Lecture on Enzymes and Metabolism

Enzymes as Catalysts

• Definition of Catalyst: Increases the rate of a chemical reaction without being consumed.
• Enzymes: Protein-based biological catalysts.
• Substrates: Reactants in enzyme-catalyzed reactions.

Importance of Enzymes

• Role in Reactions: Enable reactions to occur at life-sustaining temperatures and speeds.

Metabolism

• Definition: Sum of all enzyme-catalyzed reactions in cells.
• Types of Reactions:
  • Catabolic: Breaking down large molecules into smaller ones, releasing energy (e.g., cell respiration).
  • Anabolic: Building larger molecules from smaller ones, requiring energy (e.g., photosynthesis).

Enzyme Specificity

• Substrate Specific: Each reaction/substrate requires its own enzyme.
• Control: Enzymes allow control over metabolic reactions.

Enzyme Structure

• Globular Proteins: Soluble, three-dimensional shape determined by amino acid sequence.
• Active Site: Specific region where substrate binds, complementary in shape to the substrate.

Models of Enzyme Activity

• Induced Fit Model: Active site molds to fit the substrate, causing a conformational change to aid catalysis.
• Substrate Specificity: Despite changes, enzymes remain specific to particular substrates.

Enzyme Reaction Dynamics

• Collision Requirements:
  • Energy and Orientation: Collisions must have sufficient energy and correct orientation.
  • Movement: Enzymes/substrates can move to enable collisions.

Denaturation

• Definition: Permanent change to the enzyme's shape, preventing substrate binding.
• Causes and Effects: Various factors can cause denaturation.

Factors Affecting Enzyme Activity

1. Temperature:
   • Optimum Temperature: Temperature at which enzymes work at maximum rate.
   • Denaturation: Occurs at high temperatures beyond the optimum.
2. pH:
   • Optimum pH: Different for each enzyme.
   • Denaturation: Can occur at both high and low pH levels.
3. Substrate Concentration:
   • Saturation Point: All active sites occupied, rate plateaus.

Measuring Enzyme-Catalyzed Reactions

• Experimental Techniques:
  • Manipulating Variables: Altering temperature, pH, or substrate concentration.
  • Dependent Variable: Measure changes like gas pressure to monitor reaction rate.
  • Controlled Variables: Keep temperature and pH constant.

Rate of Reaction

• Definition: Change over time.
• Calculation Methods:
  • Fixed time: Measure change within a set time period.
  • Fixed change: Measure time taken for a specific change.

Activation Energy

• Concept: Energy threshold that must be overcome for a reaction to proceed.
• Role of Enzymes: Lower the activation energy, speeding up reactions without altering reactant/product energy levels.

Conclusion

• Enzymes facilitate cellular reactions efficiently, interacting dynamically with substrates and environmental factors.