1. Revision lesson on enzymes
AQA Unit 2 Additional Biology

2. What are enzymes and what do they do?
Enzymes are-
Protein molecules (made up of amino acids)
Biological catalysts (Increase the speed of chemical reactions)
Specific (Each one catalyses one particular reaction)
Reusable (Can be used again and again)
Affected by temperature and pH.
Found in animals, plants and microorganisms.

3. 2 main types of enzymes
Catabolic enzymes which (break down) large molecules into smaller molecules
e.g. digestion of starch by the enzyme amylase into glucose.
Anabolic enzymes which (build up) small molecules to form larger molecules
e.g. production of glucose during photosynthesis from carbon dioxide, water and light.

4. Enzymes and activation energy
Chemical reactions take place when particles collide with enough energy.
The minimum amount of energy required is called the activation energy.
Enzymes lower the amount of activation energy required, so the reaction can proceed at a greater rate.

5. Structure of an enzyme molecule
Enzymes are proteins made up on long chains of amino acids.
These long chains fold to produce a special shape which is vital for the enzyme‘s function.
Active
Site

6. How enzymes work

7. Step-by-step
Shape of the enzyme’s active site is complimentary to the shape of one particular substrate.
The two bind together to form an enzyme-substrate complex.
The reaction between them take place rapidly.
The products are released from the enzyme’s active site.
Complete Qu 1-8 on your worksheet.

8. Factors affecting enzyme action - Temperature
Enzymes work faster as the temperature increases up to 40oC, but are eventually denatured at about 60oC.
This is because the shape of the active site is lost.

9. Factors affecting enzyme action – pH
Each enzyme works best at a particular pH. This is known as the optimum pH.
Extremes of pH will cause the active site to denature.
Answer Qu on your worksheet

10. Enzymes in digestion
Enzymes break down large insoluble food molecules into smaller, soluble ones which can be absorbed through the small intestine wall to enter the bloodstream.
Different parts of the digestive tract have different pH conditions to enable different enzymes to work.

11. The main groups of digestive enzymes
Lipase enzymes digest fatty substrates.
Protease enzymes digest protein substrates.
Carbohydrase enzymes digest carbohydrate substrates.

12. Amylase (a carbohydrase) Glucose Salivary glands & pancreas pH7
Substrate
Enzyme
Product
Where enzyme produced
Optimum pH
Starch
Amylase (a carbohydrase)
Glucose
Salivary glands & pancreas
pH7
Protein
Trypsin
(a protease)
Amino acids
Stomach, pancreas, & small intestine
pH3
Lipids
Lipases (fats)
Fatty acids & glycerol
Pancreas
pH8

13. The action of bile
It’s produced by the liver and is stored in the gall bladder which, squirts it into the small intestine.
It’s alkaline to neutralise acidic chyme coming from stomach.
It emulsifies fats to break them into smaller droplets which increases the surface area for lipase enzymes to work.

14. Commercial use of enzymes
Product
Enzymes
Explanation
Biological washing powder
Lipases and proteases.
Digest biological stains off clothes.
Baby food
Proteases
Pre-digest protein to make digestion easier for babies.
Slimming foods
Isomerase (carbohydrase)
Converts glucose into fructose (less of which is needed to sweeten food).
Complete Qu on worksheet.