Enzymes
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Enzymes. Most enzymes are globular proteins. Active site: the region of an enzyme surface to which a specific set of substrates binds. Substrate : ( the reactant ) a molecule upon which an enzyme acts. A substrate molecule must fit precisely into an active site.

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  • Active site: the region of an enzyme surface to which a specific set of substrates binds.

  • Substrate: ( the reactant ) a molecule upon which an enzyme acts.

  • A substrate molecule must fit precisely into an active site.


Cells employ enzymes to lower activation energies
Cells employ enzymes to lower activation energies

  • By bringing two substrates together in the correct orientation, or by stressing particularchemical bonds of a substrate, an enzyme lowers the activation energy required for new bonds to form.


Enzymes speed up the rate of chemical reactions
Enzymes speed up the rate of chemical reactions

  • Let us consider this reaction:

    CO2 + H2O ----- H2CO3

    carbon dioxide + water ----- carbonic acid

    The reaction is very slow in the absence of an enzyme called carbonic anhydrase. Perhaps 200 molecules of carbonic acid are formed in an hour in a cell.



Enzymes are not consumed in the chemical reactions
Enzymes are not consumed in anhydrase, an estimated the chemical reactions

  • Because the enzyme itself is not changed or consumed in the reaction, only a small amount is needed, and it can be used over and over.


How enzymes work
How Enzymes Work anhydrase, an estimated



Enzymes are specific in their choice of substrate
Enzymes are specific in their choice of substrate anhydrase, an estimated

  • This specificity is due to the active site of the enzyme, which is shaped so that only a certain substrate will fit into it.

  • Enzymes typically catalyze only one or a few chemical reactions.


Factors affecting enzyme activity
Factors Affecting Enzyme Activity anhydrase, an estimated

  • Temperature: Most human enzymes have temperature optima between 35 C and 40 C.

  • pH: Most enzymes have a pH optimum;it usually lies in the range of pH 6 to 8.


Cofactors and coenzymes
Cofactors and Coenzymes anhydrase, an estimated

  • The activity of enzymes is often facilitated by cofactors, which can be metal ions or other substances.

  • Cofactors that are nonprotein organic molecules are called coenzymes


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