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Enzymes and Enzymatic Processes

Jul 12, 2024

Enzymes and Enzymatic Processes

Introduction

  • Instructor: Welcome back, gloomy November evening
  • Chapter 2: Biochemistry focus on enzymes and enzymatic processes
  • Make sure to check the description for lecture notes and links

What are Enzymes?

  • Definition: Biological catalysts (proteins) that speed up chemical reactions
  • Main Function: Lower the activation energy of a reaction
  • Do Not Affect:
    • ΔG (Gibbs Free Energy)
    • ΔH (Enthalpy)
    • ΔS (Entropy)
    • Equilibrium constant
  • Result: Increase rate of reaction
  • Symbolism:
    • Enzyme = E
    • Substrate = S
    • Enzyme-Substrate Complex = ES
    • Product = P

Classes of Enzymes

  1. Oxido-Reductases:
    • Catalyze redox reactions
    • Example: Alcohol dehydrogenase
    • Co-factors: NAD+, NADH, FAD, FADH2, NADP+, NADPH
  2. Transferases:
    • Transfer groups from one molecule to another
    • Example: Kinases (transfer phosphate groups using ATP)
  3. Hydrolases:
    • Break bonds using water
    • Example: Lipase, Amylase
  4. Lyases:
    • Cleave bonds to form double bonds or rings
    • Example: Synthase (reverse reaction called hydratase)
  5. Isomerases:
    • Catalyze rearrangement of bonds
    • Example: Phosphoglucose isomerase
  6. Ligases:
    • Catalyze addition/synthesis reactions
    • Example: DNA ligase

Mnemonic: LIL HOT (Lyases, Isomerases, Ligases, Hydrolases, Oxido-Reductases, Transferases)

Enzyme-Substrate Binding Theories

  1. Lock and Key Theory: The enzyme's active site perfectly fits the substrate
  2. Induced Fit Theory: Enzyme changes conformation to better fit the substrate
    • More accepted due to intermolecular interactions

Co-factors and Co-enzymes

  • Definition: Small molecules that assist enzymes
  • Types:
    • Co-factors (e.g., NAD+)
    • Co-enzymes (e.g., vitamins)
  • Enzymes with Co-factors: Holoenzymes
  • Enzymes without Co-factors: Apoenzymes
  • Important Co-factors: NAD+, NADH, FAD, vitamins
  • Fat Soluble Vitamins: A, D, E, K
  • Water Soluble Vitamins: B (complex) and C
  • B Vitamins: B1 (Thiamine), B2 (Riboflavin), B3 (Niacin), B5 (Pantothenic Acid), B6 (Pyridoxine), B7 (Biotin), B9 (Folic Acid), B12 (Cobalamin)

Enzyme Kinetics

  • Study: Effect of substrate and enzyme concentration on reaction rate
  • Vmax: Maximum velocity when all enzymes are saturated
    • Only increased by increasing enzyme concentration
  • Km (Michaelis Menten Constant):
    • Substrate concentration at 1/2 Vmax
    • Lower Km = Higher affinity for the substrate
  • Equation:
    • Velocity (V) = (Vmax [S]) / (Km + [S])
  • Kcat (Turnover Number): Number of substrate molecules turned over per enzyme molecule per second
  • Catalytic Efficiency: Kcat / Km
  • Graph: Hyperbolic curve describing Vmax and Km

Important Concepts

  • High Km indicates poor affinity
  • Low Km indicates high affinity
  • Relationship between substrate concentration and Km
  • Catalytic Efficiency Equation: A measure of enzyme performance
    • Important for MCAT BIOCH sections

Conclusion

  • Summary of enzyme kinetics and importance in biochemical processes
  • Reminder: Prepare for diagnostic exams during break

Note: No class on Thursday due to Thanksgiving; surprise quiz/test on Tuesday

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