Enzymes control almost everything which happens inside the cells of all living organisms. In this 
topic we consider how enzymes make reactions faster as well as the effects of different environmental factors on the rate of enzyme controlled reactions. There are many industrial uses of enzymes, including washing powder, lactose free milk, and clear fruit juice.
Key words
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Clean sweep - quick revision through the whole topic
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They contain short explanations in text and images - good revision for all students.
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Revision summary list for 2.5 Enzymes
- The role of the active site where specific substrates bind.
- The effect of the motion of molecules and the collision of substrates with the active site.
- The effect of Temperature, pH and substrate concentration on the rate of activity of enzymes. (including denaturing)
- Enzymes (often immobilised) are extensively used in industry for the production of items including Lactose-free milk, fruit juice and washing powder.
- Advantages of lactose-free milk, and ways of producing it, including immobilization in alginate beads.
- Knowledge of possible designs of experiments to test the effect of temperature, pH and substrate concentration on enzyme activity.
- Practical 3: Investigation of a factor affecting enzyme activity.
- The skill of sketching a graph of expected results in enzymes experiments and the ability to explain reasons for their shapes.
Revision mind map
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Review questions
This is a self marking quiz containing questions covering the topic outlined above.
Try the questions to check your understanding.
What is the name of the part of an enzyme where the substrate binds?
The active site is the part of an enzyme where the substrate binds.
If the temperature of an enzyme controlled reaction is increased from 15°C to 30°C what would you expect to happen to the rate of reaction? Which of the following is the best explanation?
The rate would increase because the molecules have more kinetic energy, so there is more chance of the substrate molecules colliding with the enzyme molecules.
Enzymes don't usually denature until the temperature is above 40°C.
Which is the best explanation of the effect of increasing the substrate concentration on the rate of an enzyme controlled reaction?
The best explanation explains that the increase in concentration causes more collisions between substrate and enzymes which increases the rate.
The solution is more concentrated but this is not quite an explanation why this increases the rate.
What would be the effect of gradually increasing the pH of a solution from pH4.0 to pH8.0 on the rate of a reaction catalysed by an enzyme which has an optimum pH of 9.0 ?
The maximum rate will be at the optimum pH then the rate will decrease.
We are assuming in this question that the pH4 does not permanently damage the enzyme molecules.
Enzyme substrate specificity refers to the idea that enzymes only act on one substrate, because only one specific substrate can fit in the active site.
It is true that some substrates only react with one substrate at a time, but other enzymes react with two substrates and join them together. e.g. condensation reactions.
Which of the following is an advantage of immobilising the enzymes used to produce lactose free milk?
By immobilising the enzymes, the milk can be separated from the enzymes more easily and then reused. Often the immobilised enzymes are trapped in beads, which can be filtered from the milk.
What would be the advantage of adding a protease enzyme to washing powder?
Many stains contain proteins so a protease enzyme in a washing powder would be able to break down the protein and speed up the cleaning process, so long as the wash temperature was no hotter than 40°C. Higher temperatures would denature the enzymes.
Revision fun activity
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