Lecture Notes: Metabolic Pathways

Introduction to Metabolic Pathways

• Metabolism: Refers to all chemical reactions in a cell, broken into two main types:
  • Anabolism: Synthesis of large molecules from smaller substrates (requires energy)
  • Catabolism: Breakdown of large molecules into smaller products (releases energy)
• Metabolic Pathways: Integrated series of enzyme-catalyzed reactions within a cell.
  • Pathways are controlled, involve substrates and products
  • Example: Respiration is a classic metabolic pathway

Anabolism vs. Catabolism

• Anabolism: Builds up large molecules; requires energy
  • Example: Protein synthesis from amino acids
• Catabolism: Breaks down large molecules; releases energy
  • Example: Respiration (glucose + oxygen -> energy + water + carbon dioxide)

Characteristics of Metabolic Pathways

• Reversible Steps: Some reactions can go back and forth
• Irreversible Steps: Locked step (example: initial steps in glycolysis)
• Alternative Routes: When intermediates are either converted further or rerouted

Enzyme Functionality

• Enzyme Active Site: Complementary to substrate, promotes reaction
  • Induced Fit Model: Active site changes shape for substrate binding
  • Enzymes lower activation energy, making reactions more feasible

Factors Affecting Reaction Rates

• Substrate Concentration:
  • Increased substrate leads to increased reaction rate, until active sites are saturated
  • At saturation, reaction rate is limited by enzyme concentration
• Product Concentration: Feedback inhibition occurs when end-product accumulates
  • Example: Inhibition of early enzymes to prevent resource wastage

Types of Enzyme Inhibition

• Competitive Inhibition:
  • Inhibitor competes with substrate for active site
  • Can be overcome by increasing substrate concentration
• Non-Competitive Inhibition:
  • Inhibitor binds to a distinct site, altering enzyme shape
  • Not overcome by increasing substrate concentration

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Summary

• Metabolic pathways are essential for cell function and involve controlled, enzyme-mediated reactions
• Anabolism builds up, while catabolism breaks down molecules
• Enzymes speed up reactions by lowering activation energy through the induced fit model
• Reaction rates can be affected by substrate/product concentration and enzyme inhibition mechanisms (competitive and non-competitive)