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Guest Post: Plasmids, and why they’re so good for you

A guest post by Ine:

Well, maybe not exactly you, but probably someone you know. Indeed, their life may even depend upon them. But let us first back up a bit, to get some background on these "plasmids" and the technology around them.

During the 60's, a lot of biotechnological research centred around a better understanding of DNA, the code that is our blueprint, and that primarily makes proteins which run our lives from day to day. A lot of breakthroughs happened in this period, and we were among other things able to understand approximately which part of a gene coded for which part in the corresponding protein. This made it possible to make genes synthetically, or in other words, outside of living cells. At the time that this discovery was made it was very exciting, but not terribly useful. Not surprisingly, a test tube full of synthesized genes will mostly just sit there all day, doing nothing. It also became apparent that expressing genes is nearly impossible without the network inside living cells. This is where plasmids became important.

Bacteria primarily have one big chromosome, which contains all their necessary genes. Plasmids are small rings of DNA inside bacteria, which are not part of the chromosome. They replicate on their own and make proteins on their own. Plasmids sometimes have genes that are useful for the bacteria, like making the bacteria able to digest plutonium or oil. However, since most bacteria live outside of, say, nuclear reactors, the plasmids are not necessary for survival. This means that bacteria can survive even when losing their plasmids, and actually, about half of all bacteria don't have them at all. Altogether, bacteria are very little fazed by what goes in and out of them.

And having the opportunity to remove and reinsert pieces of DNA from organisms – without the consequence of their death – has its uses. This is especially true when we also have the ability to make genes from scratch. In the 70's, the combination of all these discoveries made it possible to put synthesized genes inside bacteria. It was done by taking the plasmids out of the bacteria, splicing the desired gene into them, and putting them back into the bacteria again. These bacteria would then produce whatever protein the gene coded for. Then, if you were to put your bacteria in a tank with some nutrients, you would get more protein than you could shake a stick at.

So what? you may say to all this. Well, say that the protein that you made is called insulin. Insulin is a protein that is pretty important to us, and you usually get type 1 diabetes when your body can't produce it. It is so important to us that the most efficient treatment for this disease is daily injections of insulin. Amazingly, before we were able to synthesize insulin, it was usually harvested from dead pigs. Yuck. Of course, because of demand being higher than availability, getting diabetes type 1 almost surely lead to a slow and painful death. And this was just about thirty years ago.

Today, a lot of life-saving proteins are made using this, or similar techniques, which go under the collective term recombinant DNA technology. Interferon, which is used on tumour cells, Factor VIII for haemophiliacs, growth hormones and so on. This saves and improves an unimaginable number of people every year. All because of little rings of DNA floating around inside bacteria.


Ine is a second-year university student who spends most of her time far north and in really, really bad weather. She has been interested in science for most of her life, and loves being able to discover new things every day. The enthusiasm for critical thinking tagged along almost inevitably, which means that she often grumbles about creationism and other kinds of woo. When she has some spare time, Ine does taekwondo, draws and reads. That is, when she's not spending way too much time geeking on her computer.

Featured image credit: Wikimedia Commons

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