Enzymes: Biological Catalysts

General Properties of Enzymes

Enzymes are specialized proteins that accelerate biochemical reactions in living organisms. They are essential for regulating metabolic pathways and maintaining life processes.

• Definition: Enzymes are biological catalysts that increase the rate of chemical reactions without being consumed in the process.

• Specificity: Each enzyme typically acts on a specific substrate or group of related substrates.

• Active Site: The region on the enzyme where substrate binding and catalysis occur.

• Reusability: Enzymes are not permanently altered by the reactions they catalyze and can be used repeatedly.

Enzyme Function

• Lowering Activation Energy: Enzymes function by lowering the activation energy required for a reaction, thereby increasing the reaction rate.

• Enzyme-Substrate Complex: The substrate binds to the enzyme's active site, forming an enzyme-substrate complex, which then converts to product.

• Example: The enzyme catalase accelerates the decomposition of hydrogen peroxide into water and oxygen.

Factors Affecting Enzyme Activity

• pH: Each enzyme has an optimal pH at which it functions most efficiently. Deviations can reduce activity or denature the enzyme.

• Temperature: Enzyme activity increases with temperature up to an optimum point, after which activity declines due to denaturation.

• Substrate Concentration: Increasing substrate concentration increases reaction rate up to a saturation point (Vmax).

• Enzyme Concentration: Higher enzyme concentrations can increase reaction rates if substrate is not limiting.

• Inhibitors: Molecules that decrease enzyme activity. Types include competitive and noncompetitive inhibitors.

Enzyme Inhibition

• Competitive Inhibition: Inhibitor resembles the substrate and binds to the active site, blocking substrate access. Can be overcome by increasing substrate concentration.

• Noncompetitive Inhibition: Inhibitor binds to a site other than the active site, altering enzyme function. Cannot be overcome by increasing substrate concentration.

• Irreversible Inhibition: Inhibitor binds covalently to the enzyme, permanently inactivating it.

Michaelis-Menten Kinetics

Enzyme kinetics are often described by the Michaelis-Menten equation, which relates reaction rate to substrate concentration:

• V: Reaction velocity

• Vmax: Maximum velocity

• [S]: Substrate concentration

• Km: Michaelis constant (substrate concentration at half-maximal velocity)

Practice Questions (Sample Answers)

Additional info: The above table is inferred from the practice section and answer keys in the notes.

Summary Table: Types of Enzyme Inhibition

Key Properties of Enzymes

• Highly Specific: Enzymes typically catalyze only one type of reaction or act on a specific substrate.

• Efficient: Enzymes can increase reaction rates by factors of 106 or more.

• Regulated: Enzyme activity can be modulated by inhibitors, activators, or covalent modification.