Starter/Task
• On to a show me board, write down as
much as you know about DNA!
Higher Biology
CfE
Course Content
• Unit 1: DNA and the Genome
• Unit 2: Metabolism and Survival
• Unit 3: Sustainability and
Interdependence
Unit 1: DNA and the Genome
Key Area 1.1 The Structure of DNA
Key Area 1.2 Replication of DNA
Key Area 1.3 Control of Gene Expression
Key Area 1.4 Cellular Differentiation
Key Area 1.5 The Structure of the Genome
Key Area 1.6 Mutation
Key Area 1.7 Evolution
Key Area 1.8 Genomic Sequencing
Key Area 1.1 The Structure of DNA
(a)The Structure of DNA
(b)Organisation of DNA
Key Area 1.1(a) The Structure of DNA
Key Area 1.1 (a) Learning Outcomes
• Name the molecules in a DNA nucleotide and identify them
in a diagram.
• Name the type of bond on the backbone of the DNA
molecule.
• Give the full names of the 4 DNA bases.
• Describe the base pairing rule for DNA bases.
• Describe the role of hydrogen bonds in the DNA
structure.
• State the name of the coiled structure adopted by DNA.
• Identify the positions of 3’ and 5’ carbons on a DNA
nucleotide.
• Identify the positions of 3’ and 5’ ends on a DNA strand.
• Describe how 2 strands of DNA align themselves to each
other.
The Structure of DNA
• DNA (deoxyribonucleic acid) is a
complex molecule present in all living
cells.
• DNA stores genetic information in its
sequence of bases which determines the
organisms genotype and the structure
of its proteins.
Task
• On a show me board, draw and label the
structure of a nucleotide.
• A molecule of DNA consists of two
strands each made up of repeating units
called nucleotides.
A nucleotide is made
up of a molecule of
deoxyribose sugar
joined to a phosphate
group and an organic
base.
• The shape of the deoxyribose sugar in a
nucleotide is determined by the
arrangement of carbon atoms in the
Note
molecule.
Each carbon atom is
numbered. This can
help us describe the
arrangement of a
DNA molecule.
3C = 3’ (3 prime) carbon atom
5C = 5’ (5 prime) carbon atom
• To produce a strand
of DNA, a chemical
bond forms between
the phosphate group
of one nucleotide and
carbon 3 on the
deoxyribose sugar of
another nucleotide.
• This forms the
molecule’s sugarphosphate backbone.
Sugar-phosphate
backbone
• There are four different types of
nucleotide in a DNA molecule. They
differ from each other because they
have a different base.
The base attaches
to carbon 1.
• Two strands of nucleotides become
joined together by hydrogen bonds
forming between their bases.
• Hydrogen bonds are weak so the
strands can easily become separated.
• Each base can only join up with one
other type of base:
– Adenine (A) always bonds with Thymine (T)
– Guanine (G) always bonds with Cytosine (C)
• This is called the base-pairing rule.
• DNA takes the form of
a double helix.
• DNA is made up of two
antiparallel strands.
This means that the
strands run in opposite
directions to each
other.
• Using the numbered
carbon atoms on the
deoxyribose sugar
allows us to show the
antiparallel structure.
Left: 5’  3’
Right 3’  5’
Key Area 1.1(a) You should now be able to . . .
1.
2.
3.
4.
5.
6.
7.
8.
9.
Name the molecules in a DNA nucleotide and identify
them in a diagram.
Name the type of bond on the backbone of the DNA
molecule.
Give the full names of the 4 DNA bases.
Describe the base pairing rule for DNA bases
Describe the role of hydrogen bonds in the DNA
structure.
State the name of the coiled structure adopted by DNA.
Identify the positions of 3’ and 5’ carbons on a DNA
nucleotide.
Identify the positions of 3’ and 5’ ends on a DNA strand.
Describe how 2 strands of DNA align themselves to each
other.
Starter/Task
On to a show me board:
1) Describe the base pairing rule.
2) Name the carbon that a base attaches
to.
3) Name the type of bond that holds
bases together.
Key Area 1.1(b) The organisation of DNA
Key Area 1.1(b) Learning Outcomes
• Identify prokaryotes and eukaryote cells from
diagrams.
• Describe the key similarities and differences
between prokaryote and eukaryote cells.
• Describe structure of a plasmid and name the types
of cells where they are found.
• Describe structure of circular chromosomes and
identify the location and types of cells where they
are found.
• Compare the DNA found in mitochondria and
nucleus of eukaryote cells.
• Describe the DNA in linear chromosomes found in
nucleus of eukaryote cells.
Prokaryotes and Eukaryotes
What are Prokaryotes?
• Prokaryotes are organisms that lack a
true membrane-bound nucleus.
• Bacteria are examples of prokaryotes.
• Their DNA is found in the cytoplasm of
the cell.
What are Eukaryotes?
• Eukaryotes are organisms which have a
membrane bound nucleus that stores
their genetic material.
• Animals, plants and fungi are examples
of eukaryotes.
• Double stranded DNA can be either
circular or linear.
Linear DNA
Circular DNA
• Prokaryotes have a large circular
chromosome.
• They sometimes also have smaller rings of
DNA called plasmids.
Circular plasmids may also
be found in yeast (a
fungus), which is classified
as a eukaryote!
A bacterial cell
• In eukaryotes, the DNA is found tightly
coiled into linear chromosomes.
• DNA can also be found in mitochondria
(mtDNA) and chloroplasts (cpDNA) where it
forms circular chromosomes. This DNA is
used to make proteins essential to the
functioning of the organelle.
Some scientists
think that
mitochondria and
chloroplasts
originated from
prokaryotic cells
that were at some
point engulfed by
larger cells!
• In linear chromosomes
found in eukaryotes,
the DNA strand would
be several times
longer than the length
of the cell to which it
belongs.
• Therefore, the DNA is
actually tightly coiled
and packaged around
bundles of proteins in
order to store it
efficiently.
Summary – Prokaryotic DNA vs. Eukaryotic DNA
Characteristic
Prokaryotic cell
Eukaryotic cell
Organism that has this
type of cell
Bacteria
Fungi, green plants and
animals
True nucleus bound by
membrane
Absent
Present
Organisation of
chromosomal DNA
Composed of a ring of DNA Composed of DNA in linear
associated with few or no form associated with
proteins
proteins
Plasmids (each consisting
of a small ring of DNA)
Present in many types of
bacteria cell
Present in some yeasts;
absent in plant and animal
cells.
Chloroplasts (each
containing several small
circular chromosomes)
Absent
Present in green plant cells
Mitochondria (each
containing several small
circular chromosomes)
Absent
Present
Ribosomes
Present
Present
QQT task
• Using your notes from key area 1.1(a) and 1.1(b), make
question cards with the answer. Q: What does DNA stand
for?
A: Deoxyribonucleic acid
• Find a partner and quiz them using your question cards (it’s
important you tell them the correct answer if they get it
wrong).
• They will quiz you using their question cards.
• Swap all cards with each other and then move to a new
partner to repeat the process.
• You will now have 7 minutes to quiz as many people as you
can.
• At the end of the 7 minutes, your teacher will collect in
your quiz cards and use these to quiz the class.
Key Area 1.1(b) You should now be able to..
• Identify prokaryotes and eukaryote cells from
diagrams.
• Describe the key similarities and differences
between prokaryote and eukaryote cells.
• Describe structure of a plasmid and name the types
of cells where they are found.
• Describe structure of circular chromosomes and
identify the location and types of cells where they
are found.
• Compare the DNA found in mitochondria and
nucleus of eukaryote cells.
• Describe the DNA in linear chromosomes found in
nucleus of eukaryote cells.
Practical Technique
Extracting DNA
• DNA can be isolated from cells of pea
seeds.
• You may have tried this with kiwi fruit.
• When kiwi fruit is used instead of peas,
most often white strands that form as a
precipitate in the upper layer of cold
ethanol are made of pectin, not DNA.
• The DNA is obscured by pectin, this
result is described as a false positive.
Extraction of DNA from Peas
• You will now carry out the technique.
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
Step 5
Equipment
Safety glasses
50g peas
10ml washing up liquid (measure with
syringe)
3g salt
90ml distilled water
10ml of very cold ethanol
Access to 60˚C water bath
Access to ice bath
2-3 drops Protease enzyme
Pestle and mortar
Filter paper & funnel
2 beakers
Boiling tube
Stirring rod
Test tube rack
Extracting Pea DNA – Class Method
1.
2.
3.
In a clean beaker dissolve 3g of salt in 90ml of distilled water.
Add 10ml of washing up liquid and mix gently.
Grind 50g of peas in a pestle and mortar and add entire contents to
the beaker of salt, water and washing up liquid.
4. Stand the solution in a 60˚C water bath for exactly 15 minutes.
5. Cool the mixture by placing the beaker in an ice water bath for 5
minutes, stirring frequently.
6. Filter this mixture into a second beaker. Ensure that any foam on top
of the liquid does not contaminate the filtrate.
7. Using a syringe slowly add 10ml of your pea extract to a boiling tube,
try not to create any bubbles by running the solution down the inside
of the boiling tube.
8. Add 2-3 drops of protease enzyme to the boiling tube and mix well.
9. Very carefully pour ice cold ethanol (no more than 10ml) down the
inside of the boiling tube, to form a layer on top of the pea extract.
10. Leave the tube, undisturbed in a test tube rack, for a few minutes.
11. Nucleic acids (DNA and RNA) will precipitate into the upper layer.
12. You may scoop out the DNA and RNA using a wire loop or tweezers.
Method
Filter solution through
a filter funnel lined
with filter paper
Results
DNA precipitate forms in the layer of
ice cold ethanol