1. ENZYMES

2. Without Enzymes Reactions are extremely slow
The conversion of bread (starch) to glucose takes about 1000 years if it sits in water
If you heat up the mix, it takes about 1 hour.
But, eat some bread and our body converts it to glucose in minutes with the help of Enzymes

3. Enhancement of Reaction Rate by Enzymes
Function
Uncatalysed Reaction
Rate (s -1)
Enzymatic Reaction Rate (s -1)
Rate Enhancement
Carbonic
Anhydrase
CO2-hydratisation
1.3 x 10 -1
1 x 106
7.7 x 10 6
7,700,000
Carboxypeptidase A
Peptide hydrolysis
3 x 10 -9
578
1.9 x 10 11
190,000,000,000
Staphylococcal nuclease
Digestion of nucleic acids in Staphylococcus aureus
1.7 x 95
5.6 x 10 14
560,000,000,000,000
Radzicka, A and Wolfenden, R, Science 267, 91(1995)

4. Enzymes
Enzymes are molecules that act as catalysts to speed up biological reactions.
Most enzymes are proteins.
They work by lowering the activation energy required to start the reaction

5. Enzymes
The compound on which an enzyme acts is called its substrate.
The substance formed are called products
A normal reaction of enzyme and substrate to form product
substrate
Enzyme substrate complex
products
enzyme
enzyme + +

6. For an enzyme to speed up a reaction a substrate must bind to a particular part of the enzyme called the active site.
When the substrate binds to its enzyme an enzyme-substrate complex is formed
New product is formed
Product(s) are then released from the enzyme
Enzymes are unchanged by the reactions they catalyse ; thus they are REUSABLE.

7. Anabolic Reaction
Enzymes can join two or more substrate molecules together.(synthesis/ anabolism) e.g Formation of the disaccharide maltose

8. Catabolic Reaction
Enzymes can break molecules into smaller components (decomposition/cataboslism); e.g digestion of sucrose into the monomers glucose and fructose.

9. Enzyme Active Sites Substrate molecule:
Substrate molecules are the chemicals that an enzyme acts on. They are drawn into the cleft of the enzyme.
Active site: At the active site, the substrate/s is drawn to the enzyme’s surface and is/are are positioned in a way to promote a reaction: either joining two molecules together or splitting up a larger one.
Enzyme molecule: The complexity of the active site is what makes each enzyme so specific (i.e. precise in terms of the substrate it acts on).
This model (above) is an enzyme called Ribonuclease S, that breaks up RNA molecules.

10. How do enzymes work?
For an enzyme to speed up a reaction a substrate must bind to a particular part of the enzyme called the active site
Binding of enzyme and substrate is dependent on enzyme shape and shape of the active site
substrate
Active site
Enzyme

11. Lock and key model substrate Enzyme
This is known as the key and lock mechanism of binding.

12. Enzyme (lock) Substrate (key) 1 2 3 4 5
Get students to work in teams and find all the active sites and the substrates that fit into the active sites. Note that some enzymes can take more than one substrate at the same time.
Everyone match up the enzymes with the substrates.
So you can see that the enzyme is very specific for the substrate.

13. Symbolic representation of the lock and key model of enzyme action.
Products
Substrate
Enzyme
Symbolic representation of the lock and key model of enzyme action.
A substrate is drawn into the active sites of the enzyme.
The substrate shape must be compatible with the enzymes active site (precisely complementary) in order to fit and enable a reaction to proceed.
The enzyme modifies the substrate. In this instance the substrate is broken down, releasing two products.

14. Induced fit Model
Active site changes conformation to match the substrate
Active site is NOT perfectly complementary to the substrate
The enzyme’s active site has a shape closely complementary to the substrate but not a perfect fit
The substrate locks into the active site of the enzyme.
The shape of the active site is altered; holding the substrate more tightly and straining it.
An enzyme-substrate complex is formed.
The substrate undergoes a chemical change and a new substance(s)(product) is formed.
The product is released from the active site.
The enzyme reverts to original shape.
The free unaltered active site is ready to receive a fresh substrate.
Active site reverts back to original shape

15. Effective collision
In order for the substrate to be drawn to the active site of the enzyme, an effective collision must occur between enzyme and substrate
The more collisions that occur between the enzyme and its substrate the more chance of an effective collision occurring

16. What give the enzyme its shape
How it is folded into its 3-dimensional shape or (tertiary structure) is vital
If this structure is changed or altered then the enzyme is said to have been DENATURED
Denaturation of the enzyme will change the shape of the enzymes active site
This will mean the enzyme will no longer be able to bind to its substrate
Denaturation is permanent.

17. Effect of Temperature
Enzymes often have a narrow range of conditions under which they operate properly.
As temperature increases reaction rate increases up to a point
At this point the enzyme is denatured and it can no longer function.
Optimum temperature for the enzyme
Rapid denaturation at high temperatures
Too cold for the enzyme to operate
Rate of reaction
Temperature (°C)

18. At low temperatures is the enzyme denatured?
No! Low temperature has no affect on enzyme structure. You can freeze enzymes and then defrost them and they will again be functional
The reaction rate slows with a decrease in temperature due to a decrease in the kinetic energy of both enzyme and substrate molecules
As they are moving more slowly then will experience fewer effective collisions which results in a slower rate of catalysis.

19. Why does reaction rate increase as temperature increases?
As temperature increases the kinetic energy of molecules increase and the enzyme and substrate molecules both move faster
Thus more collisions and more effective collisions and a faster rate of catalysis
This will continue UNTIL the enzyme’s 3 dimensional shape changes and the active site becomes deformed
Then the substrate can NO LONGER bind with the enzyme
The enzyme can NO LONGER catalyse the reaction

20. Protein Denaturation

21. Effect of pH Enzymes can be affected by pH.
Each enzyme will have an optimal pH as which they function best
A shift in pH in either direction from the optimum will result in the enzyme being denatured
Once denatured the enzyme can no longer function
Denaturation of the enzyme is permanent
Pepsin
Urease
Trypsin
Enzyme activity 1 3 2 4 5 6 7 8 9 10
Acid
Alkaline pH
Enzymes often work over a range of pH values, but all enzymes have an optimum pH where their activity rate is fastest.

22. Substrate Concentration
Reaction rate increase as substrate concentration increases up to a point (saturation)
(enzyme concentration constant)
Maximum activity occurs when the enzyme is saturated

23. Reaction rate increases as enzyme concentration increase
(at constant and very high substrate concentration)
At higher enzyme concentration more substrate will bind with enzyme

24. What determines the final about of PRODUCT produced in an enzyme driven reaction?
The final amount of product is dependent on the initial amount to substrate
The amount of time taken to produce the maximum amount of product can be affected by factors such as temperature, pH, and enzyme concentration.

25. Co Enzymes
Sometimes help is needed to make the active site of an enzyme a perfect complementary fit for its substrate
Co enzymes are molecules that fulfil this role
Vitamins are an example

26. INHIBITION: COMPETITIVE - AN INHIBITOR BINDS TO THE ACTIVE SITE PREVENTING THE ENZYME FROM BINDING TO THE SUBSTRATE

27. HIV protease complexed with the protease inhibitor ritonavir
HIV protease in a complex with the protease inhibitor ritonavir. The structure of the protease is shown by the red, blue and yellow ribbons. The inhibitor is shown as the smaller ball-and-stick structure near the center. Created from PDB 1HXW

28. INHIBITION: NON-COMPETITIVE -AN INHIBITOR BINDS TO A SITE OTHER THAN THE ACTIVE SITE WHICH CAUSES A CHANGE IN THE ACTIVE SITE

29. examples
Heavy metals such as lead, mercury, copper or silver are poisonous
This is because ions of these metals are non-competitive inhibitors for several enzymes.

30. Drugs and desirable Inhibition
While some enzyme inhibitors are poisonous, others are beneficial.
Penicillin acts as an inhibitor for transpeptidase, an enzyme that bacteria need to build their cell walls. If the cell wall is lacking, osmotic pressure causes the bacterial cell to burst and the die.
However, new strains of bacteria have developed an enzyme, penicillinase, that inactivates penicillin.
To destroy these new strains, synthetically modified penicillins have been prepared so that this antibiotic remains effective.