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What is the cause of genetic disease?
The inheritance of mutant genes
What is cystic fibrosis caused by?
The inheritance of a mutant gene with 3 bases deleted from both parents
What do CF sufferers experience?
They produce a defective membrane protein called the cystic fibrosis transmembrane regulator which has one amino acid missing
What is the function of CFTR in healthy patients?
To actively transport chloride ions out of epithelial cells of the alveoli and other organs into a surrounding layer of mucus
Why can't the altered CFTR protein function properly?
- It has an altered tertiary structure
- This results in the buildup of chloride ions within epithelial cells
What effects might a buildup of chloride ions within epithelial cells have?
- The water potential is reduced
- This causes water to move into the cell via osmosis from the surrounding mucus
- This causes the mucus to become dehydrated, thick and sticky meaning the cilia cannot shift it and resulting in a buildup
- The mucus can become infected with microbes, especially in the lungs
Describe stage 1 of the insertion of healthy CFTR genes into the epithelial cells of the alveoli
The functional gene is cut out from a chromosome using restriction enzymes
Describe stage 2 of the insertion of healthy CFTR genes into the epithelial cells of the alveoli
The gene is incorporated into one of the two types of vector to introduce the gene unit the cells
Describe the Liposome vector method
- The gene is coated with hydrophobic lipids
- This allows it to pass through the cell membrane of the epithelial cells of the alveoli
Describe the Viral vector method
The gene is spliced into viral DNA by cutting the DNA from a virus using the same restriction enzyme and ligase is used to join fragments together
State one advantage of the Viral vector method of gene transmission
Viruses are specific to certain types of cell and are very efficient at incorporating genes into the host chromosome
Describe stage 3 of the insertion of healthy CFTR genes into the epithelial cells of the alveoli
An aerosol spray is employed to administer the vector
Describe stage 4 of the insertion of healthy CFTR genes into the epithelial cells of the alveoli
The gene is incorporated into the nucleus and makes the functional protein
State the issues associated with gene therapy
- The process is inefficient, only a tiny proportion of the cells receive the gene and of the ones that receive the gene few will be expressed
- The virus may not be totally harmless, potentially causing lung disease (Jesse Gelsinger)
- The patent's immune system might destroy the virus before it has reached the epithelial cells
- Incorporation of a healthy gene may inactivate host genes and could lead to cancer through the inactivation of tumour suppressing genes
- Cells that do not receive the gene will be replaced by the body and so any treatment will have to be repeated
State one alternate method of gene transmission
- The gene is inserted into fertilised eggs that will divide by mitosis, passing on the gene to all cells
- (This is currently banned as any change would pass on to offspring's DNA through gametes)
What is required in order to diagnose a particular disorder?
Determining the presence of a mutated gene
What is the cause of sickle cell anaemia?
A mutant gene with a single base substitution (one CTC in normal DNA is changed to CAC)
What are the effects of sickle cell anaemia?
- Haemoglobin is produced with a protein with an altered amino acid
- This causes it to have a different tertiary structure meaning the red blood cells become sickle shaped
What effects does the sickle shape of red blood cells have?
- The ability to carry oxygen is reduced
- Red blood cells become trapped in capillaries
What is the genotype for healthy red blood cells?
What is the genotype for people with sickle cell anaemia?
They are homozygous for the mutant allele Hbs Hbs
What is the genotype for sickle cell trait and what are its effects?
- SST is caused by codominant alleles
- Sufferers have the genes HbA Hbs
- Their red blood cells can carry less oxygen
- They are also resistant to the malaria parasite (swings and roundabouts)