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
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.