In 1928 in the United Kingdom, Frederick Griffith discovered natural transformation while he was looking for a vaccine for pneumonia due to the pandemic spreading in Spain after World War I. He conducted an experiment with live mice and harmless and pneumonia causing bacteria. First, he injected an innocuous living strain of bacteria, and as expected, the mice survived. Second, he injected a harmful strain of bacteria, and they died. Finally, he injected a dead strain of harmful bacteria and a living strain of harmless bacteria, causing the mice to die. He concluded from the experiment that the harmless bacteria absorbed the harmful strain’ s DNA, enabling them to kill the mice. This is an example of natural transformation, which is when transformation occurs by itself in nature. Today, there are two main ways, electroporation and chemical transformation, scientists use to achieve transformation. Natural transformation can occur via conjugation and transduction.
Frederick Griffith’ s Experiment
Bacterial cell membranes are made up of a hydrophobic lipid bilayer while DNA is hydrophilic, meaning that it’ s soluble. Before transformation occurs, the bacterium has to be made“ competent,” so the negatively charged DNA can pass through the cell membrane. Electroporation involves the use of an electric current to shock the cell membrane, which makes it porous or leaky.
Bacteria Expressing GFP
Transduction occurs naturally. A common example of transduction is bacteriophages. Bacteriophages are virus that infect bacteria. They attached to the outside of the bacterial cell and insert their DNA into the bacteria. Their DNA takes control of the bacterial“ machinery.” Instead of carrying its normal life processes, the bacteria is now forced to reproduce more bacteriophages. When there is too many bacteriophages inside the bacterium, it explodes. The released bacteriophages go on to other bacteria, and the cycle continues. Occasionally, the bacteriophages pick up a piece of DNA that is from the bacteria, and they also inject that same piece of bacterial DNA later on in another host. This key principle is the hallmark of transduction. To defend against virus like bacteriophages, bacteria have restriction enzymes that break up viral DNA. Transduction and restriction enzymes are both used to study effect of different genes in bacteria and also in the field of recombinant DNA technology.
The future of genetic engineering with regards to transformation and many other fields is bright. Potentially, it may be used to change the DNA of human embryos to prevent birth defects. An even bigger application is in the field of drug delivery where genetic engineering of the cell could help delivering drugs to obscure parts of the body, which were thought to be previously unreachable. It may be used to help antibodies target enemy cells better, and this principle along with the genetic engineering of the cell may lead to the cure of cancer. Another possibility is that genetic engineering could be used to treat neurological diseases by helping drugs go past the blood brain barrier, which is a major roadblock for curing many brain related diseases like Parkinson’ s today. As a result, scientists know that DNA transformation and other kinds of technology in the field of genetic engineering can bring about a lot of drastic, good change in the near future.
Bacteriophage infecting Bacterium
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Shuttleworth, Martyn. " Transforming Principle- Griffith ' s Experiment About Genetics."
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