Enzyme Function and Properties: Study Notes

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:

$V = \frac{V_{max}[S]}{K_m + [S]}$

• V: Reaction velocity

• Vmax: Maximum velocity

• [S]: Substrate concentration

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

Practice Questions (Sample Answers)

Question	Answer
Enzyme A	B
Enzyme B	A
Enzyme C	B
Enzyme D	C

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

Summary Table: Types of Enzyme Inhibition

Type	Binding Site	Effect on Vmax	Effect on Km
Competitive	Active site	No change	Increases
Noncompetitive	Allosteric site	Decreases	No change
Irreversible	Active or allosteric site (covalent)	Decreases	Varies

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.