Unit 1 Cell Biology
4. Proteins
Starter
From booklet 3 (DNA and the production
of proteins) answer the following;
What is a gene?
What does the base sequence (order of
bases A, T, C, G) in DNA code for?
What is a protein assembled from?
Which cell organelle is the site of
protein synthesis?
Proteins
Proteins are found in all living
organisms.
They are composed of smaller molecules
known as amino acids. You learned
earlier how they joined in a particular
order that was determined genetically.
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National 5 Biology Unit 1
Amino acids
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There are about 20 amino
acids.
Each amino acid links
together.
The growing chain forms a
protein
http://learn.genetics.utah.edu/content/begin/dna/transcribe/
National 5 Biology Unit 1
How proteins form
The chain twists up and coils to form a very
specific shape.
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It is this shape that determines the function of
the protein
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National 5 Biology Unit 1
Protein shape
The shape of a protein determines the
function.
The shape is determined by the sequence
of amino acids.
The amino acid sequence is determined by
the DNA code.
How proteins form
Other polypeptide chains
become folded together
into a spherical or globular
shape. This is haemoglobin.
Some polypeptide
chains become
arranged in long
parallel strands.
Such as keratin.
This is the type of
protein found in hair,
nails, claws, feathers
etc.
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This is found in the red
blood cells.
National 5 Biology Unit 1
Functions of Proteins
You contain more than 10000 different
proteins.
Each protein has its own specific
function.
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Proteins
Structural
Structural proteins
found in bones, teeth,
skin, hair, tendons,
ligaments and blood
vessels.
They provide support.
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Collagen
Proteins
Hormones
These are chemical
messengers
transported in the
blood
Insulin
We learn more about
hormones in unit 2.
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Plays a role in the control
of blood sugars
National 5 Biology Unit 1
Proteins
Antibodies
Defend the body
against disease.
Immunoglobulin
We learn more about
antibodies in unit 2.
Present in breast milk, these proteins
provide the new born with some immunity.
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National 5 Biology Unit 1
Proteins
Enzymes
Biological
catalysts found in
all living cells.
Catalase
We learn more about
enzymes in this booklet
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This enzyme breaks down hydrogen peroxide.
National 5 Biology Unit 1
Proteins
Receptors
receives chemical
signals from
outside a cell.
Hormone
receptors in the
cell membrane
We learn more about
receptors along with
hormones
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National 5 Biology Unit 1
Proteins song
https://www.youtube.com/watch?v=Dipu
IBLJ3ng
Learning Intentions
How is protein shape determined?
How is protein function determined?
What controls the sequence of amino
acids?
List several functions of proteins.
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National 5 Biology Unit 1
Properties of Enzymes
Biuret A and
Biuret B
Enzymes are protein
Your teacher may show
simple test for proteins
using Biuret solutions.
Biuret Solution turns lilac in
protein
enzyme solution
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National 5 Biology Unit 1
Experiment
Carry out the investigation to show that
enzymes are made out of protein.
Method:
1. Collect 5 test tubes, NaOH, CuSO4 the 4
solutions to be tested and a test tube rack
2. Set up apparatus and label each test tube using a
paper towel
2. Add approx. 2ml of NaOH to each test tube
3. Add 2ml of each solution to be tested to the
appropriate test tube
4. Add 0.5ml of CuSO4 to each test tube
5. Observe and record results in table
Starter
Name some proteins and their functions
Enzymes
Learning Outcomes
State that enzymes function as
biological catalysts and are made by all
living cells.
State that enzymes speed up cellular
reactions and are unchanged in the
process.
Enzymes
Read page 7 and answer the questions on
page 8.
Specificity
Starter
Summarise the features of an enzymes
you have learned so far.
Specificity
Learning outcomes
Explain the action of an enzyme in
terms of the shape of the active site of
an enzyme molecule and how it is
complementary to a specific substrate.
Enzyme action results in product(s).
Specificity
Enzymes are biological catalysts.
Catalase is an enzyme, made by living
cells, which can break down hydrogen
peroxide.
If we add a piece of living tissue to
hydrogen peroxide, we can see bubbles
of oxygen being released.
The more bubbles released, the more
catalase there is in the tissue.
Specificity
Carry out the experiment to find out
which enzyme breaks down hydrogen
peroxide
Specificity
Catalase can only speed up the
breakdown of hydrogen peroxide, not
any other reaction.
It is said to be specific.
Each enzyme catalyses only one
reaction.
The substance the enzyme catalyses is
called the substrate.
Specificity
All enzymes are made of protein.
Enzymes have an area on their surface
which is a specific shape, and it is here
that the substrate attaches.
This area is called the active site.
Specificity
The enzyme’s shape and the substrate’s
shape are said to be complimentary.
The substrate locks onto the enzyme at
the active site and the reaction occurs.
Specificity
The reaction produces the products.
Some enzymes are responsible for
breaking down large substrates into
smaller products, while others are
responsible for the building up of large
products from smaller substrates.
Model Enzymes
During an enzyme controlled reaction the
substances involved – the substrates –
become joined to the surface of the
enzyme molecule.
The chemical reaction then occurs very
quickly.
The spot on the enzyme molecule where the
catalytic activity takes place is called the
ACTIVE SITE.
Model Enzymes
Enzyme molecules have many active
sites over their surface.
Only substrates that fit the active site
exactly, react on the surface of the
enzyme.
Substrate molecules fit into these
active sites like a key fitting into a lock.
How Enzymes Work
Enzymes are globular
proteins.
They have a very specific
shape that is determined
by the amino acids that
make it up.
They have an area that is
known as the active site.
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National 5 Biology Unit 1
How Enzymes Work.
The shape of the active
site is complementary to
the enzyme’s specific
substrate.
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National 5 Biology Unit 1
How Enzymes Work.
The shape of the active
site is complementary to
the enzyme’s specific
substrate.
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National 5 Biology Unit 1
How Enzymes Work.
substrate
molecule
enzyme/
substrate
complex
enzyme
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National 5 Biology Unit 1
How Enzymes Work.
product
molecules
form
It is a
degradation
enzyme
free to be
used again
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In this
reaction a
complex
molecule has
been split
into smaller
simpler
molecules.
National 5 Biology Unit 1
Degradation and Synthesis
reactions
Starter
Describe the features of an enzyme that
allow it to combine with only one
substrate
Learning Outcomes
Enzymes can be involved in degradation
and synthesis reactions.
Give examples of enzymes and their
specific substrates and products.
Starch & Amylase
Starch is a carbohydrate.
It contains energy and is found in many
foods.
Starch molecules are very large and
cannot pass through cell membranes.
Therefore, they need to be broken
down to smaller molecules.
Amylase in Action
Carry out the experiment on page 15 to
investigate the action of amylase on
starch.
Starch & Amylase
This is done by an enzyme called
AMYLASE.
Amylase is found in our saliva.
The starch is broken down to molecules
of a sugar called maltose.
STARCH
(Substrate)
AMYLASE
(Enzyme)
MALTOSE
(Product)
Starch & Amylase
Starch molecule
Maltose molecules
Controls
When we carry out any experiment, it is
important to have a control.
The control allows us to make a valid
comparison.
e.g. if we are testing the action of amylase
by putting it in starch solution, a control
would be to have another tube and put
water in the starch solution.
This way we know it is the amylase that is
responsible for the changes that occur.
Synthesis Reactions
So far, we have looked at enzymes
which break down molecules, e.g.
amylase breaks down starch.
How is the starch built up in the first
place?
Plants make glucose using sunlight.
This glucose is converted to glucose-1phosphate.
Synthesis Reaction
es
Active site
How Enzymes Work
product
molecule
forms
Ittwo
is a
substrat
synthesis
e
molecule
s
In this
reaction 2
simple
molecules have
joined to
produce a
larger more
complex
molecule.
enzyme
freeenzyme
to be
used again
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National 5 Biology Unit 1
Synthesis Reactions
An enzyme called PHOSPHORYLASE is
used to join glucose-1-phosphate
molecules together to make starch.
This is called a synthesis reaction.
GLUCOSE-1-PHOSPHATE
(Substrate)
PHOSPHORYLASE
(Enzyme)
STARCH
(Product)
The Action of Phosphorylase
Not all enzymes
are degradative.
Some are
synthetic.
This means they
build up complex
molecules from
simpler ones.
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Phosphorylase
is found in
potatoes
National 5 Biology Unit 1
The Action of Phosphorylase
A green plant makes
glucose in its leaves.
The plant does not use
all of the glucose
straight away.
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Some is transported
to the roots and
stored as starch.
National 5 Biology Unit 1
The Action of Phosphorylase
Glucose
made
here
Glucose
transported
down stem
Glucose
converted
into starch
here
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National 5 Biology Unit 1
The Action of Phosphorylase
Set up three rows in a dimple tile as
shown
Glucose -1-phosphate
+
A
Potato extract
Glucose -1-phosphate
B
+
Distilled water
C
Potato extract
+
Distilled water
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The Action of Phosphorylase
After
After
another
3 33
After
another
Add 3 drops
minutes
minutes
of
add
add333drops
dropsof
add
drops
Iodine of
Iodine
of
Solution
Iodine
Solution
Solution
to
to
each
Iodine
dimple
to
each
dimple
each dimple
inin
Solution
the
third
the
final
in the first
column
to
each
column
column
dimple in the
second
column
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A
B
C
National 5 Biology Unit 1
The Action of Phosphorylase
 What has happened to the glucose in row A?
It has been converted into starch.
 What has happened to the glucose in row B?
It has not changed.
 What has happened to the glucose in row C?
It has not changed.
Explain in your own words what has happened.
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National 5 Biology Unit 1
The Action of Phosphorylase
G
G
G
G
G
G
G
G
G
G
G
Starch molecule
building
up
from
simple
G
G
glucose moleculesG
G
G
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National 5 Biology Unit 1
Enzymes and Temperature
Starter
Write down what you already know about
enzymes and temperature
Enzymes and Temperature
Learning outcomes
Each enzyme is most active in its
optimum conditions.
Enzymes and other proteins can be
affected by changes in temperature and
pH
Enzymes can be denatured, resulting in
a change in their shape which will affect
the rate of reaction.
Optimum Condition
Enzymes function best or are most
active in specific conditions known as
optimum conditions.
Temperature and Enzymes
Enzymes are affected by a change in
temperature.
If the temperature is particularly low,
the enzyme activity will be very slow.
As the temperature increases the
enzyme activity increases, but only up to
a certain point.
Temperature and Enzymes
The temperature at which the enzyme
works at its quickest is called the
Optimum temperature.
Most human enzymes have an optimum
temperature around 37oC
Once the temperature is too high the
enzyme (being a protein) is damaged and
we say it has been denatured.
Effect of temperature on
enzymes
Optimum
temperature
optimum activity
Higher
temperature
higher activity
Rate of
enzyme
activity
Very high
temperature
slow activity
Activity stops
Low
temperature
low activity
0
10
20
30
40
Temperature
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50
o
C
National 5 Biology Unit 1
60
70
Effect of temperature on enzymes
You noticed that at
60oC the activity of
catalase was slow.
This is because high
temperatures
denature the
proteins that make up
the enzyme.
Heating changes the
shape of the active
site.
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The substrate no
longer “fits”
National 5 Biology Unit 1
Temperature v Enzyme Activity
Increasing rate of Reaction
Optimum
temperature
Increasing
enzyme
activity
Enzyme
being
denatured
0
10
20
30
Temperature
(oC)
40
50
Enzymes and pH
Starter
Describe what happens to enzymes when
exposed to high temperatures
Enzymes and pH
Learning Outcomes
Each enzyme is most active in its
optimum conditions.
Enzymes and other proteins can be
affected by changes in temperature and
pH
Enzymes can be denatured, resulting in
a change in their shape which will affect
the rate of reaction.
Effect of pH on Enzymes
pH is a measure of how acid or alkali
something is.
The pH scale goes from 1 to 14, with 1
being very acidic, 14 being very alkaline
and 7 being neutral.
The shape of an enzyme can be
affected by changes in pH and this will
affect how well the enzymes work.
Effect of pH on Enzymes
Like temperature, enzymes have an
optimum pH, i.e. a pH when they are
most efficient.
The optimum pH varies from enzyme to
enzyme.
Our digestive system has a range of
pH’s as the food passes through it, and
this creates ideal conditions for
specific enzymes.
Effect of pH on Enzymes
Enzyme Activity (%)
100
80
Pepsin
60
Catalase
Lipase
40
20
0
0
1
2
3
4
5
6
pH
7
8
9
10
11
12
Enzymes song
https://www.youtube.com/watch?v=Nd
MVRL4oaUo