Enzymes and Gibbs Free Energy Study Notes

Gibbs Free Energy

  • Gibbs Free Energy is a concept used to determine the spontaneity of a reaction.

Endergonic Reactions

  • Reactants are converted into products.

  • \Delta G > 0

  • The reaction is not spontaneous and requires energy.

  • Energy is absorbed by the reaction.

Exergonic Reactions

  • Reactants are converted into products.

  • \Delta G < 0

  • The reaction is spontaneous and releases energy.

Anabolic and Catabolic Reactions

Anabolic Reaction

  • Smaller molecules are combined to form a larger molecule.

  • This process requires energy.

Catabolic Reaction

  • A larger molecule is broken down into smaller molecules.

  • This process releases energy.

Condensation Reaction

  • A condensation reaction involving ATP (adenosine triphosphate).

  • ATP has high-energy phosphoanhydride bonds.

  • Hydrolysis of ATP to ADP (adenosine diphosphate) releases energy that can be used for cellular work and biosynthesis.

  • ΔG∘\Delta G^\circ represents the standard free energy change.

  • This process is involved in Glycolysis, TCA cycle, oxidative phosphorylation, and photosynthesis.

  • Phosphate transfer leads to the formation of a high-energy phosphoester bond.

Activation Energy

  • Activation energy is the energy required to reach the transition state.

  • Enzymes lower the activation energy to speed up the reaction.

  • \Delta H < 0: Enthalpy change is negative.

Reaction Rate and Substrate Concentration

  • VmV_m: Maximum velocity of the reaction.

  • At VmV_m, the enzyme is saturated, meaning there is far more substrate than the enzyme can process.

  • [S]: Concentration of substrate (mol/L).

Temperature and Reaction Rate

  • There is an optimum temperature for reaction rate.

  • At high temperatures, enzymes can denature, causing the reaction rate to decrease.

Enzyme Inhibition

Competitive Inhibition

  • An inhibitor competes with the substrate for the active site of the enzyme.

Non-competitive Inhibition

  • An inhibitor binds to a different site on the enzyme, altering its shape and reducing its activity.

Allosteric Inhibition

  • An inhibitor binds to the allosteric site of the enzyme, which alters the active site and reduces its affinity for the substrate.

Allosteric Activation

  • An activator binds to the allosteric site, which alters the active site and increases its affinity for the substrate.

Feedback Inhibition

  • The end product of a metabolic pathway inhibits an earlier enzyme in the pathway.

  • This regulates the production of the end product based on its concentration.

  • Enzyme 1 catalyzes the conversion of a substrate to intermediate A, Enzyme 2 converts intermediate A to intermediate B, and Enzyme 3 converts intermediate B to the end product.

  • The end product inhibits Enzyme 1.


Term 1: Endergonic Reactions
Definition 1: Reactions with a positive ΔG\Delta G (\Delta G > 0) that require an input of energy.