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Enzymes & Enzyme Action

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.



2. Endergonic Reaction - One in which energy must be supplied for the reaction to occur (products have more chemical energy than reactants)



3. 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.

• Enzymes are proteins which cells use to speed up biological reactions.
• They are usually Globular in shape.
• Often have surface depressions called active sites which allow SPECIFIC molecules to bind to the enzyme.
• Several models of activity
• Lock & Key model
• Has static active site
• Molecules fit into active site where chemical change occurs

• Induced fit model

• Often these molecules are flexible, and change shape when an appropriate molecule binds to an active site. This is known as an Induced Fit.

1. Temperature - Most human enzymes operate at 35-40^OC. 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.

1. Competetive inhibition - Another substance binds to the active site, preventing the substrate from binding there.



2. 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.



3. 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