Genetic technology applied to medicine

Explain how genetic diseases can be treated by using gene therapy.

Feb/March 2016

Cystic fibrosis (CF) is an inherited condition.

May/June 2010

The disc diffusion method can be used to assess how sensitive bacteria are to antibiotics. First, an inoculum of the bacteria is spread over agar culture plates, and then filter paper discs soaked with antibiotic are placed on the agar surface. After incubation, the bacteria form a continuous ‘lawn’ over the agar, but a circular clear region, called the zone of inhibition, is seen around any disc where bacterial growth has been prevented. Two bacterial species, A and B, were cultured on separate plates with three different filter paper discs: 1 - no antibiotic (control) 2 - penicillin V, a natural penicillin 3 - carboxypenicillin, a synthetic penicillin. The incubated plates are shown in Fig. 3.1.

May/June 2010

The stages involved in making monoclonal antibodies are illustrated in Fig. 2.1. Step 1: An antigen, A, is injected into a mouse. Step 2: The mouse is then left for several weeks so that an immune response can develop. Step 3: Plasma cells (effector B lymphocytes) are taken from the mouse’s spleen. Step 4: Hybridoma cells are produced. Step 5: Each hybridoma cell is separated and permitted to grow and divide. Step 6: The hybridoma cells that make anti-A antibodies are picked out and grown on a large scale.

May/June 2012

The bacterium Treponema pallidum is the cause of syphilis, a sexually transmitted infectious disease. If it is not treated, the disease may be fatal, although early diagnosis can result in successful treatment. A key problem when diagnosing it in the early stages is distinguishing T. pallidum from other Treponema species that live in humans. These other treponemes do not cause harm. A mouse was injected with some cells of T. pallidum.

May/June 2012

Several stages in monoclonal antibody production are illustrated in Fig. 2.1. Step 1: antigen A is injected into a mouse. Step 2: the mouse is then left for a few weeks so that an immune response can develop. Step 3: plasma cells (effector B lymphocytes) are removed from the mouse’s spleen. Step 4: hybridoma cells are produced. Step 5: each hybridoma cell is separated and allowed to grow and divide. Step 6: the hybridoma cells that make anti-A antibodies are identified and then cultured on a large scale.

May/June 2012

Several diseases, including dengue fever, are spread by mosquitoes. In recent years the number of cases has risen sharply, and this has been associated with the spread of the mosquito Aedes aegypti. To reduce the population of A. aegypti, genetically modified (GM) male mosquitoes were created. When one inserted gene is activated, it produces a protein that is toxic to mosquitoes. In 2010, GM male mosquitoes were released in the Cayman Islands and in Malaysia so that they could mate with females. Every offspring produced died at the larval stage.

May/June 2013

Describe the benefits of batch culture for penicillin production and continuous culture for mycoprotein production.

May/June 2015

Intracytoplasmic sperm injection (ICSI) is a variation on the in-vitro fertilisation (IVF) procedure. Rather than allowing one of many sperm to enter the oocyte, a single sperm is injected into an oocyte.

May/June 2015

Describe the role of electrophoresis in genetic fingerprinting.

May/June 2015

Describe the benefits of batch culture for penicillin production and continuous culture for mycoprotein production.

May/June 2015

Cancer is a condition in which the normal control of cell division is lost, so malignant tumours develop. For many types of cancer, early detection can lead to successful treatment. The BRCA2 protein helps to suppress tumour development. The gene that codes for this protein is found on chromosome 13. Several different dominant alleles of this gene, BRCA2, code for faulty forms of the protein. Having any one of these faulty alleles raises the likelihood of developing several types of cancer, including breast cancer. However, not all people with one of these alleles develop cancer, because environmental influences, including lifestyle, are also involved. Fig. 5.1 is a pedigree (family tree) showing cancers across four generations of a family. A faulty BRCA2 allele was confirmed in person 15. The other individuals with cancer were not tested for the allele. Individuals 24-30 are all under twelve years old.

May/June 2017

If blood supply to the brain is cut down severely, brain cells die; this event is known as a stroke. The outcomes after a stroke can vary from recovery to lasting brain damage and death. A newly developed emergency gene therapy for people who may develop brain damage after a stroke was tested in mice. • The human granulocyte colony-stimulating factor, hG-CSF, is a protein that encourages stem cell production in bone marrow. • mRNA coding for hG-CSF was isolated and then used to produce cDNA. • This cDNA was inserted into an adeno-associated virus (AAV) vector and delivered in eye drops to mice immediately after they had a stroke.

May/June 2018

People with Alzheimer’s disease (AD) have a reduced ability to make new memories. A form of Alzheimer’s disease known as familial Alzheimer’s disease arises from an autosomal dominant allele of the APP gene. To investigate Alzheimer’s disease, genetically identical modified mice carrying the dominant human APP allele have been created. These animals are called AD mice and act as mouse models of Alzheimer’s disease. When AD mice are trained to swim through a water maze, they do not perform well and learn less effectively than normal mice.

May/June 2018

Gene therapy may be used to treat certain genetic disorders. A suitable vector is selected to transport the normal allele into the target cell. The three vector types commonly selected are naked DNA, viruses and liposomes.

May/June 2020

Lung epithelial cells possess a thin watery mucus coating on their surface. The normal allele of the *CFTR* gene encodes a transport protein that moves chloride ions out of epithelial cells. Fig. 4.1 shows part of the cell surface membrane together with the mucus layer of an epithelial cell that contains normal CFTR proteins. Cystic fibrosis (CF) is a genetic disorder caused by possession of two recessive alleles of *CFTR*. In severe CF, the transport proteins are not inserted into the cell surface membrane. As a result, the mucus layer becomes thick and sticky.

May/June 2020

Recombinant human proteins may be employed in the treatment of disease.

May/June 2023

One cause of the genetic disease severe combined immunodeficiency (SCID) is a mutation in the $ADA$ gene. As a result, the enzyme adenosine deaminase (ADA) is not produced in sufficient amounts. ADA is present throughout the body, but its activity is especially high in lymphocytes. When functional ADA is absent, toxic metabolites accumulate, which destroys lymphocytes and harms organs. Babies are usually diagnosed with SCID by six months old. With treatment, the life expectancy of children with SCID can be improved greatly. Several treatment choices exist. • Enzyme replacement therapy using recombinant human ADA produced by genetically modified (GM) $Escherichia\ coli$. The treatment is given as weekly intra-muscular injections. • Bone marrow transplant, provided a suitably matched donor, such as a close relative, is available. • Gene therapy.

May/June 2023

The gene $\textit{BRCA1}$ is active in breast tissue and in a number of other body tissues. $\textit{BRCA1}$ encodes a tumour suppressor protein. This protein functions either by repairing damaged DNA or by initiating cell death if the DNA cannot be repaired. Certain mutations in $\textit{BRCA1}$ are linked with a greater chance of developing breast cancer.

May/June 2024

BRCA2 is a tumour-suppressor gene. Its gene product, BRCA2, helps with DNA repair. If DNA cannot be repaired, BRCA2 also has a function in triggering cell death. BRCA2 occurs in breast tissue cells. If a mutation happens in BRCA2, damaged DNA may fail to be repaired, and this raises the risk of breast cancer. When a double-stranded section of DNA breaks, BRCA2 attaches directly to the damaged DNA and works with the enzyme RAD51 to fix the damage. DNA repair stops further mutations and gene rearrangements from happening, either of which could otherwise result in breast cancer.

May/June 2024

A number of strategies have been explored for using gene therapy to treat cystic fibrosis. One method relies on viruses to carry normal alleles of the CFTR gene into epithelial cells in the airways. Viral delivery systems have two main drawbacks: • The virus may set off an immune response that destroys the infected cells. • Most non-pathogenic viruses are poor at entering cells, so only a very small number of cells receive the allele. Researchers in the USA produced a new strain, AAV2.5T, of AAV, a non-pathogenic virus. AAV2.5T has a better ability to bind to epithelial cells in the airways. Genes for the CFTR protein and for the enzyme luciferase were inserted into the virus DNA. When luciferin is added, luciferase produces a fluorescent green protein. The standard AAV strain and the AAV2.5T strain were introduced into cultures of epithelial cells from the airways. After luciferin was added, the number of cells that had taken up the viral genes was estimated from the strength of the green fluorescence that developed. The results are shown in Fig. 5.1.

Oct/Nov 2010

In humans, the gene RPE65 codes for a protein that rebuilds the visual pigment in rod and cone cells after exposure to light. A recessive allele of this gene leads to poor vision from birth, which worsens until complete blindness in early adulthood. This condition is known as LCA. In 2008, trials investigated whether gene therapy could treat LCA safely and effectively.

Oct/Nov 2011

In humans, the gene RPE65 codes for a protein that rebuilds visual pigment in rod and cone cells after light exposure. A recessive allele of this gene leads to reduced vision from birth, which then develops into total blindness in early adulthood. This disorder is known as LCA. In 2008, trials investigated whether LCA could be treated safely using gene therapy.

Oct/Nov 2011

Gene technology allows insulin to be manufactured on a large scale using prokaryotes such as Escherichia coli. Table 7.1 outlines the sequence of steps in one method for producing insulin using E. coli. Complete Table 7.1 by writing one statement in each blank box.

Oct/Nov 2011

Table 5.1 sets out the steps in a method for producing human insulin by gene technology. The steps are not in the right sequence.

Oct/Nov 2011

Many couples who cannot conceive naturally are treated by fertilisation (IVF).

Oct/Nov 2012

Section B Answer any one question.

Oct/Nov 2013

Many tumours secrete a protein growth factor known as VEGF. This acts as a chemical messenger that makes nearby blood vessels form fresh branches into the tumour. The monoclonal antibody bevacizumab (Avastin®) binds specifically to VEGF.

Oct/Nov 2014

Using DNA (rDNA) technology, human insulin can be synthesised in a laboratory strain of Escherichia coli. The process begins with insulin mRNA, isolated from human pancreas. Four enzymes are required: reverse transcriptase, DNA polymerase, restriction enzyme, and DNA ligase.

Oct/Nov 2014

Many tumours secrete a protein growth factor called VEGF. This chemical messenger makes nearby blood vessels sprout new branches into the tumour, and the monoclonal antibody bevacizumab (Avastin®) binds specifically to VEGF.

Oct/Nov 2014

Using DNA (rDNA) technology, human insulin may be manufactured in a laboratory strain of Escherichia coli. The process starts with mRNA that codes for insulin, taken from the human pancreas. Four enzymes are required: reverse transcriptase, DNA polymerase, restriction enzyme, DNA ligase.

Oct/Nov 2014

Section B. Choose one question to answer.

Oct/Nov 2014

The diagram shows how the gene for human insulin is made using genetic engineering methods (Fig. 3.1).

Oct/Nov 2014

NicVAX, a vaccine, is being developed to help people stop smoking tobacco. When NicVAX is injected into the body, it triggers the production of antibody molecules that bind to nicotine.

Oct/Nov 2015

Haemophilia A and haemophilia B are widespread inherited blood-clotting disorders. Haemophilia A is a sex-linked genetic disorder that affects about 1 in 20000 males worldwide. It results from a recessive allele of a gene that codes for a clotting factor and causes excessive bleeding. There is still no cure, although the symptoms of haemophilia can be managed by transfusing a clotting factor to slow the bleeding.

Oct/Nov 2015

Therapeutic proteins are employed to treat disease. The first purified therapeutic protein to be used was insulin, in 1922. This insulin was obtained from animal pancreases. Since 1982, most insulin has been produced using recombinant DNA technology.

Oct/Nov 2019

Therapeutic proteins are employed to treat disease. The first purified therapeutic protein to be used was insulin, in 1922. That insulin was obtained from animal pancreases. Since 1982 most insulin has been produced by recombinant DNA technology. Calcitonin is a small protein hormone made up of 32 amino acids. One of its roles is to inhibit the activity of cells called osteoclasts, which break down bone tissue. Calcitonin has been used as a therapeutic protein to treat osteoporosis. In osteoporosis, excessive breakdown of bone tissue in older people causes lower bone density and an increased risk of bone fractures. Fig. 3.1 displays the amino acid sequences of human calcitonin and calcitonin from the salmon fish, Salmo salar.

Oct/Nov 2019

An autosomal recessive mutation is the cause of the immune system disorder adenosine deaminase (ADA) deficiency. Severe combined immunodeficiency that results from a lack of ADA is known as ADA-SCID.

Oct/Nov 2022

Haemophilia is a disorder of blood clotting in humans that results from a mutant allele on the X chromosome. Table 4.1 sets out a comparison between the two forms of haemophilia: haemophilia A and haemophilia B.

Oct/Nov 2022

Adenosine deaminase (ADA) deficiency is an immune-system disorder arising from a recessive autosomal mutation. The severe combined immunodeficiency caused by a lack of ADA is called ADA-SCID.

Oct/Nov 2022

Medicine means diagnosing disease, treating it and helping to prevent it.

Oct/Nov 2023

Medicine means the diagnosis, treatment and prevention of disease.

Oct/Nov 2023

The treatment of many diseases has been improved through the use of genetic technology in medicine.

Oct/Nov 2024