Intracellular Parasites (Related to Post 7)

[John Harvey]

That was my thinking too, Soroush; that the virus's reproduction necessitates the use of chemical building blocks, which presumably are stolen from the cell. Unless the building blocks are merely waste material, that process must surely be parasitic in the sense that it takes nutrients from the cell.

Of course, the energy required for the reproductive process must come from somewhere too, and therefore theoretically must also (at least indirectly) use some of the cell's battery of ATP. (On the other hand, a virus able to fulfill its chemical-energy needs from the heat of the cell, rather than steal the cell's chemical energy, would indirectly lower the cost of removing excess heat from the cell! But I suspect that this never occurs. There's a reason for which viruses need to be inside cells!)

I think you're right, Irene, that it doesn't matter too much whether we call a virus a parasite or not, as long as we know whether or not we're including it in descriptions applying to parasites, such as those you and Soroush have posted here about invocation of Th1 versus Th2. (And that may be why biologists apparently tend to include viruses amongst the parasites and common perception would not: that it doesn't really matter.)

My own question along these lines, about whether you're including or excluding the larger parasites, was intended to clarify for me whether you were including such larger ones in your own discussion of the processes applying to parasites.

Incidentally, as with any definition, it's more useful for a dictionary (common or biological) to specify those things, and only those things, that determine whether something is a virus or not a virus -- which is in fact the sole function of a definition -- than to attempt to include details inessential to that determination.

In that sense, it wouldn't be necessary for any dictionary definition of a virus, if it is a parasite, to say so, any more than it would be necessary to say that a virus is potentially morbific; we can define the virus very well without doing so -- and, in the most general case ("what is a virus?"), to do so more accurately and with a lower likelihood of later finding it necessary to hedge due to discoveries such as the possibilities that Ginny and Sheri have just canvassed here (that a virus is not always harmful; that it is perhaps never intrinsically harmful), or such as the hypothetical possibility that a certain virus may manage to eke out a "living" and reproduce itself without the least cost to the host.

Cheers --

John

[Irene de Villiers]

No chemical buiilding blocks.
A virus does not use nutrients, or have any way to use nutrients.
A virus consists only of a piece of genetic material (DNA or RNA molecule depending on the virus), with a protein coat called envelope protein, to hold its DNA/RNA together. It doesn't even have a chromosome to do that. That is all. It has nothing that needs nutrients. It is a bit of genetic coding molecule, is all.
It uses the host machienery to do any actual production of coding results including its own replication coding - it taken in nothig - it cannot - it has nowhere to take it in. It has no other functions than the code of its DNA or RNA.
NO biologist is that ignorant:-)
--
Irene de Villiers, B.Sc AASCA MCSSA D.I.Hom/D.Vet.Hom.
P.O. Box 4703 Spokane WA 99220.
www.angelfire.com/fl/furryboots/clickhere.html (Veterinary Homeopath.)
"Man who say it cannot be done should not interrupt one doing it."

[John Harvey]

Good point. And you have of course cut to the chase: a virus using a cell's machinery to reproduce itself is surely parasitising the host's cell, whether we choose to classify it that way or not, as it is commandeering (for at least part of the time) important cellular mechanisms and mitochondrial energy. Surely it's not conceivable that a virus can do this without exacting a substantial cost to the cell?
When I looked around the other evening at online dictionaries, I noted one or two biological ones that included viruses as parasites, and saw specific mention of the tendency of biological dictionaries to do so. Perhaps there's a reason for that other than ignorance of the common dictionary. It may be that biologists are, by calling a virus a parasite, casually recognising the essentially parasitic nature of viral activity, don't you think?

John

--
In consigning its regulatory powers to its subject corporations, a government surrenders its electoral right to govern.

[Hennie Duits]

Interesting discussion.
Should a nail that is magnetised by a magnet be considered a parasite?

Hennie

John Harvey schreef op 25-4-2014 12:09:

[John Harvey]

Only if the nail can't hear you upset its world view.

Magnetised nails are known to have a tendency to become bipolar. And, as we see in conversation even on this list of very rational people, potential differences easily become a sore point to those without an ego to protect them. A vulnerable bipolar nail that rapid change in current conventions has galvanised into self-righteous action is an unstable thing, and has a way of exacerbating potential differences with shocking consequences.

So, although you're perfectly correct and a nail performs the functions of a parasite, in this instance, the benefit of seizing the field may not be worth the sparks that communicating it will cause to fly.

Cheers --

John

(Sorry -- that was a spitball of little jokes for those with some background in electricity and magnetism.)