genetic technology Flashcards
What does the genetic code is universal mean?
that almost every organism uses the same four nitrogenous bases – A, T, C & G.
There are a few exceptions
This means that the same codons code for the same amino acids in all living things (meaning that genetic information is transferable between species)
Thus scientists have been able to artificially change an organism’s DNA by combining lengths of nucleotides from different sources (typically the nucleotides are from different species)
define recombinant DNA (rDNA)
The altered DNA, with the introduced nucleotides
transgenic organism
If an organism contains nucleotide sequences from a different species
genetically modified organism (GMO)
Any organism that has introduced genetic material
genetically modified organism (GMO)
Any organism that has introduced genetic material
What is genetic engineering?
is a technique used to deliberately modify a specific characteristic (or characteristics) of an organism.
What does the genetic engineering technique involve?
removing a gene (or genes) with the desired characteristic from one organism and transferring the gene (using a vector) into another organism where the desired gene is then expressed
What will the genetically engineered organism contain?
recombinant DNA and will be a genetically modified organism (GMO)
What are the following steps In order for an organism to be genetically engineered ?
Identification of the desired gene
Isolation of the desired gene by:
- Cutting from a chromosome using enzymes (restriction endonucleases)
- Using reverse transcriptase to make a single strand of complementary DNA (cDNA) from mRNA
- Creating the gene artificially using nucleotides
- Multiplication of the gene (using polymerase chain reaction - PCR)
- Transfer into the organism using a vector (e.g. plasmids, viruses, liposomes)
- Identification of the cells with the new gene (by using a marker), which is then cloned
What do genetic engineers need to modify and organism?
Enzymes (restriction endonucleases, ligase and reverse transcriptase)
Vectors - used to deliver genes into a cell (eg. plasmids, viruses and liposomes)
Markers - genes that code for identifiable substances that can be tracked (eg. GFP - green fluorescent protein which fluoresces under UV light or GUS - β-glucuronidase enzyme which transforms colourless or non-fluorescent substrates into products that are coloured or fluorescent)
synthetic biology
- genetic engineering is being used
This is an area of research that studies the design and construction of different biological pathways, organisms and devices, as well as the redesigning of existing natural biological systems
synthetic biology
- genetic engineering is being used
This is an area of research that studies the design and construction of different biological pathways, organisms and devices, as well as the redesigning of existing natural biological systems
The gene with the specific characteristic that is required can be obtained in the following ways:
Extracting the gene from the DNA of a donor organism using enzymes (restriction endonucleases)
Using reverse transcriptase to synthesise a single strand of complementary DNA (cDNA) from the mRNA of a donor organism
Synthesising the gene artificially using nucleotides
The extraction of the gene (containing the desired nucleotide sequence) from the donor organism. How does this occur?
using restiction endonucleases.
Restiction endonucleases/enzyme
The enzymes restrict a viral infection by cutting the viral genetic material into smaller pieces at specific nucleotide sequences within the molecule.
- many diff as bind to specific restiction site on DNA
- will seprarate 2 stands of DNA at specific base sequences by ‘cutting’ the sugar-phosphate backbone in an uneven way to give sticky ends or straight across to give blunt ends
what do sticky ends result in?
one strand of the DNA fragment being longer than the other strand
The sticky ends make it easier to insert the desired gene into another organism’s DNA as they can easily form hydrogen bonds with the complementary base sequences on other pieces of DNA that have been cut with the same restriction enzyme
blunt ends
Blunt ends are fragment ends of a DNA molecule that are fully base paired.
When using genes isolated by restriction endonucleases that give blunt ends nucleotides can be added to create sticky ends
Another method to isolate the desired gene is to use the mRNA that was transcribed for that gene
Once isolated, the mRNA is then combined with a reverse transcriptase enzyme and nucleotides to create a single strand of complementary DNA (cDNA)
The mRNA is used as a template to make the cDNA
DNA polymerase is then used to convert the single strand of cDNA into a double-stranded DNA molecule which contains the desired code for the gene
method to isolate the desired gene is to use the mRNA that was transcribed for that gene. Why is it considered advantageous?
it is easier for scientists to find the gene because specialised cells will make very specific types of mRNA (eg. β-cells of the pancreas produce many insulin mRNAs) and the mRNA (therefore the cDNA) does not contain introns
method to isolate the desired gene is to use the mRNA that was transcribed for that gene. Why is it considered advantageous?
it is easier for scientists to find the gene because specialised cells will make very specific types of mRNA (eg. β-cells of the pancreas produce many insulin mRNAs) and the mRNA (therefore the cDNA) does not contain introns
As scientists are becoming more familiar with the base sequences for our proteins (proteome) what is becoming possible?
the synthesis of genes artificially.
- With the knowledge of the genetic code (that is, which amino acids are required) scientists use computers to generate the nucleotide sequence (rather than an mRNA template) to produce the gene
- Short fragments of DNA are first produced which are joined to make longer sequences of nucleotides and then inserted into vectors (eg. plasmids)
- This method is being used to create novel genes being used to make vaccines and even to synthesise new bacteria genomes
In order to genetically engineer an organism there are a number of enzymes required what are they?
Restriction endonuclease
Revese transcriptase
DNA polymerase
DNA ligase
role of Restriction endonuclease in the transfer of a gene into an organism
Isolate the desired gene
Separate the DNA strands (at the same base sequence) in a vector so the desired gene can be inserted
cuts the DNA strands so that the desired gene can be isolated or spliced (inserted) into a vector
will separate the two strands of DNA at the specific base sequence by ‘cutting’ the sugar-phosphate backbone in an uneven way to give sticky ends or straight across to give blunt ends
Sticky ends result in one strand of the DNA fragment being longer than the other strand
The sticky ends make it easier to insert the desired gene into another organism’s DNA or into a vector as they can easily form hydrogen bonds with the complementary base sequences on other pieces of DNA that have been cut with the same restriction endonucleases
the role of reverse transcriptase in the transfer of a gene into an organism
produce a single-strand complementary DNA
molecule (cDNA) that contains the code for the
desired characteristic
- this will then be inserted into a vector (after being
converted into a double-stranded DNA molecule
Reverse transcriptase
is an enzyme encoded by retroviruses that uses an RNA strand as a template for DNA synthesis (produces 1 DNA strand)
* this DNA that’s been synthesised is called
complementary DNA (cDNA)
* the source of reverse transcriptase enzyme is
retroviruses
(DNA) ligase
Ligase catalyses the formation of phosphodiester bonds
in the DNA sugar-phosphate backbone.
Role of ligase in the transfer of a gene into an organism
Enables the isolated desired gene to be spliced into a
vector (generally a plasmid) so that it can be transferred
to the new organism.
Advantage of using reverse transcriptase enzymes
easier for scientists to find mRNA with the specific
characteristic
* this is because specialised cells make very specific
types of mRNA (e.g., β-cells of the pancreas produce
many insulin mRNA)
* mRNA also does not contain introns
- introns are non-coding regions of RNA transcript
why are vectors used?
to transfer the desired genes into a foreign cell
what are the most commonly used vector?
plasmids
- but viruses+liposomes also can be used to transfer genes.
plasmids features
- small, circular rings of double-stranded DNA
- occur naturally in bacteria, also found in archaea and eukaryotic organisms (eg. yeast and fungi) and can contain genes for antibiotic resistance
- uses as they can self replicate
- used to transfer the desired gene to a new organism
What is the procedure to insert the desired gene into the circular DNA of the plasmid?
it is ‘cut’ open.
The same restriction endonuclease that was used to isolate the desired gene is used to ‘cut’ open the plasmid.
This results in the plasmid having complementary sticky ends to the sticky ends on the desired gene fragment
DNA ligase forms phosphodiester bonds between the sugar-phosphate backbone of the DNA fragment and the plasmid to form a recombinant plasmid (a closed circle of double-stranded DNA containing the desired gene)
Scientists can modify bacterial plasmids or artificially produce them. One benefit of this is that the plasmids can have one or more marker genes so that cells that have the recombinant plasmids can be identified
How are plasmids transferring into host cells and what is the process called?
process- transformation
only small proportion of bacteria will become transformed and therefore markers used to identify these.
Transformation can occur by:
Bathing the plasmids and bacteria in an ice-cold calcium chloride solution and then briefly incubating at 40°C. This makes the bacteria membrane permeable
Electroporation - where the bacteria is given a small electrical shock making the membranes very porous (this technique can be used to get DNA fragments into eukaryotic cells)
viruses
commonly used as vectors in the process of gene therapy, which is currently used to treat genetic diseases such as cystic fibrosis
The viruses are genetically modified to carry non-mutated genes into host cells
Different types of viruses have been used; retroviruses, lentiviruses and adeno-associated viruses
Liposomes
are small spherical vesicles with a phospholipid layer
These vesicles can also be used in gene therapy to carry non-mutated genes into host cells
What is the advantage of using liposomes as a vector?
they can fuse with the cell surface membrane
define promoter
(an example of a length of non-coding DNA that has a specific function)
is the region of DNA that determines which gene will be expressed. This is because it is the site where RNA polymerase binds to in order to begin transcription
- ensures that RNA polymerase can recognise which strand is the DNA template strand- it can recognise as the promoter contains the transcription start point which is where the enzyme will bind
- is used to regulate gene expression because only if it is present will transcription and therefore the expression of the gene occur
If genetic engineers want to ensure the desired gene is expressed when modifying the plasmid what do they have to add?
an appropriate promoter
What is a marker?
is a gene that is transferred with the desired gene to enable scientists to identify which cells have been successfully altered and now contain recombinant DNA
What was once commonly used as marker genes ?
Antibiotic-resistant genes
Scientists genetically modified the bacteria so that the plasmid contained the desired gene along with a specific antibiotic-resistant gene (and promoter) and then grew the bacteria on agar plates embedded with that antibiotic. The bacteria that contained the recombinant plasmids could be identified as these were the bacteria that grew
Why does using antibiotic-resistant genes as marker genes concern scientists?
-There is a risk that the antibiotic-resistant genes could be accidentally transferred to other bacteria including pathogenic strains creating pathogenic antibiotic-resistant bacteria
-If the resistance spread to other bacteria this could make antibiotics less effective
The spread of the antibiotic-resistant genes can occur due to?
the conjugation (the transfer of genetic material from one bacterium to another) or due to transduction (the transfer of genetic material from one bacterium to another via a virus)
So genes that express proteins that are fluorescent are now commonly used as markers
The fluorescence is due to the presence of?
a green fluorescent protein (GFP)
What is the GFP gene along with the desired gene linked to ?
a specific promoter and once this promoter is activated, and the protein is expressed, the recombinant bacteria are detected when they glow green under exposure to ultraviolet light
Why is the use of flurescent genes as markers preferable?
-They are easier to identify (all that is required is the ultraviolet light)
-More economical (do not need to grow the bacteria on plates of agar infused with antibiotics)
-No risk of antibiotic resistance being passed onto other bacteria
There are antibiotics that are no longer effective and therefore would not stop any bacteria from growing
Gene, or genome, editing allows genetic engineers to alter what?
the DNA of organisms by inserting, deleting or replacing DNA at specific sites in the genome known to cause disease.
How does Gene/genome, editing differ from genetic engineering?
it involves modification of the existing DNA of an organism rather than the insertion of DNA from another organism.
Note that the term ‘genome’ refers to all of the DNA, or genetic information, found inside a cell.
What does gene editing enable scientists to be?
more accurate in their manipulation of the genome
Older gene editing techniques include?
Modifying viruses to insert DNA, e.g. into the gene causing a disease
This sometimes resulted in DNA being inserted into other genes causing unforeseen consequences
Liposomes (small spheres of lipid molecules) containing the normal version of a gene being sprayed into noses
This was only a short-term solution as the epithelial cells lining the nasal passageway were short lived
Today scientists have developed new gene editing techniques. What is the most commonly used one ?
CRISPR
(Clustered Regularly Interspaced Short Palindromic Repeats)
What does the CRISPR technique involve using?
involves using the natural defense mechanism bacteria (and some archaea) have evolved to cut the DNA strands at a specific point as determined by a guide RNA attached to an enzyme (Cas9)
Once cut scientists can then either insert, delete or replace faulty DNA with normal DNA
Gene editing is involved in gene therapies (e.g. developing treatments for cystic fibrosis and sickle cell anaemia).
What is Gene therapy?
is the treatment of a genetic disease by altering the person’s genotype
As scientists learn more about the human genome (from the Human Genome Project) and the proteome, and have the technology to process large quantities of data through computational biology, they can gain a better understanding of which genes are responsible for genetic diseases and where they are located,and therefore what base changes need to occur to treat or cure the disease
Polymerase chain reaction (PCR)
PCR is an artificial method of rapidly replicating DNA
under laboratory conditions, producing large quantities
Each PCR reaction requires ?
1) DNA (or RNA) sample to be amplified
2) primers - They define the region that is to be amplified by identifying to the DNA polymerase where to begin building the new strands
3) free nucleotides to be used in the construction of the
DNA or RNA strands
4) buffer solutions to provide the optimum pH for the
reactions to occur in
5) DNA polymerase - is the enzyme used to build the new DNA or RNA strand. The most commonly used polymerase is Taq polymerase
Taq polymerase
is a heat-stable form of DNA polymerase
extracted from a thermophilic bacterium (Thermus
aquaticus) and is used in PCR
Features of Taq polymerase that enable it to be used in PCR
1) it’s not destroyed in the denaturation step, so it
doesn’t have to be replaced each cycle
2) its high optimum temperature (72°C) means the
temperature for the elongation step does not have to
be dropped below that of the annealing process, so
efficiency is maximised
PCR can be summarised in 3 steps, and they all require
different temperatures
Denaturation – the double-stranded DNA is heated to 95°C which breaks the hydrogen bonds that bond the two DNA strands together
Annealing – the temperature is decreased to between 50 - 60°C so that primers (forward and reverse ones) can anneal to the ends of the single strands of DNA
Elongation / Extension – the temperature is increased to 72°C for at least a minute, as this is the optimum temperature for Taq polymerase to build the complementary strands of DNA to produce the new identical double-stranded DNA molecules
Annealing-joining of primers to compl bases at end of DNA fragment.
Gel electrophoresis
is a technique used widely in the analysis of DNA, RNA and proteins.
During electrophoresis the molecules are separated according to their size / mass and their net (overall) charge
Factors affecting the movement of charged molecules in
gel electrophoresis so why the seperation occurs..
1) net (overall) charge – negatively charged molecules
move to anode (+), positively charged molecules
move to cathode (-), highly charged molecules move
faster than those with less overall charge
eg. DNA is negatively charged due to the phosphate groups and thus when placed in an electric field the molecules move towards the anode
2) size– smaller molecules move faster than larger
ones. The tiny pores in the gel result in smaller molecules moving quickly, whereas larger molecules move slowly
3) composition of gel– size of pores within gel (e.g.,
agarose for DNA has different pore size than
polyacrylamide for prote
Electrophoresis of DNA
is used to separate DNA
fragments for DNA fingerprinting to investigate crime
scenes or to analyse genes.
To separate the DNA fragments in gel electrophoresis the scientists :
Create an agarose gel plate in a tank. Wells (a series of groves) are cut into the gel at one end
Submerge the gel in an electrolyte solution (a salt solution that conducts electricity) in the tank
Load (insert) the fragments into the wells using a micropipette
Apply an electrical current to the tank. The negative electrode must be connected to the end of the plate with the wells as the DNA fragments will then move towards the anode (positive pole) due to the attraction between the negatively charged phosphates of DNA and the anode
The smaller mass / shorter pieces of DNA fragments will move faster and further from the wells than the larger fragments
The fragments are not visible so must be transferred onto absorbent paper or nitrocellulose which is then heated to separate the two DNA strands. Probes are then added, after which an X-ray image is taken or UV-light is shone onto the paper producing a pattern of bands which is generally compared to a control fragment of DNA
What are probes?
Probes are single-stranded DNA sequences that are complementary to the VNTR regions sought by the scientists. The probes also contain a means by which to be identified. This can either be:
A radioactive label (eg. a phosphorus isotope) which causes the probes to emit radiation that makes the X-ray film go dark, creating a pattern of dark bands
A fluorescent stain / dye (eg. ethidium bromide) which fluoresces (shines) when exposed to ultraviolet (UV) light, creating a pattern of coloured bands
What are probes?
Probes are single-stranded DNA sequences that are complementary to the VNTR regions sought by the scientists. The probes also contain a means by which to be identified. This can either be:
A radioactive label (eg. a phosphorus isotope) which causes the probes to emit radiation that makes the X-ray film go dark, creating a pattern of dark bands
A fluorescent stain / dye (eg. ethidium bromide) which fluoresces (shines) when exposed to ultraviolet (UV) light, creating a pattern of coloured bands
Protein separation
The different amino acids (because of the different R groups) determine the charge of proteins. The charge of the R groups depends on the pH and therefore buffer solutions are used during the separation of proteins to keep the pH constant
Gel electrophoresis is used to separate polypeptide chains produced by different alleles eg. the haemoglobin variants (α-globin, β-globin and the sickle cell anaemia variant of β-globin)
Microarrays
are laboratory tools used to detect the expression of thousands of genes at the same time and to identify the genes present in an organism’s genome
identify the genes present in an organism’s genome
- find out which genes are expressed within cells
- compare the genes present in 2 different species
What does a microarray consist of?
a microarray consists of a small (usually 2cm²) piece of glass, plastic, or silicon (also known as chips) that have probes attached to a spot (called a gene spot) in a grid pattern
- each probe represents a known gene sequence
- if a gene is active within a cell, then the cDNA (produced from the mRNA transcript) will bind to its complementary probe
How are microarrays are used in the analysis of genomes?
1) DNA is collected from the species that are going to
be compared
2) restriction enzymes are used to cut the DNA into fragments
3) the fragments are denatured to form single-stranded DNA molecules (cDNA)
4) the DNA is labelled with fluorescent tags (the fragments from the different sources are tagged different colours, usually red and green)
5) the labelled DNA samples are mixed together and allowed to hybridise with the probes on the microarray
6) any DNA that has not bound to the probes is washed off
7) the microarray is inspected using UV light, causing the tags to fluoresce
8) the presence of colour indicates that hybridisation has taken place (as the DNA fragments are complementary to the probes)
‣ red and green: DNA from one species has hybridised with probes
‣ yellow: DNA from both species hybridised (the two species have DNA with exactly the same base sequence)
‣ no colour/blue: no hybridisation, gene not present in either species
9) the microarray is scanned so data is read by a computer and stored
How microarrays are used in detecting mRNA in studies of gene expression?
Microarrays are used to compare which genes are
active by identifying the genes that are being transcribed onto DNA.
1) mRNA is collected from 2 types of cells and reverse transcriptase is used to convert mRNA to cDNA
2) PCR may be used to increase quantity of cDNA as mRNA quantity is quite low at any one time
3) cDNA is labelled with fluorescent tags and denatured to give single stranded DNA
4) single stranded DNA is allowed to hybridise with probes on the microarray
5) UV light is shone; spots that fluoresce indicate the genes that were being transcribed in the cell
‣ intensity of light emitted by each spot indicates the level of activity by each gene
‣ high intensity: indicates many mRNA molecules are present in sample
How do restriction endonuclease work?
restriction enzymes cut straight across the sugarphosphate backbone to give blunt ends
- they can also cut in a staggered fashion to give
sticky ends
To analyse data scientists are use?
bioinformatics
Define Bioinformatics
where biological data is collected, organised, manipulated, analysed and stored
Once a genome is sequenced what does bioinformatics allow?
scientists to make comparisons with the genomes of other organisms using the many databases available.
This can help to find the degree of similarity between organisms which then gives an indication of how closely related the organisms are and whether there are organisms that could be used in experiments as a model for humans (eg. the fruit fly Drosophila)
What has recombinant DNA been used to produce?
recombinant proteins (RP), thus recombinant proteins are manipulated forms of the original protein
how are recombinant proteins generated?
using microorganisms such as bacteria, yeast, or animal cells in culture.
They are used for research purposes and for treatments (eg. diabetes, cancer, infectious diseases, haemophilia)
what are most recombinant human proteins produced using? and why?
eukaryotic cells(eg. yeast, or animal cells in culture) rather than using prokaryotic cells, as these cells will carry out the post-translational modification (due to presence of Golgi Apparatus and / or enzymes) that is required to produce a suitable human protein
what are the advantages of genetic engineering organisms to produce recombinant human proteins ?
- More cost-effective to produce large volumes (i.e. there is an unlimited availability)
- Simpler (with regards to using prokaryotic cells)
- Faster to produce many proteins
- Reliable supply available
- The proteins are engineered to be identical to human proteins or have modifications that are beneficial
- It can solve the issue for people who have moral or ethical or religious concerns against using cow or pork produced proteins
what was the first recombinant human protein to be approved for use in diabetes treatment?
insulin
What are modified to include the human insulin gene?
bacteria plasmids
What is used to cut open plasmids?
Restriction endonucleases are used to cut open plasmids and DNA ligase is used to splice the plasmid and human DNA together
making of insulin
- Restriction endonucleases are used to cut open plasmids and DNA ligase is used to splice the plasmid and human DNA together
- These recombinant plasmids are then inserted into Escherichia coli by transformation (bath of calcium ions and then heat or electric shock)
- Once the transgenic bacteria are identified (by the markers), they are isolated, purified and placed into fermenters that provide optimal conditions
- The transgenic bacteria multiply by binary fission, and express the human protein - insulin, which is eventually extracted and purified
what are the advantages for scientists to use recombinant insulin ?
- It is identical to human insulin, unless modified to have different properties (eg. act faster, which is useful for taking immediately after a meal or to act more slowly)
- There is a reliable supply available to meet demand (no need to depend on availability of meat stock)
- Fewer ethical, moral or religious concerns (proteins are not extracted from cows or pigs)
- Fewer rejection problems or side effects or allergic reactions
- Cheaper to produce in large volumes
- That it is useful for people who have animal insulin tolerance
what is Factor VIII?
is a blood-clotting protein that haemophiliacs cannot produce
what have been genetically modified to produce Factor VIII?
Kidney and ovary hamster cells
describe how Factor VIII is produced
- Kidney and ovary hamster cells have been genetically modified to produce Factor VIII
- Once modified these recombinant cells are placed into a fermenter and cultured
- Due to the optimal conditions in the fermenter, the hamster cells constantly express Factor VIII which can then be extracted and purified, and used as an injectable treatment for haemophilia
what are the advantages for scientists to use recombinant Factor VIII ?
- Fewer ethical, moral or religious concerns (proteins are not extracted from human blood)
- Less risk of transmitting infection (eg. HIV) or disease
- Greater production rate
what is Adenosine deaminase (ADA) enzyme used to treat?
the inherited condition called Adenosine Deaminase Deficiency
what is ADA Deficiency is a common cause of ?
Severe Combined Immunodeficiency (SCID)
This is because the immune system is damaged
what has been genetically modified to produce the enzyme adenosine deaminase?
The larva of the cabbage looper moth so that it can be used as a treatment whilst the patients wait for gene therapy or when gene therapy is not possible
what are the advantages for scientists to use recombinant adenosine deaminase?
- Fewer ethical, moral or religious concerns (proteins are not extracted from cows)
- Less risk of transmitting infection or disease (from cows)
- More reliable production of enzyme
- Faster to produce many proteins
what can be determined by genetic screening?
In certain circumstances (eg. in the pregnancy in an older woman, or pregnancy where there is a family history of a genetic disease) may require individuals to determine if they have a particular allele present in their genome
what can genetic screening can help identify?
individuals who are carrying an allele at a gene locus for a particular disorder
what is genetic screening?
is the testing of an embryo, fetus or adult to analyse the DNA
genetic screening Q.
how is the sample of DNA to be analysed obtained by ?
- Taking tissue samples from adults or embryos produced by in-vitro fertilisation
- Chorionic villus sampling or amniocentesis of embryos and fetuses in the uterus
As genetic screening can leave future parents with many questions who are available to help?
genetic counsellors
genetic counsellors role
will read the results and explain them.
Counsellors can also be seen before screening has occurred.
what may genetic counsellors discuss with prospective parents?
- The chances of the couple having a child with a certain disease
- Termination of the pregnancy
- Therapeutic treatments possible for the child
- Financial implications of having the child
- Effect on existing siblings
- Ethical issues
what do BRCA1 and BRCA2 genes produce?
tumour suppressor proteins and thus they play an important role in regulating cell growth
what are the breast cancer genes?
BRCA1 and BRCA2
Faulty alleles of these particular genes exist which increase the risk of an individual developing breast and ovarian cancers during their lifetime
who can the faulty BRCA1 and BRCA2 alleles be inherited from?
either parent
what are the advantages of genetic screening for an adult who has a family history of BRCA1 and BRCA2 gene mutations ?
- That the person may decide to take preventative measures (e.g. by having an elective mastectomy – breast removal – to reduce the risk of developing cancer)
- Screening for breast cancer may begin from an earlier age or more frequently, and the individual (if female) will have more frequent clinical examinations of the ovaries
- That it enables the person to participate in research and clinical trials
what is Huntington’s disease?
is a progressive (gets worse with time) inherited disease that affects the brain
signs of huntingtons
typically appear in affected individuals after reaching their 40’s and include uncontrolled movements, lower cognitive (thinking) ability and emotional problems
There is no cure for the Huntingdon’s disease, with treatments available only alleviating the symptoms but not curing it
what type of disease is huntington’s?
is an autosomal dominant disease (therefore if the person has an allele for Huntington’s they will get the disease)
what are the advantage of genetic screening for Huntington’s is it enables?
- People to plan for the future (how they will live and be cared for)
- Couples to make informed reproductive decisions (as the risk that their children may inherit the disease is 50%)
- People to participate in research and clinical trials
what is cystic fibrosis?
is an autosomal recessive genetic disorder that is caused by a mutation of the gene that codes for a transported protein called CFTR
what type of disease is cystic fibrosis?
It is a progressive disease that causes mucus in various organs (lungs, pancreas, lungs) to become thick and sticky.
This is because the faulty CFTR protein no longer transports chloride ions across the cell plasma membrane and therefore water does not move by osmosis across the membrane either (the presence of water would normally make the mucus thinner enabling cilia to remove it)
is there a cure for cystic fibrosis?
NO cure.
there are many different treatments that help alleviate symptoms. The common cause of death is bacterial infection in the lungs
what are the advantage of genetic screening for cystic fibrosis?
- It enables couples to make informed reproductive decisions (as both may be carriers and therefore not display any symptoms)
- That people can participate in research and clinical trials
what does gene therapy involve using?
various mechanisms to alter a person’s genetic material to treat, or cure, diseases
what are the appropriate delivery systems for gene therapy?
Vectors are currently used as the delivery system, with viruses being the most commonly used, but non-viral vectors are also being researched (eg. liposomes and ‘naked’ DNA)
Viruses (eg. retroviruses and lentiviruses) are the most commonly used vectors as they have the mechanisms needed to recognise cells, and deliver the genetic material into them
what are the possibilities of gene therapy ?
being able to replace a faulty gene, inactivate a faulty gene or insert a new gene are growing
Changes in genetic material are targeted to…?
specific cells and so will not be inherited by future generations (as somatic gene therapy does not target the gametes)
Often the effects of changing the somatic cells are short-lived
what are the 2 types of somatic gene therapy?
Ex vivo – the 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 these cells. These cells are then grown in the laboratory and returned to the person by an injection into a vein
In vivo – the new gene is inserted via a vector into cells inside the body
There is the potential for new genetic material to be inserted into ….?
germ cells (cells involved in sexual reproduction eg. gametes or an early embryo)
However, this is illegal in humans as any changes made to the genetic material of these cells is potentially permanent and could therefore be inherited by future generations
what is Severe combined immunodeficiency (SCID) caused by?
the body’s inability to produce adenosine deaminase (ADA), an enzyme that is key to the functioning of the immune system.
without ADA enzyme what can occur?
children can die from common infections and therefore need to be keep isolated often inside plastic ‘bubbles’
what is used to treat SCID?
scientists have used ex vivo somatic gene therapy. During this therapy, a virus transfers a normal allele for ADA into T-lymphocytes removed from the patient and the cells are then returned via an injection
is there a permanent cure for SCID?
no as the T-lymphocytes are replaced by the body over time and therefore the patient requires regular transfusions every three to five months to keep their immune systems functioning
Originally retroviruses were used as the vectors, however these viruses insert their genes randomly into a host’s genome which means they could insert the gene into another gene or into a regulatory sequence of a gene (which could result in cancer)
what did initial treatments of SCID cause?
cases of leukaemia in children, so researchers switched to using lentiviruses or adeno-associated viruses as vectors. Lentiviruses also randomly insert their genes into the host genome however they can be modified to not replicate, whereas adeno-associated viruses do not insert their genes into the host genome and therefore the genes are not passed onto the daughter cells when a cell divides. This is an issue with short-lived cells like lymphocytes but has not been a problem when used with longer living cells such as liver cells
