Pre assessment
1 What are the monomers of proteins? Tick 1 correct answer
A lipids
B fatty acids and glycerol
C amino acids
D glucose
E starch
2 Proteins are used in the body for __________________ and repair in the body. Fill in the blank
3 What is a catalyst? Tick 1 correct answer
A a substances that slows down chemical reactions
B a substances that stops chemical reactions
C a substances that speeds up chemical reactions
Enzymes: function,
structure and
specificity
Biological molecules and enzymes
Learning objectives
To describe how enzymes are used as biological catalyst and how it works.
Outcome
I can explain what an enzyme is and why the shape of an
enzyme is important for how it works.
Keywords
enzyme
catalyst
active site
substrate
model
Lesson outline
Enzymes: function, structure and specificity
Enzyme function
Enzyme structure
Enzyme specificity
Enzyme function
Explanation
All organisms are made of one or more cells.
All cells contain biological
molecules called enzymes.
Enzymes are critical for life.
They are essential for all
biological processes.
Without enzymes, life on
Earth would not exist.
Animal cells
Plant cells
Enzyme function
Explanation
Chemical reactions in cells happen
millions of times faster with
enzymes than without.
Without enzymes, many chemical
reactions would not happen quickly
enough to keep cells alive.
Rate of reaction
Enzymes are critical because they
speed up the rate of chemical reactions.
They act as biological catalysts.
without with
enzyme enzyme
Enzyme function
What is an enzyme?
a
a chemical reaction
b
a biological catalyst
c
a lock and key
Check
Enzyme function
Explanation
Some industrial chemical processes use catalysts to
speed them up.
For example:
N2
+
3H2
(nitrogen)
(hydrogen)
Fe
(iron)
catalyst
2NH3
(ammonia)
These catalysts are not enzymes. They are not biological molecules.
Enzyme function
Explanation
Some processes in cells happen without enzymes.
One example is diffusion, which
happens because of the random
motion of particles.
Diffusion moves particles of
substances into, around and out
of cells.
random motion
of particles
Simulation by PhET Interactive Simulations,
University of Colorado Boulder, licensed
under CC-BY-4.0 (https://phet.colorado.edu)
Enzyme function
Explanation
But enzymes are essential to control a vast range of
chemical reactions that happen within and outside of cells.
respiration
photosynthesis
immune
responses
muscle
contraction
protein
synthesis
digestion
Life on Earth is able to exist in all its complexity and diversity
as a direct result of enzymes.
Enzyme function
Check
Which of these reactions are controlled by enzymes?
Fe
(iron)
catalyst
N2 + 3H2
2NH3
Haber process
diffusion
photosynthesis
a
b
c
Task A
Enzyme function
Practice
1. Write a definition for the term ‘enzyme’.
2. List three biological processes that use enzymes.
3. Draw a bar chart which shows the change in rate of
reaction without and with an enzyme.
4. Enzymes are made from amino acids. What type of
biological molecule must they be?
Task A
Enzyme function
Feedback
1. Write a definition for the term ‘enzyme’.
An enzyme is a biological catalyst that speeds up the rate of
a chemical reaction without being used up.
2. List three biological processes that use enzymes.
You may have included respiration, photosynthesis, movement,
digestion, immune response, protein synthesis, cell division, or
other biological processes which require enzymes.
Task A
Enzyme function
Feedback
Your graph should look like the one
shown.
4. Enzymes are made from amino acids.
What type of biological molecule must
they be ?
Amino acids are joined together to make
proteins, so enzymes must be proteins.
Rate of reaction
3. Draw a bar chart which shows the difference in the rate
of reaction without and with an enzyme.
without
enzyme
with
enzyme
Lesson outline
Enzymes: function, structure and specificity
Enzyme function
Enzyme structure
Enzyme specificity
Enzyme structure
Explanation
An enzyme is a protein.
a protein molecule
It is made of amino acids built into a chain, folded into a
complex 3D shape.
Enzyme structure
Explanation
The shape of an enzyme includes
an active site.
active site
This is where the chemical reaction
takes place.
Enzymes are not used up in their
reactions: they are free to catalyse
reactions over and over again.
enzyme
a simplified diagram of
an enzyme
Enzyme structure
Explanation
During an enzyme reaction:
substrate
products
active
site
enzyme
the substrate(s)
binds to the
active site
an enzymesubstrate complex
is formed
the product(s) is
released and the
enzyme is reused
Enzyme structure
Check
Put these phases of the enzyme reaction in the
correct order.
a
The enzyme-substrate complex is formed. 2
b
The product is released.
3
c
The substrates bind to the active site.
1
Enzyme structure
activation energy
without enzyme
with enzyme
Energy
When the enzymesubstrate complex forms,
this lowers the activation
energy so that less energy
is required in the reaction.
Explanation
This causes the rate of the
reaction to increase.
Reaction time
Enzyme structure
Check
True or false?
When the substrate binds to the active site, an enzymesubstrate complex forms.
T True
F
False
Justify your answer
a
This increases the activation energy so the reaction can
happen faster.
b
This lowers the activation energy so the reaction can
happen faster.
Task B
Enzyme structure
Practice
1. Draw a labelled diagram to show the key steps in an
enzyme-controlled reaction.
You must include drawings and labels of:
– substrate
– active site
– enzyme
– enzyme-substrate complex
– products
2. Explain what happens to the enzyme at the end of the
reaction, and why this is beneficial.
Task B
Enzyme structure
Feedback
1. Draw a labelled diagram to show the key steps
in an enzyme-controlled reaction.
active site
enzyme
substrate
enzyme-substrate
complex
products
Task B
Enzyme structure
Feedback
2. Explain what happens to the enzyme at the end of the
reaction, and why this is beneficial.
Your answer should include:
● The enzyme is not used up in the reaction.
● It is available to catalyse another reaction.
● This is beneficial because one enzyme can catalyse the reaction
many times.
● Fewer enzymes are required, and the reaction can occur more
efficiently.
Lesson outline
Enzymes: function, structure and specificity
Enzyme function
Enzyme structure
Enzyme specificity
Enzyme specificity
Explanation
We can use a lock and key as a model of an enzyme
and substrate.
In this model:
the lock is
the enzyme
the keyhole is the active site
the key is the
substrate
Enzyme specificity
Explanation
Locks are specific for their key.
Keys come in many
different shapes.
But only one key
has the correct
shape …
… to fit into the
lock’s keyhole.
Enzyme specificity
Explanation
Enzymes are specific for their substrate.
Substrate molecules
can have many
different shapes.
But only one
substrate has the
correct shape …
… to fit into
the enzyme’s
active site.
Enzyme specificity
Explanation
Because an enzyme is specific for its substrate, each
enzyme can only catalyse one chemical reaction.
substrate 1
enzyme X
substrate 2
enzyme Y
substrate 3
enzyme Z
Different chemical reactions need different enzymes.
Enzyme specificity
Check
Match the enzyme to its substrate.
a
d
b
e
c
f
Enzyme specificity
Each enzyme is highly specific. It can only catalyse
one chemical reaction.
Most enzymes have the ending -ase.
● Enzymes that break down carbohydrates are called
carbohydrases.
● Enzymes that break down proteins are called proteases.
What do you think enzymes are called which break down
lipids (fats)?
● These are called lipases!
Explanation
Enzyme specificity
Explanation
To summarise:
carbohydrates
proteins
lipids (fats)
carbohydrases
proteases
lipases
sugars
amino acids
fatty acids and
glycerol
Enzyme specificity
What is the name of the group of enzymes that
break down fats?
a
carbohydrases
b
proteases
c
lipases
Check
Task C
Enzyme specificity
Practice
1. Using the words below, describe how an enzyme catalyses a
biological reaction.
specific
catalyse
activation energy
used up
shape
active site
substrate
2. Use the lock and key model to explain enzyme specificity.
Task C
Enzyme specificity
Feedback
1. Using the words below, describe how an enzyme catalyses a
biological reaction.
specific
catalyse
shape
activation energy
used up
active site
substrate
Example answer:
Enzymes catalyse biological reactions but are not used up
themselves.
The substrate fits the enzyme’s active site: it is a specific shape like
a lock with a key.
When the substrate binds, the activation energy is lowered which
increases the rate of the reaction.
Exit questions
1 Match each keyword to its meaning. Write the correct letter in each box
2 True or false? All enzymes are proteins. Tick 1 correct answer
True
False
Exit questions
3 Put the following steps in order to describe how an enzyme works. Use numbers to show
the correct order
4 What part of the enzyme is A? Fill in the blank
Exit questions
5 Who is correctly describing the effect of adding an enzyme on the activation energy
of an enzyme-controlled reaction? Tick 1 correct answer
Andeep: Enzymes increase the activation
energy so the reaction happens faster.
Lucas: Enzymes lower the activation
energy so the reaction happnes faster.
Summary Enzymes: function, structure and specificity
● Enzymes are proteins that catalyse chemical reactions but are
not used up during them.
● The substrate binds to the enzyme at its active site and forms an
enzyme-substrate complex, before the products are released.
● When the substrate binds to the enzyme, this lowers the
activation energy of the chemical reaction.
● Each enzyme is specific to its substrate, like a lock and key.
● Life on Earth would not exist without enzymes.