Download DNA Self study assisst

DNA
Unit 7 – Proteins and DNA Structure
Self study unit
http://topnews.net.nz/content/221657-importance-exercising-increases-it-alters-dna
You will be studying this unit by yourselves.
University are increasingly using self study to teach whole
units. The Access course also does not teach all the units
seen on the A level, so there will be areas you need to read
up on and make notes. In the work place you will also have
to look up topics by yourself.
Use the syllabus table and write a set
of questions that you will need to ask
yourself in order to fulfil the criteria
http://topnews.net.nz/content/221657-importance-exercising-increases-it-alters-dna
Syllabus
you are not sure
how toand
do replication of DNA.
Learning Outcome 3 –If Appreciate
theabout
structure
this, you may find
Levelusing
3 the
following questioning words useful
and material
apply them to each statement.
3.1 Recognise that our genetic
Level 2
3.1 Accurately describe the structure of
DNA, is in the form of chromatin
Who, what, where,
when,
nucleotides, distinguish between
during interphase and arranged inwhy, how
purines and pyrimidines.
chromosomes during cell division.
3.2 Describe DNA as a very large molecule
consisting of two strands held
together by bases (full names of bases
not required for L2 but needed for L3)
and twisted into a spiral or helix.
3.3 Explain correctly how in replication
the two strands of the DNA molecule
unwind and separate, each strand
acting as a template for the synthesis
of its complementary strand.
3.2 Explain correctly the structure of the
DNA molecule, such as, a
polynucleotide, antiparallel chains,
complimentary base pairs and also
the nature of the bonds between the
bases in the pairs.
3.3 Explain correctly the semiconservative replication of DNA
during interphase.
Learning Outcomes Part A –
Assessment criteria 3.1 Level 2.
Recognise that our genetic material DNA, is in the form of chromatin
during interphase & arranged in chromosomes during cell division.
By the end of this section you should be able to
•
•
•
•
WHAT – What is meant by the term DNA?
WHAT - Describe what is the purpose/function of DNA.
WHERE - Identify the location of DNA in a cell.
HOW and WHY - Describe the complex structure of
DNA in the form of chromatin in interphase and why
this is important
• WHY - Explain why DNA is arranged into chromosomes
during cell division
What is
DNA?
Where is
found?
HOW DNA CONTROLS THE CELL’S ACTIVITIES
1. All chemical reactions in cells and therefore, all cell activities,
are controlled by enzymes.
2. Enzymes are proteins that catalyse (speed up) reactions.
3. Proteins are strings of amino acids.
4. The shape and order of amino acids in a protein determines
what it does.
5. DNA is a code for proteins and therefore controls what
proteins are made and when.
Learning Outcomes – Part B
Assessment criteria 3.2 Level 2
• Describe DNA as a very large molecule consisting of two strands held
together by bases (full names of bases not required for L2 but
needed for L3) and twisted into a spiral or helix.
By the end of this section you should be able to
• WHAT - Draw a diagram to show a molecule of DNA
• WHAT – Describe the gross structure, to include
number of chains, concept of bases and the spiral twist
DNA is made up of two strands of
nucleotides
http://upload.wikimedia.org/wiki
pedia/en/b/b8/DNA-structureand-bases.png
Learning Outcomes – Part C
Assessment criteria 3.1 Level 3 and 3.2 Level 3
• Accurately describe the structure of nucleotides, distinguish between purines and
pyrimidines.
• Explain correctly the structure of the DNA molecule, such as, a polynucleotide, antiparallel
chains, complimentary base pairs and also the nature of the bonds between the bases in
the pairs.
By the end of this section you should be able to
• WHAT – Draw and annotate a detailed diagram to show the
structure of a DNA molecule
• WHAT – Draw a labelled diagram of a nucleotide
• WHAT – Identify the bases as purines or pyrimidines and
which are in DNA and which in RNA
• WHY – Extension - Appreciate the contributions by Franklin
and Watson and Crick in elucidating the structure of DNA
• HOW – Explain how the two strands remain together,
identifying the base pair combinations
• WHY – Describe why the chains are said to run antiparallel
to each other, explaining both ‘anti’ and ‘parallel’
A nucleotide
A nucleotide has three components
A nitrogen-containing
base
A phosphate
group
A pentose Sugar
Sugar –
Nucleotide
Sugar –
Phosphate
base pairs
Phosphate
backbone
backbone
Hydrogen bonds
Deoxyribonucleic acid
DNA
Base
Base pair
Nucleotide
http://oak.cats.ohiou.edu/~ballardh/pbio475/Heredity/DNA-double-helix.JPG
Nucleic acids
Rosalind Franklin (1920- 1958)
James Dewey Watson (1928-)
Francis Harry Compton Crick (1916-2004)
Nobel prize 1962
X-Ray Crystallography - Rosalind Franklin (d1958)
It shows that
the DNA
molecule is
double stranded
This reflection
shows that the
molecule is a
double spiral,
with a twist
occurring every
3.4nm which is
the equivalent of
10 base pairs
http://www.npr.org/programs/atc/features/2002/oct/darklady/dna.jpg
There is a set
distance (2 nm)
between the two
strands, evidence
that there is always
a purine bonded to
a pyrimidine ring
Questions to test your knowledge so far
• What does DNA stand for?
• What does RNA stand for?
Answer:
single human DNA
• Where and when are they found in Amolecule,
stretched out
the cell?
a straight line, has a
width of about 20
• What is the single unit of DNA
Angstrom (about 2
called?
nanometers or
0.0000002 cm) and a
• Why is it called a double helix?
length of approximately
5 cm.
• How wide is a DNA molecule?
• After how many units does the spiral
repeat (i.e. nucleotides are above Answer:
About every 10 base pairs
one another).
Read more:
http://wiki.answers.com/Q/What_is_the_
width_of_DNA_molecule#ixzz1sNcJDEsX
(can be 11 or 12 as they think there are other forms of DNA
shapes only seen in dehydrated forms) (Wikipedia)
• The model of DNA proposed by Watson and Crick won
them a Nobel prize in 1962. There are many features
of their model.
– There are five possible bases in polynucleotides.
•
•
•
•
•
Which is the odd one out and why?
Which are purines and which are pyrimidines?
Which bases are complementary to each other?
How do they join together?
How are these linked to the width of a DNA double helix?
– Extension – How Watson and Crick use the information
from the work of Rosalind Franklin to support the model
we now accept as the structure of DNA?
– What is meant by anti and parallel in the term antiparallel?
– What is meant by the designations 3’ and 5’?
Learning Outcomes- Part D
Assessment criteria 3.3 Levels 2 and 3
• Explain correctly how in replication the two strands of the DNA molecule unwind and
separate, each strand acting as a template for the synthesis of its complementary strand.
• Explain correctly the semi-conservative replication of DNA during interphase.
By the end of this section you should be able to
• WHAT – Identify what is meant by semi-conservative
replication of DNA
• HOW - Identify the steps involved in the replication of
DNA
• WHY – Explain the advantages of this type of
replication (as opposed to conservative replication)
• HOW – Evaluate the evidence this process to occur
semi-conservatively
• WHEN – Describe when in the cell cycle this occurs
DNA replicates semiconservatively – from the
diagram can you work out
what these means?
http://www.genelex.com/paternitytesting/images/dna-molecule.jpg
The DNA molecule unwinds and unzips
Work out the correct order to complete the flowchart
The enzyme DNA polymerase joins these
nucleotides together to form a complimentary
strand. Each strand acts as a template.
Free DNA nucleotides come in and line up opposite
their complementary base pair.
Each new molecule contains half of the original
molecule. For this reason the process is called:
semi-conservative replication.
Two complete DNA molecules are formed.
1. The DNA molecule unwinds and unzips
2. Free DNA nucleotides come in and line up opposite
their complementary base pair.
3. The enzyme DNA polymerase joins these
nucleotides together to form a complementary
strand.
Each strand acts as a template.
4. Two complete DNA molecules are formed.
Each new molecule contains half of the original
molecule. For this reason the process is called:
semi-conservative replication.
Other possible models of DNA replication
http://masterman2013.pbworks.com/w/page/23837643/SD%20DNA%20Replication
Meselson and Stahl experiment
http://www.biog1105-1106.org/demos/106/unit01/6.dnareplicationmodels.html
EXTRA INFORMATION FOR
CURIOSITY
Forensic uses of DNA
http://fig.cox.miami.edu/~cmallery/150/gene/DNA.forensics.jpg