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9.2 Maintaining a Balance
The Role of Enzymes
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Where does it fit in the Syllabus?
1. Most organisms are active in a limited temperature
range
Students learn to:
• identify the role of enzymes in metabolism,
describe their chemical composition and use a
simple model to describe their specificity on
substrates
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Where does it fit in the Syllabus?
Students learn to:
• identify the role of enzymes in
metabolism
• describe the chemical composition of
enzymes
• describe an enzyme’s specificity on
substrates using a simple model.
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Identifying the role of enzymes on
metabolism
Let’s see what you remember…
Question 1
Metabolism is a term used to describe….
a. All the chemical processes occurring in the body
b. Only the chemical processes associated with
digestion
c. Only the chemical processes associated with
respiration and circulation.
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Identifying the role of enzymes on
metabolism
Question 1
Metabolism is a term used to describe….
a. All the chemical processes occurring in the body
EXCELLENT!!!
All the processes of chemical and physical change
which goes on in the living organism are a part of
metabolism. Building up of new tissue, replacing of old
tissue, converting food to energy, disposing of waste
materials, etc – all the activities that maintain our lives!
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Identifying the role of enzymes on
metabolism
Question 1
Metabolism is a term used to describe….
b. Only the chemical processes associated with
digestion
NICE TRY!!!
Metabolism is the process of chemical and physical
change which goes on continually in the living
organism for it’s maintenance. Whether it is producing
new tissue, replacing of old tissue, converting food to
energy or disposing waste material – metabolism
consists of all the activities that help maintain our life!
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Identifying the role of enzymes on
metabolism
Question 1
Metabolism is a term used to describe….
c. Only the chemical processes associated with
respiration and circulation.
Getting there!!!
Metabolism is the process of chemical and physical
change which goes on continually in the living
organism for it’s maintenance. Whether it is producing
new tissue, replacing of old tissue, converting food to
energy or disposing waste material – metabolism
consists of all the activities that help maintain our life!
TRY AGAIN?
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Identifying the role of enzymes on
metabolism
Question 2
There are two basic phases of metabolism – these are
called Anabolism and Catabolism.
Which of the following answers best defines these phases?
a. Catabolism involves the synthesis of large molecules
from smaller ones, while Anabolism is the breakdown
of large molecules to smaller ones.
b. Anabolism involves the synthesis of large molecules
from smaller ones, while Catabolism is the
breakdown of large molecules to smaller ones.
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Identifying the role of enzymes on
metabolism
Question 2
Which of the following answers best defines these phases?
a. Catabolism is the synthesis of large molecules from
smaller ones, while Anabolism is the breakdown of
large molecules to smaller ones.
almost!!!
This is often one of those concepts that is
easy to be confused by, but a simple way to
think of it is the ABCD of Metabolism –
Anabolism Builds, Catabolism Destroys.
In the image on your left Anabolism is
shown by the green arrows, whereas
Catabolism is shown by the orange arrows
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Identifying the role of enzymes on
metabolism
Question 2
Which of the following answers best defines these phases?
b. Anabolism is the synthesis of large molecules from
smaller ones, while Catabolism is the breakdown of
large molecules to smaller ones.
Great work!!!
A simple way to remember this is the ABCD
of Metabolism – Anabolism Builds,
Catabolism Destroys.
In the image on your left, Anabolism is
shown by the green arrows, whereas
Catabolism is shown by the orange arrows
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Identifying the role of enzymes on
metabolism
Great work!
After answering these two questions, we now
understand that metabolism is important for
life to function, & that the phases of
metabolism include
• Anabolism (synthesizing large molecules or
products from smaller molecules) &
• Catabolism (breaking down large molecules or
products to smaller molecules).
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Identifying the role of enzymes on
metabolism
These reactions
can sometimes
occur without
assistance, but
the rate of
metabolic
reaction is rather
low, because of
the energy
demand.
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Figure 1. Activation energy requirements without catalyst
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Identifying the role of enzymes on
metabolism
However, metabolic reaction is increased with the
presence of enzymes which are biological catalysts,
which require lower energy. This means that it is
involved, but not changed by a chemical reaction.
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Figure 2. Activation energy requirements without catalyst and with enzyme catalyst
Describe the chemical composition
of enzymes
Question 3
So what is an enzyme’s composition?
a. Enzymes are made up of amino acids
b. Enzymes are protein molecules that have different
compositions depending on their function.
c. All of the above
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Describe the chemical composition
of enzymes
Question 3
So what is an enzyme’s composition?
a. Enzymes are made up of amino acids
Partly right!!!
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Fig 3. Structure of αAmylase, an enzyme in
Human Saliva
The major chemical composition
of enzymes is proteins.
These proteins are made up of
amino acids which are joined by
peptide bonds.
The chemical composition of
these amino acids can determine
the function of the enzyme.
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Describe the chemical composition
of enzymes
Question 3
So what is an enzyme’s composition?
b. Enzymes are protein molecules that have different
compositions depending on their function.
Partly right!!!
TRY AGAIN?
Fig 3. Structure of αAmylase, an enzyme in
Human Saliva
The major chemical composition
of enzymes is proteins.
These proteins are made up of
amino acids which are joined by
peptide bonds.
The chemical composition of
these amino acids can determine
the function of the enzyme.
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Describe the chemical composition
of enzymes
Question 3
So what is an enzyme’s composition?
c. All of the above
That’s right!!!
TRY AGAIN?
Fig 3. Structure of αAmylase, an enzyme in
Human Saliva
The major chemical composition
of enzymes is proteins.
These proteins are made up of
amino acids which are joined by
peptide bonds.
The chemical composition of
these amino acids can determine
the function of the enzyme.
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Describe the chemical composition
of enzymes
Enzymes, as we know, interact with other
substances to undergo chemical reactions. We
also know that their chemical composition
determines what they react with. The chemicals
that enzymes react with are called substrates.
So let’s see how enzymes and substrates
interact…
Enzyme
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Different
Substrates
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Describe an enzyme’s specificity on
substrates using a simple model.
Enzymes are designed to accommodate certain
substrates to undergo a chemical reaction. This
reaction occurs at a specific site on the enzyme
called the active site
Enzyme
(with a red
active site)
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Substrates
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Describe an enzyme’s specificity on
substrates using a simple model.
When the substrate/s meet at the active site of
the enzyme and interact, this is called the
enzyme-substrate complex.
In the example below, this interaction leads to
the two substrate components forming a
combined product.
Enzyme
(with a red
active site)
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Two Substrates
forming a larger
compound
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Describe an enzyme’s specificity on
substrates using a simple model.
Question 4
What kind of reaction is occurring in each example?
a. Example A – Catabolism, Example B – Anabolism
b. Example A – Anabolism, Example B – Catabolism
Enzyme
Enzyme
A
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Substrate/s
B
Substrate/s
Describe an enzyme’s specificity on
substrates using a simple model.
Question 4
What kind of reaction is occurring in each example?
a. Example A – Catabolism, Example B – Anabolism
That’s right!!!
This model shows the
enzyme breaking the large
product into separate
substrates = catabolism
Enzyme
A
TRY AGAIN?
This model shows the enzyme
assisting the smaller substrate
components form to a large
product = anabolism
Enzyme
Substrate/s
B
Substrate/s
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Describe an enzyme’s specificity on
substrates using a simple model.
Question 4
What kind of reaction is occurring in each example?
b. Example A – Anabolism, Example B – Catabolism
Almost there!
This model shows the
enzyme breaking the large
product into separate
substrates = catabolism
Enzyme
A
TRY AGAIN?
This model shows the enzyme
assisting the smaller substrate
components form to a large
product = anabolism
Enzyme
Substrate/s
B
Substrate/s
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Describe an enzyme’s specificity on
substrates using a simple model.
• To look at the overall reaction as an equation
would look like this:
E + S ↔ ES↔ P + E
where
E = Enzyme
S = Substrate
ES = Enzyme–Substrate Complex
P = Product
NB. Notice how the Enzyme remains unchanged throughout the whole reaction
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Describe an enzyme’s specificity on
substrates using a simple model.
This model below demonstrates how enzymes
are substrate specific. This particular model is a
‘lock and key model’. The appropriate substrate
(the ‘key’) is the proper fit for the enzyme (the
‘lock’). Inappropriate substrates may not interact
with the enzyme.
Enzyme
Enzyme
Appropriate
Substrates
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Inappropriate
Substrates
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Describe an enzyme’s specificity on
substrates using a simple model.
Question 5
Which example provides the best comparison to the ‘lock
and key’ model?
a. A basketball fitting into a basketball hoop
b. A hand fitting into a glove
c. A USB fitting in a USB port
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Describe an enzyme’s specificity on
substrates using a simple model.
Question 5
Which example provides the best comparison to the ‘lock
and key’ model?
a. A basketball fitting into a basketball hoop
NOT QUITE THERE…
This example has many limitations, namely that
the basketball itself (as a substrate or product)
does not necessarily bind to an active site on the
basketball ring. Also, the basketball is not
metabolized in any fashion by the ring. The
basketball ring does not change amidst the
reaction, which is a common trait between it and
the enzyme.
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Describe an enzyme’s specificity on
substrates using a simple model.
Question 5
Which example provides the nearest comparison to the
‘lock and key’ model?
b. A hand fitting into a glove
Not quite…
This example has many limitations, namely that
the glove itself might need to expand or shrink to
accommodate the hand. There is an active site on
the inside lining of the glove, so it does have a
common element with an enzyme, but perhaps not
one in which there is a reaction that occurs without
the glove being affected.
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Describe an enzyme’s specificity on
substrates using a simple model.
Question 5
Which example provides the best comparison to the ‘lock
and key’ model?
c. A USB fitting in a USB port
WELL DONE!!!
This example demonstrates a reasonable
comparison to the ‘lock and key’ model. They are
both specific ( a USB port can’t interact with a CD
or pencil for instance), so there is a highly specific
active site, and the substrate (the USB) could
undergo a reaction (if only by its data) from it’s
interaction with the port.
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Describe an enzyme’s specificity on
substrates using a simple model.
Another model used to demonstrate enzyme –
substrate interactions is the ‘induced fit’ model.
In this model, the enzyme’s active site alters to
accommodate the specific substrate/s for which
it reacts.
Enzyme
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Describe an enzyme’s specificity on
substrates using a simple model.
Question 6
Which example provides the best comparison to the
‘induced fit’ model?
a. A tyre fitting on a car
b. A softball fitting in a catcher’s mitt or hand
c. An appliance fitting in an operating power socket
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Describe an enzyme’s specificity on
substrates using a simple model.
Question 6
Which example provides the best comparison to the
‘induced fit’ model?
a. A tyre fitting on a car
On the right track…
This example is actually more suited to perhaps a
lock and key approach. What it has in common is
an active site, but the enzyme (in this instance a
car) doesn’t reshape itself to accommodate the
tyre.
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Describe an enzyme’s specificity on
substrates using a simple model.
Question 6
Which example provides the best comparison to the
‘induced fit’ model?
b. A softball fitting in a catcher’s mitt or hand
Excellent!
This example is a good model of the
‘induced fit‘ enzyme–substrate
interaction. The ball, being the
substrate is easily accommodated by
the mitt (or enzyme) which then
changes it’s active site to better
accommodate the substrate.
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Describe an enzyme’s specificity on
substrates using a simple model.
Question 6
Which example provides the best comparison to the
‘induced fit’ model?
c. An appliance fitting in an operating power socket
Not exactly…
This example actually is much more of a ‘lock
and key’ model. If we were to talk about the
bread in this image as a substrate however, we
would notice that the bread rack (a possible
enzyme active site) may press firm against the
bread, and is an induced fit, but the appliance
and the socket don’t share the same comparison
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Well done!!!
You have completed this lesson on enzymes
which will provide you with a basis to do your
research task where you will need to develop your
own model to describe enzyme-substrate
interactions!
If you would like to go back to any questions, click
on the images below…
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Question 1
Question 2
Question 3
Question 4
Question 5
Question 6
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start
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Revision Page
Question 1
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References
Images sourced from the following:
• (1-2)
Nature Education, (2010). Figure 3: Enzymes and activation
energy, Protein Function, Nature Education.
http://www.nature.com/scitable/topicpage/proteinfunction-14123348
• (3)
Ramasubbu, N., Paloth, V., Luo, Y., Brayer, G.D., Levine, M.J.
(1996). Structure of human salivary alpha-amylase at
1.6 A resolution: implications for its role in the oral
cavity, Acta Crystallographica, 52(3). 435 –446.
DOI:10.1107/S0907444995014119