SCH2141 Advanced Biomedical Techniques - Lecture 10: Enzymes and Receptors

Comprehensive vocabulary flashcards covering enzyme classification, kinetics, regulation, analytical assay techniques, and receptor-ligand pharmacology from SCH2141 Lecture 10.

Enzymes

Biological catalysts that are proteins, functioning to lower the activation energy required for a chemical reaction to occur.

Ribozymes

Biological catalysts consisting of RNA rather than protein.

Bond Specificity

Enzyme specificity determined by the presence of specific functional groups within the substrate adjacent to the bond to be cleaved, such as in peptidases and esterases.

Group Specificity

Enzyme specificity where an enzyme promotes a particular reaction on a structurally related group of substrates, such as kinases phosphorylating substrates containing a common amino acid or sugar.

Stereospecificity

The ability of an enzyme to distinguish between optical and geometrical isomers of substrates.

Oxidoreductases (EC 1)

Enzymes that catalyse the transfer of hydrogen, oxygen atoms, or electrons from one substrate to another (e.g., dehydrogenases, reductases, oxidases, peroxidases, and catalase).

Transferases (EC 2)

Enzymes that catalyse the transfer of chemical groups between substrates (e.g., kinases, aminotransferases, acetyltransferases, and carbamyltransferases).

Hydrolases (EC 3)

Enzymes that catalyse the hydrolytic cleavage of chemical bonds (e.g., peptidases, esterases, phosphatases, and sulfatases).

Lyases (EC 4)

Enzymes that catalyse elimination reactions that result in the formation of double bonds (e.g., adenylyl cyclase, enolase, and aldolase).

Isomerases (EC 5)

Enzymes that inter-convert isomers of various types by intramolecular rearrangements (e.g., phosphoglucomutase and glucose-6-phosphate isomerase).

Ligases (EC 6)

Enzymes that catalyse covalent bond formation coupled with the concomitant breakdown of a nucleoside triphosphate, commonly ATP (e.g., carbamoyl phosphate synthase and DNA ligase).

Isoenzymes (Isozymes)

Enzymes that exist in multiple structural forms but catalyse the exact same chemical reaction.

Isoschizomers

Restriction endonucleases from different bacterial strains that recognize the exact same nucleotide recognition sequence.

Neoschizomers

A specific subset of isoschizomers that recognize the identical nucleotide sequence but cleave it at different positions (e.g., SmaI and XmaI).

Multi-Enzyme Complexes

Associations of multiple pathway enzymes that segregate specific biochemical pathways into one cellular location to carry out sequential reactions (e.g., fatty acid beta-oxidation complex from Pseudomonas fragi).

$$V_{\max}$$

The maximum reaction velocity achieved by an enzymatic system under saturating substrate concentrations.

Michaelis Constant ($K_M$)

The substrate concentration at which the reaction velocity equals half of the maximal velocity ($50\%$ of $V_{\max}$).

Pre-Steady State

The brief initial timeframe immediately after enzyme-substrate mixing during which the concentration of the enzyme-substrate complex is actively forming and product formation slowly builds.

Steady-State Kinetics

The phase of an enzymatic reaction following the pre-steady state where the reaction rate and intermediate enzyme-substrate complex concentration remain relatively constant over time.

Burst Phase

A rapid initial phase in an enzymatic reaction measuring a single turnover of the enzyme, where the y-intercept of the product-versus-time graph corresponds to the quantity of functional enzyme present.

Thermal Deactivation

The process by which excessive heat breaks intramolecular interactions between polar groups (hydrogen bonding, dipole-dipole, ionic), unfolding the secondary and tertiary structures and eliminating substrate-binding ability.

Optimum pH

The specific pH level at which an enzyme displays its highest catalytic activity.

Allosteric Site

A unique non-active site on an enzyme where effectors or modulators bind, inducing a conformational change in the active site that leads to activation or inhibition.

Fixed-Time Assay

An enzyme assay format where reaction mixtures are incubated for an established linear period of time and then stopped simultaneously across multiple samples using a stop solution.

Isothermal Titration Calorimetry (ITC)

A label-free analytical technique that quantitatively determines all binding parameters in a single experiment by directly measuring heat absorbed or released during biomolecular interaction.

Site-Directed Mutagenesis

A molecular biology method used to modify or replace a specific amino acid residue suspected of participating in substrate binding or catalysis to verify its functional importance.

Constitutive Enzymes

Enzymes that are synthesized by the cell at a continuous, constant rate rather than being induced or repressed.

Poly-Ubiquitination

The tagging of a protein's C-terminus with multiple ubiquitin monomers, marking it for degradation by the 26S proteasome.

Orthosteric Site

The primary endogenous agonist-binding domain located on the extracellular domain of a receptor.

Dose-Response Curve

A graphical representation showing receptor response as a function of increasing agonist concentration, characterized by an initial threshold, a rapid upward slope, and a final plateau at maximum response.

Full Agonist

A receptor ligand that binds to a receptor and produces the maximal possible biological response.

Partial Agonist

A ligand that binds to and activates a receptor but produces a lower maximal response than a full agonist, even at saturating concentrations.

Inverse Agonist

An agent that binds to the same active site on a receptor as an agonist but induces a pharmacological response opposite to that of the agonist by reducing constitutive baseline activity.

Protean Agonist

A receptor ligand that can act as either an agonist or an inverse agonist at the same receptor, depending on the receptor's baseline level of constitutive activity.

Biased Agonist

An agonist that preferentially activates one downstream intracellular signaling cascade over other possible pathways mediated by the same receptor.

Antagonist

A receptor ligand that binds to and blocks a receptor, blunting or preventing the biological response produced by agonists without activating the receptor itself.

Scintillation Proximity Assay (SPA)

A homogeneous radioligand binding technique where a radiolabelled ligand emits beta-particles that excite a scintillant within a receptor-bearing bead to emit light only when bound, while unbound ligand dissipates energy harmlessly into the solution.