1. 8.1 Metabolism

2. Understanding
Metabolic pathways consist of chains and cycles of enzyme- catalysed reactions
Enzymes lower the activation energy of the chemical reactions that they catalyse
Enzyme inhibitors can be competitive or non-competitive
Metablic pathways can be controlled by end-product inhibition

3. Applications
End-product inhibition of the pathway that converts threonine to isoleucine
Use of databases to identify potential new anti-malarial drugs

4. Skills
Distinguishing different types of inhibition from graphs at specified substrate concentration
Calculating and plotting rates of reaction from raw experimental results

5. Metabolic Pathways
Most chemical reactions in living things are pathways
They can be linear (chains)
A B C D
Where A is the initial reactant, B and C are intermediates and D is the final product

6. Linear Pathways Example: Glycolysis This is a 10 step, linear
metabolic pathway
Glucose is the initial reactant
and lactate is the final
product (in animals)
Every step is controlled
by an enzyme

7. Cycles Example: The Krebs Cycle
Some pathways don’t have a beginning or an end. These are called cycles.
Example: The Krebs Cycle
This is an 8 step pathway
It doesn’t really have a start or a
finish
Many “coupled reactions” occur
in conjunction with the cycle

8. Activation Energy
As learned in 2.5, enzymes speed up reactions by decreasing the activation energy required to start a reaction

9. Competitive vs Non-Competitive Inhibition
Also learned in 2.5, enzymes can be inhibited by certain substances
Most drugs work by inhibiting enzymes
Inhibition can be competitive or non-competitive

11. Competitive vs Non-Competitive
While both serve to slow down metabolic reactions, there are differences
Competitive inhibitors can be overcome by increasing the substrate concentration but that is not the case with non- competitive inhibitors
With enough substrate
concentration, the rate
of reaction can be
just as high as without
an inhibitor

12. End Product Inhibition
Also called Feedback Inhibition
The process of enzyme control where the end product acts as an inhibitor for one of the enzymes involved in an earlier step in the pathway.

13. End Product Inhibition
Example:
Threonine to Isoleucine
This is a five step pathway that creates a new amino acid.
Isoleucine inhibits the enzyme threonine deaminase, the enzymetht catalyses the first step in the pathway.