19.2. Genetic technology applied to medicine
A subsection of Biology, 9700, through 19. Genetic technology
Listing 10 of 37 questions
Factor VIII can be made as a recombinant human protein. Name the disease that is treated using recombinant human factor VIII. Before recombinant human factor VIII was available, this disease was treated with factor VIII from donated blood. Give two advantages of using recombinant human factor VIII, instead of factor VIII from donated blood, to treat this disease. The gene that codes for human factor VIII can be synthesised from messenger RNA purified from human liver cells. Name the enzyme that uses messenger RNA as a template to produce complementary DNA. Outline two sources, other than messenger RNA, from which genes can be obtained for genetic engineering. The gene that codes for human factor VIII can be transferred into mammalian cells in tissue culture. Explain why a promoter also needs to be transferred into the mammalian cells so that human factor VIII can be synthesised.
9700_m22_qp_42
THEORY
2022
Paper 4, Variant 2
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A severe reduction of blood flow to the brain causes cells to die. This is called a stroke. The after-effects of a stroke can range from recovery to permanent brain damage and death. A new emergency gene therapy treatment for people who are at risk of brain damage from a stroke was tested in mice. • The human granulocyte colony-stimulating factor, hG-CSF, is a protein that stimulates the production of stem cells in bone marrow. • mRNA coding for hG-CSF was obtained and used to make cDNA. • This cDNA was inserted into an adeno-associated virus (AAvector and given in eye drops to mice just after they experienced a stroke. Explain what is meant by gene therapy. Describe the roles of reverse transcriptase and DNA polymerase in making cDNA for hG-CSF. The AAV vector used was unable to replicate itself within the target cells. Suggest why the researchers chose a vector that could not replicate. A study was carried out to investigate the effect of the gene therapy described in . Four groups of mice were used. • Group A mice had a stroke. They received eye drops containing AAV vector carrying cDNA for hG-CSF once only. • Group B mice had a stroke. They received eye drops containing AAV vector carrying cDNA for hG-CSF four times. • Group C mice had a stroke. They received eye drops containing AAV vector carrying the GFP gene coding for green fluorescent protein, instead of the cDNA for hG-CSF, once only. • Group D mice did not have a stroke. They were not given any eye drops. Explain why the mice in group C were used in the study. Explain why the mice in group D were used in the study. Table 5.1 summarises some results from the study and shows: • the percentage of mice surviving • the percentage of brain volume occupied by fluid-filled space • the score on a behavioural test in which normal mice score 0.5 and brain-damaged mice score nearer to 1.0. Table 5.1 mouse treatment group percentage of mice surviving percentage of brain occupied by fluid-filled space behavioural test score / arbitrary units A 3.6 0.67 B 3.0 0.67 C 5.2 0.90 D 3.0 0.50 Use the results in Table 5.1 to evaluate the benefits of gene therapy treatment, with AAV vector carrying the gene for hG-CSF, for people who have a stroke.
9700_s18_qp_42
THEORY
2018
Paper 4, Variant 2
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Gene therapy can be used to treat some genetic disorders. An appropriate vector is chosen to carry the normal allele into the target cell. Three types of vectors commonly chosen are naked DNA, viruses and liposomes. A trial of gene therapy to treat cystic fibrosis used a viral vector. The viral vector caused a primary immune response with the production of memory cells. Explain why the production of memory cells prevents the gene therapy from working in long-term chronic conditions such as cystic fibrosis. With reference to the three types of vectors that are commonly used, discuss the challenges in choosing appropriate vectors for use in gene therapy. Do not include problems associated with an immune response in your answer. A trial was carried out to find a new vector for use in gene therapy. The new vector was made from red blood cells taken from the person with the genetic disorder. The cells had most of their cytoplasmic content removed and were then broken up to make small spherical vectors. Most of these vectors lacked the ability to bind to receptors on the target cells. To solve this problem, genetically engineered stem cells taken from the person were used to form red blood cells. These red blood cells had membrane proteins that were complementary to the target cell receptors. The vectors that were produced were well-tolerated by the immune system. Explain why the vectors were well-tolerated by the immune system. Suggest why it is not possible to produce genetically engineered red blood cells, except by using genetically engineered stem cells.
9700_s20_qp_42
THEORY
2020
Paper 4, Variant 2
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One cause of the genetic disease severe combined immunodeficiency (SCID) is a mutation in the ADA gene. This mutation results in a deficiency of the enzyme adenosine deaminase (ADA). Although ADA is found throughout the body, it is especially active in lymphocytes. The absence of functional ADA causes the build-up of toxic metabolites that kill lymphocytes and damage organs. Babies are often diagnosed with SCID by six months old. Treatment can greatly improve the life expectancy of children with SCID. Some treatment options are available. • Enzyme replacement therapy with recombinant human ADA made by genetically modified (GM) Escherichia coli. Weekly intra-muscular injections are given. • Bone marrow transplant if a well-matched donor, such as a close relative, can be found. • Gene therapy. Suggest and explain why it may be more appropriate to use enzyme replacement therapy to treat SCID instead of a bone marrow transplant. Outline the procedure used for gene therapy treatment of a person with SCID. Suggest the social and ethical implications of gene therapy for SCID that need to be considered before treatment is carried out.
9700_s23_qp_43
THEORY
2023
Paper 4, Variant 3
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Many attempts have been made to find methods of using gene therapy to treat cystic fibrosis. One approach uses viruses to deliver normal alleles of the CFTR gene into epithelial cells of the airways. Viral delivery systems have two main problems: • The virus may trigger an immune response which destroys the infected cells. • Most non-pathogenic viruses are not very good at getting into cells, so very few cells receive the allele. A team of researchers in the USA developed a new strain (AAV2.5T) of AAV, a non- pathogenic virus. AAV2.5T has an improved ability to bind with epithelial cells of the airways. Genes for the CFTR protein and for an enzyme, luciferase, were added to the DNA of the viruses. Luciferase produces a fluorescent green protein when luciferin is added. The normal AAV strain and the AAV2.5T strain were added to cultures of epithelial cells from the airways. After adding luciferin, the numbers of cells that had taken up the viral genes was estimated using the intensity of the green fluorescence which developed. The results are shown in . intensity of green fluorescence / arbitrary units time / days AAV AAV2.5T With reference to , compare the ability of the two viral strains, AAV and AAV2.5T, to infect epithelial cells from the airways. Explain why the researchers added a gene for luciferase to the viral DNA. Suggest how delivering normal alleles of the CFTR gene into epithelial cells in the airways could relieve the symptoms of cystic fibrosis.
9700_w10_qp_43
THEORY
2010
Paper 4, Variant 3
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In humans, the gene RPE65 encodes a protein responsible for regenerating visual pigment in rod and cone cells after they have been exposed to light. A recessive allele of this gene causes impaired vision from birth, progressing to complete blindness in early adulthood. This condition is called LCA. In 2008, trials were carried out into the possibility and safety of treating LCA using gene therapy. Suggest and explain why LCA is suitable for treatment using gene therapy. Six adults with this condition were used in the study. Genetically modified adenoviruses (a type of virus that can cause respiratory infections) were used as vectors. The vectors were injected beneath the retina of one eye of each of the participants. Suggest two ways in which the genome of the adenoviruses used as vectors would differ from that of normal adenoviruses. 1. 2. Improvements were found in the vision of all the participants, but the small number in the trials made most of these improvements not statistically significant. Suggest why these trials were designed to include such a small number of participants.
9700_w11_qp_41
THEORY
2011
Paper 4, Variant 1
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Insulin can be produced on a large scale using gene technology and prokaryotes such as Escherichia coli. Table 7.1 summarises the sequence of steps in one method of production of insulin by E. coli. Complete Table 7.1 by adding one statement in each of the empty boxes. Table 7.1 step reason for step obtain copies of gene with sticky ends the gene codes for the synthesis of insulin acts as a vector for the transfer of the gene into the host use restriction endonuclease enzyme mix vector and gene to seal the sugar-phosphate backbone to obtain transformed host E. coli cells screen for, and obtain, successfully transformed cells to obtain large amounts of insulin for extraction and purification
9700_w11_qp_41
THEORY
2011
Paper 4, Variant 1
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Questions Discovered
37