How is the gene gun a way of introducing a novel gene into a plant cell.
Fires small spheres of gold or tungsten coated with a preparation of the gene at plant cells. Some penetrate the cell wall and are taken up through the membrane.
How is electroporation a way of introducing a novel gene to a plant cell.
Electric field increases the permeability of cell membranes increasing gene uptake.
How does micro injection introduce the novel gene to plant cells
Membrane pierced w an ultra fine needle and gene injected into cytoplasm or nucleus.
What is the most common method for making transgenic plant cells
Using the bacterial vector agrobacterium tumefaciens.
Give the 6 steps of transforming plants with agrobacterium tumefaciens.
- Plasmid extraction from bacterium
- Restriction enzymes cut tumour forming genes from plasmid
- Section of DNA containing the gene for disease resistance is located and isolated using same r endonuclease
- Gene inserted replacing tumour forming gene and DNA Ligase joins them. Plasmid inserted
- Bacterial cell introduced into plant cell and bacterial cell divides and is inserted into plant chromosome
- Transgenic plant cells grown in tissue culture and transformed plants regenerated.
Why is A. Tumefaciens used?
Usually it infects plants and can integrate into the plants chromosomes. The plasmids genes are transcribed as translated and causes a tumour giving the plant Crown Gall disease. The plasmid is the TI rumour inducing plasmid. By splicing chosen genes it can be transferred to plant cells which are grown and regenerated to express introduced genes.
How are soya beans GM?
‘Roundup ready’ soybeans are GM crops that contain a gene making them herbicide resistant; meaning crops can be sprayed to remove weeds without inhibiting their growth.
How can BT tomatoes be GM?
Bacillus thuringiensis is a bacterium containing the plasmid with a gene coding for a protein that acts like an insecticide. The gene has been incorporated into BT tomatoes. The insecticidal protein is made in the leaves which insects eat. Farmers don’t need to spray it. They are resistant to many species. They haven’t been commercialised.
How can antisense tomatoes be GM?
Tomatoes ripen naturally due to an enzyme which breaks down protein in cells walls but they can overruled and become unsuitable to sell. A. Tumefaciens was introduced into the ‘flavr save’ tomato with a second copy of the gene for the ripening enzyme but this copy had a base sequence complimentary to that of a normal gene - ‘antisense’ gene.
How did the antisense gene work.
The MRNA of the antisense gene was complimentary to the MRNA of the original gene. The 2 types of RNA base pair in the cytoplasm to make a double stranded molecule. Stops original MRNA being translated and stops production of ripening enzyme so ripe in is delayed and longer shelf life is made.
5 arguments in favour of GM crops.
- Higher crop yield
- Pesticide reduction
- Improves food eg nutritional quality enhance like golden rice
- Introducing genes for herbicide resistance decreases plant loss
- ‘Pharming’ refers to production of pharmaceutical molecules in GM crop plants. Plants modified to make antibodies, blood products, hormones and vaccines.
6 arguments against GM crops.
- Pollen from GM plants might transfer genes to relatives like weeds
- Pesticide resistant plants introduce genes enable them to resist insect attack’s could increase pop of resistant insects
- Marker genes: GM organisms contain marker genes which might confer antibiotic resistance which could transfer to humans
- Plant feeding may fall to hands of commercial companies limiting crop varieties so old varieties eliminated. Reduction in biodiversity
- New proteins may have adverse health effects
- Economic concerns: GM crops are subject to intellectual property law an it is feared that the expense will be borne by farmer
