1. Metabolic Pathways (d)
Describe the effect of substrate concentration on the direction and the rate of enzyme reactions
Describe the effect of end product concentration on the direction and the rate of enzyme reactions
State 2 ways in which enzymes often act

2. What happens to the rate of a reaction when you increase the substrate concentration?
What happens to the rate of a reaction when you FURTHER increase the substrate concentration?

3. Reaction rate increases! Reaction rate remains steady
Catalase from liver / potato
Hydrogen peroxide
Reaction rate is slow
At a low substrate concentration there are many active sites that are not occupied. This means that the reaction rate is low.
Reaction rate increases!
When more substrate molecules are added, more enzyme-substrate complexes can be formed. As there are more occupied active sites the rate of reaction increases.
Reaction rate remains steady
Eventually, increasing the substrate concentration even further will have no effect. The active sites will be saturated so no more enzyme-substrate complexes can be formed.

5. The effect of increasing substrate concentration on catalase activity

6. The effect of increasing substrate concentration on catalase activity
*Describe the trend:
Includes both the increasing slope and the steady part
Normally use figures from the graph
Problem solving Q
Explain the trend:
Display of Biology knowledge & understanding

7. Enzyme action Enzymes often act in 2 ways:
In groups where the product of one reaction becomes the substrate for the next or
As multi-enzyme complexes where a number of enzymes work together at the same time on the same substrate molecule(s)
An example of this is demonstrated by pyruvate dehydrogenase which is a complex of three different enzymes that collectively catalyse the breakdown of pyruvate (during glycolysis).

8. Direction of enzyme action
The actual direction taken depends on the relative concentrations of the reactants and the products.
Driving the reaction forward:
As substrate 1 becomes available, enzyme 1 becomes active, producing substrate 2. in the presence of substrate 2, enzyme 3 becomes active and so on…
A continuous supply of substrate 1, drives the sequence of reactions from substrate 1 to the end product.
Reversing the reaction:
If due to another reaction, the concentration of substrate 3 were to increase dramatically and the concentration of substrate 2 were to decrease dramatically, this would cause enzyme 2 to reverse and drive the reactions backwards until a balanced state is established