1. Metabolic Pathways (e)
Describe the action of competitive inhibitors
Describe the action of non-competitive inhibitors
Describe the action of feedback inhibition
Describe and identify the impact of each of the above on the rate of reaction and through a graph of results
State how competitive inhibition can be reversed

2. Controlling metabolic pathways through Inhibition
You have already learnt that metabolic pathways can be controlled by:
Absence or presence of enzymes (by switching genes on or off)
(since these can either stop or start a metabolic reaction)
Substrate and end-product concentrations
(since they can drive a metabolic pathway in a particular direction)
Regulating the rate of reactions of enzymes through intra and extracellular signals AND now…
Inhibitors!!

3. Controlling metabolic pathways through Inhibition
An inhibitor is a substance that decreases the rate of an enzyme-controlled reaction.

4. Controlling metabolic pathways through Inhibition
There are 3 types of inhibition:
Competitive
Non-competitive
Feedback inhibition

5. Competitive inhibition
Video
Competitive inhibition
Substrate
Inhibitor

6. However, enough substrate could lead to…or

7. Controlling metabolic pathways through Inhibition
There are 3 types of inhibition:
Competitive (binds to active site),
Competitive inhibitors are similar in structure to the enzyme’s substrate.
They compete with the substrate for the active site causing a reduction in reaction rate.
Competitive inhibition can be reversed by increasing substrate concentration

8. Controlling metabolic pathways through Inhibition
There are 3 types of inhibition:
Competitive
Non-competitive
Feedback inhibition

9. Non-competitive inhibition
Substrate
Inhibitor

10. Non-competitive inhibition
Video
Non-competitive inhibition
Substrate X

11. 2. Non-Competitive Inhibition

12. 2. Non-Competitive Inhibition (Allosteric sites)

13. 2. Non-Competitive Inhibition (Allosteric sites)

14. Controlling metabolic pathways through Inhibition
There are 3 types of inhibition:
2. Non-competitive (binds to allosteric site)
Does not bind to the active site. Instead binds to a non active (allosteric) site and changes the shape of the entire enzyme molecule.
Active site changes shape and can no longer combine with the substrate.
Non-competitive inhibition cannot be reversed by increasing substrate concentration

16. Controlling metabolic pathways through Inhibition
There are 3 types of inhibition:
Competitive
Non-competitive
Feedback inhibition

17. X X X X 3. Feedback Inhibition
Video
Feedback inhibition occurs when an end product binds to an enzyme that catalyses a reaction early in the pathway. X X X X

18. Metabolic Pathways (e)
Describe the action of competitive inhibitors
Describe the action of non-competitive inhibitors
Describe the action of feedback inhibition
Describe and identify the impact of each of the above on the rate of reaction and through a graph of results
State how competitive inhibition can be reversed

19. Key Area 6: Past Papers Paper Section Question 2016 1 4 2015 6 2 2a
Specimen 3
Exemplar 7
YELLOW Booklet
Paper (revised)
Section
Question
2015 1
10,11
2014
7,8 2
2013 7
2012 11
RED Booklet