H Human Biology U1KA6

Dec 6, 2024

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

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)