BBT314 Protein & Enzyme Chemistry Vocabulary

Vocabulary-style practice flashcards covering key terms, concepts, and analytical procedures in enzyme catalysis, kinetics, classification, and protein purification.

Active Site

The small portion of an enzyme surface where substrate binding occurs via noncovalent forces, containing catalytic groups that directly participate in bond making and breaking.

Lock-and-Key Model

A model of enzyme action where the enzyme active site possesses a rigid shape that is exactly complementary to the substrate prior to binding.

Induced Fit Model

A model of enzyme action proposing that substrate binding induces a flexible conformational change in the enzyme to produce a complementary fit and optimize catalysis.

Zero-Order Reaction

A reaction whose rate is constant and independent of substrate concentration, occurring when all enzyme active sites are fully saturated with substrate.

First-Order Reaction

A reaction whose rate is directly proportional to substrate concentration, occurring at low substrate levels where enzyme active sites are unsaturated.

Michaelis Constant ($K_M$)

The substrate concentration at which the initial reaction velocity reaches half of its maximum ($\frac{1}{2}V_{\max}$), mathematically defined as $\frac{k_{-1} + k_2}{k_1}$.

Turnover Number ($k_{cat}$)

The number of substrate molecules converted into product per enzyme active site per unit time when the enzyme is fully saturated with substrate, equal to $\text{k}_2$.

Catalytic Efficiency

The ratio $\frac{k_{cat}}{K_M}$, which functions as the second-order rate constant for the reaction of free enzyme and free substrate when $[S] \ll K_M$.

Steady-State Assumption

The kinetic assumption that the concentration of the enzyme-substrate complex ($[ES]$) remains constant throughout the monitored reaction period, where $\frac{d[ES]}{dt} = 0$.

Lineweaver-Burk Double Reciprocal Plot

A linear plot of $\frac{1}{V_0}$ versus $\frac{1}{[S]}$ with a slope of $\frac{K_M}{V_{\max}}$, a y-intercept of $\frac{1}{V_{\max}}$, and an x-intercept of $-\frac{1}{K_M}$.

Hexokinase

A transferase enzyme that catalyzes the first step of glycolysis in most tissues with a low $K_M$ ($0.15\,\text{mM}$) for D-glucose, maintaining activity at low glucose concentrations.

Glucokinase

A liver and pancreatic beta-cell enzyme with a high $K_M$ ($20\,\text{mM}$) for D-glucose, enabling effective removal of excess glucose following a meal.

Apoenzyme

The protein component of an enzyme that is inactive because it lacks its required nonprotein cofactor or coenzyme.

Holoenzyme

A complete, catalytically active enzyme formed by the combination of an apoenzyme with its necessary cofactor or coenzyme.

Prosthetic Group

A coenzyme or organic cofactor that is tightly or covalently bound to the enzyme protein structure.

Oxidoreductases

Enzymes in EC class 1 that catalyze oxidation-reduction reactions involving the transfer of electrons, hydride ions, or hydrogen atoms.

Transferases

Enzymes in EC class 2 that catalyze group-transfer reactions from one molecule to another.

Hydrolases

Enzymes in EC class 3 that catalyze hydrolysis reactions by transferring functional groups to water.

Lyases

Enzymes in EC class 4 that catalyze the addition of groups to double bonds or the formation of double bonds by group removal.

Isomerases

Enzymes in EC class 5 that catalyze intramolecular group transfers to yield isomeric forms of a molecule.

Ligases

Enzymes in EC class 6 that catalyze the formation of $\text{C}-\text{C}$, $\text{C}-\text{S}$, $\text{C}-\text{O}$, and $\text{C}-\text{N}$ bonds coupled with ATP cleavage.

Activation Energy ($\Delta G^{\circ \ddagger}$)

The minimum energy barrier that reactant molecules must surmount to reach the transition state and undergo a chemical reaction.

Transition State

A transient, high-energy activated complex formed during a reaction where existing bonds are partially broken and new bonds are partially formed.

Salting Out

A protein fractionation method based on solubility differences where high concentrations of neutral salts (e.g., ammonium sulfate) selectively precipitate proteins.

Dialysis

A separation procedure that uses a porous semipermeable membrane to remove small solutes and salts from larger protein molecules based on size.

Size-Exclusion Chromatography

A column chromatography technique (gel filtration) that separates proteins by size, where larger proteins elute first while smaller proteins enter porous beads and move slower.

Ion-Exchange Chromatography

A chromatography technique that separates proteins based on net surface charge using charged matrix resin such as cationic CM-cellulose or anionic DEAE-cellulose.

Affinity Chromatography

A purification technique where column beads carry covalently attached ligands that specifically bind a target protein based on biological affinity.

High-Performance Liquid Chromatography (HPLC)

An advanced chromatographic system utilizing high-pressure pumps and finely divided stationary phase particles to achieve rapid, high-resolution separations.

Electrophoretic Mobility ($\mu$)

The ratio of a particle's migration velocity ($V$) to the electric field strength ($E$), defined mathematically as $\mu = \frac{Z}{f}$ where $Z$ is net charge and $f$ is frictional coefficient.

SDS-PAGE

Sodium Dodecyl Sulfate PolyAcrylamide Gel Electrophoresis; a method that denatures proteins and imparts a uniform negative charge-to-mass ratio, separating polypeptides strictly by molecular weight.

Isoelectric Focusing

An electrophoretic technique that separates proteins according to their isoelectric points ($pI$) along an established pH gradient in a gel.

Two-Dimensional Electrophoresis

A high-resolution method combining isoelectric focusing in the first dimension (separation by $pI$) with SDS-PAGE in the second dimension (separation by molecular weight).

ELISA

Enzyme-Linked Immunosorbent Assay; an antibody-based assay technique that uses enzyme-catalyzed colorimetric reactions to detect and quantify specific antigens.

Immunoblotting

A analytical technique (Western blotting) where gel-separated proteins are blotted onto a nitrocellulose membrane and identified using specific antibody-enzyme conjugates.