Enzymes are protein catalysts that speed up metabolic reactions inside cells. They have specific active sites that allow only certain substrate molecules to bind via lock and key interactions. Enzymes can be intracellular, acting inside cells, or extracellular, acting outside cells. Experiments show that enzyme activity is optimized at certain temperatures and pH levels, and outside those ranges enzymes become denatured and lose function. Biological detergents use enzymes that can function at low temperatures, providing environmental advantages over traditional detergents.

1. ENZYMES

2. What are ‘enzymes’?
 enzymes are protein in nature and act as
catalysts

3. Catalysts are
 chemical substances which speed up
metabolism (chemical reactions inside cells)

4. Enzymes are needed e.g. for digestion
Examples of enzymes:
Lipase
Maltase
Sucrase
Lactase
Amylase

5. Naming Enzymes
A short name ending in :
Lipase
Maltase
Sucrase
Lactase
Amylase
Except exist:
Pepsin
Trypsin

6. Enzymes :
Exert their
Produced
function both
inside cells inside & outside
the cell

7. Extracellular Intracellular
enzymes enzymes
 act outside a cell  act inside a cell
Respiration

9. Lock and Key theory explains how
enzymes work

10. Lock and Key theory
Bond formation
Bond breaking

11. Question: MAY, 2008
a) What is an enzyme? (2)
An enzyme is a protein which speeds up a
chemical reaction i.e. a biological catalyst.

12. b) Explain, using diagrams, why an enzyme acts
on just one particular substrate. (3)
Enzymes have a specific site known as the
active site. The active site has a specific
‘shape’ to which only a specific substrate will
fit. When different substrates collide with an
enzyme, only the substrate with a
complementary shape will fit the enzyme.
(Lock and Key hypothesis)

13. Properties of enzymes
1. Enzymes are always proteins
2. Enzymes are specific in their action
3. Enzymes can be used all over again

14. Properties of enzymes
4. Enzymes are destroyed (denatured) by heat
Protein in egg white is
denatured by cooking.

15. Substrate CANNOT fit in active site
Enzyme + Enzyme
substrate denatured by
heat or extreme
pH
Denatured enzyme
cannot combine
with substrate

16. Wrong to say ‘enzyme is killed’

17. Fig. 2 Graph to show the effect of
temperature on the rate of reaction.
Enzyme becomes
denatured above
the optimum
temperature.

18. Temperature Affects Enzyme Action:
 Little activity at low temperature
 Rate increases with temperature
 Most active at optimum temperatures (usually
37°C in humans)
 Activity lost with denaturation at high
temperatures
18

19. Properties of enzymes
5. Enzymes are sensitive to pH
 enzymes are denatured by extremes of
pH
Rate of reaction
pH

20. Fig. 3 Graph to show the effect of pH
on the rate of four different enzymes.
What is the optimum pH of pepsin?

21. ONE use of enzymes
 Enzymes are obtained from bacteria and are
used to make biological detergents.

22. Question: [SEP, 2010]
a) Explain why biological detergents can only
be effective when used in low temperatures.
(2)
Enzymes are proteins whose shape is
affected by temperature.
Above their optimum temperature, enzymes
become denatured.
The substrate does not fit in active site.

23. Question: [SEP, 2010]
b) Give TWO environmental advantages
associated with the use of biological washing
powders. (4)
1) No harm is done to the environment as they
are natural products.
2) As they work at low temperatures, there is
no need to heat the water. Thus less fossil
fuels need to be burned.

25. Two experiments:
Effect of temperature
Effect of pH

26. Aim: To investigate the effect of temperature
on the activity of amylase.

27. A dropping/spotting tile

29. Aim: To investigate the effect of pH on
the activity of catalase.
Catalase is found in potatoes and liver.

30. Froth height is an
indication of the
reaction.

31. CONCLUSION:
Catalase is most
active at around
pH 9 but works
fairly well over a
range of pH from
about 7 to 11.

32. Which
material (liver
or potato)
contains more
catalase?
Liver

33. The End