phosphate group covalently bound to it, making it more reactive (less stable) than the unphosphorylated molecule


a macromolecule serving as a catalystm a chemical agent that increases the rate of a reaction without being consumed by the reaction; most are proteins


a chemical agent that selectively increases the rate of a reaction without being consumed by the reaction

activation energy

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


the reactant on which an enzyme works.

enzyme-substrate complex

a temporary complex formed when an enzyme binds to is substrate molecule(s).

active site

the specific region of an enzyme that binds the substrate and that forms the pocket in which catalysis occurs

induced fit

caused by entry of the substrate, the change in shape of the active site of an enzyme so that it binds more snuggly to the substrate


any nonprotein molecule or ion that is required for the proper functioning of of an enzyme; can be permanently bound to the active site or may be loosely bound and reversibly, along with the substrate during catalysis.


an organic molecule serving as a cofactor; in metabolic reactions, most vitamins function as this.

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

noncompetitive inhibitor

a substance that reduces the activity of an enzyme by binding to a location remote from the active site, changing an enzyme's shape so that the active site no longer effectively catalyses the conversion of substrate to product

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


a kind of allosteric regulation whereby a shape change in one subunit of a protein caused by substrate binding is transmitted to all the other subunits, facilitating binding of additional substrate molecules to those subunits

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.

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