Understanding Key Concepts in Bioenergetics and Metabolism
ATP Synthase: A membrane-embedded protein complex that regenerates ATP from ADP with energy from protons diffusing through it.
ATP: The cell’s energy currency.
Acetyl CoA: The combination of an acetyl group derived from pyruvic acid and coenzyme A, which is made from pantothenic acid (a B-group vitamin).
Activation Energy: The amount of initial energy necessary for reactions to occur.
Active Site: A specific region on the enzyme where the substrate binds.
Allosteric Inhibition: The mechanism for inhibiting enzyme action in which a regulatory molecule binds to a second site (not the active site) and initiates a conformation change in the active site, preventing binding with the substrate.
Anabolic: Describes the pathway that requires a net energy input to synthesize complex molecules from simpler ones.
Anaerobic Cellular Respiration: The use of an electron acceptor other than oxygen to complete metabolism using electron transport-based chemiosmosis.
Bioenergetics: The concept of energy flow through living systems.
Catabolic: Describes the pathway in which complex molecules are broken down into simpler ones, yielding energy as an additional product of the reaction.
Chemiosmosis: The movement of hydrogen ions down their electrochemical gradient across a membrane through ATP synthase to generate ATP.
Citric Acid Cycle: A series of enzyme-catalyzed chemical reactions of central importance in all living cells that harvest the energy in carbon-carbon bonds of sugar molecules to generate ATP. The citric acid cycle is an aerobic metabolic pathway because it requires oxygen in later reactions to proceed.
Competitive Inhibition: A general mechanism of enzyme activity regulation in which a molecule other than the enzyme’s substrate is able to bind the active site and prevent the substrate itself from binding, thus inhibiting the overall rate of reaction for the enzyme.
Electron Transport Chain: A series of four large, multi-protein complexes embedded in the inner mitochondrial membrane that accepts electrons from donor compounds and harvests energy from a series of chemical reactions to generate a hydrogen ion gradient across the membrane.
Endergonic: Describes a chemical reaction that results in products that store more chemical potential energy than the reactants.
Enzyme: A molecule that catalyzes a biochemical reaction.
Exergonic: Describes a chemical reaction that results in products with less chemical potential energy than the reactants, plus the release of free energy.
Feedback Inhibition: A mechanism of enzyme activity regulation in which the product of a reaction or the final product of a series of sequential reactions inhibits an enzyme for an earlier step in the reaction series.
Fermentation: The steps that follow the partial oxidation of glucose via glycolysis to regenerate NAD+; occurs in the absence of oxygen and uses an organic compound as the final electron acceptor.
Glycolysis: The process of breaking glucose into two three-carbon molecules with the production of ATP and NADH.
Heat Energy: The energy transferred from one system to another that is not work.
Kinetic Energy: The type of energy associated with objects in motion.
Metabolism: All the chemical reactions that take place inside cells, including those that use energy and those that release energy.
Noncompetitive Inhibition: A general mechanism of enzyme activity regulation in which a regulatory molecule binds to a site other than the active site and prevents the active site from binding the substrate; thus, the inhibitor molecule does not compete with the substrate for the active site. Allosteric inhibition is a form of noncompetitive inhibition.
Oxidative Phosphorylation: The production of ATP by the transfer of electrons down the electron transport chain to create a proton gradient that is used by ATP synthase to add phosphate groups to ADP molecules.
Potential Energy: The type of energy that refers to the potential to do work.
Substrate: A molecule on which the enzyme acts.
Thermodynamics: The science of the relationships between heat, energy, and work.