1.1.5

Enzymes

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Enzymes

Enzymes increase the speed of reactions. They are often called biological catalysts. The active site of an enzyme is very important:

Active site

Active site

  • To catalyse (speed up) a reaction, the reacting chemical (substrate) must bind to the enzyme's active site.
  • The active site will only fit specific substrates.
Lock and key

Lock and key

  • The active site is like a lock and the substrate is like a key.
  • In the same way, there is usually only one enzyme for every substrate (or one key for each lock).

Factors Affecting the Rate of Enzyme Action

The factors that affect the rate (speed) of enzyme action are:

Temperature

Temperature

  • Increasing the temperature of a working enzyme initially increases the reacting activity.
  • Enzymes have an optimum temperature. Once this temperature is reached, the activity decreases.
  • Past a certain temperature, the active site changes shape, and the enzyme is denatured (loses its catalytic activity).
pH (measure of acidity)

pH (measure of acidity)

  • Enzymes have an optimum pH (measure of acidity).
  • If the pH changes away from the optimum pH, then the enzyme activity decreases.
  • If the pH is too low or too high, then the enzyme is denatured and will not function.
Substrate concentration

Substrate concentration

  • Increasing the substrate concentration will increase the rate of activity to a certain point until it levels off.
  • This is because if there are more substrate molecules available for the enzyme to bind to, the rate increases.
  • But once there are enough substrate molecules for all the enzymes to bind to, increasing the substrate concentration any more will have no effect on the rate of activity.
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1

Biology

1.1

Practicals

1.1.1Microscope & Bacteria1.1.2Bacteria1.1.3Osmosis Tests1.1.4Osmosis & Food Tests1.1.5Enzymes1.1.6Enzymes 21.1.7Photosynthesis & Plant Responses1.1.8Photosynthesis Experiments1.1.9Reaction Time1.1.10Quadrats1.1.11Decay
2

Chemistry

2.1

Practicals

2.1.1Salts2.1.2Neutralisation2.1.3Titration2.1.4Electrolysis2.1.5Electrolysis 22.1.6Rate of Reaction2.1.7Rate of Reaction 22.1.8Chromatography2.1.9Identifying Gases2.1.10Identifying Gases 22.1.11Identifying Ions2.1.12Carbonates, Halides & Sulfates2.1.13Flame Emission Spectroscopy2.1.14Water Purification2.1.15Water Purification 2
3

Physics

3.1

Practicals

3.1.1Specific Heat Capacity3.1.2Thermal Capacity & Insulation3.1.3Latent Heat3.1.4Resistance & Current3.1.5Resistance & Current 23.1.6Density3.1.7Density 23.1.8Force & Extension - Springs3.1.9Waves - Ripple Tank3.1.10Light3.1.11Light Reflection & Refraction3.1.12Radiation3.1.13Radiation 2

Practice questions on Enzymes

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    What is another name for an enzyme?Multiple choice
  2. 2
    Which of the following describe an enzyme's active site?True / false
  3. 3
    What happens to enzymes when pH is very high?Multiple choice
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Osmosis & Food Tests

Enzymes 2