Enzymes are protein molecules that act as biological catalysts. They specifically bind with substrate molecules to form enzyme-substrate complexes. Enzymes are not consumed in reactions but can be used repeatedly by lowering the activation energy required. Without enzymes, reactions would occur slowly as they require energy to break and reform chemical bonds. Enzymes achieve catalysis through an induced-fit model where the active site is flexible and molds closer to the substrate.

1. MACROMOLECULES
Enzymes

2. Enzymes-Induced Fit Model
Enzymes are protein molecules that act as
biological catalysts
They bind in a complementary manner with
the reactant molecules or substrates to
form an enzyme- substrate complex.
They are specific in their action. i.e. one
enzyme bonds with one substrate

3. Enzymes-Induced Fit Model
They are not consumed in the reaction, but
can be used over and over again
Speed up reactions by lowering amount of
energy needed for the reaction to occur

4. Activation Energy
Without enzymes reactions would occur slowly.
Chemical reactions involve the breaking and
reforming of chemical bonds.
For bonds to break an initial energy is required
known as activation energy which will in turn
release considerable free energy

5. Activation Energy

6. Enzyme practical - lipase
This practical gives you a chance to:
 investigate how lipase activity changes with
temperature
 consider how indicators can help us to
follow chemical reactions.
Procedure
SAFETY: Keep the phenolphthalein solution
away from naked flames.
Wear eye protection and quickly rinse any
splashes of enzyme solution or sodium
carbonate from the skin.

7. Induced Fit

8. 2H2O2 2H2O + O2
Example,
Hydrogen peroxide a substrate reacts with the enzyme catalase
producing water and oxygen
The active site is a flexible area so the enzyme and substrate
induces a closer fit

9. Effects of pH and Temperature
on Enzymes
Most biological fluids have a narrow pH band
between 6 and 8 and as a consequence most
enzymes work optimally in that range.
Changing pH can alter enzyme – substrate
binding.
High temperatures can the change active site and
denature protein structure stopping substrate
binding – above 500

10. Effect of Temperature
on Pepsin
Action of Pepsin
and Trypsin

11. Other factors affecting action
of Enzymes
Inhibitors
Chemical reactions that reduce action of enzymes.
Competitive inhibitors block the substrate entering the
active site by binding to it. They “mimic” the shape of
the substrate. E.g. poisons such as DDT, arsenic and
cyanide and penicillin blocks the active site which assists
the creation of cell walls by many bacteria
Non- competitive inhibitors bind elsewhere on the
enzyme changing shape of enzyme reducing enzyme-
substrate binding.

12. Cofactors
Many enzymes require non-protein cofactors to
assist their action.
Cofactors bind to an active site or substrate before
an enzyme can function
Cofactors include copper, iron, zinc as well as many
vitamins which are also known as co enzymes.

13. Physical and Chemical Factors
affecting the binding of Enzymes

14. Assessed practical design
Research
What is rennin?
Where is it normally found?
What does rennin do to milk?
What might you measure in this investigation?
Due …….