(a)
State three advantages of using human insulin produced by genetic engineering.
[ 3 ]
[Maximum number: 3]
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.
(a)
Suggest and explain why it may be more appropriate to use enzyme replacement therapy to treat SCID instead of a bone marrow transplant.
[ 3 ]
[Maximum number: 3]
The cilia of ciliated epithelial cells show variation in length, within an individual and between different individuals.
Samples of ciliated epithelial tissue were removed from the airways of healthy people and the mean cilia length for each individual was calculated.
The people in the study formed two groups:
- people who were exposed to a harmful environmental factor
- people who were not exposed to a harmful environmental factor.
The results are shown in Fig. 3.1.
Fig. 3.1
(a)
Microarray analysis has shown that ciliated epithelial cells and other epithelial cells in the airways express genes that code for receptor proteins on cell surface membranes. These receptor proteins detect specific chemicals.
When the receptor proteins bind to specific chemicals, this causes coughing, constriction of the airways and an increase in cilia activity. In people who have asthma, the response can be severe and life-threatening.
Suggest how knowledge of the genes for these receptor proteins could help in the treatment of asthma.
[ 3 ]
[Maximum number: 6]
Human insulin can be synthesised in a laboratory strain of Escherichia coli using recombinant DNA (rDNA) technology.
The starting point for the process is mRNA coding for insulin, isolated from human pancreas cells.
Four enzymes are needed:
- reverse transcriptase
- DNA polymerase
- restriction enzyme
- DNA ligase.
(a)
(i)
Describe and explain one advantage of treating diabetics with human insulin produced by rDNA technology.
[ 2 ]
(b)
It is possible to use rDNA technology to produce insulin with a slightly different structure from that of human insulin. The effect of the changed structure can then be investigated.
The activities of equal quantities of two insulins, both produced by E. coli, were compared in healthy, non-diabetic subjects:
- human insulin
- insulin X, in which the positions of two amino acids, lysine and proline, were exchanged. Lysine has a hydrophilic R group and proline has a hydrophobic R group.
The results of the investigation are shown in Fig. 3.1.
Fig. 3.1
[ 4 ]
(i)
With reference to Fig. 3.1 describe the differences in activity between human insulin and insulin X.
[ 4 ]
(a)
Recombinant human proteins can be used to treat disease.
[ 3 ]
(i)
From the 1920 s until the 1970 s, insulin obtained from the bodies of animals was used to treat diabetes. From the 1970s, recombinant human insulin was used instead.
Explain the advantages of using recombinant human insulin to treat people with diabetes.
[ 3 ]
[Maximum number: 2]
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 Fig. 5.1.
Fig. 5.1
(a)
With reference to Fig. 5.1, compare the ability of the two viral strains, AAV and AAV2.5T, to infect epithelial cells from the airways.
[ 2 ]
[Maximum number: 3]
Factor VIII can be made as a recombinant human protein.
(a)
(i)
Name the disease that is treated using recombinant human factor VIII.
[ 1 ]
(ii)
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.
[ 2 ]
[Maximum number: 2]
Fig. 5.1 shows some of the steps involved in in-vitro fertilisation (IVF).
Fig. 5.1
(a)
In 2010, researchers found that they could predict with 93 % certainty which embryos produced by in-vitro fertilisation would develop into healthy babies when implanted into the uterus.
Their technique involved the use of time-lapse microscopy. The successful embryos met three criteria:
- the first cytokinesis lasted between 0 and 33 minutes
- the time interval between the first and second cell division was between 7.8 and 14.3 hours
- the time interval between the second and third cell division was between 0 and 5.8 hours.
[ 2 ]
(i)
Suggest one advantage of the use of this new technique in the IVF procedure.
[ 2 ]
(a)
Explain the advantages of treating diabetic people with human insulin produced by gene technology.
[ 6 ]