BIO 024 Module 9: Enzymes - Nature, Nomenclature & Classification

Vocabulary flashcards on enzyme structure, properties, cofactors, nomenclature, and classification based on Module 9 notes.

Enzyme

A complex organic biological catalyst (predominantly protein) that accelerates chemical reactions up to $10^7$-fold without being consumed or permanently altered in the process.

Enzymology

The specialized scientific study of enzymes, their kinetics, and their metabolic pathways.

Apoenzyme

The inactive, protein portion of a conjugated enzyme that requires a cofactor to function and is heat labile.

Cofactor

The non-protein component or activator required by an apoenzyme to perform catalytic activity.

Holoenzyme

The complete, biologically active conjugated enzyme complex consisting of an apoenzyme combined with its cofactor.

Active Site

A distinct 3D cleft or crevice on an enzyme's surface where substrate binding and catalysis occur through weak non-covalent interactions.

Enzyme-Substrate Complex

An intermediate structure formed when a substrate specifically binds to the active site of an enzyme during catalysis.

Zymogen

An inactive enzyme precursor (proenzyme) requiring a specific biochemical cleavage to become active, preventing host tissue auto-digestion.

Prosthetic Group

A cofactor or coenzyme that is firmly and tightly bound to the apoenzyme protein structure.

Cosubstrate

A coenzyme that is loosely and transiently bound to the enzyme, dissociating freely after catalysis.

Coenzyme

A low-molecular-weight, heat-stable organic cofactor derived from dietary vitamin precursors that transfers or accepts chemical groups during catalysis.

Metalloenzymes

Enzymes that contain an inorganic metal ion cofactor that is firmly and tightly bound to the apoenzyme (e.g., Carbonic Anhydrase, Cytochrome Oxidase).

Metal-Activated Enzymes

Enzymes requiring an inorganic metal ion cofactor that is loosely bound and easily dissociates (e.g., Hexokinase, Phosphofructokinase).

IUBMB System

A standard nomenclature system created in 1964 by the International Union of Biochemistry and Molecular Biology, assigning each enzyme an EC code with four numerical digits.

Oxidoreductases

Class 1 (EC 1) enzymes that catalyze oxidation-reduction reactions involving electron transfer between two substrates.

Transferases

Class 2 (EC 2) enzymes that catalyze the transfer of functional chemical groups (other than hydrogen) from one substrate to another.

Hydrolases

Class 3 (EC 3) enzymes that catalyze bond cleavage (ester, ether, peptide, glycosyl, or C−C) through the addition of water.

Lyases

Class 4 (EC 4) enzymes that catalyze the non-hydrolytic cleavage of C−C, C−O, or C−N bonds, leaving double bonds.

Isomerases

Class 5 (EC 5) enzymes that catalyze intramolecular transfer or structural rearrangements to convert a molecule into its isomer.

Ligases

Class 6 (EC 6) enzymes, also known as synthetases, that catalyze the condensation and joining of two molecules coupled with ATP hydrolysis.

Transaminases

Class 2 Transferase enzymes that catalyze the transfer of amino groups ($-\text{NH}_2$) between amino acids and $\alpha$-keto acids.

Kinases

Phosphotransferase enzymes belonging to Class 2 that transfer terminal phosphate groups from ATP to specific substrates.

Synthetase vs. Synthase

Synthetases are ATP-dependent enzymes belonging to Class 6 (Ligases), whereas synthases do not consume ATP and belong to other enzyme classes.

Desmolases

Lyase enzymes that specifically catalyze reactions involving the splitting or formation of C−C bonds through non-hydrolytic mechanisms.

Thermal Inactivation

Permanent loss of catalytic function occurring at temperatures exceeding $45^\circ\text{C}\text{--}50^\circ\text{C}$ due to tertiary protein denaturation.