P.101
Enzyme reaction rates and activity are influenced by several factors.
What kind of effect do
● Temperature
● pH
● substrate concentration
have on the activity of enzyme.
Draw in your notebook simple graphs that illustrate every situation with different
parameters.
Specify what variables you have, dependent & independent and how to put them on
axes. Write everything down naming them.
Explain the effects of all: temperature, pH & substrate concentration on enzyme activity.
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At first do this just in general form to an enzyme.
Use the help of book pages 96-104, read this first.
If you are quick with this part, go check https://ib.bioninja.com.au/standard-level/topic-2molecular-biology/25-enzymes/enzyme-experiments.html and choose a real enzyme
and reaction.
Check key:
Enzyme reaction rates are influenced by
Increasing the concentration of reactants (substrates) increases the rate of reaction by
increasing the frequency with which substrate molecules collide with enzyme molecules. If the
concentration of substrates is increased beyond a certain point, called the point of saturation,
then there will not be a further increase in enzyme activity since the enzymes would already be
contacting substrates at the maximum rate possible.
As the temperature increases there is more movement of molecules and therefore more
collisions between enzymes and substrates – so the enzyme activity increases. However, there
is a limit to which enzyme activity can increase because at a certain temperature an enzyme will
denature.
When the pH is too acidic or too basic for an enzyme, its hydrogen bonds begin to break,
causing its active site to change its shape. An altered active site can’t bind with its substrate so
enzyme activity decreases. If the pH is too unfavorable then covalent bonds can break, causing
the enzyme to denature.
Denaturation is a permanent structural change in a protein that results in a loss of its biological
properties. In other words, some chemical bonds break, and the active site is destroyed.
Human enzymes can denature in individuals running a high fever.
Some arctic fish have enzymes that denature at 10ºC.
The enzymes of some thermophilic bacteria denature at 85ºC.
When designing an experiment to test the effect of factors affecting enzyme activity, the three key
decisions to be made are:
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●
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Which factor to investigate (i.e. the independent variable)
Which enzyme / substrate reaction to use
How to measure the enzyme activity (i.e. the dependent variable)
Choosing the Independent Variable
The main factors which will affect the activity of an enzyme on a given substrate are:
● Temperature (use water baths to minimise fluctuations)
● pH (acidic or alkaline solutions)
● Substrate concentration (choose range to avoid saturation)
● Presence of inhibitor (type of inhibitor will be enzyme-specific)