1. What do you remember about enzymes?

2. Create a mind map Include What they are made of How they work
What factors affect them
Any good examples

3. All enzymes are proteins
Enzymes are similar in many ways:
Globular proteins with a specific 3D shape (tertiary structure)
They act as catalysts
Specific
Active site
(pocket or cleft area)
Activity affected by temperature and pH
A catalyst is a molecule (or element) that speeds up a chemical reaction but does not get used up in the reaction. At the end of the reaction the catalyst remains unchanged.

4. Enzymes sucrose + water glucose + fructose
substrate(s) – substance(s) used up in an enzyme-controlled reaction
product(s) – substance(s) formed in an enzyme-controlled reaction
Sucrase – the enzyme

5. Active site
area on an enzyme to which substrate binds (not bonds or joins)
Tiny part of enzyme
Very few (often fewer than 10) amino acids form the actual active site
Individual cell may contain as many as 1000 different enzymes

6. Inside and out Intracellular
(enzymes catalyse reactions inside the cell)

7. Extracellular enzymes:
released from cells that make them and their action takes place outside cells eg
Salivary amylase
Fungal hyphae secrete digestive enzymes

8. Why do reactions need enzymes?
Increase rate of reaction
Enzymes increase the rate of reaction by 107 (10 million times faster!)

9. Reactions need a level of energy before they can proceed = activation energy

10. Lowering the amount of energy required to get reaction started makes the reaction more likely to occur

11. Enzymes control metabolic processes?
E.g.
Photosynthesis
Respiration

12. Draw a similar diagram to the one above and explain how the end product can control the rate of the reaction

13. Specificity Due to the 3D shape of the active site
Active site shape is determined by tertiary (3D) structure of enzyme
Due to the 3D shape of the active site
Specificity
Determined by the primary structure of the protein which forms the enzyme
The active site is only complementary to a specific substrate
Each enzyme can only catalyse one reaction
Formed during protein synthesis and coded for by DNA

14. Enzyme action

15. Theories of Enzyme Action
Lock and Key Hypothesis
Induced Fit Hypothesis

16. Lock and key hypothesis
Lock = Enzyme
Key = Substrate
This theory relies on the complementary shapes of the substrate and active site creating enzyme-substrate complexes
Textbook p

17. Induced Fit Hypothesis
substrate molecule changes shape to fit enzyme molecule more closely as they bind, putting a strain on the substrate bonds.
(Think of it as a hand in a glove)
Charges on amino acids at active site also hold substrate in place.
Enzyme-substrate complexes are formed as before.
Products no longer fit the active site so they leave.
Animation – hydrolysis
of sucrose

18. Examiners tip:
Don’t write:
“the enzymes shape is complementary to the substrate”
Do write:
“the shape of the enzymes active site is complementary to the shape of the substrate molecule”

19. Enzyme action
Enzyme and substrate molecules have their own kinetic energy and are moving – they collide randomly

20. Enzyme action
2 substrate molecule binds to active site of enzyme forming an enzyme-substrate complex (lock and key / induced fit)

21. Enzyme action
3 Enzymes reduce activation energy by holding substrate in a way which causes reaction to occur more easily forming enzyme-product complex

22. Enzyme action
4 The products no longer fit active site and move out – enzyme is free to catalyse same reaction with another substrate molecule

23. Enzyme action
‘a single enzyme molecule typically acts on a thousand substrate molecules per second’

24. Straw is plentiful and it could be used for the production of many organic substances. The first step is the conversion of cellulose to glucose. It has been suggested that an enzyme could be used for this process. There is a difficulty - the lignin that covers the cellulose would protect the cellulose from attack by the cellulose-digesting enzyme.
Use your knowledge of the way in which enzymes work to explain why cellulose-digesting enzymes do not digest the lignin. (2 marks)
This is a straightforward question relating to enzyme specificity and its accompanying mark scheme. Rather more is needed in a full answer than a superficial statement about enzymes being specific.
Enzymes are specific;
Shape of lignin molecules will not fit active site of enzyme;

25. Enzyme action - Catalase

26. 1 2
Catalase is a globular protein made from four polypeptide chains (an example of a protein with a quaternary structure) 3 4
One molecule of catalase can break down molecules of hydrogen peroxide every second!

27. Catalase is found in living cells and breaks down toxic hydrogen peroxide into harmless water and oxygen
2H2O H2O + O2
catalase
Enzyme structure
and action

28. Investigating the time course for an enzyme controlled reaction
Enzyme: catalase Substrate: H2O2
(3 different sources – peas, potato, yeast )
Independent Variables Time, Source of catalase
Dependent Variable Volume of oxygen
Controlled variables:
Method:
Prepare measuring cylinder(full of water)
Add enzyme source to test-tube
Add 10cm3 hydrogen peroxide to test-tube (use syringe)
Quickly place bung into top of test-tube
Ensure delivery tube carries gas into cylinder
Measure volume of O2 produced every 30 seconds for 10 minutes
apparatus
temperature
Volume of H2O2

29. Follow the progress of an enzyme-catalysed reaction
measuring cylinder – select an appropriate size
Prepare a results table
Set up the apparatus (minus the hydrogen peroxide) as shown
Add the hydrogen peroxide, return bung and immediately start a stop clock
Record volume of O2 collected in measuring cylinder every 10s until reaction stops
If reaction is too fast / slow – adjust volume / surface area of catalase source/ size of measuring cylinder/ time intervals
delivery tube
clampstand
bung
water
boiling tube
source of catalase – adjust size etc as needed
10cm³ hydrogen peroxide – add last using a syringe
plastic tub

30. Total Volume O2 produced (cm3)
Results table:
Total Volume O2 produced (cm3)
Time (s)
Potato
Peas
Yeast 30 60 90
120
150
180
210
240
270
300
330
360

31. 390
420
450
480
510
540
570
600

32. Graph: Graph to show the effect of enzyme source on the time
course of an enzyme controlled reaction
Volume of O2 produced (cm3)
Time (s)

33. Calculating initial rate of reaction
Comparing the initial rate of an enzyme controlled reaction is useful as it should be the fastest point of a reaction.
Tangents taken later on the reaction curve allow you to calculate the rate at later stages.
You can also use these calculations to plot a graph of rate against time
Volume of O2 produced (cm3) b a
Time (s)
Volume O2
Initial rate =
cm3 s-1
Time taken (s) a
cm3 s-1 b
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34. Calculating Mean Rates of a Reaction

35. Factors Affecting Enzyme Activity
Temperature pH
Concentration of the substrate
Concentration of the enzyme
Presence of inhibitors