Download CfE Higher Biology

CfE Higher Biology
Expectations…..
• A lot of content to be covered, so self study is required.
• Everyone to try their best and put in 100%
• Research project within this course so be prepared for write up
at home, not during class time.
• Homework will be given regularly………..Check homework board!
• Open classroom…….no question is a stupid question!!!
And most importantly……
Learning Intention
Consolidate our knowledge
of DNA structure and
function
Success Criteria
• All pupils will…..
• State the basic structure of DNA and base pair matches.
• Most pupils will…..
• Identify the 3’ and 5’ end of DNA along with phosphate group,
deoxyribose sugar, and hydrogen bond.
• Some pupils will……
• Explain the function of DNA and its role.
Recap
Because before the holidays seems like such a long time ago………..!
DNA
True or False
DNA is found in
some living
things.
DNA is found in all living things as it contains
the information needed for a living thing to
develop, survive and then reproduce itself.
DNA is the heredity
material – it is passed
on from one generation
to the next.
Your DNA is the same
as the DNA of the
person sitting next to
you.
Everyone's DNA is different as we are all
different. These differences in DNA, which are
differences in its chemical sequence, create
individual differences.
DNA is found in the
cytoplasm of the cell.
DNA is found in the nucleus.
The DNA sequence –
the chemical language –
doesn’t matter as it
doesn’t change anything
about the living thing.
The DNA sequence provides the heredity
information for the living thing to develop and
survive.
The DNA sequence of a
living thing is called its
genotype.
Structure of DNA
• You will be given sheets of paper that have cut outs of nucleotides.
• Your task (in pairs) is to cut and construct the molecular structure of
DNA.
• You must label the 5’ and 3’ ends along with the other labels on the
sheet.
CfE Higher Biology
Lesson 2
Starter Question:
•If there is 30% Adenine, how much
Cytosine is present?
23
Answer:
• There would be 20%
Cytosine
• Adenine (30%) = Thymine
(30%)
• Guanine (20%) = Cytosine
(20%)
• Therefore, 60% A-T and
40% C-G
24
Learning Intention
Consolidate our
understanding of DNA
replication.
Success Criteria
• All pupils will…..
• State what the nucleus must contain in order for replication to
occur.
• Most pupils will…..
• Describe the steps and process of PCR.
• Some pupils will……
• Explain or draw a diagram to show what happens to DNA during
PCR. (must include the words ; leading strand, replication fork,
direction of replication, primers and ligase.)
Replication of DNA
What does the cell need to replicate DNA?
1. A DNA template
2. Primers (short bits of DNA that are complementary to the
DNA being copied)
3. A supply of DNA nucleotides (all 4 types – ATGC)
4. Enzymes – DNA polymerase and Ligase
5. ATP for energy
Formation of the leading strand
1. The double helix
unwinds
Hydrogen bonds between
the bases are broken and
the molecule ‘unzips’
exposing the bases.
This point where the bases
are exposed is called the
‘replication fork’
Formation of the leading strand
2. The primer binds to
the 3’ end.
New hydrogen bonds form
between the
complementary base pairs
of the primer and DNA.
Free DNA nucleotides align
themselves so they bond
with the exposed bases of
the DNA.
Formation of the leading strand
3. DNA polymerase
catalyses the reaction
DNA polymerase catalyses
the formation of the sugar
phosphate bond between
the 3’ end of the primer.
DNA polymerase can only
ADD nucleotides to the to
the 3’ end of the strand.
Formation of the leading strand
4. DNA polymerase
moves along the strand
DNA polymerase moves
along the 3’ end
continuously adding
nucleotides.
This strand is called the
leading strand.
Formation of the Lagging strand
• Because DNA polymerase can only add nucleotides from the 3’ end that
leaves the 5’ end exposed.
• The enzyme LIGASE is able to add nucleotides in this direction.
• This strand is called the lagging strand and its formation known as
discontinuous.
• After both strands have been joined by their complementary bases 2 new
DNA molecules are formed.
• These then coil to make 2 new identical Double helix.
• As both molecules have one of the original strands it is known as Semiconservative.
Replication forks
• Many chromosomes are very long.
• So to ‘unzip’ the entire DNA molecule to replicate a small
sequence would be silly.
• Also, sometimes more than one part of the molecule needs
to be replicated at the same time.
• To overcome this several replication forks will open at one
time like in the diagram above.
Video
Polymerase Chain Reaction (PCR)
• PCR has many uses.
• The most well known probably being to
identify an individual that committed a
crime.
• It can also be used for
• Paternal/maternal DNA tests ( like on
Jeremy Kyle)
• Identify strains of infectious diseases.
• Medical use to look for genetic diseases.
• Historical/Antrapological uses
PCR – How do you do it?
1. Denature original sample at 95 oC
2. Sample is then cooled at 55 oC for one
min to allow primers to bind (anneal) to
target sequence.
3. Sample is then heated again to 72 oC.
This allows the heat tolerant DNA
polymerase to add nucleotides to the 3’
end.
4. DNA polymerase continues to add
nucleotides until replication is
complete.
Answer
• Stage 1 separates strands or breaks H bonds (1)
• Stage 2 allows primer to bond/anneal to strand/target
sequence (1)
Answer
(b) 7
(1)
(c) Identical set up but without primers
(1)