| Term | Definition |
|---|
| metabolism | 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). |
| 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. |
| bioenergetics | (1) The overall flow and transformation of energy in an organism. (2) The study of how energy flows through organisms. |
| energy | 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) | The total amount of kinetic energy due to the random motion of atoms or molecules in a body of matter; also called thermal energy. Heat is energy in its most random form. |
| potential energy | The energy that matter possesses as a result of its location or spatial arrangement (structure). |
| thermodynamics | The study of energy transformations that occur in a collection of matter. See first law of thermodynamics; second law of thermodynamics. |
| first law of thermodynamics | The principle of conservation of energy: Energy can be transferred and transformed, but it cannot be created or destroyed. |
| entropy | 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. Ordered forms of energy are at least partly converted to heat. |
| 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 ΔG = ΔH – TΔS, where H is enthalpy [in biological systems, equivalent to total energy], T is absolute temperature, and S is entropy.) |
| exergonic reaction | A spontaneous chemical reaction, in which there is a net release of free energy. |
| endergonic reaction | A nonspontaneous chemical reaction, in which free energy is absorbed from the surroundings. |
| polyphosphorylated | Referring to a molecule that is covalently bonded to a phosphate group. |
| enzyme | A macromolecule serving as a catalyst, a chemical agent that changes the rate of a reaction without being consumed by the reaction. |
| catalyst | A chemical agent that increases the rate of a reaction without being consumed by the reaction. |
| substrate | The reactant on which an enzyme works. |
| enzyme-substrate complex | A temporary complex formed when an enzyme binds to its substrate molecule(s). |
| 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. |
| cofactor | Any nonprotein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely with the substrate during catalysis. |
| coenzyme | An organic molecule serving as a cofactor. Most vitamins function as coenzymes in metabolic reactions. |
| 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 the enzyme's shape so that the active site no longer functions effectively. |
| 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. |
| cooperativity | A kind of allosteric regulation whereby a shape change in one subunit of a protein caused by substrate binding is transmitted to all the others, facilitating binding of subsequent substrate molecules. |
| 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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