Biological catalysts like enzymes act as catalysts in cells and are secreted by cells. Enzymes are protein catalysts that have an active site which binds specifically to substrate molecules. The active site facilitates the chemical reaction, converting the substrate to product, without being changed itself. Each enzyme only works on specific substrates. The rate of enzyme reactions is affected by temperature and pH levels, with an optimum level for maximum rate of reaction. Changes beyond this can denature the enzyme and disrupt its active site. Enzymes help drive many essential metabolic reactions in living things.

1. Biological catalysts
IGCSE Biology (Cambridge)

2.  A catalyst is a substance that speeds up the rate of
a chemical reaction but is not itself changed by the
reaction.

3. hydrogen peroxide
Hydrogen peroxide breaks down to water and oxygen
The escaping oxygen causes the foaming
2H2O2 2H2O O2+
water + oxygen
manganese oxide

4.  They occur inside cells or are secreted by the cells.
 Catalase is the enzyme that catalyses the break
down of hydrogen peroxide.
Enzymes act as biological catalysts
Catalase

5.  Proteins are long molecules that are folded into a specific shape.
catalase amylase trypsinpepsin
Enzymes are proteins

6. Active site:
Enzyme

7. Active site:
The site on the
enzyme where the
reaction occurs
Enzyme
Substrate molecules

8. Active site:
The site on the
enzyme where the
reaction occurs
Enzyme
Product molecules

10.  The lock and key hypothesis states that the active site specifically
matches the shape of the substrate molecule
enzyme
Each enzyme is specific to one substrate molecule
or type of molecule
active site

11.  At low temperatures enzyme controlled reactions go slowly
because the molecules have low kinetic energy.
The rate of an enzyme controlled reaction is
affected by temperature

12. But this only occurs up to the
optimum temperature
(usually about 40o
C)
The temperature at which
the rate of reaction is
fastest is known as the
optimum temperature
When temperature increases the reaction also
increases as the molecules have more kinetic energy

13. After the optimum temperature the heat causes
the enzyme to denature
 The enzyme changes shape and the active site no longer matches
the shape of the substrate molecule

14. protein polypeptides
trypsin
white clear
Controlled variables:
•Volume and concentration of substrate (milk)
•Volume and concentration of enzyme (trypsin)
•pH (controlled by buffers)
•Temperature

15. Rate
Of
Reaction
Temperature/o
C
0 10 20 30 40 50 60 70
Optimum temperature
Enzyme
is denaturing
Rate of reaction of an enzyme reaction changes
at different temperatures
Molecules gain
kinetic energy

16.  Enzymes prefer to work at an optimum pH. Outside of its pH range
the enzyme is denatured.
Rate
Of
Reaction
pH
1 2 3 4 5 6 7 8 9 10 11 12
pepsin amylase
The activity and shape of enzymes is also
affected by pH
Optimum pH

17.  Proteases break down the coloured, insoluble proteins that
cause stains to smaller, colourless soluble polypeptides.
 Can wash at lower temperatures

18.  Pectinase break down substances in
apple cell walls and enable greater
juice extraction.
 Lactase breaks down lactose in milk
into glucose and galactose.
This makes milk drinkable for lactose
intolerant people.

19. starch
embryo plant
amylase
secreted
maltose
absorbed

20.  Keywords:
enzyme
active sitesubstrate product
denaturetemperature
pH
optimum
catalase amylase
trypsin pepsinpectinase
lactase
protease
catalyst catalyse protein

21. www.clickbiology.com