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Enzymes & Enzyme Action

In biological systems, the are 3 general energy paths a reaction can take.

  1. Exergonic Reaction - One in which energy is released (Products have less chemical energy than reactants). This often, however requires Activation energy to initiate a reaction.
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  3. Endergonic Reaction - One in which energy must be supplied for the reaction to occur (products have more chemical energy than reactants)
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  5. Catalyzed Reaction. - Usually an exergonic reaction - Which in the presence of a catalyst, is speeded up because the action of the catalyst reduces the amount of activation needed for the reaction to occur.

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    1. By bringing two substrates together, and facilitating a bond to form between them.
    2. By breaking a substrate apart to produce 2 or more products.


    1. Temperature - Most human enzymes operate at 35-40OC. At lower temperatures, allosteric changes cannot occur. At higher temperatures, proteins (enzymes) can be denatured.
    2. pH - Charged areas of an enzyme can be effected by [H+, OH-], thus reducing their action in high or low pH.

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  1. Competetive inhibition - Another substance binds to the active site, preventing the substrate from binding there.
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  3. Non competitive inhibition - Another substance binds to the enzyme, at a site other than the active site. This blocks the binding of the regular substrates.
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  5. Allostery - An Inhibitor or Activator binds to a separate allosteric site on the enzyme, changing the shape of the enzyme, either Inhibiting or activating it's function. Often the products serve as inhibitors. This is known as Feedback inhibition.

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Mr. Stanley

Last updated: March 11, 2004