Enzymes Overview

Definition and Function

• Enzymes are catalysts that speed up chemical reactions by lowering activation energy. -An enzyme is a catalyst that is not used up in the reaction.
• Most enzymes are protein-based, but ribozymes are RNA-based catalysts.

Energy Diagram

• Y-axis: Energy
• X-axis: Reaction coordinate
• Catalyzed reactions lower the transition state energy, reducing activation energy.

Identification

• Enzymes typically have an -ase suffix.
  • Example: Sucrase breaks sucrose into glucose and fructose.

Structure

• Active Site: Unique 3D shape specific for substrate binding.
• Substrate: The molecule that an enzyme acts upon.
• Enzyme-Substrate Complex (ES): Forms during the reaction and returns to original state after reaction.

Models of Enzyme Action

• Lock and Key Model: Substrate fits exactly into enzyme active site.
• Induced Fit Model: Enzyme changes shape to fit substrate more tightly.

Factors Affecting Enzyme Activity

pH

• Enzymes have an optimal pH, typically between 6-8. -The optimal pH is represented by the peak of the activity curve, often around pH 7, where the enzyme operates at its highest efficiency.
• Example: Pepsin works optimally in acidic conditions (pH 2-3).

Temperature

• Enzymes have an optimal temperature range. -Enzymes work best within a certain temperature range. There is a specific temperature where the enzyme's activity is highest. Below this optimal temperature, increasing the temperature increases enzyme activity. However, if the temperature goes above this optimal point, the enzyme's activity decreases quickly.
• High temperatures can lead to denaturation, losing enzyme function.

Concentration

• Increasing the concentration of substrate or enzyme increases reaction rate up to a limit.

Inhibitors and Activators

• Inhibitors: Decrease enzyme activity with a substrate.
  • Competitive Inhibitors: Bind to active site, blocking substrate. The inhibitor competes with the substrate for the same active site.
  • Non-Competitive Inhibitors: Bind to allosteric site, altering enzyme shape.
• Activators: Enhance enzyme interaction with substrate.

Cofactors and Coenzymes

• Cofactors: Inorganic metal ions (e.g., Zn²⁺).
• Coenzymes: Organic molecules (e.g., vitamins).

Important Enzyme Types

Protease

• Breaks down proteins and polypeptides into amino acids.

Lipase

• Breaks down fats into glycerol and fatty acids.

Isomerase

• Catalyzes rearrangement reactions to form isomers.

Transferase

• Transfers functional groups between molecules.

Kinase

• Transfers phosphate groups from ATP to another molecule.

Dehydrogenase

• Removes hydrogen atoms from molecules.

Amylase

• Breaks down starch into simple sugars (e.g., glucose).

Oxidoreductase

• Catalyzes electron transfer in redox reactions.

Hydrolase

• Catalyzes hydrolysis reactions using water to split molecules.

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These notes cover the essential concepts about enzyme function, structure, and types, as well as the factors influencing enzyme activity.