Chapter 6 Enzymes

Oxidoreductases

Enzymes that catalyze oxidation-reduction reactions, transferring electrons, hydride ions, or hydrogen atoms.

Transferases

Enzymes that catalyze group transfer reactions from one molecule to another.

Hydrolases

Enzymes that catalyze hydrolysis reactions, breaking bonds by adding water.

Lyases

Enzymes that add groups to double bonds or form double bonds by removing groups.

Isomerases

Enzymes that transfer groups within a single molecule to yield isomeric forms.

Ligases

Enzymes that catalyze the bonding together of two substrate molecules.

Rate of Disappearance

The rate at which reactants are consumed in a reaction.

(−Δ[A]/Δt)

Rate of Appearance

The rate at which products are formed in a reaction.

(Δ[P]/Δt)

Michaelis-Menten Model

A model describing the relationship between substrate concentration and reaction rate.

Enzyme-Substrate Complex

A temporary complex formed when an enzyme binds to its substrate.

Binding Affinity

The strength of the interaction between an enzyme and its substrate.

Michaelis Constant (KM)

An inverse measure of affinity between an enzyme and its substrate.

Optimal pH

The pH level at which an enzyme exhibits maximum activity.

Amino Acids in Active Sites

Specific amino acid residues that serve as proton donors or acceptors in enzymatic reactions.

Steady State Condition

The state in which the concentration of the enzyme-substrate complex remains constant.

Lineweaver-Burk Plot

A double reciprocal plot used to determine Vmax and KM.

Vmax

The maximum rate of an enzyme-catalyzed reaction at saturating substrate concentration.

Competitive Inhibition

Inhibition where the inhibitor competes for the active site of the enzyme.

Non-Competitive Inhibition

Inhibition where the inhibitor binds to an allosteric site, affecting enzyme activity.

Feedback Control

Mechanism in which the product of a reaction inhibits an earlier enzyme in the pathway.

Allosteric Control

Regulation through binding of an activator or inhibitor to a site other than the active site.

Covalent Modification

Regulation involving the making or breaking of chemical bonds to activate or deactivate enzymes.

Genetic Control

Regulation of enzyme synthesis at the DNA level, influencing how many enzyme molecules are produced.

Hydrolase Reaction Indicator

Look for H2O as a reactant in hydrolysis reactions.

Lyase Reaction Indicator

Look for the formation or loss of a double bond in the product or reactant.

Isomerase Reaction Indicator

Look for one substrate and one product with rearranged atoms.

Ligase Reaction Indicator

Look for two molecules joining with ATP cleavage.

Oxidoreductase Picture Clue

Identified by the presence of coenzymes like NAD+, NADH, FAD, or FADH2.

Transferase Picture Clue

Identified by ATP becoming ADP or group transfers between molecules.

Hydrolase Picture Clue

Identified by a hydrolysis reaction involving water.

Rate Expression

Rate can be expressed as rate of disappearance of reactants or appearance of products.

Enzyme Reaction Dependency

Enzyme activity depends on concentrations of enzyme, substrate, and product.

Substrate Binding

The binding of substrate to enzyme is crucial for enzymatic activity.

pH Change Effect

Altering pH affects protonation states of amino acids in active sites.

Rearrangement Indicator for Isomerases

One substrate and one product indicates a rearrangement.

ATP Cleavage in Ligases

Ligases often require ATP cleavage to drive bonding reactions.

Vmax Interpretation

Vmax remains unchanged in competitive inhibition but decreases in non-competitive inhibition.

Effect of Inhibitors on KM

Competitive inhibitors increase KM, while non-competitive inhibitors do not affect KM.

Active Site Distortion in Non-competitive Inhibition

Inhibitor binding distorts the active site, preventing product formation.

Bell-Shaped Curve in Enzyme Activity

Enzyme activity vs. pH often shows a bell-shaped curve, reflecting optimal conditions.

Product Inhibition Mechanism

Feedback control prevents excessive product formation by inhibiting upstream enzymes.

Covalent Modifications Examples

Includes phosphorylation and zymogen activation.

Enzyme Concentration Effect

Higher enzyme concentration can increase reaction rates up to a saturation point.