What are plasmids?
It is a circular piece of DNA found in bacteria
Please, explain to detail and their uses.
they are used in creating clone of medical drugs such as insulin
They are used in genetic engineering. This is because they can easily be taken out of bacteria, cloned and put into other organisms
Okay.. So, as I've mentioned before, a plasmid is a circular piece of DNA which is found in bacteria. They are separate from the chromosome found in the bacteria and can replicate independently. It should be noted that it is much smaller than the main chromosome. It is used in genetic engineering especially when you want clones of specific genes. The whole of it is to insert the piece of gene of interest in the plasmid and get it absorb by a bacteria for replication so that you get clones of that particular plasmid. This technology is know as recombinant DNA technology. For such practices, you use restriction enzymes which will cut the plasmid at specific sites and then you use the same restriction enzymes to cut your gene of interest from any other organism. This is because, the incision by different restriction enzymes lead to different ends - you may have stairs-like ends or plain blunt ends. That's why you have to use the same restriction enzymes 'cause for instance if you use different restriction enzymes to cut the plasmid and the piece of gene of interest respectively, this may lead to different types of ends.. and hence, you won't be able to ligate them. After ligation, you expose the bacteria to the modified plasmids in a medium. Now, when the modified plasmid gets into the bacteria, plating should follow this particular step. Subsequently, you will get colonies of the bacteria. However, how will you distinguish between those bacteria having the modified plasmid and those which have not.. 'cause bear in mind that you don't know which bacterium has the modified plasmid,.. and you can't go around checking one by one. So, what is really interesting is that you can insert a piece of DNA, which is resistant to a certain antibiotic, into the plasmid along with your piece of gene of interest. Following the step during which the bacteria will take up the modified plasmid, you plate the broth on a medium containing that particular antibiotic. Obviously, only those which have the resistant gene which will grow whilst the growth of the other colonies will be inhibited by the presence of the antibiotic. That's how plasmids are used in genetic engineering.
Common example of genetic engineering product: production of human insulin from a synthetic gene
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