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  • catalyse metabolic reactions
  • globular proteins
  • have an active site to bind to enzymes determined by the tertiary structure

Activation energy

Requird to start the react. Enymes reduce the amount of activation energy needed. Reactions occur at a lower temperature therefor the enzymes speed the reaction up.

Enzyme-Substrate Complex

Formed when an enzyme binds to a substrate. When two substrates are held close together by the enzyme they're binded to repulsion is reduced and they can bond more easily. Or in a break down reaction the binding strain the bonds of the substrate breaking it up more easily.

The Induced Fit

As the substrate binds the active site changes shape slightly.

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Factors Affecting Enzyme Activity

..can be measured by the rate the substrate disappears or the appearance of the product.


  • more kinetic energy
  • more collisions
  • more energy in collisions - results in more reactions

If the temperature goes above the optimum temperature bonds will be broken in the enzyme and the active site will change shape, the enzyme becomes denatured.


  • all enzymes have an optimum pH level
  • above and below can damage the bonds in the tertiary structure and enzyme denatures

Enzyme Concentration

  • more likely to be a collision
  • limited substrate - all the active sites can fill up and there will be no further affect
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  • some enzymes only work with a cofactor (non protein) bound to them.
  • they aren't changed in any way
  • help enzyme and substrate bind


  • organic cofactors
  • they can be changed
  • recylced - use by other enzymes
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Competitive Inhibition

  • similar shape to the substrate
  • compete with substrates to bind with the enzyme
  • block the active site

Non-Competitive Inhibition

  • bind to enzyme away from the active site
  • causes the active site to change shape

Inhibition can be reversible if the bonds are weak hydrogen or ionic bonds but is irreversible if the bonds are strong covalent.

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