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Biology A-Level > Genetic Technology in Medicine (Chapter 19) > Flashcards

Genetic Technology in Medicine (Chapter 19) Flashcards

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1
Q

How can human proteins be produced using recombinant DNA techniques?

A

Using bacteria, yeasts and cultures of mammalian cells

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2
Q

Name two human proteins produced by recombinant DNA techniques other than insulin

A

1) factor VIII (blood clotting protein)

2) adenosine deaminase (ADA)

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3
Q

What is the advantage of using bacteria, yeasts and cultures of mammalian cells in recombinant DNA techniques to produce human proteins?

A

1) these cells have simple nutritional requirements ∴ large volumes of the product are produced, the production facilities do not require much space and the processes can be carried out almost anywhere in the world
2) there are few practical and ethical problems bc proteins do not have to be extracted from animal sources or from blood collected from many human donors

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4
Q

What is the disadvantage of using bacteria to produce human proteins?

A

Bacteria do not modify their proteins in the same way as eukaryotes do ∴ it is much better to use eukaryotic cells to make human proteins

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5
Q

What is factor VIII?

A

A protein essential for blood clotting

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6
Q

What condition to people who cannot make factor VIII have?

A

Haemophilia

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7
Q

What is used to produce factor VIII?

A

Genetically modified hamster cells

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8
Q

How are GM hamster cells used to produce factor VIII?

A

1) the human gene for making factor VIII is inserted into hamster kidney and ovary cells which are then cultured in fermenters
2) the cells constantly produce factor VIII which is extracted and purified before being used to treat people with haemophilia
3) these people need regular injections of factor VIII

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9
Q

What problem does recombinant factor VIII avoid?

A

The risk of infection from e.g. HIV when factor VIII used to come from donated blood

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10
Q

What is ADA?

A

An enzyme used to treat severe combined immunodeficiency disease (SCID)

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11
Q

What is used to make ADA?

A

Genetically modified insect larva of the cabbage looper moth caterpillar

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12
Q

When is ADA administered to patients?

A

While they are waiting for gene therapy

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13
Q

Where else are some proteins produced?

A

In the milk of transgenic animals

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14
Q

What two proteins are produced in the milk of transgenic animals?

A

1) human antithrombin (anti-blood clotting protein) in goat’s milk
2) human alpha-antitrypsin (anti emphysema) in sheep’s milk

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15
Q

What is genetic screening?

A

The analysis of a person’s DNA to check for the presence of a particular allele

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16
Q

Who can genetic screening be carried out on

A

1) adults
2) fetus or embryo in the uterus
3) a newly formed embryo formed by IVF

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17
Q

Give an example of how genetic screening can be used

A
  • A woman with a family history of breast cancer could choose to be screened for the fault alleles of the gene Brca-1 and Brca-2, which considerably increase the chance of developing breast cancer
  • If the results are positive for the faulty alleles, she can choose to have an elective mastectomy before the cancer appears
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18
Q

What is IVF?

A

When the mother’s eggs are mixed with the father’s sperm in a dish

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19
Q

What two techniques were used to make the first ‘designer baby’ in 1989?

A

Using pre-implantation genetic diagnosis (PGD) and IVF

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20
Q

How was the first ‘designer baby’ made?

A

1) at the 8-cell stage, one of the cells from the embryo was removed and its DNA analysed to predict whether or not the embryo would have a disease for which both parents were carriers e.g. haemophilia or sickle cell anaemia
2) embryos with the allele causing disease were discarded and the embryo without the allele was chosen for implantation

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21
Q

How have PGD and IVF been used since 1989?

A

To avoid pregnancies where the baby would have had Duchenne muscular dystrophy, thalassaemia, haemophilia or Huntington’s disease

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22
Q

What does genetic testing leave the parents with if the embryo is found to have a genetic condition?

A

Very difficult decisions to make e.g. whether or not to have a termination of pregnancy

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23
Q

What two techniques can be used to screen a fetus for a genetic disease?

A

1) amniocentesis
2) chronic villus sampling
(then parents can decide whether to terminate)

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24
Q

What are two problems with screening a fetus?

A

1) Some parents have decided to terminate just for a relatively minor ‘defect’ where the child could live a fairly normal life or when the child is not the sex they want
2) PGD has been used to select the sex of the embryo to implant - many think this sex preselection is totally unethical

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25
Q

Describe amniocentesis

A
  • Used to obtain a sample of amniotic fluid at 15-16 weeks of pregnancy
  • Samples are tested to check for the heath of the fetus and any chromosomal mutation
  • When obtaining the sample, ultrasound scanning is used to choose a suitable position for the syringe needle away from the fetus, placenta and umbilical cord
26
Q

Describe chronic villus sampling

A
  • Used to get an earlier warning of any genetic abnormalities in the fetus at 10-13 weeks
  • Chorion (small part of the placenta) is remove by a needle and tested for any genetic abnormalities
  • There is a small (1-2%) increase in the risk of miscarriage
27
Q

What is thalassaemia and why has its incidence increased significantly?

A
  • A blood disease similar to sickle cell anaemia

- Its incidence has significantly decreased as a result of genetic screening and giving advice to parent carriers

28
Q

What is a therapeutic abortion?

A

Termination a pregnancy for a medical reason

29
Q

Why might it be difficult for someone to decide whether to be genetically screened for Huntington’s disease?

A
  • It is late onset, with no cure and just because the dominant allele is there, it does not mean that the disease will develop
  • However, even if the disease does not develop, it could be passed down
30
Q

What is gene therapy?

A

Curing genetic disorders by inserting ‘normal’ alleles of these genes into the cells

31
Q

What are the difficulties with gene therapy?

A

Getting normal alleles of the genes into a person’s cells and then making them work properly when they get there

32
Q

What are the most common vectors used to carry normal alleles into the host cells?

A

1) viruses (retroviruses or lentiviruses)
2) liposomes
3) naked DNA

33
Q

What does the defect in SCID involve?

A

The inability to make ADA, which is vital for the functioning of the immune system

34
Q

What are the two types of gene therapy for SCID?

A

1) Some of the T lymphocytes are removed and normal alleles of the ADA gene were introduced into them, using a virus as a vector, and the cells were then replaced - however, this was not a permanent cure as regular transfusions (every 3-5 months) were necessary to keep the immune system functioning
2) Using stem cells harvested from bone marrow

35
Q

What is the problem with using a retrovirus as a vector?

A
  • Retroviruses insert their genes into the host’s genome randomly ∴ they may insert their genes within another gene or into the regulatory sequence of a gene, which may activate a nearby cancer-causing gene
  • e.g. 4 children who had received gene therapy for X-linked SCID developed leukaemia as a result
36
Q

Why can it be better to use lentiviruses as vectors instead of retroviruses?

A

Lentiviruses also insert their genes randomly into the host genome but can be modified to inactivate replication

37
Q

Give 2 examples of successful use of lentiviruses as vectors

A

1) HIV has been disabled to act as a vector
2) AAV (adeno-associated virus) is used as a vector but does not insert its genes into the host genome ∴ they are not passed onto daughter cells when a cell divides - this can be a problem with short-lived cells (lymphocytes) but successful with long-lived cells (neurones and liver cells)

38
Q

Give some examples of successful gene therapies thanks to work on vectors

A

1) improvement of the eyesight of young men with Leber congenital amaurosis (form of hereditary blindness) in which retinal cells gradually die off from an early ages
2) successful insertion of the normal allele of the beta-globin gene into blood stem cells to correct beta-thalassaemia
3) reduction of symptoms of haemophilia B
4) successful treatment of SCID (5 children in 2013)

39
Q

What is cystic fibrosis (CF) ?

A

A genetic disorder in which abnormally thick mucus is produced in the lungs and other parts of the body

40
Q

What are the symptoms of CF?

A

1) very prone to bacterial infections in lungs bc the mucus is not properly removed, allowing bacteria to breed (∴ need daily percussion therapy)
2) pancreatic duct may become blocked
3) sterility (males) bc thick secretions block ducts in the reproductive system

41
Q

What is CF caused by?

A
  • A recessive allele of the gene that codes for a faulty version of the transporter protein CFTR that does not act properly as a Cl- ion transporter
42
Q

What is the CFTR protein?

A

A protein that sits in the CSMs of cells in the alveoli (and elsewhere in the body) and allows Cl- ions to pass out of the cells

43
Q

What happens when CFTR is functioning normally?

A

1) the cells lining the airways and in the lungs pump our Cl- ions through the channel in the CSM formed by CFTR
2) this results in a relatively high [Cl-] outside the cells
3) this reduces the water potential below that of the cytoplasm of the cells ∴ water moves out of the cells by osmosis, down the water potential gradient
4) water mixes with the mucus there, making it thin enough for easy removal by sweeping movements of the cilia

44
Q

What happens at the CFTR in someone with CF?

A

Much less water moves out of the cells ∴ the mucus on their surfaces stays thick and sticky so that the cilia or even coughing can’t remove it all

45
Q

Describe the CFTR gene

A

Found on chromosome 7 with roughly 250,000 bases

46
Q

Describe the most common CFTR mutation

A
  • The result of the deletion of 3 bases
  • ∴ CFTR protein made is missing one amino acid
  • ∴ the cell recognises it is not the right protein and does not place it in the CSM
47
Q

Describe the principle of gene therapy for CF and then the problem

A
  • Principle: caused by a recessive allele on a single gene ∴ if the normal dominant allele could be inserted into cells in the lungs, correct CFTR should be made
  • Problem: difficulties with getting the allele into the cells
48
Q

Describe the two trials of gene therapy to treat CF

A

1) the normal allele was inserted into liposomes and then sprayed as an aerosol into noses - succeeded in introducing allele into a few cells lining the nose but the effect only lasted for a week bc these cells have a very short natural lifespan
2) introduction of the normal allele into normally harmless viruses which carried the allele into passages of the gas exchange system via an inhaler - allele did enter some cells but some people had unpleasant side effects due to infection by the virus

49
Q

Describe the less common mutation of the CFTR gene and its effect

A

1) mutation has replaced one bases with another, creating a stop codon in the middle of the gene
2) the gene is transcribed the normal way but translation on the ribosomes stops when this codon is reached ∴ only a short length of the CFTR protein is made

50
Q

What is the treatment for the less common mutation of the CFTR gene and how does it work?

A
  • Drug called PTC124 allows translation to just keep going across stop codon ∴ entire protein is made with a wrong or missing amino acid in the middle of it
  • This may allow enough CFTR to be made to significantly relieve the symptoms for some people with CF
  • Easy bc only need to take one pill every day
51
Q

What would need to happen for CF gene therapy to be successful?

A

Allele needs to get into many cells throughout respiratory system including the ones that divide to form new surface cells

52
Q

How is naked DNA used in gene therapy and what is the advantage of using it?

A
  • DNA can be inserted into tissues without the use of any vector - used in trials of gene therapy for skin/muscular/heart disorders
  • Advantage: removes problems associated with vectors
53
Q

What are germ cells?

A

Cells involved in sexual reproduction e.g. gametes or an early embryo

54
Q

How could germ cells be used instead of somatic cells in germ therapy?

A
  • A woman with CF could opt to try to conceive a baby using IVF
  • Eggs would be harvested in the normal way and then the ‘correct’ allele of the CFTR gene could be injected into an egg
  • Currently illegal in humans but successful in other animals although high chance of offspring having other, unpredicted diseases
55
Q

What are the problems with germ cell therapy?

A

1) all cells of the child are produced from this genetically engineered zygote and ∴ will all carry the gene that has been inserted
2) when the child grows up and produces eggs/sperm, these gametes will also contain the allele ∴ it will be passed onto their children
3) the allele is in the ‘germ line’, being passed on from generation to generation

56
Q

What is preimplantation genetic diagnosis?

A

A process which allows parents to have the option of detecting potential defects in an embryo within days after conception e.g. Down’s syndrome

57
Q

What are the two types of gene therapy?

A

1) gene augmentation therapy - replaces non-functioning gene with functioning gene
2) gene inhibition therapy - inserts blocking gene which blocks the faulty gene e.g. by preventing transcription fo the gene or creating a product which inhibits the faulty protein

58
Q

How does a liposome act as a vector?

A

It fuses with the cell membrane to release the contents (DNA) inside of its circular phospholipid membrane

59
Q

What are possible negative implications of gene therapy?

A

1) effects may be short-lived
2) not all cells are transformed
3) may be side-effects

60
Q

What is the role of a genetic counsellor and why might someone go to a genetic counsellor?

A
  • Role: do genetic screening, explain test results and implications, pedigree analysis (family history), discuss IVF/gene therapy/termination/ethical issues/financial implications
  • Circumstances: families with known genetic diseases, recurrent miscarriages, older women

Biology A-Level (44 decks)

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