B: Genetic Modification of Crop Plants Flashcards
State 4 aims of crop genetic modification.
- Novel products
- Overcoming environmental resistance
- Pest resistance
- Herbicide resistance
What happens in genetic modification of crops?
a gene is inserted to achieve an aim
Outline ‘novel products’ as an aim of crop genetic modification.
gene is inserted to allow crop plants to make something they could not make before
Outline ‘overcoming environmental resistance’ as an aim of crop genetic modification.
genes are inserted to give greater tolerance to saline soils, frosts, or some other factor limiting crop growth
Outline ‘pest resistance’ as an aim of crop genetic modification.
gene is inserted for making a toxin that kills pests eating the crop
Outline ‘herbicide resistance’ as an aim of crop genetic modification.
gene is inserted so a herbicide can be used without killing the crop plants
Describe the technique for genetic modification.
- DNA containing target gene, marker gene and sequences for controlling gene expression = prepared
- known as ‘recombinant DNA’
- recombinant DNA must be inserted into a cell of crop plant and be taken up by a chromosome in nucleus or by DNA of the chloroplast (to be successful)
- in some cases, recombinant DNA must be introduced to whole plant
- could also be introduced into a leaf disc, or into a protoplast which is a single cell from which the cell was has been removed
Name 3 different types of methods that recombinant DNA can be introduced to the organism.
- direct physical methods
- direct chemical methods
- indirect methods using vectors
Name 3 direct physical methods of introducing recombinant DNA to an organism.
- electroporation - electric fields cause pores to open briefly in membranes so DNA can enter cells
- microinjection - one micropipette holds the cell while another injects the DNA through a tiny needle
- biolistics (gunshot) - tiny metal balls with DNA on surface = fired at the plant and penetrate cells
Name 2 direct chemical methods of introducing recombinant DNA to an organism.
- calcium chloride - cells incubated in cold CaCl2 solution take up DNA when given heat shock
- liposomes - artificial vesicles containing DNA fuse with cell membranes of protoplasts
Name 3 indirect methods using vectors of introducing recombinant DNA to an organism.
- Agrobacterium tumefaciens - a bacterium that inserts a plasmid into plant cells with the target gene
- tobacco mosaic virus - virus that inserts RNA into plant cells, with RNA including target gene
State 3 examples of genetic modification of crop plants.
- amflora potato
- production of hepatitis B vaccine in tobacco plants
- glyphosate resistance in soybeans
Describe GM in amflora potato.
- amylopectin form of potato starch used as adhesive and coating for paper
- granule-bound starch synthase (GBSS) = enzyme used to make amylose but not amylopectin
- gene inserted into potato cells with same base sequence as gene for GBSS, but in reverse
- mRNA transcribed therefore has base sequence complementary to base sequence of mRNA transcribed from normal GBSS gene
- it has antisense sequence rather than sense sequence
- antisense mRNA pairs with sense mRNA to form double-stranded RNA
- this cannot be translated by ribosomes in GBSS is not produced, so 99%+ of starch made by potato plants is amylopectin
- new GM variety of potato = named Amflora
Describe GM in production of hepatitis B vaccine in tobacco plants
- tobacco mosaic virus (TMV) enters tobacco cells then uses metabolism of cell to translate some of its own genes into proteins and to replicate the RNA that is its genetic material
- can spread from cell to cell to infect whole tobacco plant
- if TMV GM’d, novel genes are expressed in infected tobacco cells
- vaccination programmes in remote areas = difficult bc problems with access and refrigeration of vaccines
- Hepatitis B vaccine contains Hepatitis B small surface antigen (HBsAG)
- TMV = GM’d with gene from Hepatitis B virus for making GBsAG
- tobacco plants = infected with GM TMV, to try to produce HBsAG in bulk
- tobacco plants harvested and dried
- if person eats some of the dried material, the HBsAG should stimulate production of antibodies against Hep B and therefore induce immunity to the disease
= easier way to give vaccine than sterile injection of a liquid vaccine that has to be refrigerated
Describe glyphosate resistance in soybeans.
- general herbicides e.g. glyphosate kill all plants so cannot normally be sprayed onto growing crops
- but a gene for glyphosate resistance => transferred to soybeans makes this possible
- gene transferred using strain of bacterium Agrobacterium tumefaciens containing a tumour-inducing plasmid (Ti plasmid).
- bacterium injects the Ti plasmid through a pilus into plant cells and DNA from it becomes incorporated into chromosomes in nucleus
- a glyphosate reseistance gene = inserted into Ti plasmid along with a kanamycin resistance gene
- recombinant Ti plasmids = reinserted into A.tumefaciens and sections of soy bean leaf were exposed to these bacteria
- Kanamysicn = used to kill leaf cells that had not taken up Ti plasmid and glyphosate-resistant variety of soybeans was developed from surviving cells
