Factors Affecting Enzyme Activity (WJEC GCSE Biology)

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Cara Head

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Cara Head

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Effect of Temperature on Enzyme Activity

  • Temperature affects the movement of molecules, so influences the number of collisions that occur between enzymes and their substrate molecules in a solution

Increasing temperature

  • As temperature increases more collisions occur between enzymes and substrates, increasing the rate of an enzyme-controlled reaction
    • This is because the molecules have more kinetic energy so they move faster and collide with more energy
  • Enzyme-controlled reactions occur at the highest rate at their optimum temperature
    • In the human body, this optimum temperature for enzymes is around 37 ⁰C

High temperatures

  • Heating solutions to high temperatures that are too far above the optimum will break the bonds that hold the enzyme together and the active site will lose its shape
    • This is known as denaturation and the enzyme is said to have denatured
    • Substrates cannot attach to denatured active sites as the complementary shape has been lost
    • Denaturation is irreversible; once enzymes are denatured they cannot regain their shape and activity will stop

Low temperatures

  • Reactions occur slowly at low temperatures; this is because molecules move around more slowly and collisions occur less frequently and with less energy
    • Note that enzymes do not denature at low temperatures, so heating up a solution again will increase the rate of reaction

Enzyme denaturation diagram

effect-of-temperature-on-enzyme-activity-igcse-and-gcse-chemistry-revision-notes

Enzymes denature at high temperatures; this means that the specific shape of the active site is lost

  • The effect of temperature on the rate of an enzyme-controlled reaction can be plotted on a graph as shown

Effect of temperature on enzyme activity graph

Graph showing the effect of temperature on rate of enzyme activity, IGCSE & GCSE Biology revision notes

The effect of temperature on enzyme activity can be shown on a graph

Effect of pH on Enzyme Activity

  • The optimum pH for enzyme activity varies between different types of enzymes
    • Enzymes that function in acidic conditions, such as the stomach, have a low optimum pH, e.g. pH2
    • Enzymes that function in alkaline conditions, such as the small intestine, have a high optimum pH, e.g. pH 8 or 9
  • If the pH is too far above or too far below the optimum the bonds that hold the amino acid chain together can be disrupted or broken
  • This changes the shape of the active site so the substrate can no longer fit into it, reducing the rate of activity
    • This is denaturation

Effect of pH on enzyme activity diagram

Effect of pH on enzyme activity, IGCSE & GCSE Biology revision notes

Extreme pH can also cause enzymes to denature

  • The effect of pH on the rate of an enzyme-controlled reaction can be plotted on a graph as shown below

Effect of pH on enzyme activity graph

Graph showing effect of pH on rate of activity for an enzyme from duodenum, IGCSE & GCSE Biology revision notes

Enzymes in the small intestine have an optimum pH of around 8; pH levels that are too far below or above this can result in denaturation

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Cara Head

Author: Cara Head

Expertise: Biology

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding