This document discusses enzymes and how pH affects their activity. It begins with learning objectives about enzymes and describes them as proteins that speed up chemical reactions using an active site shaped to match reactants. A practical experiment is described where students investigate how different pH levels affect the enzyme catalase breaking down hydrogen peroxide. The results show that enzyme activity is greatest around pH 7 and lower at more extreme pH levels 4 and 9. The document also discusses how enzymes work using a lock-and-key model and how temperature affects biological processes.

1. IB4.2.2H Images
Enzymes and pH
Learning outcomes
summarise the role of enzymes in living
organisms
describe enzyme action in terms of active site
shape
describe the effect of pH on enzyme activity
Keywords- enzyme, pH, active site,
enzyme action, catalyst, reactants,
products, Lock and key model.
© Oxford University Press 2011

2. IB4.2.2H Images
What do you know about enzymes?
Write a list
© Oxford University Press 2011

3. IB4.2.2H Images
In B2 we learned that:
Enzymes are proteins that speed up
chemical reactions, in the context that
genes determine which proteins are made
in cells.
Enzymes can be thought of as catalysts
as well as agents that break large
molecules into smaller ones
© Oxford University Press 2011

4. IB4.2.2H Images
What effect does catalase (in celery)
have on hydrogen peroxide?
Discuss the role of catalase in cells.
What is hydrogen peroxide?
H2O2
© Oxford University Press 2011

5. IB4.2.2H Images
Watch the demonstration of the reaction of
catalase and hydrogen peroxide
Then carry out your investigation
You will consider the effect of different pH levels
Each group will carry put two (2) investigations
and results will be added to the board
© Oxford University Press 2011

6. IB4.2.2H Images
As a class we carried out a practical,
looking at the effect of enzymes on
pH. We started with 3 buffer
solutions of pH 4, pH 7 and pH 9.
we used yeast as the catalase and
added this to the hydrogen peroxide,
collecting the oxygen produced.
© Oxford University Press 2011

7. IB4.2.2H Images
What can we conclude from out
results
What happens?????????
What ‘reactants’ and ‘products’ in the
context of this particular enzyme.
Catalase + hydrogen peroxide  oxygen and water
© Oxford University Press 2011

8. IB4.2.2H Images
An enzyme
A computer
graphic of an
enzyme, its
active site, and
the product of a
reaction
© Oxford University Press 2011

9. IB4.2.2H Images
How does the enzyme speed up the reaction? look at
the first two screens of Animation IB4.2.4 Enzymes
introducing the idea of the lock-and-key model.
complete Activity AB4.2.2 Lock-and-key model using
Textbook Section B and Animation IB4.2.4 Enzymes.
© Oxford University Press 2011

10. IB4.2.2H Images
Enzyme
animations
© Oxford University Press 2011

11. IB4.2.2H Images
Your core body
temperature is about
37°C, but a small
variation either side of
this is normal. a core
temperature over
42°C or under 28°C
usually results in
death.
© Oxford University Press 2011

12. IB4.2.2H Images
Around 80% of the energy from your food
is used for keeping warm © Oxford University Press 2011

13. IB4.2.2H Images
Shrews have a large surface area
for their volume. They lose heat to
the environment over their whole
body surface. To release enough
energy to maintain their body
temperature, they have to eat 75%
of their body mass in food each
day.
© Oxford University Press 2011