19.2 - Gene tech applied to medicine

Question 1

What is recombinant DNA?

Answer 1

• DNA that has been altered

- by introducing nucleotides sequences from another source

Question 2

How are recombinant proteins formed?

Answer 2

• recombinant DNA has been used to produce recombinant proteins
• produced using eukaryotic cells (yeast) as prokaryotic cells will carry out post-translational modification (due to presence of Golgi Apparatus)
• RP are manipulated forms of the original protein

Question 3

State the advantages of using GE organisms to produce RP

Answer 3

> cost-effective to produce in large volumes
more simple than prokaryotic cells
faster in producing many proteins
reliable supply available
proteins engineered are identical to human proteins
- have modifications that are beneficial
no moral, ethical or religious concerns against usuing cow/ pork produced proteins

Question 4

Describe and explain how recombinant insulins are produced

Answer 4

> bacteria plasmids are modified to include human insulin gene
- restriction endonucleases are used to cut open plasmids
- DNA ligase used to splice plasmid and human DNA together
recombinant plasmids are then inserted into Escherichia coli by transformation (bath of Ca+/ electric shock)
transgenic bacteria isidentified by markers and are isolated, purified and placed in fermenters providing optimal conditions
transgenic bacteria multiply by binary fission and express the human protein insulin
- insulin expressed is extracted and purified

Question 5

State the advantages of using recombinant insulin

Answer 5

> identical to human insulin
- unless modified (act faster)
reliable supply available
- meet demand
- no need to depend on availability of meat stock
fewer ethical, moral or religious concerns
- the proteins are not extracted from cows or pigs
fewer rejection problems/ side effects or allergic reactions
cheaper to produce in large volumes
useful for people who have animal insulin tolerance

Question 6

Describe how recombinant Factor VIII produced and used

Answer 6

• Factor VIII is a blood - clotting protein
• kidney and ovary hamster cells have been genetically modified to produce factor VIII
• once modified, the recombinant cells are placed into a fermenter and cultured
• due to optimal conditions in fermenter, hamster cells constantly express factor VIII
• the protein is then extracted and purified to be used as an injectable treatment for haemophilia

Question 7

State the advantages of using recombinant Factor VIII

Answer 7

> fewer ethical, moral or religious concerns
- proteins are not extracted from human blood
less risk of transmitting infection/ diseases (HIV)
greater production rate

Question 8

Explain what is ADA and how it is produced and used

Answer 8

• adenosine deaminase (ADA) is an enzyme used to treat the inherited condition called Adenosine Deaminase Deficiency which causes Severe Combined Immunodeficiency (SCID)
• immune system is damaged
• larva of the cabbage looper moth has been genetically modified (using a virus vector) to produce the enzyme adenosine deaminase
• it can be used as a treatment whilst patient wait for gene therapy/ or when gene therapy is not possible

Question 9

State the advantages of using recombinant adenosine deaminase

Answer 9

> fewer ethical, moral or religious concerns
- proteins are not extracted from cows
less risk of transmitting infection/ disease
- from cows
more reliable of production of the enzyme
faster to produce many proteins

Question 10

What is genetic screening, and what is it used for?

Answer 10

• the testing of an embryo, fetus or adult to analyse the DNA
• help identify if individuals carry an allele at a gene locus for a particular disease

Question 11

How are the sample of DNA obtained to be analysed by genetic screening?

Answer 11

> taking tissues from adults/ embryos produced by in-vitro fertilisation
chorionic villus sampling/ amniocentesis of embryos and fetuses in the uterus

Question 12

State the uses of genetic counsellors

Answer 12

> can be seen before or after screening has occured
to discuss:
- the chances of the couple having a child with the certain disease
- termination of pregnancy
- therapeutic treatments possible for the child
- financial implications of having the child
- effect on existing siblings
- ethical issues

Question 13

Describe how breast cancer (BRCA1 and BRCA2) occurs

Answer 13

• BRCA1 and BRCA2 are genes that produce tumour suppressor proteins
• the genes play an important role in regulating cell growth
• when faulty alleles of these particular genes exist, it increases the risk of an individual developing breast/ ovarian cancers
• BRCA1 and BRCA2 alleles can be inherited from either parent

Question 14

State the advantages of genetic screening for BRCA1 and BRCA2

Answer 14

> person may decide to take preventative measures
- e.g: having elective mastectomy to reduce the risk of developing cancer
screening for breast cancer may begin from an earlier age and more frequently
- individual (if female) will have more frequent clinical examination of the ovaries
enables person to participate in research and clinical trials

Question 15

What is Huntington’s disease

Answer 15

• A progressive and inherited disease that affects the brain
• include uncontrolled movements, lower cognitive (thinking) ability
• no cure, only treatments available to alleviate symptoms
• it is an autosomal dominant disease
• therefore, if the person has an allele for Huntington’s they will get the disease

Question 16

State the advantages of genetic screening for Huntington’s

Answer 16

> people to plan for the future
- how they will live and be cared for
couples to make informed reproductive decisions
- risk that children may inherit the disease is 50%
- people participate in research and clinical trials

Question 17

Describe cystic fibrosis

Answer 17

• an autosomal recessive genetic disorder
• caused by a mutation of a gene that codes for a transported protein, called CFTR
• a progressive disease that causes mucus in various organs (lungs, pancreas) to become thick and sticky
• due to faulty CFTR protein that no longer transports chloride ions across the cell plasma membrane
• therefore, water does not move by osmosis across the membrane wither
• presence of water would make mucus thinner, enabling cilia to remove it
• no cure for cystic fibrosis, only treatments to alleviate symptoms
• common death is bacterial infection in the lungs

Question 18

State the advantages of genetic screening for cystic fibrosis

Answer 18

> enables couple to make informed reproductive decisions
- both may be carriers and therefore not display any symptoms
people can participate in research and clinical trials

Question 19

State the common advantage in genetic screening

Answer 19

• allows couple to make informed reproductive decisions

- people can participate in research and clinical trials

Question 20

What is gene therapy?

Answer 20

• involves using various mechanisms to alter a person’s genetical material
• able to replace a faulty gene, inactivate a faulty gene, or insert a new gene
• to treat, cure diseases

Question 21

Why, effects of changing the somatic cells are short-lived?

Answer 21

• somatic changes in genetic material are targeted to specific cells
• will not be inherited by future generations
• as somatic gene therapy does not target the gametes
• gene therapy cells is not permanent, whereas in germ cells (gametes) it is permanent

Question 22

State and describe the two types of somatic gene therapy

Answer 22

> ex vivo
- new gene is inserted via a virus vector into the cell outside the body
- blood or bone marrow cells are extracted and exposed to the virus which inserts the gene into the cells
- the cells are grown in the laboratory and returned to the person via injection into vein
in vivo
- the new gene is inserted via a vector (virus/ liposomes/ plasmid) into cells inside the body

Question 23

Why are viruses the most commonly used vectors?

Answer 23

• they have mechanisms needed to recognise cells

- and deliver the genetic material into them

Question 24

What causes SCID?

Answer 24

• severe combined immunodeficiency is caused by the body’s inability to produce adenosine deaminase enzyme (ADA) which is the key to the functioning of the immune system
• without the enzyme, children die from common infections and is often isolated

Question 25

What are the genetic diseases that are treated using gene therapy?

Answer 25

• SCID (severe combined immunodeficiency)

- inherited eye diseases

Question 26

What diseases are genetic screening used for?

Answer 26

• breast cancer (BRCA1 and BRCA2)
• Huntington’s disease
• cystic fibrosis

Question 27

Describe how SCID is treated using gene therapy

Answer 27

• via ex vivo somatic gene therapy
• a virus transfers a normal allele for ADA into T-lymphocytes which were removed from the patient
• the transgenic cells are grown in the laboratory and then returned to the patient’s body via an injection into the vein
• it is not a permanent cure as T-lymphocytes are replaced
• therefore, patient requires regular transfusions every 3 - 5 months to keep their immune system functioning

Question 28

Which vectors are used in the treatment of SCID using gene therapy?

Answer 28

• retroviruses were once used as vectors however it insert their genes randomly into a host’s genome which means they insert the gene into another gene or into a regulatory sequence which could result in cancer (leukaemia)
• lentiviruses or adeno-associated viruses are used
• lentiviruses randomly insert their genes, however they can be modified to not replicate
• adeno-associated viruses do not insert genes into the host genomes, therefore genes are not passed onto daughter cells when cell divides (problem only for short-lived cells)

Question 29

Describe how inherited eye diseases are treated using gene therapy

Answer 29

• leber congenital amaurosis is a group of inherited eye diseases that causes blindness due to damage to the light receptors in the retina
• no cure for these diseases
• treat using in-vivo somatic gene therapy
• doctors inject adeno-associated viruses that contained the normal alleles of one of the genes that caused damage to the photoreceptors
• (at least 18 known mutated genes causing this group of diseases)

Question 30

State the uses of genetic screening in medicine

Answer 30

> allow people with a family history of a genetic disease to have DNA analysed to determine if they’re at risk
carry out pre-implantation genetic diagnosis (PGD)
- embryos that are created outside the body with IVF have their DNA analysed
- allows embryos that are not carrying a harmful allele that would cause the disease to be chosen for implantation

Question 31

State the use of gene therapy in medicine

Answer 31

• used to introduce corrected copies of genes into patients with genetic diseases
• cystic fibrosis, haemophilia, SCID

Question 32

State the social and ethical considerations for genetic screening

Answer 32

> being able to take preventative measures
- elective mastectomy when BRCA1 and BRCA2 are detected
- give individuals control to prevent illness
pre-implantation genetic diagnosis to select embryos that do nor carry fault, disease-causing alleles
- lead to fear of “designer babies” being created
- diagnosis via IVF: cells are extracted from the embryo in an embryo biopsy and genetically screened in order to preselect the embryos without faulty alleles
Using genetic counsellors to help people understand their choices and make informed decision
- financial costs, whether termination of fetus is appropriate if quality of life is poor
Risk of miscarriage (which has emotinal consequences) due to the procedures used to collect DNA which are not 100% risk-free
Amniocentesis – is used to obtain a sample of amniotic fluid using a hypodermic needle at 15 to 16 weeks of pregnancy
Chorionic villus sampling – is used to obtain a small sample of the placenta using a needle between 10 and 13 weeks of pregnancy
Choosing to terminate a pregnancy (therapeutic abortion) because the embryo has a genetic disorder
- minor ‘defect’ that could have seen the child lead an almost normal life
Being able to make informed reproductive decisions
Determining whether it is best to know the risk of having a disease
- even when no cure (Huntington’s)
Confidentiality of the data collected
- who will have the right to view the results obtained

Question 33

State the social and ethical considerations of using gene therapy

Answer 33

> potential for side effects that could cause death
- the children who were treated for SCID developed leukaemia
Whether germline gene therapy (the alteration of genes in egg and sperm cells which results in the alteration being passed onto future generations) should be allowed
- it could be a cure for a disease, or it could create long-term side effects
The commercial viability for pharmaceutical companies
- if it is a rare disease, the relative small number of patients may not mean that the companies will make a profit
The expense of treatments
- as multiple injections of the genes may be required if the somatic cells are short-lived (SCID)
- make the cost of gene therapy accessible to a limited number of people
people will become less accepting of disabilities as they become less common
Who has the right to determine which genes can be altered and which cannot
Another method of enhancing sporting performances unfairly through gene doping
- give unfair advantage