1. ENZYMES
A protein with catalytic properties due to its power of specific activation
© 2007 Paul Billiet ODWS

2. Chemical reactions
Chemical reactions need an initial input of energy = THE ACTIVATION ENERGY
During this part of the reaction the molecules are said to be in a transition state.
© 2007 Paul Billiet ODWS

3. Reaction pathway
© 2007 Paul Billiet ODWS

4. Making reactions go faster
Increasing the temperature make molecules move faster
Biological systems are very sensitive to temperature changes.
Enzymes can increase the rate of reactions without increasing the temperature.
They do this by lowering the activation energy.
They create a new reaction pathway “a short cut”
© 2007 Paul Billiet ODWS

5. An enzyme controlled pathway
Enzyme controlled reactions proceed 108 to 1011 times faster than corresponding non-enzymic reactions.
© 2007 Paul Billiet ODWS

6. Enzyme structure Enzymes are proteins They have a globular shape
A complex 3-D structure
Human pancreatic amylase
© Dr. Anjuman Begum
© 2007 Paul Billiet ODWS

7. The active site
One part of an enzyme, the active site, is particularly important
The shape and the chemical environment inside the active site permits a chemical reaction to proceed more easily
© H.PELLETIER, M.R.SAWAYA ProNuC Database
© 2007 Paul Billiet ODWS

8. The substrate
The substrate of an enzyme are the reactants that are activated by the enzyme
Enzymes are specific to their substrates
The specificity is determined by the active site
© 2007 Paul Billiet ODWS

10. The Lock and Key Hypothesis
Fit between the substrate and the active site of the enzyme is exact
Like a key fits into a lock very precisely
The key is analogous to the enzyme and the substate analogous to the lock.
Leaving it free to become attached to another substrate
© 2007 Paul Billiet ODWS

11. The Lock and Key Hypothesis
Enzyme may be used again
Enzyme-substrate complex E S P
Reaction coordinate
© 2007 Paul Billiet ODWS

12. The Lock and Key Hypothesis
This explains enzyme specificity
This explains the loss of activity when enzymes denature
© 2007 Paul Billiet ODWS

13. Factors affecting Enzymes
substrate concentration pH
temperature
inhibitors
© 2007 Paul Billiet ODWS

14. The effect of pH Optimum pH values Enzyme activity Trypsin Pepsin pH 13 5 7 9 11
© 2007 Paul Billiet ODWS

15. The effect of pH Extreme pH levels will produce denaturation
The structure of the enzyme is changed
The active site is distorted and the substrate molecules will no longer fit in it
At pH values slightly different from the enzyme’s optimum value, small changes in the charges of the enzyme and it’s substrate molecules will occur
© 2007 Paul Billiet ODWS

16. The effect of temperature
Temperature / °C
Enzyme activity 10 20 30 40 50
Q10
Denaturation
© 2007 Paul Billiet ODWS

17. The effect of temperature
For most enzymes the optimum temperature is about 30°C
Many are a lot lower, cold water fish will die at 30°C because their enzymes denature
A few bacteria have enzymes that can withstand very high temperatures up to 100°C
Most enzymes however are fully denatured at 70°C
© 2007 Paul Billiet ODWS