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Lecture 6

Lecture 6: Enzymes

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Western University
Biology 1002B
Niki Sharan

Lecture 6Enzymesy Uncatalyzed OMP decarboxylation has a halftime of 78 million years while catalyzed OMPenzyme decarboxylation has a halftime of 20 milliseconds1220y Enzymes increase the rate of a spontaneous reaction by 1010 times What Enzymes Do and Dont Do y Enzymes are a specific group of proteins that catalyze reactionsthey speed up reactions but do not get consumedy Conversion of substrate A into substrate B is an exergonic reaction as it has a negative G G0y An enzyme can speed up this reaction and increase the rate of this spontaneous reactiony However it cannot help the conversion of substrate B into substrate C as it is an endergonic reaction with a positive G G0this reaction would require energy coupling in order to proceed y An enzyme cant provide energy for a reaction it cannot change G of a reactiony To drive the conversion of substrate B into substrate C you would need to couple it with the breakdown of ATP so it can proceedExergonic Reaction Energy Profile y G is negativemolecules AC and BD products have less free energy associated with them than the starting molecules AB and CD reactantsy For the reaction to proceed the substrates need to acquire more free energy which is gained from the surroundingsthey need to acquire a higher energy state known at the transition statey This higher level of free energy that the reactants have is where the bonds are ready to break at the transition statey The amount of energy that you need to get to the transition state is known as activation energy E Ay E represents a kinetic barrier which prevents the reaction Afrom going very fasty A good example is the molecules propane the breakdown of propane is a spontaneous reaction o Thermodynamically it is unstable but kinetically stable does not have a tendency to simply combust o Any reaction that is exergonic is known to be thermodynamically unstable Enzymes Lower Activation Energyy Enzymes lower activation energy the energy requirement to acquire the transition statey Rate is proportional to the number of activated molecules
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