• A Catalyst increases the rate of reaction by providing alternative energy pathway ; usually increasing the rate of by 1012-1020. However it does not affect free energy ∆G (can’t make endergonic reaction go). Instead an enzyme can couple an exergonic reaction with an endergonic reaction via ATP breakdown.
  • It will decrease EA for a spontaneous reaction and make it proceed faster
  • Often needed for molecules with HIGH KINETIC STABILITY (HIGH ENERGY BARRIER)
  • Rate is proportional to # of molecules you can activate; therefore reduce EA. More molecules can be activated therefore increasing rate of reaction.
  • Why do we need catalyst enzymes?
  • Catalyst enzymes make reaction proceed faster with having to wait a long duration of time and without a significant increase in temperature.

activation energy How does Enzyme Catalysis Work

Enzyme Structure

  • Tertiary Structure (very flexible; bigger than substrate)
  • Two theories of thought on how substrate active site- with enzyme wrapping around it
  • INDUCED FIT: Initiates bonds between substrate and enzyme are weak; enzymes chances conformation upon binding to strength binding
  • LOCK & KEY: The active site of enzyme is a rigid/ specific active site; however this fails to explain stabilization of transition state.
  • **Substrate must be in the transition state to be catalyzed
  • There is usually MUCH more substrate than enzyme and shift the reaction to the right
  • An increase of temperature can lead to potentially more molecules reaching the EA

induced fit lock key How does Enzyme Catalysis Work

How do Enzymes lower EA?

  • Orient substrate properly; makes substrate collide & react
  • Change interaction, exposing it to alternative charge (ionic reaction)
  • Changing shape of substrate molecule (forcing it into transition state)
  • NOTE: Enyzmes do these things to increase probability of substrate reaching EA.


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