Enzymes
 Enzymes are proteins that act as
biological catalysts
 They lower the activation
energy of a specific chemical
reaction
 Catalysts – speed up the
chemical reaction and are not
changed by the reaction
 Lowering the activation energy
has a profound effect on how
rapidly the reaction is completed
Enzymes: Vocabulary Check
 Catalyst: A substance that speeds up a chemical
reaction without itself being changed
 Enzyme: A biological catalyst that is usually a
protein
 Substrate: The reactant(s) upon which an enzyme
has its action
 Product: A substance that results from a chemical
reaction
Enzymes Lower Activation Energy
What are enzymes?
 Enzymes are typically
proteins
 Enzymes are specific
 Enzymes act as catalysts to
speed up the rate of reaction
of a biological process
 Enzymes are not used up by
the reaction they catalyse
Enzymes change substrates into
products
How do enzymes work?
 Substrate specificity
 Induced fit versus Lock and key mechanism
Enzymes have active site (s)
An intricate pocket or cleft – a 3dimensional entity – structurally
tailored to accept a particular
substrate
Only fits its particular substrate
What are the models used to
describe enzyme action?
What are the models used to
describe enzyme action?
 Lock and key mechanism
 Induced fit mechanism
The induced fit theory
The substrate plays a role in
determining the final shape of the
enzyme and that the enzyme is has
some flexibility.
This explains why certain
compounds can bind to the enzyme
but do not react because the
enzyme has been distorted too
much.
Other molecules may be too small
to induce the proper alignment and
therefore cannot react.
Only the proper substrate is capable
of inducing the proper alignment of
the active site
 Induced fit in a moment....
Naming Enzymes
(the official classification)
Naming Enzymes (simplified
classification)
Enzymes can be named
according to the type of
reaction that they catalyse
 Enzymes can be named
 Carbohydrases
 Maltase
 Lipases
 Sucrase
according to the substrate the
interact with:
 Proteases
Some enzymes just have
individualised names:
 Pepsin
 Trypsin
 Catalase
Key properties of enzymes
1. All enzymes are proteins
2. Enzymes are denatured (inactivated) by extreme
temperatures
3. Enzymes work best at a particular temperature (which
depends on the organism)
4. Enzymes work best at a particular pH (which depends
on the organism)
5. Enzymes are catalysts (not degraded, ccan be used
over and over again)
6. Enzymes are specific
Factors affecting Enzymes
1. Temperature
2. pH
3. Substrate concentration
4. Enzyme concentration
The best way to understand temperature, pH and
substrate concentration effects is through paying with this
game....
and here's another....
Factors which affect enzyme
activity 1: Temperature
From: GCSE Bitesize:26.08.12
http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/homeostasis/importancerev4.shtml
The effect of temperature
 For most human enzymes the optimum
temperature is about 37°C
 Many are a lot lower. For example, cold water fish
can die at 30°C since many of their enzymes
denature
 Many plant enzymes have optimal temperature of 28
– 30 C
 A few bacteria in hot springs have enzymes that can
withstand very high temperatures up to 100°C
 Most enzymes are fully denatured at 70°C
Factors which affect enzyme
activity 2: pH
Optimum pH values
Enzy
me
activit
y
Tryps
in
1
3
5
7
pH
9
11
Pepsi
n
The effect of pH
 The pH of a solution affects the shape of an
enzyme
 At non-ideal pH values, the active site is
distorted and the substrate molecules will no
longer fit
 Extreme pH levels will produce denaturation
 Many enzymes have pH values which are NOT
neutral (pH = 7): e.g. pepson, trypsin in the
stomach and gut
Denaturation
Denaturation is a change in the shape of an enzyme
which prevents it from fulfilling its function.
Enzymes (and other proteins) can be denatured by heat,
pH changes, or certain chemicals
NB: Denaturation is not the same as ‘killing’ – proteins
and enzymes are not living things, so can’t be killed!
What does ‘enzyme denaturation’
mean?
Factors which affect enzyme activity 3:
Substrate and enzyme concentration
From: http://www.skinnersbiology.co.uk/enzyme.htm
August 26th 2012
Substrate concentration: Enzymic reactions
Vmax
Reaction
velocity
Substrate concentration
Celebrity enzymes
1. Amylase
2. Pepsin
3. Pectinase
4. Catalase
Amylase
 all about amylase...
 amylase digestion
Pepsin
 All about pepsin
 pepsin working in the
stomach
Pectinase
 Pectinase is widely used to
increase the yield in fruit juice
extraction, and also to make juice
clear rather than cloudy
 Pectinase breaks down the
pectin chains in the middle
lamellae connecting fruit cells
 Pectinases and amylases can
both break down these insoluble
polysaccharide compounds
within fruit cells, releasing soluble
sugars which clarify the juice
producing a clearer, sweeter
product.
Catalase
 Better, stronger, faster
What does hydrogen peroxide
do in the body?
 H2O2 is a strong oxidising
agent produced as a byproduct of metabolism
 Can damage cells
 Instantaneously broken down
by catalase
What is hydrogen peroxide
 Bleach
 stain remover
 Wound treatment (?)
Where is Hydrogen peroxide
located?
What is catalase?
 A biological enzyme present
in all living cells exposed to
oxygen
 ‘Extremely high turnover
number’
 Catalyses the decomposition
of hydrogen peroxide to
water and oxygen
Your Research Challenge
Investigate
the
effect
of
enzyme
concentration on yeast (saccharomyces
cerevesiae) catalase enzyme activity using
quantitative methods
p. 44 of your IGCSE book
What is the hypothesis you
are going to test?
Research Question:
Does catalase concentration affect the rate at which catalase
breaks down H2O2?
What is the hypothesis you are going to test?
Quantitative experiment
How can we measure the rate at which catalase breaks down
H2O2?
Does enzyme concentration affect the rate
at which catalase breaks down H2O2?
Working Observation
 Most enzymes have
maximal efficacy at a
specified temperature
(somewhere between 30 –
37 0C in mammals)
 Temperature extremes
should reduce the rate at
which catalase breaks
down H2O2
Experimental Design
 Working Observation: As enzyme
concentration increases, the rate of breakdown
of H2O2 by catalase should increase
 (Null hypothesis: a change in enzyme
concentration has no effect on the rate of H2O2
decomposition by catalase does not change)
 (Alternative hypothesis: enzyme concentration
is directly related to the rate of H2O2 decomposition
by catalase )
Quantitative experiment
 How can we measure the rate at which catalase breaks
down H2O2?
 Quantity of oxygen produced over a set time (volume,
%, pressure)
Starting questions
1. What apparatus and other materials will you need for
your experiment?
A few starting questions:
1. How exactly will you ‘measure’ the reaction between
H2O2 and catalase??
How exactly will we ‘measure’ the
reaction between H2O2 and catalase?
We will measure the rate of reaction between catalase
and hydrogen peroxide indirectly by measuring the
pressure change in a closed chamber, using a
Vernier Gas pressure probe
Data Collection
Catalase experiment
Dependent Variable
Independent Variable
Controlled variables
Uncontrolled variables
Catalase experiment
Dependent Variable
% of oxygen in closed chamber
Independent Variable
Catalase concentration %
Controlled variables
pH
Temperature
Substrate concentration
Uncontrolled variables
Human error – timing and
measurement
Starting questions:
3. Can you think of other factors that may affect enzyme
activity?
 Substrate concentration
 Temperature
 pH
 Human error
Starting Questions…
 How will we record our data?
 “Results table?
…and a few questions about study
design…
1. Which concentrations should we test? – and
why?
2. Do you want this to be a controlled
experiment? What will be the control group?
3. How many test groups should we have?
4. How many times will you repeat each test?
5. How will we prepare our stock catalase
solutions?
Predictions/ Conclusions
 Make a prediction about your conclusions.
 Do you expect to find support for your hypothesis?
 Why or Why not?