Enzymes Overview


  • Increase rate of reaction by lowering activation energy
  • Most are proteins
  • Specific – conversion of one specific substance to one product
  • May require cofactors or coenzymes
  • Carefully regulated

ΔG = free energy

  • Free energy of the product minus the free energy of the reactants
  • ΔG is negative for enzymatic reaction because energy is released (exergonic reaction)

ΔEa = activation energy

  • Energy barrier that must be overcome for a reaction to proceed
  • Enzymes lower activation energy of a reaction by stabilizing transition state
  • Energy required to get to equilibrium (rate of forward and reverse reactions are the same) correlates with ΔG and is unchanged in the presence or absence of enzyme
  • Enzyme doesn’t dictate whether reaction will proceed but determines speed of reaction


  • 3D structure produces active site
  • Shaped so that substrate fits in
  • Product of an enzymatic reaction has lower affinity for binding site: exits binding site and is released


  • Bind cofactor binding site (distinct from active site)
  • Some enzymes inactive without cofactor or coenzyme
  • Many are vitamin-derived, metal ions, or other smaller organic molecules

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