2013-10-06 13:17:23
The most common viruses are very small
Viruses are the cellular parasites that cause the most insidious and difficult to defeat infectious diseases. You only have to think about diseases like the flu or AIDS to realize the damage that these microorganisms can cause. If we also consider viruses that attack animals or plants, we will conclude that viruses are ubiquitous microorganisms that attack all living beings.
As we know, viruses cannot reproduce on their own and to achieve this they need to infect cells, which can reproduce autonomously. Viruses cannot reproduce without help because they are nothing more than simple molecular machines, a small group of genes protected by a capsule of proteins, lipids and carbohydrates, that is, an inert molecular assembly, except when inside a cell. Viruses are dead molecular systems that, however, are resurrected when they come into contact with a cell and infect it. The infection bends the cell and puts at its service all the mechanisms it has for the reproduction of genes and proteins. The infected cell does not stop making its own proteins and keeping the genes that allow it to stay alive working, but it sees a large part of its energy hijacked by the virus’s genes to manufacture high quantities of new viral genes and proteins. When enough have been manufactured, they automatically assemble inside the cell, forming new complete virus particles that go outside in search of other cellular victims.
Small nanomachines
Considering this way of reproducing, it seems sensible to think that viruses, in their evolution, should tend to possess the minimum number of genes and proteins that allow them to infect certain cells (viruses normally infect one or a few cell types). In this way, the cell’s energies will be better used for the benefit of the virus and it will be able to manufacture more viral particles than if the virus had many genes, which would require the production of as many proteins and a greater expenditure of energy. For this reason, the most common viruses are very efficient and very small. The aforementioned flu has a genome of only 13,500 letters (base pairs) that only produces 11 proteins. The virus’s genome and proteins are assembled in a particle only about 100 nanometers in diameter, which means that 10,000 viruses could fit in single file in a single millimeter. The AIDS virus is of similar size.
For the reasons outlined above, no one expected the existence of much larger viruses. So much so that, in 1992, while studies were being carried out on the Legionellosis disease, a strange organism was identified by chance inside an amoeba, a protozoan that lives in swampy waters, although there are also marine waters. The organism was so large that it was believed to be a bacteria capable of infecting the amoeba and living inside it.
Megavirus
However, the new organism spurred the curiosity of some French scientists from the University of Marseille, who for almost 10 years dedicated themselves to studying the new microorganism in depth. To their surprise, and that of the rest of the world, the researchers discovered that this was not a bacteria, but a gigantic virus, which they called Mimivirus. This finding was published in the journal Science in 2003.
The existence of this enormous virus raised new scientific questions. Was this the largest virus capable of existing, or were there even larger viruses? New studies carried out by the same researchers led to the discovery of another even larger virus from a sample of seawater from the Chilean coast, which is why it was named Megavirus chilensis. This virus, which also infects amoebas, is truly enormous, measuring 500 nanometers in diameter and having 1.26 million letters in its genome.
The largest viruses
Once again, the discovery of this virus once again raised the question of whether even larger viruses existed. Analysis of new samples of seawater from the Chilean coast and water obtained from an Australian pond near Melbourne has now led to the discovery of two huge new viruses, called Pandoravirus salinus and Pandoravirus dulcis. These viruses have genomes of 2.5 and 1.9 million letters, respectively, and a size of 1,000 nanometers, that is, ten times the size of the influenza virus. Obviously, perhaps there may be larger viruses, still unknown.
Of course, it is very surprising that such viruses exist. Even more surprising is that analysis of their genomes indicates that they contain more than 2,000 genes, which is huge compared to just 11 for the flu virus. And finally, even more surprising is that only 7% of these genes are similar to those of other known organisms. 93% of them do not bear similarity with other genes of any living being, which suggests that their study can reveal new molecular processes that lead to the development of innovative therapies, unsuspected today. These findings, recently published in the journal Science, once again tell us about the wonders of Nature, which perhaps we will never fully know, but which are always fascinating and useful to try to discover.
WORKS BY JORGE LABORDA.
One Moon, one civilization. Why the Moon tells us that we are alone in the Universe
One Moon one civilization why the Moon tells us we are alone in the universe
The intelligence funnel and other essays
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