GETTING TO KNOW ENZYMES
Name:_______________________________
Click on: All Programs -> Science-> sunflower for science-> (side tab) Biology-> enzymes->
worksheets-> Speeding up reactions-Extension.
Activity 1:
Speeding up Reactions (Extension)
Follow most of the instructions on the screen but write the answers on the work sheet. A couple of
questions have been changed a little and some have been omitted.
Introduction:
Most food molecules are too big to pass through the wall of the gut into your blood. They need
to be broken into smaller molecules first. Enzymes make the reactions happen quickly. They are
biological catalysts. They speed up all the reactions in your body (eg. The reactions that form the
steps of cellular respiration); not just breaking down food. You can’t live without them.
Key words:
Write a brief but precise definition for each of the following:
Enzymes: a protein catalyst that speeds up the rate of a reaction by lowering the activation
energy and without being change by the reaction it is catalysing
Substrate: The substance/molecule that the enzyme binds to.
Product: The molecule or molecules release from the active site of the enzyme after the
reaction is complete
Active site : The specific part of the enzyme molecule to which its substrate binds. (the shape
of the active site on an enzyme is complementary to a portion of the substrate molecule in
terms of shape and charge. The two fit together very precisely which accounts for the specific
nature of enzyme action)
Catalyst : In general terms a catalyst is something which speed up the rate at which a process
occurs.
The programme is a simulation of a reaction. The reaction needs an enzyme. The substances
that react are called the substrates.
a) Select from the following terms to label the molecules involved in the reaction shown.
Words: substrate, product, enzyme, label the molecule (words can be used more than once
if required)(2)
b) Explain why an enzyme can be used over and over again to make molecules react.(2)
An Enzyme is unchanged by the reaction it catalyses.(1) (it speeds up a reaction between
substrates or within a substrate, but in itself the enzyme doesn’t react WITH them)
AND
Once the product is formed it is released from the active site leaving the enzyme is free to
collide with more substrate and catalyse further reactions.(1)
(this is why a small amount of enzyme can catalyse a large amount of substrate
1. The program now shows a different reaction. Describe the differences between this reaction
and the reaction in questions 1? In your answer use the words “break” and “build” (2)
The reaction shown in question 1 is a build-up/anabolic reaction; the enzyme (c) catalyses
the bonding of substrate (a) and substrate (d) to form the product (b).
This reaction is different because it involves the break-down of the substrate into two
products. This is a catabolic reaction.
2. The substrate molecules binds to a part of the enzyme called the active site. Describe what
happens in an anabolic(building up) enzyme driven reaction using the words substrate,
molecules, active site, enzyme, enzyme substrate complex and product.(4)
There is an effective collision between the enzyme molecule and the substrate molecules
enabling the substrates to bind to the active site of the enzyme molecule to form an
enzyme substrate complex. The joining/bonding of the substrates is catalysed by the
enzyme and the product is released from the active site. The enzymes is then free to bind
with other substrates and catalyse their joining.
3. The simulation now shows two reactions at the same time.
a) Why does each reaction need a different enzyme?(2)
Enzymes are specific in their action (1) Each one has a unique active site that will be
complementary in shape(and charge) to only one substrate, so each different substrate requires
its own particular enzyme.(1)
OR a slightly different approach
Each reaction involves different substrates which have a unique shape.(1) Each substrate will only
bind with an enzyme whose active site is a complementary match in terms of shape and charge. So
each differently shape substrate will need a different enzymes that will match it precisely. (1)
b) One theory about how enzymes function is called the “lock and Key” theory. Explain
what you think this means? (2)
Below are two sample responses
That the shape of the enzyme and substrate are a perfect complementary fit(1), like a lock that
only has one key that will fit precisely and open it.(1) So Only if the enzyme is a perfect fit will it
bind with a catalyse a reaction in a substrate.
OR
A lock will usually only open with a particular key. They are designed to fit together because their
shapes are perfectly complementary. (1) Without the right key you cannot open the lock. A
enzymes I like the key for the it needs to fit the shape of the active site of the enzyme very
precisely or the reaction won’t be catalysed.(1)
4. a) If you add more substrate to a reaction involving an enzyme it will speed up. Why?(2) Use
the term effective collision in your answer.
It will initially speed up the rate of the reaction.
As you increase the number of substrate molecules there will be more of these molecules moving
around and colliding with each other and with the enzymes, thus the likely hood of an effective
collision is increase.
b) However there will come a point where adding more substrate will have no effect on the
rate. Why (3)
At some point enzyme saturation will be reached.(1) At this point all active sites are
occupied by substrate at any moment in time. (as soon as a product is released a new
substrate immediately collides with the active site )(1) The reaction is happening as fast as
it can in the conditions provided and adding more substrate can’t increase the reaction
rate as there are not extra enzymes for this to bind to(1)
Activity 2: Right conditions
Open worksheet for activity 2: worksheets-> Right Conditions -Extension.
Key words:
Write a brief but precise definition for each of the following:
Optimum : = best. In the context of enzymes optimum refers to the value of a particular
factor that produces the highest enzymatic reaction rate for a specific reaction. Generally you well
be interested in determining the optimum pH or temperature for the action of an particular
enzyme.
Inactive: an enzyme is not catalysing a reaction due to the absence of effective collisions
with a substrate. An example of this would be a sample of enzyme that is frozen.
Denatured: The three dimensional structure (tertiary structure) of the enzyme has be
permanently altered, causing the active site of the enzyme to be changed/deformed so that it can
no longer bind with its usual substrate.
NOTE: this terms refers to the enzyme, not to the active site. Eg. The enzyme was
denatured, NOT the active site was denatured.
1. The simulation shows an enzyme controlled reaction
a) At what temperature is the reaction fastest? (adjust the temperature with the slider to
find out.(1)
37 degrees Celsius
b) As the temperature increases (up to the optimum temperature) the rate of the reaction
increases. Why?(2)
 Because as temp. increases the kinetic energy of the enzyme and substrate
molecules increase(1).
 As they are moving faster they will collide more frequently resulting in more
frequent effective collisions between enzyme and substrate(1) resulting in an
increase in the reaction rate.
c) Use the slider to increase the temperature above the optimum. Watch closely. What
happens to the enzymes?(1) they start to change shape/become denatured/their
active sites become deformed.
Suggest why the rate of reaction decreases above this temperature.(3)



Above the critical temperature enzymes become denatured and their active
site becomes changed/deformed.
Therefore the substrate is no longer able to bind with the enzyme
And the reaction can therefore no longer be catalysed by this enzyme which
will lower the reaction rate overall
d) Why is the optimum temperature for most human enzymes about 40 degrees C(1)
Change this to one mark. This question could just have easily said 37oC; resources also
say optimum temp for human enzymes is about 37 not 40.
Human core temperature is maintained at about 37degrees celsius. (1)
Since human enzymes work inside of our bodies you would expect them to function
optimally at core body temperature.
e) Suggest why hypothermia has such a devastating effect of the body(2) I(think this
should be worth 3)
Hypothermia is the condition involving a significant fall in core temperature.(temp falls
below a level where normal metabolism can be maintained)
As temperature falls molecules will have less kinetic energy/will be moving more slowly(1)
and so there will be fewer effective collision between enzyme and substrate(1), thus
slowing reactions to a point where the essential requirements of cells (eg ATP) are not
being supplied quickly enough to sustain life.(1)
2. The simulation now shows a different enzyme controlled reaction.
a) At what pH is the reaction fastest?
pH 7 (neutral)
c) What happens to the enzyme either side of the optimum pH?(2)
The enzymes become denatured/their 3D shape changes;(either side of the optimum 1) and
active site is deformed(1)
3. What name is given to the process described in2 b)(1 )
denaturation
4. The simulation now shows two reactions. Each works best at a different pH
a) What is the optimum pH for each reaction?
Reaction 1:pH 2 Reaction 2: pH 8
The pH of the mouth , stomach and the small intestine are listed in the table below:
Part of the alimentary canal
Approximate pH
Mouth
Variable but about 6.8
Stomach
1-2
Small intestine
8
b) Suggest where within the digestive system each of these enzyme would normally
act?(2)
Enzyme catalysing reaction 1 probably normally acts in the stomach, while the enzyme catalysing
reaction 2 is likely to normally act in the small intestine
c) Why is it important for enzymes to be able to work well in some conditions and not
others.(2)
So that the system in which the enzyme functions can control when a reaction occurs (1)to
prevent a reaction happening where it should not or enable reactions to happen in a sequence(1)
Eg. Pepsin acting the the small intesting could result in digestion of the small intestine lining.
5. As with most simulations there are a number of inaccuracies present. This is not a perfect
representation of what happens in real life enzyme driven reactions. Outline 4 ways in
which this simulation fails to accurately represent what is going on in this simulation.

In the computer simulation ,the enzymes molecules are not moving; in reality both
enzyme and substrate molecules would be moving.

Some of the movement is not random. Sometime a substrate molecule looks like
it is changing direciton to collide with the active site ; this wouldn’t happen.

Enzymes that begin as denatured and shown to become undenatured at the pH is
adjusted to a more favourable level for a particular enzyme. This would not
happen in real life .

The molecules are moving much much slower on the screen than they would in
real life.