BIO/BIOCHEM Review – Enzymes & Kinetics

Vocabulary flashcards covering enzyme specificity, classes, mechanisms, coenzymes, kinetics, and inhibition based on the provided lecture notes.

Enzyme Specificity

Property whereby an enzyme catalyzes only one reaction or one group of closely related reactions.

Urease

Enzyme that specifically hydrolyzes urea into ammonia and carbon dioxide.

Chymotrypsin

Protease that hydrolyzes peptide bonds on the carboxyl side of aromatic residues phenylalanine, tyrosine, and tryptophan.

Trypsin

Protease that cleaves peptide bonds on the carboxyl side of lysine and arginine residues.

Hydrolysis

Chemical process that breaks covalent bonds by adding water; catalyzed by hydrolases.

Hydrolytic Enzyme

Enzyme that uses water to cleave covalent bonds, e.g., proteases, lipases, nucleases.

Oxidoreductase

Class of enzymes that catalyze oxidation-reduction reactions by transferring electrons; examples include dehydrogenases and oxidases.

Transferase

Enzyme class that moves a functional group from one molecule to another; includes kinases and transaminases.

Hydrolase

Enzyme class that breaks molecules using water; examples are phosphatases and proteases.

Lyase

Enzyme that breaks or forms covalent bonds without water or redox chemistry; often called synthase when forming bonds.

Ligase

Enzyme that joins two molecules with covalent bonds, usually using ATP; DNA ligase is a classic example.

Isomerase

Enzyme that converts a molecule into one of its isomers, either constitutional or stereoisomeric.

Kinase

Transferase that adds a phosphate group to a substrate, typically using ATP.

Phosphatase

Hydrolase that removes a phosphate group from a substrate.

Oxidation

Loss of electrons, loss of hydrogen, or gain of oxygen in a reaction.

Reduction

Gain of electrons, gain of hydrogen, or loss of oxygen in a reaction.

Oxidant

Electron acceptor in a redox reaction; becomes reduced.

Reductant

Electron donor in a redox reaction; becomes oxidized.

Cofactor (Metal Ion)

Non-protein inorganic ion required for enzyme activity; contrasts with organic coenzymes.

Coenzyme

Organic molecule (often vitamin-derived) required for enzyme catalysis, e.g., NAD⁺, FAD, CoA.

Thiamine Pyrophosphate (TPP)

Coenzyme derived from vitamin B₁; essential for the pyruvate dehydrogenase complex.

FMN / FAD

Flavin coenzymes derived from riboflavin (B₂); function as electron carriers in redox reactions.

NAD⁺ / NADP⁺

Niacin-derived coenzymes that serve as ubiquitous electron carriers.

Coenzyme A

Pantothenic-acid-derived coenzyme that carries acyl groups (e.g., acetyl-CoA).

Pyridoxal Phosphate

Vitamin B₆-derived coenzyme used in amino-acid and glycogen metabolism, especially transamination.

Biotin

Vitamin coenzyme required for carboxylase reactions such as gluconeogenesis and fatty-acid synthesis.

Transaminase (Aminotransferase)

Transferase that moves an amino group from an amino acid to a keto acid.

Synthase

Lyase that forms a new molecule without using ATP.

Synthetase

Ligase that forms a new molecule with ATP hydrolysis.

General Acid–Base Catalysis

Enzyme mechanism in which amino-acid side chains donate or accept protons to accelerate reaction.

Electrostatic Catalysis

Stabilization of charged transition states by oppositely charged residues within an enzyme’s active site.

Covalent Catalysis

Temporary covalent bond formation between enzyme and substrate during the catalytic cycle.

Lock-and-Key Model

Old model where enzyme active site is pre-shaped exactly to fit the substrate.

Induced-Fit Model

Modern model where enzyme undergoes conformational change upon substrate binding to achieve complementarity.

Michaelis–Menten Equation

v = (Vmax [S]) / (Km + [S]); describes hyperbolic relationship between velocity and substrate concentration.

Km (Michaelis Constant)

Substrate concentration at which reaction velocity is half of Vmax; inversely related to substrate affinity.

Vmax

Maximum reaction velocity achieved at saturating substrate concentration when all enzyme active sites are occupied.

Enzyme Saturation

Condition where increasing substrate concentration no longer increases reaction rate because all active sites are filled.

Lineweaver–Burk Plot

Double reciprocal plot (1/v vs 1/[S]) that linearizes Michaelis–Menten data; slope = Km/Vmax.

Competitive Inhibitor

Molecule that competes with substrate for active site; increases Km but leaves Vmax unchanged.

Noncompetitive Inhibitor

Molecule that binds allosterically to enzyme (or ES) with equal affinity; lowers Vmax without changing Km.

Mixed Inhibitor

Allosteric inhibitor with unequal affinity for E and ES; decreases Vmax and changes Km (↑ or ↓).

Uncompetitive Inhibitor

Inhibitor that binds only the ES complex; decreases both Km and Vmax equally, giving parallel Lineweaver-Burk lines.

Allosteric Site

Regulatory site on an enzyme distinct from the active site; binding here alters enzyme activity.