Plasmids can be modified by genetic engineering and inserted into bacteria. These bacteria can then make useful substances normally made by another organism. Explain how modified plasmids are made by genetic engineering and how the use of markers enable bacteria containing these plasmids to be detected. ( 6 marker)
Firstly, the target gene must be identified and isolated from the rest of the DNA by reverse transcriptase or restriction endonucleases.
If using restriction endonucleases it may cut straight across both chains which forms a blunt end and some form a staggered cut which produces sticky end. Two restriction fragment can anneal if they have complementary sticky ends but only by weak hydrogen bonds. DNA ligase completes the backbones by forming covalent phosphodiester bond. Antibiotic resistance is a type if marker where replica plating is used to identify which have taken up the DNA fragment. Bacterial cells which survive being in nutrient agar with the first antibiotic are known to have taken up the plasmid. Bacterial cells with the DNA fragment would be killed in the second antibiotic plate would have been made useless if DNA fragment was taken up.
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