Gene insertion into plants through the use of the Agrobacterium tumefaciens bacteria
A conventional way to elucidate the function of a developmental gene, a gene that is involved in a certain behavior, or a gene that confers disease resistance, is to over-express the gene in the whole organism. The organism that carries a foreign gene (a gene that comes from a different organism) within each of its cell's genome is called a transgenic organism while the foreign gene is called a transgene. During the second half of the twentieth century, researchers were investigating effective ways to transmit foreign DNA of their choice into plant cells that were growing in culture in order to create a transgenic plant. During the 1970's, researchers found that a certain bacteria, Agrobacterium tumefaciens, could infect and insert DNA into plants. For this reason, it was dubbed the "earliest natural genetic engineer." How can we use this bacteria's natural ability to insert a selected piece of DNA into a plant? For the answer please watch the following animation.
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Using restriction enzymes to digest DNA
Restriction enzymes cut a strand of DNA into smaller pieces in a sequence-specific manner. Restriction enzymes are found in bacteria where they play an important role in protecting the bacteria from invading viruses (bacteriaphages). These enzymes cut the DNA into smaller strands thus stopping the proliferation of these viruses in the bacterium. Hundreds of different restriction enzymes have been identified and are used by genetic engineers to cut specific strands of DNA for use in various reactions.
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PCR
PCR stands for Polymerase Chain Reaction. This method allows us to make copies of a desired strand of DNA in a test tube. The PCR method was developed in 1983 by Kerry Mullis who later received a Nobel Prize for this achievement. DNA Polymerase is an enzyme that the cell uses to replicate the DNA. In order for the polymerase to work it needs a strand of DNA, nucleotides and primers. These primers, which are about 17 nucleotides long, complement the two ends of the DNA that we would like to copy. The primers bind to the complementary nucleotides on the DNA and act as anchors for the enzyme.
By using the PCR method, we can have millions of copies of any sequence of DNA. The PCR method has improved greatly the fields of genetic disease diagnosis, legal medicine and even fossil research.
"Step by step" animation
You are about to watch an animation showing the PCR method. This animation will go through all the steps of PCR with a pause at each step. Each step begins with an explanation. To see that step animated, press "play." Once the animation ends, you will have to press "play" again in order to go on to the next step and so on till the end of the PCR process.
(To go back to the previous step in the process, press the button "back." To go back to the beginning of the animation, press "replay.")