Download HIV and DNA replication answers

2.2 DNA replication
Teacher notes
AQA Biology
Antiviral drugs
Specification reference

3.1.5.1

3.1.5.2
Learning objectives
After completing this worksheet students should be able to:

describe and explain the process of DNA replication

understand a clinical use for this knowledge

understand the importance of molecule shape in the correct operation of cellular processes.
Introduction
The discovery of the structure of DNA in the 1950s was perhaps one of the landmark advances
in biology in the last century. Once the structure had been worked out biologists rapidly began to
explain how the molecule acts.
Modern medical biologists recognise that a detailed understanding can help in developing
effective drug treatments for a variety of diseases related to abnormalities in DNA function. Two
common examples include cancer therapies and antiviral drugs.
The aim of this task is to show how a knowledge of DNA replication has been helpful in the
development of the antiviral drugs used in the treatment of HIV/AIDS.
Teacher notes

Students will need to use the student book to recap their knowledge of DNA replication. They
will use this knowledge to produce the first task a diagram to explain the replication.

The teacher should check the ideas of complementary base pairing, the use of DNA
polymerase, semi-conservative methods, DNA template strands, and free nucleotides and
their structure.

The second task now asks them to apply this knowledge. They need to read the text and
study the diagrams of the AZT molecule.

They will then need to draw a second diagram which shows AZT being substituted for the
thymine base. This should then stop the replication. No real details of the molecule structure
or enzyme inhibition are needed.

Stretch – students should look up the ideas of competitive inhibition of enzymes and then
apply that idea to the action of AZT. They can be told to look that up, and even be told that
AZT is an inhibitor.

Support – students could draw or build models of the DNA replication, and introduce the drug
AZT as an odd shaped molecule.
Answers
1
a
W  cytosine
(1 mark)
Q  deoxyribose
(1 mark)
Y  phosphate
(1 mark)
Z  thymine
(1 mark)
© Oxford University Press 2015
www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
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2.2 DNA replication
Teacher notes
AQA Biology
b
2
a
b
c
d
3
a
b
c
d
Any two of:
the base uracil is substituted for thymine;
DNA contains deoxyribose, RNA contains ribose sugar;
DNA is double stranded, RNA is single stranded.
S phase
DNA polymerase
free (DNA) nucleotides.
Bases combine in complementary base pairing;
A with T, C with G
The new DNA molecule is made of two strands;
one original parent strand, one new strand.
AZT has no phosphate group;
AZT has substituted the OH (on the sugar) with N3
AZT will combine with adenine;
as it is a similar shape to thymine/or complementary shape to adenine.
It would be unable to make a sugar phosphate backbone/won’t combine with the
phosphate on the neighbouring nucleotide.
The virus is unable to make DNA so can’t reproduce.
© Oxford University Press 2015
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www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
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