CHE 421 Biochemistry (I) Lecture - Enzymes

These flashcards cover key vocabulary and concepts from the lecture on enzymes, their mechanisms, and classifications.

Enzymes

Globular proteins that catalyze (or speed up) chemical reactions without being consumed.

Ribozymes

RNA catalysts that function as enzymes.

Active site

Specific region where substrates bind to an enzyme.

Substrate

The reactants that bind to the active site of an enzyme.

Equilibrium concentrations

The balanced concentrations of substrates and products that enzymes help achieve more quickly.

Energy of Activation (EA)

The energy difference between substrates and the transition state necessary to initiate a reaction.

Transition state (‡)

An unstable transient entity at the maximum energy point of a reaction.

Thermodynamic favorability

Refers to the stability of a reaction, which enzymes do not change.

Equilibrium constant (Keq)

A measure of the ratio of products to reactants at equilibrium, unaffected by enzymes.

Enzyme-Substrate Complex (ES)

An intermediate formed when an enzyme binds to its substrate.

Binding energy (ΔGB)

The energy difference between uncatalyzed and catalyzed transition states.

Lock & Key Model

Model where active site shape is rigid and fits substrates like a puzzle piece.

Induced Fit Model

Model where active site shape adjusts to better fit the transition state.

Optimal pH

The specific pH level where an enzyme displays the highest activity.

Denature

The process where an enzyme loses its functional shape.

Hydrolyases

Enzymes that break bonds by adding water in hydrolysis reactions.

Isomerases

Enzymes that convert molecules into their isomers by rearranging functional groups.

Ligases

Enzymes that use energy to join two molecules covalently.

Cofactors

Non-protein portions of enzymes that assist in catalysis.

Apoenzyme

Inactive enzyme without its cofactor.

Holoenzyme

Catalytically active enzyme with its cofactor.

Coenzymes

Small organic molecules, often derived from vitamins, that act as cofactors.

Oxidoreductases

Enzymes that catalyze redox reactions by transferring electrons between molecules.

Transferases

Enzymes that transfer functional groups between molecules.

Covalent catalysis

Mechanism where transient covalent bonds form between enzyme and substrate.

Metal ion catalysis

When metal ions assist in enzyme reactions by stabilizing the transition state.

Electrostatic catalysis

Stabilization of charges in the transition state through electrostatic interactions.

Catalytic triad

Asp-102, His-57, and Ser-195; critical amino acids in chymotrypsin's active site.

Acylation phase

The first phase of chymotrypsin proteolysis involving covalent catalysis.

Deacylation phase

The second phase of chymotrypsin proteolysis where the ester bond is hydrolyzed.

Peptidases

Enzymes that catalyze the breakdown of proteins.

Covalent intermediate

A stable acyl-enzyme complex formed during chymotrypsin's mechanism.

Hydration shells

Layers of water molecules surrounding substrates that can interfere with reactions.

Entropy

A measure of disorder or randomness in a system, which enzymes aim to reduce.

Nucleophile

A species that donates an electron pair to form a chemical bond.

Specific Acid-Base Catalysis

A process where solvent (usually water) serves as the sole source of H+ transfer.

General Acid-Base Catalysis

A mechanism where any acid or base in the enzyme's active site aids in H+ transfer.

Weak noncovalent interactions

Forces that stabilize enzyme-substrate complexes.

Michaelis-Menten kinetics

Mathematical model describing the rate of enzymatic reactions with a single substrate.

Peptide bond cleavage

The breaking of bonds between amino acids in proteins by enzymes like chymotrypsin.

Oxyanion hole

Region in active site of an enzyme that stabilizes charged transition states.

Energetic pathway

The series of energy changes as substrates convert to products in a reaction.

Kinetics

Study of reaction rates and how they change under various conditions.

Hydrophobic effect

A phenomenon where hydrophobic interactions contribute to protein folding.

Electrostatic effect

Attraction or repulsion between charged groups in proteins that influence stability.

Catalysis by proximity

Mechanism where enzymes increase reaction rates by bringing substrates close together.

Functional groups

Specific groupings of atoms within molecules that are responsible for the characteristic reactions.

Hydrophobic pocket

Area in an enzyme's active site that preferentially binds nonpolar substrates.

Cis- to trans-fatty acid isomerization

The conversion of cis-fatty acids to trans-fatty acids facilitated by isomerases.