10. Enzymes and Receptors Summary

Vocabulary practice flashcards covering enzyme classification, kinetics, assays, allosteric regulation, protein turnover, and receptor pharmacology from Lecture 10.

Ribozymes

Biological catalysts consisting of RNA rather than protein.

Transition State

The bound state of an enzyme where the required activation energy is lowered to facilitate the chemical reaction.

Bond Specificity

Enzyme specificity determined by the presence of specific functional groups within the substrate adjacent to the bond to be cleaved (e.g., peptidases and esterases).

Group Specificity

Enzyme specificity in which an enzyme promotes a particular reaction on a structurally related group of substrates sharing a common structural feature (e.g., kinases phosphorylating specific amino acids or sugars).

Stereospecificity

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

Oxidoreductases (EC 1)

A class of 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)

A class of enzymes that transfer chemical groups between substrates (e.g., kinases, aminotransferases, acetyltransferases, and carbamyltransferases).

Hydrolases (EC 3)

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

Lyases (EC 4)

A class of enzymes that catalyse elimination reactions resulting in the formation of double bonds (e.g., adenylyl cyclase, enolase, and aldolase).

Isomerases (EC 5)

A class of enzymes that interconvert isomers of various types by intramolecular rearrangements (e.g., phosphoglucomutase and glucose-6-phosphate isomerase).

Ligases (EC 6)

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

Isoschizomers

Restriction endonucleases from different bacteria that recognize the exact same DNA target sequence.

Neoschizomers

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

Multi-Enzyme Complexes

Assemblies of associated enzymes involved in a particular pathway that carry out a sequence of biochemical reactions and allow segregation of metabolic pathways within the cell.

Michaelis-Menten Equation

An equation relating reaction rate ($v$) and product formation ($\frac{d[P]}{dt}$) to substrate concentration ($[S]$): $v = \frac{d[P]}{dt} = \frac{V_{\max}[S]}{K_M + [S]}$.

$$V_{\max}$$

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

$K_M$ (Michaelis Constant)

The substrate concentration at which the enzymatic reaction velocity reaches half of its maximum ($\frac{V_{\max}}{2}$).

Pre-Steady State

The initial brief period immediately after mixing enzyme and excess substrate during which the enzyme-substrate complex and products are slowly building up.

Steady-State Kinetics

The phase following the pre-steady state during which the concentration of the intermediate enzyme-substrate complex remains relatively constant and the reaction rate changes slowly with time.

Burst Phase

A rapid initial phase of an enzymatic reaction occurring in the first few seconds that corresponds to a single turnover of the enzyme, where the y-intercept reveals the amount of functional enzyme present.

Thermal Deactivation (Denaturation)

The unfolding of an enzyme's secondary and tertiary structure into a random coil caused by excessive heat breaking intramolecular polar interactions (hydrogen bonds, dipole-dipole attractions, ionic interactions).

Optimum pH

The specific pH value or region at which an enzyme exhibits its maximal catalytic activity and stability.

Allosteric Site

A distinct regulatory binding site on an enzyme separate from the active or substrate-binding site that binds effectors or modulators to induce conformational changes.

Fixed-Time Assay

An analytical method that measures enzyme concentration by allowing reactions to proceed for a fixed period before quenching them with a stop solution, often evaluated simultaneously in microplate readers.

Isothermal Titration Calorimetry (ITC)

A label-free quantitative technique that directly measures the heat absorbed or released during biomolecular binding events to determine all binding parameters in a single experiment.

Site-Directed Mutagenesis

A molecular technique used to replace or modify a specific amino acid residue to confirm its functional role in substrate binding or catalysis.

Constitutive Enzymes

Enzymes that are synthesized at an essentially constant rate within the cell, rather than being regulated by fluctuating gene expression.

Poly-ubiquitination

The post-translational covalent tagging of multiple ubiquitin monomers onto a protein's C-terminal, targeting it for degradation by the 26S proteasome.

Bortezomib

A proteasome inhibitor developed as an anti-tumour agent that blocks the degradation of ubiquitinated protein aggregates.

Dose-Response Curve

A graphical relationship between increasing concentrations of an agonist and receptor response, displaying an initial threshold, a steep slope, and a maximum plateau.

Full Agonist

A drug or ligand that binds to a receptor and elicits the maximal biological response.

Partial Agonist

A drug or ligand that binds to a receptor but produces a submaximal (less than maximal) biological response.

Inverse Agonist

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

Antagonist

A type of receptor ligand or drug that blocks or dampens a biological response by binding to and occluding the receptor.