IB Biology 2015

1. 2.5 Enzymes
Essential idea: Enzymes control the metabolism of the cell.
http://cdn.instructables.com/F7F/38MA/HAFHKT7I/F7F38MAHAFHKT7I.LARGE.jpg
Below is an enzymatic reaction browning, which
may protect the developing seeds from pathogens

2. Understandings, Applications and Skills
Statement Guidance
2.5 U.1 Enzymes have an active site to which specific
substrates bind.
2.5 U.2 Enzyme catalysis involves molecular motion and
the collision of substrates with the active site.
2.5 U.3 Temperature, pH and substrate concentration
affect the rate of activity of enzymes.
Students should be able to sketch graphs to
show the expected effects of temperature,
pH and substrate concentration on the
activity of enzymes. They should be able to
explain the patterns or trends apparent in
these graphs.
2.5 U.4 Enzymes can be denatured.
2.5 U.5 Immobilized enzymes are widely used in
industry.
2.5 A.1 Methods of production of lactose-free milk and
its advantages.
Lactase can be immobilized in alginate
beads and experiments can then be carried
out in which the lactose in milk is
hydrolyzed.
2.5 S.1 Design of experiments to test the effect of
temperature, pH and substrate concentration on
the activity of enzymes.
2.5 S.2 Experimental investigation of a factor affecting
enzyme activity. (Practical 3)

3. 2.5 U.1 Enzymes have an active site to which specific substrates bind.
2.5 U.2 Enzyme catalysis involves molecular motion and the collision of substrates with the active site.
Enzyme: A globular
protein that increases the
rate of a biochemical
reaction by lowering the
activation energy
threshold (i.e. a biological
catalyst)
http://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.swf
Use the animation to find out more about enzymes and how they work.
A good alternative is How Enzymes Work from McGraw and Hill
http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

4. • Enzymes are protein catalysts that enormously speed
up reactions. They often have an “-ase” ending to their
name.
– e.g., hexokinase, catalase, peptidase, mutase
• They are not themselves changed (except for a brief
period of time) and are the same before and after a
reaction.
• Enzymes:
1. Lower the activation energy: this is the MOST important
characteristic
2. Do not add or remove energy from a reaction
3. Do not change the equilibrium for a reaction
4. Are reused over and over
2.5 U.1 Enzymes have an active site to which specific substrates bind.

6. Enzymes Lower EA

7. Lock & Key Hypothesis
a) Large globular protein enzyme
b) Active Site where the substrate combines to the enzyme
c)Substrate which fits the active site
d) Activated complex. The substrate is weakened to allow the reaction.
e)Unchanged enzyme/ re-used at low concentrations
f) Product of the reaction

8. Induced Fit Hypothesis
• Better explains enzyme activity if
the lock and key model were true
one enzyme would only catalyze
one reaction, while we some
enzymes capable of catalyzing
several reactions.
• As the substrate approaches the
enzyme a conformational change
takes place in the activation site, it
changes shape to induce a fit.
• This stress reduces the activation
energy or the reaction

9. 2.5 U.2 Enzyme catalysis involves molecular motion and the collision of
substrates with the active site.
http://www.kscience.co.uk/animations/model.swf
The simulation from KScience
allows you to both see enzyme
kinetics happening and secondly
how it is affected by different
factors
• Two substances must have the
proper alignment and energy
(in the form of motion) to
create a chemical reaction
• The direction and movement is
constantly changing and is
random
• Collisions occur at random
between the substrate and
enzyme
• Successful reactions only occur
if the substrate and the active
site of the enzyme are correctly
aligned and the collide with
sufficient KE

10. Optimal environmental
condition(s) favor the most
active enzyme conformation.
• Temperature
• pH
• Concentration of
substrate/enzyme
• Cofactors
• Enzyme inhibitors
• Allosteric regulation
(noncompetitive)
• Ionic concentration
2.5 U.3 Temperature, pH and substrate concentration affect the rate of
activity of enzymes.

11. 1. The Effect Of Temperature
(a) •Increase Kinetic energy of substrate
and enzyme.
•Increased chance of collisions
•Low temperatures has a low rate of
reaction
(b) •Optimum temperature = maximum
rate of reaction
•Balance between enzyme stability
and kinetic energy of reactants
(c) •Rapid decrease in the rate of reaction
•High temperatures destabilize the
enzyme molecule
•Enzyme is denatured

12. Proteins found in the
egg white include
albumins, globulins and
mucoproteins
Under intense heat,
hydrogen bonds that
formed during the
secondary structure
are broken
The proteins then lose their
shapes, thus changing their
functions
By cooking it, you have effectively denatured the egg
What happens when you cook an egg?

13. a structural change in a protein that results in a loss (usually permanent) of its biological
properties.
• Enzymes are globular proteins
• Enzymes have tertiary structure
• Tertiary structure is maintained by hydrogen, ionic and covalent bonds
• Shape of the active site is maintained by hydrogen, ionic and covalent
bonds
The bonds within enzymes (and proteins) has an increasing strength of:
Hydrogen
Ionic
Covalent
2.5 U.4 Enzymes can be denatured.

14. 2. The Effect Of pH
(a) Decrease in pH (increase in H+)
• H+ interact with exposed R groups
on active site.
• Enzyme active site changes shape
• Specificity reduced
• Decrease in rate of reaction
(b) Optimum rate of reaction for the pH=
(d)
• Active site structure and structure
specific to the complementary shape
of the substrate.
• Successful activated complex and
therefore reactions occur.
(c) Increase in pH (increase in OH-)
• Increase in base (OH-) concentration
• Enzyme active site changes shape
• Specificity reduced
• Decrease in rate of reaction

15. Denaturation of an enzyme by a change in pH
• Enzymes have an optimum pH at which they achieve their maximum rate of
reaction
• Pepsin has an optimal pH of 2 at (a)
• Amylase has an optimal pH of (c)
• pH affects the charge of the amino acids of the active site
• This changes the properties of the active site
• e.g. carboxyl R group will be uncharged COOH at low pH but COO- at high pH.

16. Denaturation of an
enzyme by a change in pH
• If there is a deviation from
the optimal pH the hydrogen
sulfide bridges break and the
enzyme loses shape.
• Loss of the activation site
shape leads to loss of
function

17. 3. The effect of
substrate concentration
(a) •Increase conc. of substrate molecules
•Increased chance of collision with
enzyme
•Greater chance of forming activated
complex
•Increase in rate of reaction
(b) •Rate begins to level
•Active sites beginning to become
saturated with substrate (fully occupied)
•New substrate must wait for previous
reaction to complete and the product to
exit the active site
(c) •Full saturation of the active sites by
substrate
•Rate becomes constant for further
increases in substrate concentration.

18. 2.5.U5 Immobilized enzymes are widely used in industry.
Common uses of enzymes in industry include:
http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/Articleimage/2013/CS/c3cs35506c/c3cs35506c-f1.gif
1.Detergents
2.Biofuels
3.Textiles
4.Brewing
5.Medicine &
Biotechnology
6.Juice yield
7.Paper production

19. 1. Detergents contain proteases
and lipases to help breakdown
protein and fat stains https://i1.ytimg.com/vi/lQ6fCZgYc8g/hqdefault.jpg

20. 2. Enzymes are used to breakdown
the starch in grains into biofuels
that can be combusted
http://chromblog.thermoscientific.com/Portals/49739/images/biofuel9.jpg
http://greenodin.com/wp-content/uploads/2014/12/GreenOdin-GO-Biodiesel-Van-1200.png

21. 3. In the textiles industry enzymes help in the processing of
fibers, e.g. polishing cloth to make it appear more shiny

22. 4. In the brewing industry
enzymes help a number of
processes including the
clarification of the beerhttp://www.brewreviewcrew.com/cans-vs-bottles-fight/

23. 5. In Medicine & Biotechnology enzymes are
widely used in everything from diagnostic tests
tests to contact lens cleaners to cutting DNA in
genetic engineering.
http://www.medwesteye.com/wp-content/uploads/2014/12/learn-the-proper-care-of-contact-lenses.jpg

24. 6. Enzymes are widely used in the food industry, e.g.
• fruit juice, pectin to increase the juice yield from
fruit
• Fructose is used as a sweetener, it is converted from
glucose by isomerase
• Rennin is used to help in cheese productionhttps://theramblingreed.files.wordpress.com/2014/08/img_6338.jpg

25. 7. Paper production uses enzymes
to helping in the pulping of wood
http://i00.i.aliimg.com/img/pb/479/389/262/1281752366918_hz-cnmyalibaba-web2_15708.jpg

26. 2.5 U.5 Immobilized enzymes are widely used in industry.
http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/Articleimage/2013/CS/c3cs35506c/c3cs35506c-f1.gif
Advantages of enzyme immobilization:
• Concentration of substrate can be increased as the enzyme is not dissolved – this
increases the rate of reaction
• Recycled enzymes can be used many times, immobilized enzymes are easy to separate
from the reaction mixture, resulting in a cost saving.
• Separation of the products is straight forward (this also means that the the reaction can
stopped at the correct time).
• Stability of the enzyme to changes in temperature and pH is increased reducing the rate
of degradation, again resulting in a cost saving.
Enzymes used in industry are usually
immobilized. They are attached to a material
so that their movement is restricted.
Common ways of doing this are:
• Aggregations of enzymes bonded together
• Attached to surfaces, e.g. glass
• Entrapped in gels, e.g. alginate gel beads

27. Lactose Intolerance
• Lactose (milk sugar) can cause allergies in some people.
• This is often because they are unable to produce the enzyme lactase
in sufficient quantities.
• Most people produce less lactase as they get older. After all, we don’t
live off milk once we have been weaned.
• In some regions such as Europe, a mutation has allowed lactose
production to continue into adulthood. This mutation is not present
in people who are lactose intolerant
2.5 A.1 Methods of production of lactose-free milk and its advantages.

28. Green High Tolerance
Red Low Tolerance
Global estimates of lactose intolerance.

29. How can we cope with lactose intolerance?
• Take a lactase
supplement. These
are produced
industrially using the
Aspergillus niger
fungus
• Drink lactose free
milk. Milk treated
with lactase
(produced by A.
niger) and essentially
‘pre-digested’ before
being packaged.

30. 2.5 A.1 Methods of production of lactose-free milk and its advantages.
Other uses of lactose free milk:
• As a means to increase the sweetness of milk (glucose and
galactose are sweeter in flavor), thus negating the need for
artificial sweeteners
• As a way of reducing the crystallization of ice-creams
(glucose and galactose are more soluble than lactose)
• As a means of shortening the production time for yogurts or
cheese (bacteria ferment glucose and galactose more readily
than lactose)
Production of Lactose-free milk
• Lactase obtained from commonly from yeast
(bacteria is an alternative)
• Lactase is bound to the surface of alginate beads
• Milk is passed (repeatedly) over the beads
• The lactose is broken down into glucose and
galactose
• The immobilized enzyme remains to be used
again and does not affect the quality of the
lactose free milk

31. 2.5 S.1 Design of experiments to test the effect of temperature, pH and substrate concentration
on the activity of enzymes.
2.5 S.2 Experimental investigation of a factor affecting enzyme activity. (Practical 3)
Possible research questions, what are you going to investigate (independent variable)?
• What is the effect of substrate concentration?
• What is the effect of temperature?
• What is the effect of pH?
• Which type of yeast has a higher concentration of catalase?
Important things to consider:
• How are you going to vary the mass/volume/concentration of your variable?
• What units will you be measuring your variable in?
• Have you chosen an effect range or values to answer your question?
• Are the concentrations/chemicals you are using safe to handle?
Catalase is one of the most widespread enzymes. It catalyzes the conversion of
hydrogen peroxide, a toxic by-product of metabolism, into water and oxygen.

32. How are you going to measure your results (dependent variable)?
• Are you measuring the increase of a product or the disappearance of a substrate?
• Are you measuring directly (e.g. testing for the concentration of the product) or
indirectly (change in pH)?
• What equipment will you be using to measure your results?
• What are the units and uncertainty given both the equipment and how you choose
to use it?
• What time period do you need to run the experiment for? How fast is the enzyme
action likely to be?
• How many repeats will you need to make sure your results are reliable?
2.5 S.1 Design of experiments to test the effect of temperature, pH and substrate concentration
on the activity of enzymes.
2.5 S.2 Experimental investigation of a factor affecting enzyme activity. (Practical 3)

33. How are you going to make sure it is a fair test (control variables)?
• What variables other than your independent variable could affect the results?
• Why would these variables affect the results?
• How will you ensure each is kept constant and monitored?
• What level should they be kept constant at? If a control variable is too far from it’s
optimum then it could limit the enzyme action and no change would be seen in the
results.
• If a variable cannot be controlled it should still be discussed and considered as an
uncontrolled variable.
Safety and ethics:
• Are you using any equipment that may cause you or others harm? What steps have you taken to
minimize this risk?
• If you intend to use animals have you first considered alternative subjects?
• If you still intend to use animals are subjects have you ensured both:
o no harm comes to them as a result of the experiment
o The experiment does not induce stress or conditions beyond that normally found in their
natural environment
2.5 S.1 Design of experiments to test the effect of temperature, pH and substrate concentration
on the activity of enzymes.
2.5 S.2 Experimental investigation of a factor affecting enzyme activity. (Practical 3)

34. Bibliography / Acknowledgments
Jason de Nys