Factors affecting enzyme action:


Effect of temperature on enzyme activity:

  • Rise in temperature increases the kinetic energy
  • Molecules move more rapidly and collide with each other more often
  • This means more enzyme-substrate complexes are formed
  • So rate of reaction increases
  • When temperature goes above the optimum, the enzyme begins to denature
  • Substrate no longer fits into the active site 

On some graphs, the rate of reaction plateaus because there is no longer a substrate.

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Effect of pH on enzyme activity:

  • Each enzyme has an optimum pH, a pH at which it works fastest.
  • An increase or decrease in pH reduces the rate of enzyme action, as more of the enzyme molecules will have active sites that are not complementary to the subtrates.
  • If the change in pH is more extreme, then the enzyme becomes denatured.

How pH affects how an enzyme:

  • a change in pH alters the charges of amino acids that make up the active site.
  • therefore the enzyme can no longer attach to the active site so an ESC cannot be formed.
  • the change in pH may cause the bonds that maintain the tertiary structure to break.

The change in the ionic bonds causes the active site to change shape. 

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Effect of enzyme concentration on enzyme activity:

  • Increasing the enzyme concentration increases the rate of reaction because there will be more enzyme-substrate complexes formed.
  • This will only have an effect up until a certain concentration, as enzyme concentration is no longer a limiting factor.
  • It has no effect as there are already enough active sites to accomodate all the available substrate molecules.
  • A decrease of enzyme concentration decreases the rate as there is not enzyme molecules to allow all the substrates to find an active site at one time.

reaction rate as enzyme concentration increases

Diagram shows enzyme concentration increase.

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Effect of substrate concentration on enzyme activi

  • increasing the substrate concentration increases the rate of reaction.
  • as more substrate molecules will be forming enzyme-substrate complexes
  • so more product will be formed
  • after a certain concentration any increase will have no effect on the rate of reaction.
  • this is because substrate concentration will no longer be a limiting factor.
  • the enzymes will effectively become saturated and will be working at their maximum possible rate.

at a low substrate conc there are too few substrate molecules to occupy all the available active sites.

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Effect of Competitive Inhibitors on enzyme action:

  • Competitive enzyme inhibitors work by preventing the formation of enzyme-substrate complexes because they have a similar shape to the substrate molecule.
  • This means that they fit into the active site but remain unreacted because they have a different structure to the substrate. 
  • Therefore less enzyme-substrate complexes are formed so the rate of reaction decreases.
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Effect of Non-competitive Inhibitors on enzyme act

  • Non-competitive Enzyme Inhibitors work not by preventing the formation of Enzyme-Substrate Complexes, but by preventing the formation of Enzyme-Product Complexes.
  • So they prevent the substrate from reacting to form product.
  • Usually, Non-competitive Inhibitors bind to a site other than the Active Site, this distorts the 3D Tertiary structure of the enzyme,so that it can no longer catalyse a reaction.
  • Since they do not compete with substrate molecules, Non-competitive Inhibitors are not affected by substrate concentration.
  • Many non-competitive inhibitors are irreversible and permanent, and  denature the enzymes. 
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