1. Control of Metabolic Pathways (2)
Higher Human Biology
Unit 1 - Human Cells

2. Control by regulation of enzyme action
Some metabolic pathways are required to operate continuously
Their genes that code for their enzymes need to be switched on continuously
These metabolic pathways are controlled by regulating the action of their enzymes

3. Signal molecules
Some enzyme activity is controlled by signal molecules
E.g. Epinephrine (Adrenaline)
Triggers liver cells to activate an enzyme that converts glycogen to glucose.
Intracellular - molecules that originate in the cell itself
Extracellular - molecules that originate from the cells environment

4. Effect of inhibitors
Inhibitors decrease the rate of an enzyme-controlled reaction
There are 2 types
Competitive inhibitors
Non-competitive inhibitors

5. Competitive Inhibitor
These compete with molecules of substrate for the active sites on an enzyme
Molecular structure similar to the substrate
Rate of reaction is reduced

6. Competitive Inhibition

7. Effect of increasing substrate concentration

8. Non-competitive inhibitors
Does not combine directly with an enzyme’s active site
Attaches to a non active (allosteric) site
Changes the shape of the enzyme
Active site becomes altered indirectly
Prevents it combining with the substrate

9. Activators and Inhibitors
Some enzyme molecules are composed of several subunits.
Several active sites
Several allosteric sites
These may be active or inactive

11. Feedback inhibition by end product
As the concentration of an end product builds up, some of it binds to an enzyme in the pathway.
This slows down the conversion of intermediate metabolites
Which in turn lowers the concentration of the product.
When the concentration of the product drops, fewer molecules of the enzyme are affected
More end product is produced and so on……..
Negative feedback control
Prevents wasteful conversion and accumulation of intermediates and final products

12. Metabolite W
Enzyme 1
Metabolite X
Some of end product (Z) binds to enzyme 1 and prevents conversion of W to X
Enzyme 2
Metabolite Y
Enzyme 3
Metabolite Z