HBiol Sheet 1_7
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1. SCID is a severe inherited disease. People who are affected have no immunity.
Doctors carried out a trial using gene therapy to treat children with SCID. The doctors who carried out the trial obtained stem cells from each child’s umbilical cord.
The doctors mixed the stem cells with viruses. The viruses had been genetically modified to contain alleles of a gene producing full immunity. The doctors then injected this mixture into the child’s bone marrow.
a) Give two characteristic features of stem cells.
b) The viruses that the doctors used had RNA as their genetic material. When these viruses infect cells, they pass their RNA and two viral enzymes into the host cells. One of the viral enzymes is called integrase. Integrase inserts the DNA copy anywhere in the DNA of the host cell. It may even insert the DNA copy in one of the host cell’s genes.
The insertion of the DNA copy in one of the host cell’s genes may cause the cell to make a non-functional protein. Explain how.
2. The graph below shows the changes in number of human stem cells in a culture. The activity of the enzyme glutaminase present in the cells over an eight day period is also shown.
a) How many units of glutaminase activity were recorded when the cell number was 50% of its maximum over the eight day period?
b) Calculate the percentage decline in the glutaminase activity between days 2 and 6.
