A hospital is trialling a gene therapy for people with cystic fibrosis. Fig. 1 shows a harmless virus used as a vector. A working copy of a gene is placed i...
Question 1 Report
A hospital is trialling a gene therapy for people with cystic fibrosis. Fig. 1 shows a harmless virus used as a vector. A working copy of a gene is placed inside the virus and delivered to cells lining the airways. The vector is designed to insert the gene into the DNA of some airway stem cells. These cells can then divide and produce new cells with the working gene.
(a) Name the molecule labelled P. [1]
(b) Describe how the virus vector transfers the working gene into an airway stem cell. [3]
(c) Explain why this treatment is not expected to alter the DNA passed from this person to their children. [3]
(d) Complete the sequence by stating three events that allow a treated stem cell to produce functioning airway cells. [3]
(e) State two possible limitations or risks of using a virus as a gene-therapy vector. [2]
(f) Explain why mitosis can make the treatment last longer in the airway lining. [3]
Answer Details
(a) Molecule P is DNA. [1 mark]
(b) The virus vector enters, or infects, an airway stem cell. It carries the working gene into the cell nucleus, where the gene is inserted into the cell's DNA. [3 marks]
(c) The treatment targets airway cells, which are somatic body cells. It does not target gametes, such as egg cells or sperm cells. Therefore, the altered gene is not normally present in the DNA inherited by offspring. [3 marks]
(d) A correct sequence is: the inserted gene is copied when DNA replicates; the stem cell undergoes mitosis; daughter cells inherit the working gene; the cells make the required protein and become functioning airway-lining cells. Any three linked events gain credit. [3 marks]
(e) Any two risks or limitations are: an immune response to the vector; infection of unintended cells; insertion disrupting another gene or causing uncontrolled cell division; or failure to reach enough target cells. [2 marks]
(f) A treated stem cell divides by mitosis. Its daughter cells receive the inserted gene and the same DNA. Repeated division replaces airway cells with cells able to make the working protein, so the effect can last longer in the airway lining. [3 marks]
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