1. Human Cells Metabolic pathways
Higher Human Biology
Human Cells
Metabolic pathways

2. What do you already know?
Write down 3 things you know about metabolic pathways already.

3. What you will be learning
What metabolic pathways are.
How metabolic pathways are controlled.
Why it is necessary to control metabolic pathways.

4. Metabolism in cells
Cell metabolism is the whole, vast array of biochemical reactions taking place in a cell.
It is complex but controlled and integrated.
Enzymes play a vital role by catalysing these biochemical reactions.

5. Metabolic pathways There are 2 types of metabolic pathways
Anabolic pathways are biosynthetic (building up) processes that require energy (e.g. building proteins)
Catabolic pathways involve the breakdown of complex molecules and usually release energy (e.g. respiration)

7. Metabolic pathways
Some metabolic pathways have reversible and irreversible steps
One reason for this is that the enzyme controlled reactions produce new molecules that can act as regulatory molecules
Some metabolic pathways have alternative routes
Alternative routes mean cells can make use of alternative chemicals for metabolic pathways

8. Control of metabolic pathways – enzymes are key
Enzymes control the rate of reactions in metabolic pathways
The absence or presence of particular enzymes will determine whether a reaction can proceed or not
Enzymes allow the activation energy for a chemical reaction to be lowered so that the reaction is more likely to take place

10. Control of metabolic pathways – enzymes are key
Enzymes are produced by gene expression
Some genes for enzymes are continuously expressed
These enzymes are always present in cells
The presence of a substrate or the removal of a product will effect the rate of reaction and it’s direction
The presence of a substrate will often drive the reaction forward
The presence of the end product will often slow or stop a metabolic pathway
Many metabolic reactions are reversible

11. Control of metabolic pathways – enzymes are key
Enzymes react with their substrates at an active site
The active site allows the enzyme to be specific for a substrate
The substrate will have a affinity (chemical attraction) for the active site
The active site is flexible and as the substrate combines with it, the site changes shape slightly
This change of shape allows the active site to fit very closely to the substrate
This is called INDUCED FIT

12. Control of metabolic pathways – enzymes are key
Enzymes allow the correct orientation of the substrate or substrates at an active site due to their shape
Enzymes lower the activation energy for a reaction to take place
Enzymes produce products that have a low affinity for the active site so they are released
Enzymes can be utilised many times in a metabolic pathway

13. Factors affecting enzyme activity
These include:
Substrate concentration
End product inhibition
Multi enzyme complexes
Inhibitors
Signal molecules

14. Substrate concentration

15. End product inhibition

16. Multi enzyme complexes
This is when there are a number of enzymes working together to make a process happen.
An example of this is DNA polymerase and RNA polymerase activity

17. Enzyme inhibitors
Inhibitors are molecules that will decrease the rate of an enzyme controlled reaction
Competitive inhibitors – bind to the active site directly so are in direct competition with the substrate
Increasing the substrate concentration will increase the rate of reaction as more sites will be occupied by the substrate than the inhibitor

19. Enzyme inhibitors Non competitive inhibitors
These become attached to another part of the enzyme NOT the active site
They alter the shape of the active site so the substrate can no longer bind to it
This slows the rate of reaction

21. Uses of enzyme inhibitors

23. Signal molecules Enzyme activity can be controlled by signal molecules
If the signal molecule originates and has it’s effect within a cell then they are called INTRACELLULAR signal molecules
If the signal molecule originates from one cell and have their effect somewhere else they are called EXTRACELLULAR signal molecules

24. Gene expression discovered
LAC OPERON theory
Jacob and Monod
E. coli and it’s use of lactose as an alternative substrate for respiration
Enzyme needed is β galactosidase to breakdown lactose into glucose and galactose
Enzyme only produced when lactose is present

26. What do you know now? What is metabolism? What are anabolic reactions?
What are catabolic reactions?
What molecules control metabolic pathways?
What is an active site?
What is induced fit in reference to enzymes?
What is activation energy?
How do enzymes change activation energy?
What are competitive inhibitors?
What are non competitive inhibitors?
What is the effect of substrate concentration on enzyme reactions?