Quick test
1.
2.
3.
4.
5.
6.
7.
8.
What is the definition of a catalyst?
What type of molecule is an enzyme?
What is the active site?
What is the name of the substance that binds at the active
site?
What is a synthesis reaction?
What does specificity mean in the context of enzymes?
What type of enzyme breaks down proteins?
Name one process in the body that relies on enzymes
Starter questions on enzymes
•Enzymes _______ up the rate of chemical ________.
•Enzymes are ________ because they only work on one substrate.
•The substrate fits into the ________ site of the surface of the _______.
•Enzymes can be re-used, so only _______ amounts are needed.
•To which group of chemical compounds do enzymes belong? _________
•Why is an enzyme specific for a particular substrate?
_________________________________________
•Why can an enzyme be used again and again?
_________________________________________
Starter questions on enzymes
•Enzymes speed up the rate of chemical reaction
•Enzymes are specific because they only work on one substrate.
•The substrate fits into the active site of the surface of the enzyme
•Enzymes can be re-used, so only small amounts are needed.
•To which group of chemical compounds do enzymes belong?
Proteins
•Why is an enzyme specific for a particular substrate? The active site
of the enzyme is complementary to one type of substrate only.
•Why can an enzyme be used again and again? They are catalysts
which means that they allow the reaction to happen at a faster rate,
without being used up or changed themselves.
Factors affecting enzyme action
Learning objectives
Describe and explain the effect of temperature and
pH on the rate of enzyme catalysed reactions
Understand that denaturation results in a change to
the active site.
Exam technique
• DESCRIBE – what does it look like? Imagine
someone can’t see the graph/table. Give
enough detail so that they can picture exactly
what the pattern is.
• EXPLAIN – why does it look like that? Use
scientific knowledge to account for the
pattern described.
Describe how the rate of reaction of an enzyme reaction
changes at different temperatures
(always include data)
Optimum temperature
Rate
Of
Reaction
0
10
20
30
40
Temperature/oC
50
60
70
Describe
• As the temperature increases the rate of reaction
increases from 0oC to 40oC.
• The optimum temperature (peak rate of reaction) is
at 40oC.
• As the temperature increases beyond 40oC, the rate
of reaction decreases. (More rapidly than the
increase in rate to 40oC).
• The rate of reaction reaches 0 at 60oC
Explain why the rate of reaction of an enzyme reaction
changes at different temperatures
Optimum temperature
Enzyme molecules
are denaturing
Molecules gain
kinetic energy
Rate
Of
Reaction
All enzyme molecules
are denatured
0
10
20
30
40
Temperature/oC
50
60
70
Explain why the rate of reaction of an enzyme reaction
changes at different temperatures
0-40oC
An increase in temperature increases the kinetic energy of the enzyme and substrate
molecules.
The molecules move about faster and result in an increase in collisions resulting in
the formation of enzyme-substrate complexes.
Collisions are more frequent and energetic.
>40oC
High temperatures cause the amino acid chains to alter, which distorts the shape of
the active site.
The substrate can no longer fit at the active site – it has been denatured.
The enzyme is no longer able to catalyse the reaction.
In humans the optimum temperature for enzymes is 37oC
Explain
Optimum temperature
Enzyme molecules
are denaturing
Molecules gain
kinetic energy
Rate
Of
Reaction
All enzyme molecules
are denatured
0
10
20
30
40
Temperature/oC
50
60
70
Effects of pH on enzyme action
The activity of enzymes is also affected by pH
• Enzymes work best at an optimum pH.
• The pH change alters the forces that hold the amino acid chains in place at
the active site.
• Outside of its pH range the enzyme is denatured.
Optimum pH
pepsin
amylase
Rate
Of
Reaction
1
2
3
4
5
6
7
8
pH
9
10
11
12
Denaturing
• A change to the 3D shape of the active site of the
enzyme caused by high temperatures or a change in
pH.
• The enzyme no longer works as a catalyst.
• The damage can sometimes be irreversible
• The enzyme has NOT died….it was never alive!
Substrate
Substrate
Complementary
active site
Active site
changed
Enzyme
Enzyme is denatured
Describe and explain the effect of temperature on the
rate of the enzyme controlled reaction
Include these key words in your answer….
Denatured
Optimum temperature
Active site
Kinetic energy
Substrate
Reaction
Collision
Enzyme-substrate complex
Frequent
Energetic
Amino acid
Examples of enzymes in your body…
Enzyme
Use
Protease (in the stomach)
Breaking down proteins
Amylase (in the mouth)
Breaking down carbohydrates
Lipase (in the intestines)
Breaking down fats
Catalase (in the liver)
Breaks down hydrogen peroxide
Write a scientific clue/definition for the words below. There can only be 1
correct ‘splat’ to your question.
respiration
rate
shape
chain
amylase
amino acid
specificity
protease
lock & key
enzyme
biological
product
reaction
protein
synthesis
catalyst
active site
reactant
substrate
Practical next lesson……
• To investigate the effects of temperature on the
activity of pectinase in forming apple juice.
(Pectinase degrades pectin in the apples so that juice is
produced more readily)
Plan a practical
Include a step by step method
Identify the independent, dependent and control
variables
Safety points