1. 2.5 Enzymes
Understanding:
Enzymes have an active site to which specific substrates bind
Enzyme catalysis involves molecular motion and the collision of substrates with the active site
Temperature, pH and substrate concentration affect the rate of activity of enzymes
Enzymes can be denatured
Immobilized enzymes are widely using in industry
Skills:
Design of experiments to test the effect of temperature, pH and substrate concentration on the activity of enzymes
Experimental investigation of a factor affecting enzyme activity
Applications:
Methods of production of lactose-free milk and its advantages
Nature of science:
Experimental design: accurate quantitative measurements in enzymes experiments require replicates to ensure reliability

2. Enzyme structure Proteins that work as a catalyst.
Speed up chemical reactions without being altered themselves.
Understanding:
Enzymes have an active site to which specific substrates bind

4. Enzyme structure Enzymes only catalyze one reaction
Thousands of reactions take place in a cell
Majority need to be catalyzed.
Organisms produce thousands of enzymes
Enzymes are specific
Understanding:
Enzymes have an active site to which specific substrates bind

5. Specificity Enzymes have an active site Specific to a substrate
Only that substrate can fit
Cannot catalyse other reactions
Understanding:
Enzymes have an active site to which specific substrates bind

6. Three Stages Substrate binds to active site of enzyme.
2. Substrates change into different chemical substances
3. These products separate from the active site, leaving it vacant for substrates to bind again
Understanding:
Enzyme catalysis involves molecular motion and the collision of substrates with the active site

7. Collisions Random movement of substrates and enzymes
Means there are collisions
Only bind together if they are aligned exactly
Dissolving in water allows more collisions
Understanding:
Enzyme catalysis involves molecular motion and the collision of substrates with the active site

8. Denaturation
Structure can be irreversibly altered by certain conditions.
Active site shape changes – substrate can no longer bind
Understanding:
Enzymes can be denatured

9. Your Experiment
Each of you will be investigating one of the following factors affecting the rate of reaction of enzymes.
Temperature pH
Concentration of substrate
You need to plan and carry out this experiment
(each group has a different variable)
You will then present your results
Skills:
Design of experiments to test the effect of temperature, pH and substrate concentration on the activity of enzymes
Experimental investigation of a factor affecting enzyme activity
Understanding:
Temperature, pH and substrate concentration affect the rate of activity of enzymes

10. Rate of Reaction
How much of a product is formed OR how much a reactant is used up
Many things affect the rate of reaction.
High rate of reaction = fast reaction
Low rate of reaction = low rate

11. Volume of gas measured with a gas syringe or measuring cylinder
Rate of Reaction
Measure the mass of a substance
(usually start and end – hard to find midpoints)
Volume of gas measured with a gas syringe or measuring cylinder
(can find midpoints)
Rate of reaction = Amount of product formed OR reactant used
Time taken

12. Example
If 24 cm3 of hydrogen gas is produced in 2 minutes what is the mean rate of reaction?

13. Example
If 24 cm3 of hydrogen gas is produced in 2 minutes what is the mean rate of reaction?
24/2 = 12cm3 hydrogen/min

14. Different enzymes have a different optimum pH
Some like more alkali, some more acidic
Too acidic or alkaline = denature and active site changes shape
Closer to optimal pH = increased enzyme activity

15. Increase in temperature means more kinetic energy
Enzymes and substrate move around more
More collisions
Optimal temperature – this is at a maximum
Past optimal temperature = denaturation and active site changes shape
No enzymes can fit into active site

16. More substrate = more change collisions
More chance of enzyme substrate complex
Gets to a point where all enzymes are being used to the max
No available active sites
Unless increase concentration of enzymes as well
Plateau but does not decrease

17. Immobilised Enzymes Attach enzymes to another material
Enzyme movement is restricted
What are the advantages?
Understanding:
Immobilized enzymes are widely using in industry

18. Commercially Used Understanding:
Immobilized enzymes are widely using in industry

19. Immobilised Enzymes Less likely to denature
Can be re-used again and again
Do not contaminate end product
Do not need to filter end product
Can stop and start the reaction quickly
But…
Requires extra time & money to make them
Extra equipment to make them
Reduction in reaction rate as there will be fewer collisions
Understanding:
Immobilized enzymes are widely using in industry