The viruses
Version française : Steemit | Busy
In the previous chronicle I presented you the seven-living kingdom, however, I didn’t include the viruses. Means that they are dead? Question is open 24 hours a day, 7 days a week…
In Latin, the word virus means venom or poison.
Let’s discover that is hiding behind this terrifying word.
Their size
Their size is between 20nm and 1000nm (1µm), actually, the biggest virus (like Ebola) are the smallest bacteria size like, and the smallest viruses are 10 times bigger than the DNA wide, they very small so.
Their composition
Being very small, their structure is also simple, every virus has a capsid (from the Latin capsa which means box), some can have a supplemental envelop (lipid structure like the cell membrane). Inside this box, there is a genome, that can be in linear or circular shape and it can be simple-strained or double-strained.
If there is a genome, this is a living thing so!
Indeed, I agree with you. Actually, what is doubting me is that they have not metabolism, it means that their genetic sequence can’t execute itself, the DNA can’t replicate itself by the way.
Mmmmh, yes, it’s true, you tell me that the genetic code is read by the ribosomes but there are no ribosomes in the capsid. But what are these things? How can they exist yet?
The virus’ secret is that they use the machinery of other organisms, they are somehow tenants. They introduce itself inside a cell and use cell tools to read his genome (without authorization of course). Using this cell machinery, the virus can replicate his DNA and multiply itself in order to send another virus to other cells. This constitutes the life cycle of viruses.
Let’s see what does a virus’ life cycle look like!
Let’s start with the virion, this is the genome and the capsid (is the virus individual if you want). This virion will recognize the cell membrane and attach itself to it. Some virus recognizes every type of cell while other recognize just few types of cell.
Then it penetrates inside this one and opens his box to release his genome. It can open his box in the cytoplasm or in the nucleus.
Now can start the viral genome replication, there exist two type of replication depends on where the capsid opens itself:
- If it opens in the nucleus, this means that the virus has released DNA (DNA virus) and wish that is executing by the cell’s machinery.
- If it opens in the cytoplasm, it’s an RNA virus, which has his machinery to replicate itself, it just needs the cell and his RNA polymerase.
This RNA again! You don’t tell me what it is! Yes, it’s true, it will be the next chronicle so!
In the second case, the genome replication is not reliable because the RNA polymerase made more mistake than his cousin the DNA polymerase. Consequently, the virus undertakes a lot of mutations, so, they have a big genetic variability. This is why some virus are very persistent, these occur mutations give them an advantage.
Finally, the creation of new virions, the assemblage of these virions is a not well-known process (auto assemblage or via a third protein). The release of virions is made by two ways: either virions accumulate themselves in a cell until this cell bursts or they are releases as and when their creation.
That is the virus’ operation, so, living or not living, what do you think?
One the most common virus is influenza! Let’s talk about this:
Is an RNA virus (frequent mutations so), with an envelope.
Source: 
You can see the RNA fragments (in reality there are 8 fragments), that you see around are neuraminidases in red and hemagglutinins. They are surface protein:
- The hemagglutinins allow the entrance of the virus, there are 16 different type ranging from H1 to H16
- The neuraminidases allow the release of the virus, there are 9 different type ranging from N1 to N9
Hence the different names (H5N1, H1N1, …).
So, in nature there are primary reservoirs of the virus in human, pork and avian species (like chicken). In these reservoirs the virus exists in different form, generally, it’s not virulent.
However, if a cell is infected by two viruses different at the same time, the virus will change during the assemblage (new set of RNA fragment, new surface proteins). Is this way we have new influenza.
These new viruses are stored in secondary reservoirs (water, sol, microfauna, …).
This is why influenza is extremely complicated to fight and to predict because they are always subject to mutations and they can combine between different types. Consequently, there is, on average, there is new epidemic every second year (seasonal flu) and, of course, sometimes new virulent epidemic (epidemic flu) like:
- Spanish flu (1918-1920), H1N1
- Hong Kong flu (1968-1969), H3N2
The avian flu H5N1, infect only birds.
Actually, Humans can’t be contaminated by birds but can be contaminated by a pork and the bird can be contaminated by a pork. But the pork can be contaminated both by birds and humans. Consequently, the new viruses appear in the pork. We must be careful with pig and hen breeding on the same terrain.
Référence :
https://fr.wikipedia.org/wiki/Virus#Nature
https://fr.wikipedia.org/wiki/Grippe
https://fr.wikipedia.org/wiki/Grippe_aviaire
What this Dr.Plantes want me?
#01_Where are we? What time is it?
#02_The bacteria
#03_The DNA
#04_The evolution
#05_The cell
#06_The fission
#07_DNA replication
#08_The reproduction
#09_The molecules
#10_The seven kingdoms of living
