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21 Manipulating genomes
Stretch and challenge
OCR Biology A
Gene therapy using artificial chromosomes
Specification reference
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6.1.3
Introduction
In this worksheet you will read investigate a method of gene technology and use
your knowledge about genetic modification to answer the questions that are related
to gene therapy using artificial chromosomes.
Learning outcomes
After completing this worksheet you should be able to:
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apply knowledge and understanding of the ethical issues relating to the genetic
modification of organisms
apply knowledge and understanding of the principles of, and potential for, gene
therapy in medicine
describe how PCR is different from semi-conservative replication
identify the problems with gene therapy
discuss the advantages of using artificial chromosomes and compare this
technique to standard single gene therapy.
Background
Synthetic biology: artificial chromosomes
One possible future advance in gene therapy could be the use of artificial
chromosomes. The technique allows large amounts of DNA to be introduced into a
cell without disrupting the existing genome. Artificial chromosomes can carry several
genes, but do not insert themselves into the existing genome. Instead, the artificial
chromosomes sit inside the cell’s nucleus expressing their genes alongside the
original chromosomes.
It has been shown to be possible to add an extra gene to an artificial chromosome.
Furthermore, when cells containing the artificial chromosome were grown under
laboratory conditions and then transplanted into a mouse, the gene functioned
as normal.
Researchers in Tottori University in Japan have now successfully corrected a
genetic defect in mouse stem cells. They used an artificial chromosome containing
the normal gene to correct a serious genetic disease, added it to a stem cell, and
transplanted the stem cell into a mouse.
Researchers have also inserted artificial chromosomes into human embryonic stem
cells. The advantage of using chromosomes is that they can be more easily purified
from cell cultures and can be transferred to stem cells with greater efficiency.
There is much work to do before the technique is used clinically because
chromosomes must be shown to be stable in stem cells over a long period of time.
© Oxford University Press 2016
www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
1
21 Manipulating genomes
Stretch and challenge
OCR Biology A
Task
This worksheet will require you to read an article about a method of gene therapy
that uses artificial chromosomes. You will be asked to compare this method to more
traditional techniques and discuss the possible advantages of each one. There are
also some shorter questions that look at the techniques involved in gene therapy.
Questions
1
Suggest why many genetic disorders are unsuitable for treatment by
gene therapy.
(2 marks)
2
Gene therapy requires the use of PCR to amplify the amount of DNA fragments
obtained from the healthy source. Compare the process of PCR with the
semi-conservative replication of DNA.
(2 marks)
3
Suggest why the researchers put the artificial chromosome into a stem cell.
(1 mark)
4
Once the target gene has been obtained and cloned, it must be spliced into an
artificial chromosome. Using your knowledge of recombinant DNA technology
and gene cloning, suggest how this may be achieved.
(2 marks)
5
Explain how inserting a single gene into a chromosome could disrupt the
function of other genes.
(2 marks)
© Oxford University Press 2016
www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
2
21 Manipulating genomes
Stretch and challenge
OCR Biology A
6
Compare the technique of using artificial chromosomes to gene therapy where only
one gene is inserted. Give similarities and differences between the use of artificial
chromosomes and the use of gene therapy to correct one defective gene.
(4 marks)
7
In trials, gene therapy has had limited success owing to problems with the
technique, such as semi-conservative replication delivering the gene to the
correct site, ensuring the long-term effectiveness, and ensuring gene expression.
There are also issues regarding the use of viral vectors. The use of artificial
chromosomes overcomes some of these problems. Discuss the possible
benefits of using artificial chromosomes.
(4 marks)
© Oxford University Press 2016
www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
3