1. Enzymes What are enzymes?
R Hardy 2007
What are enzymes?
Enzymes are biological catalysts that can change the rate of chemical reactions.

2. Enzymes as organic catalysts
The lowering of activation energy.
Mechanism of enzyme action: lock and key hypothesis.
The properties of enzymes.

3. The lowering of activation energy
Enzymes can accelerate reaction rate by lowering activation energy of the substrate. The amount of energy needs to bring one mole of a substance to the activated state at a given temperature termed activation energy.

4. Characteristics of enzymes:
protein in nature
remain unchanged at the end of reaction
denatured by high temperature
work best at a particular pH medium
specific in nature
Catalytic function of enzymes
Specific active site of enzyme for specific substrate molecule to combine with.

5. Examples of enzymatic reactions
Sucrose + water glucose + fructose
Fats + water fatty acids + glycerol

6. Lock and key mechanism The substrate acts as ________. (lock / key)
The enzyme acts as _________.
Enzyme + Substrate [Enzyme-substrate-complex] Enzyme + Product

7. Lock and key hypothesis
The enzyme molecule has a specific region termed active site to combine with the substrate molecules, , substrate molecules which have a shape fitting the active site bind to the enzyme (seem a lock and key) in the enzyme-substrate complex. The substrate is activated and reactions occur readily between substrate molecules changing them into the product molecule which no longer fit into the active site and escape into the surrounded medium.

8. The model of lock and key hypothesis

9. Factors affecting enzymatic reactions:
Temperature pH
substrate concentration
enzyme concentration
Inhibitors
The presence of cofactor
The presence of inhibitor

10. Factors affecting enzymatic activity

11. Temperature
At high temperature, heat can denature the protein structure of enzyme and then change the active site , hence it will prevent the substrate from binding on the enzyme and decrease the reaction rate.
And the low temperature will curb the activity of the enzyme.

12. Effect of temperature on the rate of an enzymatic reaction

13. pH value
Extreme pH change can affect the ionic state of functional groups within the active site.

14. The enzyme activity in different pH value

15. Graph to show the effect of pH on the rate of reaction of four different enzymes7

16. Substrate concentrate
Increasing the substrate concentration at the suitable enzyme concentration, the reaction rate will be increased because of more enzyme-substrate complex formed.
Over the saturation point, further increasing the substrate concentration has no effect on the reaction rate.
The merely way to increase the reaction rate in this time is to raise the enzyme concentration.

17. The rate of reaction vs the substrate concentration

18. Graph to show the effect of substrate concentration on the rate of an enzyme-controlled reaction

19. Enzyme concentration
Increasing the enzyme concentration at the suitable substrate concentration, the reaction rate will be increased because of more enzyme-substrate complex formed.
Over the saturation point, further increasing the enzyme concentration has no effect on the reaction rate.
The merely way to increase the reaction rate in this time is to raise the substrate concentration.

20. Graph to show the effect of enzyme concentration on the rate of an enzyme-controlled reaction

21. Cofactor 1
The non-protein component of an enzyme which present for enzyme activity.
The enzyme-cofactor complex is termed holoenzyme.
The enzyme portion without cofactor is termed apoenzyme.

22. Cofactor 2
The cofactors may be simple inorganic ions or complex organic molecules.
The cofactors can keep unchanged or be regenerated at the end of the reaction.
The are stable at relatively high temperature.
There are several kinds of cofactors.

23. The kinds of cofactors
Enzyme activator.
Coenzyme.
Prosthetic group.

25. Enzyme activator
It is an inorganic ion which certainly bound to an enzyme or an substrate to increase the chance to an enzyme-substrate complex forming.
e.g. copper, iron, calcium etc.

26. Coenzyme
It is an organic non-protein molecule firmly associated with the enzyme and is essential for enzyme activity.
It acts a carrier for transferring chemical groups or atoms from one enzyme to another.
Many coenzymes are synthesized from vitamins.
e.g. ATP, NADP etc.

27. Prosthetic group
It is an organic non-protein group which is tightly bound to the enzyme.
It is part of enzyme and is essential for enzyme function.
It can act as carriers of atoms or electrons while transferring one compound to another in an overall metabolic pathway.
e.g. FAD, biotin etc.

28. Inhibitor
They are substances interact with an enzyme and lead to a loss in a catalytic activity of enzyme.
There are reversible inhibitor and irreversible inhibitor.

30. Reversible inhibitor
The activity of enzyme is restored when the inhibitor is removed.
There are including competitive inhibitors and non-competitive inhibitors.

31. Types of inhibitors Competitive inhibitors:
compete with the substrate for the active sites of enzyme molecules
Non-competitive inhibitors:
example: cyanide is a respiratory inhibitor
they attach to the enzyme and alter its shape so that the active site no longer fits the substrate

32. Competitive inhibitors
Substance with a similar molecular structure as the substrate, competing with the substrate for the active site on the enzyme.
The degree of inhibition rely on the relative concentration of substrate and inhibitor.
Competitive inhibition can be overcome by increasing the concentration of substrate due to more chance to react the active site.

33. Competitive inhibition

34. Non-competitive inhibitors
The inhibitor has no structural similarity to the substrate, it forms an enzyme-inhibitor complex in the next part or site of the enzyme other than the active site.

35. Non-competitive inhibition

36. Irreversible inhibitor
The inhibitor permanently attaches to the active site excluding the substrate molecule.
The degree of inhibition depends completely on the inhibitor concentration and cannot be reversed by increasing substrate concentration.

37. The biological importance of inhibitors
They can affect the catalytic function of enzymes.
They can be the end product in some metabolic pathways.