Chapter 6


The capacity to do work

Kinetic energy

The energy of motion

Potential energy

Stored energy


The process by which an atom or molecule loses an electron.


The process by which an atom or molecule gains an electron.

Oxidation-reduction (redox) reactions

Chemical reactions in which both oxidation and reduction occur. These play a key role in the flow of energy through biological systems.

First Law of Thermodynamics

Energy cannot be created or destroyed; it can only change from one form to another.

Second Law of Thermodynamics

The disorder in the universe, more formally called entropy, is continuously increasing. Disorder is more likely than order.

Free energy

The energy available to do work in any system.


A chemical reaction in which the products contain more energy than the reactants, so that free energy must be put into the reaction from an outside source to allow it to proceed.


A chemical reaction in which the products contain less free energy than the reactants, so that free energy is released in the reaction.

Activation energy

The extra energy needed to destabilize existing chemical bonds and initiate a chemical reaction. The rate of reactions can be increased in two ways: (1) by increasing the energy of reacting molecules or (2) by lowering activation energy


The process of influencing chemical bonds in a way that lowers the activation energy needed to initiate a reaction. (Carried out by catalysts)

ATP Structure

ATP is composed of three smaller components: A 5C sugar (ribose), which serves as the framework to which the other two subunits are attached. The second is adenine, an organic molecule composed of two carbon-nitrogen rings. Each of the nitrogen atoms in t

Adenosine triphosphate (ATP)

The chief energy currency that all cells use for their energy transactions is this nucleotide.


Molecules that will undergo a reaction.

Active sites

The region of an enzyme surface to which a specific set of substrates binds, lowering the activation energy required for a particular chemical reaction and so facilitating it.

Enzyme-substrate complex

The complex formed when an enzyme binds with its substrate. This complex often has an altered configuration compared with the nonbound enzyme.

Multienzyme complexes

An assembly consisting of several enzymes catalyzing different steps in a sequence of reactions. Close proximity of these related enzymes speeds the overall process, making it more efficient.

Multienzyme complex advantages

1.) The rate of any enzyme reaction is limited by how often the enzyme collides with its substrate. If a series of sequential reactions occurs within a multienzyme complex, the product of one reaction can be delivered to the next enzyme without releasing


RNA molecules that greatly accelerate the rate of particular biochemical reactions and show extraordinary substrate specificity.

Intramolecular catalysis

Process in which ribozymes with folded structures catalyze reactions on themselves.

Intermolecular catalysis

Process in which ribozymes act on other molecules without being changed themselves.

Optimum temperature

The highest point in which an enzyme catalyzed reaction can be increased to.

Optimum pH

pH of 6 to 8


A substance that binds to an enzyme and decreases its activity

Feedback inhibition

Process in which the end product of a biochemical pathway acts as an inhibitor of an early reaction in the pathway.
(The end-product of the pathway binds to an allosteric site on the enzyme that catalyzes the first reaction in the pathway.)

Competitive inhibitors

Inhibitors that compete with the subsrate for the same active site, occupying the active site and thus preventing substrates from binding.

Noncompetitive inhibitors

Inhibitors that bind to the enzyme in a location other than the active site, changing the shape of the enzyme and making it unable to bind to the substrate.

Allosteric enzymes

Enzymes which can exist in either an active or inactive conformation.

Allosteric site

Specific binding sites where most noncompetitive inhibitors bind which serve as chemical on/off switches; the binding of a substance to the site can switch the enzyme between its active and inactive confirgurations.

Allosteric inhibitor

A substance that binds to an allosteric site and reduces enzyme activity

Allosteric activator

A substance that binds to allosteric sites to an enzyme in its active configuration, thereby increasing enzyme activity.


Chemical components that facilitate enzyme activity. (Both activators and cofactors increase enzyme activity)


Nonprotein organic molecule cofactor


The total of all chemical reactions carried out by an organism

Anabolism (Anabolic reactions)

Chemical reactions that expend energy to build up molecules.

Catabolism (Catabolic reactions)

Chemical reactions that harvest energy breaking down molecules.

Biochemical pathways

The organisational units of metabolism - the elements an organism controls to achieve coherent metabolic activity. The products of one reaction becomes the substrate for the next. These evolved in stepwise fashion, with the earliest reactions evolving las