GMOs: Genetically Modified Organisms PDF

GMOs Genetically modified organisms Why produce GM crops? To increase yield for food security/ fight world food hunger Bigger yields per cultivated area should lead to lower prices For better quality/more nutritious food Avoid use of herbicides/pesticides -against human health Flavr Savr tomatoes Fi...

GMOs Genetically modified organisms Why produce GM crops? To increase yield for food security/ fight world food hunger Bigger yields per cultivated area should lead to lower prices For better quality/more nutritious food Avoid use of herbicides/pesticides -against human health Flavr Savr tomatoes First genetically modified crop, Calgene, California 1994 GENE SILENCING Polygalacturonaseenzyme for softening tomato skin/ripening BASIC RECOMBINANT DNA TECHNOLOGY Most methods for cloning pieces of DNA in the laboratory share general features, such as the use of BACTERIA and their PLASMIDS. Basic Concept: DNA cloning yields multiple copies of a gene or other DNA segment and expressed. Escherichia coli E. coli Most used bacterium in genetic engineering/ biotechnology Bacteria grow in colonies PLASMIDS Extrachromosomal small circular double stranded DNA molecules that replicate separately from the bacterial chromosome. Fig. 20-3-1 Bacterial RESTRICTION ENZYMES ‘molecular scissors’ cut DNA molecules at specific DNA sequences called restriction sites. Restriction site DNA 1 5¢ 3¢ 3¢ 5¢ Restriction enzyme cuts sugar-phosphate backbones. Sticky end The most useful restriction enzymes cut DNA in a staggered way, producing fragments with “sticky ends” that bond with complementary sticky ends of other fragments A restriction enzyme usually makes many cuts, yielding restriction fragments. Fig. 20-3-2 Restriction site DNA 1 5¢ 3¢ 3¢ 5¢ Restriction enzyme cuts sugar-phosphate backbones. Sticky end 2 DNA fragment added from another molecule cut by same enzyme. Base pairing occurs. One possible combination Restriction site DNA 1 5¢ 3¢ 3¢ 5¢ Restriction enzyme cuts sugar-phosphate backbones. Sticky end 2 DNA fragment added from another molecule cut by same enzyme. Base pairing occurs. One possible combination 3 DNA ligase seals strands. Recombinant DNA molecule In gene cloning, the original plasmid is called a cloning vector A cloning vector is a DNA molecule that can carry foreign DNA into a host cell and replicate there How to produce a recombinant DNA molecule (DNA cloning): SCALE UP Fig. 20-2 Cell containing gene of interest Bacterium 1 Gene inserted into plasmid Bacterial chromosome Plasmid Recombinant DNA (plasmid) Gene of interest DNA of chromosome 2 Plasmid put into bacterial cell Recombinant bacterium 3 Host cell grown in culture to form a clone of cells containing the “cloned” gene of interest Gene of Interest Protein expressed by gene of interest Copies of gene Basic Protein harvested 4 Basic research and various applications research on gene Gene for pest resistance inserted into plants Gene used to alter bacteria for cleaning up toxic waste Protein dissolves blood clots in heart attack therapy Basic research on protein Human growth hormone treats stunted growth Bt Corn Fig. 20-25 TECHNIQUE Agrobacterium tumefaciens Ti plasmid Site where restriction enzyme cuts T DNA DNA with the gene of interest RESULTS Recombinant Ti plasmid Plant with new trait The Ti plasmid b The bacterium infects a plant and transfers the Ti plasmid into it. a A bacterial cell contains a Ti plasmid (purple) that has a foreign gene (blue). e Young plants with a fluorescent gene product. c The plant cell divides. d Transgenic plants. Fig. 16-13, p.253 In agriculture: Generation of pest-resistant crops reducing the use of pesticides Bacillus thuringiensis (Bt) Soil dwelling bacterium Produces crystal proteins or ‘Cry’ proteins or Bt toxins which are toxic to pests. The Bt toxin action is specific to insects, the toxicity is activated by the alkaline environment of insect guts. The cry gene from Bt was first expressed in tobacco Wild type Genetically engineered Green flourescent transgenic tobacco In cotton, benefits the textile industry and other cotton related markets In food crops, benefits human health Cry proteins are ENVIRONMENTALLY FRIENDLY Bt toxins have no effects to humans and therefore have beneficial health implications. peanut chinese cabbage corn Anti quorum sensing gene was incorported into the genome of tobacco plants AHL lactonase- the enzyme which degrades the autoinducers for quorum sensing Xylella fastidiosa Agrobacterium vitis Potato tubers genetically engineered with anti-quorum sensing genes were inoculated with plant pathogens POLLEN DRIFT -cross pollination of crops by pollen grains thru wind or insects WHO Food Safety Programme - to assist national authorities in the identification of foods that should be subject to risk assessment, including GM foods, and to recommend the correct assessments. ARE GM FOODS SAFE? According to WHO: individual GM foods and their safety should be assessed on a caseby-case basis and that it is not possible to make general statements on the safety of all GM foods. GM foods currently available on the international market have passed risk assessments and are not likely to present risks for human health. In addition, no effects on human health have been shown as a result of the consumption of such foods by the general population in the countries where they have been approved.