Enzymes
30th September 2020
Learning objectives
• Define the term enzyme.
• Explain how enzymes work.
Big Picture
• Many reactions take place within our cells.
• These reactions are controlled by enzymes.
• Enzymes are proteins that act as biological catalysts.
• A catalyst is a substance that speeds up the rate of a
chemical reaction.
• Enzymes are chemicals that speed up a reaction but are not
changed by the reaction.
• Most enzymes in human cells work best at a temperature of
37°C, because this is our normal body temperature.
Enzymes are proteins
• Enzymes are proteins, and can be composed of hundreds of amino
acids.
• For example, human salivary amylase contains 496 amino acids.
• http://biology.kenyon.edu/BMB/jsmol2015/3BLKAmylase/index4.htm
l
Building up a starch
molecule
Student’s activity
Research on how
enzymes work.
Create a poster or
a powerpoint to
explain how
enzymes work.
Enzyme action
7th October 2020
• L.O Explain how enzyme works.
• Plan an investigation on the effect of temperature on enzyme activity.
Keywords
• Enzyme- A biological catalyst.
• Complementary- each piece fits
into each other like a key and a
padlock or a jigsaw.
• Substrate- The substance the
enzyme works upon such as a
glucose or maltose.
Enzyme action
• An example of an enzyme-controlled reaction is the
joining up of two glucose molecules to make a larger
molecule called maltose.
• You can see that the enzyme and substrate molecules
have complementary shapes (like adjacent pieces of a
jigsaw) so they fit together.
Other substrate molecules would not fit into this
enzyme as they would have the ‘wrong’ shape.
Can this enzyme act on the food substance?
Molecule of a substance
Other substrate molecules would not fit into this
enzyme as they would have the ‘wrong’ shape.
Can this enzyme act on the food substance?
A molecule of the substance
Building up ‘reaction’ involving an enzyme and a substrate
The product (substance AB) is released by the enzyme molecule
and the enzyme is then free to repeat the reaction with more
substrate molecules.
Breaking up reaction involving an enzyme and a substrate.
Enzyme action
• Molecules of the two substances might have combined
without the enzyme being present, but they would have
done so very slowly (it could take hours or days to happen
without the enzyme).
• By bringing the substances close together, the enzyme
molecule makes the reaction take place much more rapidly.
Enzyme action
• The process can be extremely fast: it has been found that
catalase, a very common enzyme found in most cells, can
break down 40 000 molecules of hydrogen peroxide every
second!
• A complete chemical reaction takes only a few seconds
when the right enzyme is present.
Students’ activity
• Use the worksheet provided to plan an investigation on the effect of
temperature on enzyme activity.
• Use the planning sheet to:
ØWrite down the research question
ØIdentify the variables
ØMake a hypothesis
ØMaterials needed
ØMethod used
ØSafety precautions
Temperature, pH and Enzymes
• L.Os
• Explain how temperature affects enzyme activity.
• Explain the effect of pH on enzyme activity.
14th Oct 2020
Temperature and enzyme activity
Temperature
At 370C (warm water)
At 200C (cold water)
At 4OC (ice water)
observation
The colour of iodine
changed from blue-black
to colourless.
The colour of iodine
changed to light blue.
The colour of iodine
changed to light blue.
Explanation
The enzyme broke down
starch into sugar. There is
no starch in the mixture.
The enzyme broke down
some starch into sugar.
The process was very slow.
The enzyme broke down
some starch into sugar.
The process was
extremely slow.
Temperature and enzymes
• Most enzymes in the human body work best at about
37°C, because this is our normal core body
temperature.
• The temperature at which an enzyme works best is
known as the optimum temperature.
Describe the shape of this graph?
As the temperature increases, the particles gain kinetic
Energy and move faster. The particles collide more frequently.
The enzyme collides with the substrate more frequently thus
Increasing the rate of reaction.
Above optimum temperature, the enzyme is denatured and
Therefore the rate of reaction decreases.
The rate of reaction increases as the temperature increases,
reaching a maximum at the optimum temperature for this
enzyme (close to 37 °C).
This section of the graph follows the same general pattern as
many other reactions: the rate of reaction approximately
doubles for every 10 °C increase in temperature.
If the temperature rises above the optimum for an enzymecatalysed reaction, the rate of reaction decreases very
quickly.
This is different to the rate/temperature graph for a reaction
catalysed by an inorganic compound, which will continue to
show an increased rate as temperature increases.
• An increase in temperature increases the rate of an
enzyme-catalysed reaction because it makes the
molecules move more.
• This increases the chances of a collision between the
active site of the enzymes and the substrate
molecules
If the temperature rises above an enzyme’s optimum
temperature, the shape of the enzyme will start to change.
This changes the shape of the active site as well, so the
substrate can no longer bind with the enzyme.
This will decrease the rate of reaction.
When the shape of the enzyme changes, the enzyme is
said to have been denatured.
pH
• Different enzymes work best at different pH values.
• For example, salivary amylase, pepsin and trypsin are all digestive
enzymes.
• Amylase digests starch into maltose. It has an optimum pH of 7.
• Pepsin, which digests proteins, has an optimum pH of 2.
• Trypsin is an enzyme produced by the pancreas. It also digests
proteins, by breaking them into small peptides. It has an optimum pH
of 8.5.