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5.0 ENZYMES5.2 Activation Energy and Mechanism of Enzyme Action
LEARNING OUTCOMESExplain activation energy in relation to the function of enzyme.Explain the mechanism of enzyme based on Lock and Key Model.
KEY CONCEPTActivation EnergyLock and Key Model
Many chemical reactions don't happen spontaneously they need a "push" for the amount of energy that needs to be added, called the activation energy.Activation energy
Activation energy: The amount of energy that substrate (reactant) must absorb to start a chemical reactionActivation energy
This activation energy is often thought as the amount of energy that needs to be added in order to push the reactants "uphill" to get them over the "hill" so they can then "roll downhill" to yields products with lower energy.New energy level of reactant/substratereactant/substrateproductActivation energytimeFree energyWithout catalyst/ enzyme
reactant/substrateproducttimeFree energyenzymeLowered activation energy with catalystWith catalyst/ enzymeEnzymes speed up the reaction rate by lowering the "hill" yield products faster because the catalyst (enzyme) lowers the activation energy
reactant/substrateproductActivation energytimeFree energyanalogyWithout catalyst/ enzymeThe high barrier
reactant/substrateproducttimeFree energyenzymeLowered activation energy with catalystanalogyWith catalyst/ enzymeThe low barrier
ANALOGY: ENZYME LOWERS THE ACTIVATION ENERGYUncatalyzed reaction: Waves not large enough to surmount barrierCatalyzed reaction: Waves often surmount barrier
HOW ENZYME WORKS?
The basic mechanism:begins with the binding of the substrate to the active site of the enzyme.forming a temporary structure called the enzyme-substrate complex.Mechanism of enzyme based on Lock and Key Model
this causes changes in the chemical bonds of the substrate that lead to the formation of products.the products are then released from the enzyme.
Mechanism of enzyme based on Lock and Key Model
Enzymes operate on a LOCK AND KEY MODELlockkey
key = substrateCorrect fit, will reactlock = enzymeLOCK AND KEY ANALOGYMechanism of enzyme based on Lock and Key Model
Incorrect substrateNo reactionMechanism of enzyme based on Lock and Key Model
Lock and Key ModelIn this analogy, the lock is the enzyme the key is the substrate. only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme).Mechanism of enzyme based on Lock and Key Model
Substrate (key)Enzyme (lock)Mechanism of enzyme based on Lock and Key Model
Mechanism of enzyme based on Lock and Key Model
EnzymeProductsMechanism of enzyme based on Lock and Key Model
Substrate (key)Enzyme (lock)Enzyme-substrate complexProduct Enzyme (lock)
*Almost no metabolic reaction occurs in a cell unless its own enzyme is present