1. Investigating Cells
Enzymes
Mr G Davidson

2. Investigating Enzymes
Most chemical reactions occur very slowly at normal temperatures e.g. hydrogen peroxide breaks down very slowly at room temperature.
Hydrogen peroxide (H2O2) Water (H2O) + Oxygen (O)
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G Davidson

3. Investigating Enzymes
If the temperature is increased the reaction speeds up, however this is not possible with living organisms.
Therefore, a special chemical called a catalyst is used to speed the reaction up.
Biological catalysts are called ENZYMES.
Living cells produce enzymes to speed up reactions within the cells.
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G Davidson

4. Investigating Hydrogen peroxide
CATALASE is an enzyme which breaks down hydrogen peroxide to water and oxygen.
If the enzyme is working properly, bubbles of oxygen are released.
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G Davidson

5. Living Tissue Dead Tissue
Each test tube contains 20ml hydrogen peroxide
Living Tissue
Dead Tissue
Control
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G Davidson

6. Investigating Hydrogen peroxide
Results: The living tissues all produce bubbles, but the dead tissue doesn’t.
Conclusion: Living tissues contain catalase which breaks down hydrogen peroxide.
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G Davidson

7. Catalysts and Enzymes
Catalysts are not changed by the reactions that they are acting on and so can be used again.
There are many chemical reactions occurring in living cells at any one time.
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G Davidson

8. Catalysts and Enzymes
With the help of catalysts – enzymes, because the temperature is so low, these reactions would occur so slowly that life would be impossible.
Enzymes themselves are NOT living – they are chemicals made of PROTEIN.
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G Davidson

9. Catalysts and Enzymes
It is possible to extract enzymes from living cells, and once this is done they can be dried and stored in powdered form.
Most enzymes act within the cells in which they are produced.
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G Davidson

10. Catalysts and Enzymes
A small number do, however, work outside the cells, e.g. digestive enzymes.
Some of the chemical reactions in living organisms involve the building up of large molecules.
Others involve the breakdown of large, complex molecules into smaller simpler ones.
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G Davidson

11. Amylase
Starch is a large molecule made of hundreds of smaller glucose molecules joined together.
An enzyme called amylase can break down starch and turn it into sugar.
STARCH SUGAR
AMYLASE
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G Davidson

12. Testing Amylase Object: to investigate the enzyme amylase. Method:
1. Add 10ml starch solution to a test tube.
2. Add 2ml amylase solution.
3. Shake the tube to mix.
4. Test a drop for starch using iodine solution.
5. Test a drop for starch every 1 minute.
Results:
Conclusion:
The iodine solution does NOT turn blue/black.
Amylase breaks down starch to sugar.
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G Davidson

13. Specificity
Other enzymes act on different substances (SUBSTRATES) and so have no effect on starch.
Each enzyme acts only on a specific substrate; other substances are not affected.
The substance produced as a result of the reaction catalysed by an enzyme is called the PRODUCT.
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G Davidson

14. Specificity SUBSTRATE ENZYME PRODUCT(S) Starch Amylase Simple sugar
Fats
Lipase
Fatty acids & Glycerol
Protein
Pepsin
Amino acids
Glucose-1-phosphate
Phosphorylase
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G Davidson

15. Synthesis of Starch Starch may be synthesised from glucose.
An enzyme is used to speed up the synthesis of starch.
Potatoes contain large amounts of starch.
Potato extract contains the enzyme phosphorylase which speeds up starch synthesis.
PHOSPHORYLASE
GLUCOSE-1-PHOSPHATE STARCH
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G Davidson

16. Synthesis of Starch Object: To investigate the enzyme phosphorylase.
Method: Set up the following: A B D C
1. Test the potato extract for the presence of starch.
2. Put 2 spots of glucose-1-phosphate into each of the hollows.
3. Add a drop of potato extract to each hollow and start the clock.
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G Davidson

17. Synthesis of Starch After 4 minutes test A for the presence of starch.
After the next 4 minutes test B and so on.
Results:
Conclusion:
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G Davidson

18. Pepsin Activity
The activity of an enzyme is affected by the pH of its surrounding medium.
Pepsin is an enzyme produced in the stomach.
It speeds up the breakdown of protein.
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G Davidson

19. Pepsin Activity
Copy and Complete the table using the results on your sheet. pH
Initial Length
(mm)
Final Length
Decrease in Length
2.5 50
3.7
4.9
7.0
8.4
9.0
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G Davidson

20. Effect of pH on Enzyme Activity
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G Davidson

21. Model Enzymes
During an enzyme controlled reaction the substances involved – the substrates – become joined to the surface of the enzyme molecule.
The chemical reaction then occurs very quickly.
The spot on the enzyme molecule where the catalytic activity takes place is called the ACTIVE SITE.
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G Davidson

22. Model Enzymes
Enzyme molecules have many active sites over their surface.
Only substrates that fit the active site exactly, react on the surface of the enzyme.
Substrate molecules fit into these active sites like a key fitting into a lock.
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G Davidson

23. Enzyme/substrate complex
Model Enzymes
Enzyme
Substrate
Enzyme/substrate complex
Products
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24. Model enzymes
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G Davidson

25. Effect of Temperature on Enzyme Activity
Because enzymes are proteins, they are affected by heat and the pH of the surrounding medium.
At temperatures above 50oC most enzymes are permanently inactivated or DENATURED.
Enzymes have a temperature at which they work best, and this is called the OPTIMUM temperature.
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G Davidson

26. Effect of Temperature on Enzyme Activity
Optimum Temperature
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27. Investigating Urease
Urease is an enzyme which catalyses the breakdown of urea.
The activity of urease can be followed using a pH indicator to detect the presence of ammonia.
Ammonia is a strong alkali.
UREA WATER AMMONIA CO2
UREASE
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G Davidson

28. Investigating Urease
Test a little ammonium hydroxide with pH paper and note the colour.
Place a little urea, water and 3 drops of indicator in a test tube.
Add a pinch of urease and note what happens.
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G Davidson

29. Inhibitors
Some substances are able to stop or INHIBIT the activity of an enzyme.
Repeat the urea experiment but add a few drops of silver nitrate to the test tube.
The enzyme fails to work because the silver nitrate INHIBITS it.
22 February, 2019
G Davidson