1. Enzymes Enzymes are proteins Enzymes are biological catalysts
They increase the rate of reactions
Ex. photosynthesis, respiration, protein synthesis
Each enzyme is specific to a substrate
Substrates are changed into products
Enzymes are not used up in a reaction – they can be used over and over again

2. The “lock and key” theory
Each enzyme has a different shape
Within the shape is the active site
Only one type of substrate fits into the active site (like a lock and key)

3. The “lock and key” theory
The enzyme is the “lock”
The substrate is the “key”

4. The “lock and key” theory
Once the substrate is attached to the active site it is turned into the 2 products

5. Denaturing enzymes TEMPERATURE pH Enzymes can be denatured
If the shape of enzyme changes, the substrate cannot fit into the active site
Two factors can cause enzymes to be denatured
TEMPERATURE pH

6. How? Temperature
As temperature increases, so does the rate of reaction.
But only up to a certain point as the enzyme becomes denatured at too high temperatures.
At 40°C the enzyme works at its optimum

7. How? pH Different enzymes work best at different pH values.
The optimum pH value depends on the enzymes and where it works. This enzymes optimum is pH8.
But enzymes become denatured at pH values too far from their optimum.
Enzymes in the stomach have an optimum pH of 2