Lecture Notes on Gibbs Free Energy and Enzymes

Introduction

• Midterm is approaching, with reminders about registration.
• Discussion on Gibbs Free Energy and its importance in understanding chemical reactions.

Gibbs Free Energy

• Delta G (ΔG): Represents the change in Gibbs Free Energy.
• Equation: ΔG = ΔH - TΔS, where:
  • ΔH = Change in total energy (enthalpy).
  • T = Temperature in Kelvin.
  • ΔS = Change in entropy.
• Importance: Provides insight into the direction and spontaneity of reactions.
  • Spontaneous Reactions: Negative ΔG, exergonic (energy releasing).
  • Non-spontaneous Reactions: Positive ΔG, endergonic (energy requiring).

Reaction Dynamics

• Anabolic Reactions: Require energy (endergonic). Products have higher energy than reactants.
• Catabolic Reactions: Release energy (exergonic). Reactants have higher energy than products.
• Graphical Representation:
  • Energy vs. Time graph shows the transition from reactants to products.
  • Uphill (endergonic) and downhill (exergonic) reactions are depicted.

Enzymes and Reaction Coupling

• Enzymes: Proteins that catalyze reactions, lowering activation energy.
  • Active Site: Specific location where substrates bind.
  • Substrate Specificity: Enzymes are highly specific to their substrates.
• Coupled Reactions: Combine reactions to drive processes in one direction.
  • Example: Glycolysis involves 10 reactions, some with positive ΔG.
  • Negative ΔG reactions drive the pathway directionally.

ATP and Energy Transfer

• ATP Hydrolysis: Releases energy (negative ΔG) stored in phosphate bonds.
  • Hydrolysis Reaction: ATP + H2O → ADP + Pi.
• Energy Storage: ATP is a medium-energy molecule, transferring energy between reactions.

Glycolysis Overview

• 10 Steps in Glycolysis: Converting glucose to pyruvate.
  • 3 reactions have significant negative ΔG, driving the pathway forward.
• Substrate-Level Phosphorylation: Direct transfer of phosphate to ADP to form ATP.

Enzyme Function and Mechanism

• Reaction Facilitation: Enzymes reduce activation energy, enabling faster reactions.
• Enzyme-Substrate Complex: Binding induces conformational change, facilitating reactions.
• Catalysis: Enzymes are not consumed in the reaction and can be reused.

Additional Concepts

• Transition State: High-energy intermediate state in reactions.
• Activation Energy: Initial energy required to start a reaction.
• Enzyme Specificity: Active sites bind specifically to substrates but may differ in exact configuration.

Summary

• Understanding Gibbs Free Energy and enzyme activity is crucial for grasping biochemical pathways.
• Enzymes play a key role in managing the direction and speed of cellular reactions.

Note: The content discussed is foundational for exams and further studies in biochemistry and molecular biology.