Metabolism and Enzyme Regulation Vocabulary

Vocabulary flashcards covering enzyme structure, activity, regulation, redox reactions, and key metabolic processes based on the lecture transcript.

Apoenzyme

The protein portion of an enzyme that pairs with a non-protein cofactor.

Cofactor

The non-protein portion of an enzyme system, which can be inorganic (such as calcium or iron) or organic.

Holoenzyme

The active enzyme complex formed by the combination of an apoenzyme and an inorganic cofactor.

Coenzyme

An enzyme system or component where the cofactor is organic, such as nicotinamide or flavin adenine dinucleotide (FAD).

Active site

The major site on an enzyme where the reaction takes place and the substrate binds.

Energy of activation

The specific amount of energy required for a chemical reaction to occur, which is lowered by an enzyme acting as a catalyst.

Endoenzyme

An enzyme manufactured inside the cell that remains within the cell to function, such as a metabolic enzyme.

Exoenzyme

An enzyme manufactured inside the cell that is secreted or released outside the cell, such as a defense enzyme.

Constitutive enzyme

An enzyme that is constantly being produced by the cell, such as those needed for glucose metabolism.

Induced enzyme

An enzyme that is manufactured by the cell only when needed, such as lactose metabolism enzymes when glucose is depleted.

Catabolic reaction

A decomposition reaction in which a larger substrate is broken down into smaller products.

Anabolic reaction

A synthesis reaction in which smaller subunits are joined together to form a macromolecule.

Oxidation

The loss of an electron during a chemical reaction.

Reduction

The gain of an electron during a chemical reaction.

Turnover number

The maximum number of times that an enzyme converts a substrate into products each second, typically ranging from $1,000$ to $10,000$ or higher.

Competitive inhibition

A method of enzyme regulation where an inhibitor binds directly to the active site, physically blocking substrates from entering.

Allosteric site

A secondary site on an enzyme, distinct from the active site, where a non-competitive inhibitor binds.

Non-competitive inhibition

An enzyme regulation method where an inhibitor binds to the allosteric site using strong covalent bonds, altering the active site's shape so the substrate no longer fits.

Ribozymes

A class of catalytic enzymes composed of RNA (nucleic acid) rather than protein.

Terminal electron acceptor

The final endpoint molecule that receives an electron in metabolism, such as oxygen in aerobic cells or sulfur/iron in anaerobic cells.

Phosphorylation

The process of adding a phosphate group to a molecule, such as generating ATP from ADP.

Decarboxylation

The chemical reaction involving the removal of $\text{CO}_2$ from a substrate, such as converting pyruvate to acetyl.

Coenzyme A

A coenzyme that binds with an acetyl group to form acetyl coenzyme A, serving as a shuttle to transport acetyl into the cyclic portion of the Krebs cycle.

Flavoproteins

A class of carrier molecules in the electron transport chain that consist of protein molecules containing flavin derived from vitamin B12.

Cytochromes

A class of electron transport chain carrier molecules that are proteins containing iron.

Coenzyme Q

A class of non-protein carrier molecules that function within the electron transport chain.

Proton motive force

An electrical and pH gradient generated by the accumulation of hydrogen ions in the cristae of eukaryotes or the periplasmic space of prokaryotes.

ATP synthase

A transmembrane protein enzyme activated by hydrogen ions diffusing down their concentration gradient, which catalyzes the phosphorylation of ADP to produce ATP.