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-   -   Viruses aren't living things but.. (http://www.physicsforums.com/showthread.php?t=87408)

Math Is Hard Sep4-05 12:13 AM

viruses aren't living things but..
 
I noticed that we give them certain names (I was reading a science journal this weekend about a "phi-6 bacteriophage"). If they don't belong to a kingdom, do they have a domain? If not, what's the classification structure used? Sorry -I am very new at this.

honestrosewater Sep4-05 12:59 AM

I just thought this was an interesting question and googled a bit. It appears that viruses have their own taxonomy.
Quote:

Universal, unambiguous virus taxonomy (naming and categorization) is vital for distinguishing the thousands of viruses which have been isolated from humans, animals, plants, fungi, bacteria, and archae.
- http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/index.htm
The ICTV seems to be the head honcho in the virus department. Seventh Report of the International Committee on Taxonomy of Viruses
Doesn't really answer your question, but maybe it will be helpful later.

Moonbear Sep4-05 07:28 AM

The difficulty with viruses is that biologists just aren't sure if they should be classified as living organisms. For example, they can't reproduce on their own, but instead require host cells for replication, and the retroviruses don't even have DNA but carry only RNA instead. They are distinctly in that gray area between things we can say with certainty are living and things we can say with certainty are non-living.

pattylou Sep4-05 09:28 AM

Classification is based on several things.

-DNA vs. RNA genome
-Single stranded vs. double stranded genome
-Positive vs. negative genome (this means whether the genome codes directly for proteins or whether it needs to be transcrbed or replicated first, to make a "plus strand)
-general coat morphology
-I think the type of host may also play into classification (viruses are extremely host specific.)

There may be some others, for example retroviruses are those that create DNA from RNA and then insert into the host genome.

Some viruses appear to have developed, at least partly, out of genes that were host genes to begin with (cellular oncogenes).

Viruses can pick up host material fairly easily during packaging. As moonbear said, they don't reproduce sexually, so variation in viruses is due solely to mutation and picking up *host* DNA.

Virus classification starts at the level of family for most, and class for a few (if I recall correctly, you may want to check this.) Genera are established (like Herpes) but species names are not always established (again, this is from memory.)

So the classification is not as complete as that for truly living organisms.

JamesU Sep4-05 09:58 AM

Quote:

Quote by Moonbear
The difficulty with viruses is that biologists just aren't sure if they should be classified as living organisms. For example, they can't reproduce on their own, but instead require host cells for replication, and the retroviruses don't even have DNA but carry only RNA instead. They are distinctly in that gray area between things we can say with certainty are living and things we can say with certainty are non-living.

It's weird isn't it? non-living things don't reproduce, however, some don't even have DNA! maybe they should have their own catagorization....

LIVING || Thred life :biggrin: || Viral life || Non-LIVING

Math Is Hard Sep4-05 12:21 PM

Thanks, all. This is very helpful. I was just looking at that link Rose posted:
Quote:

The ICTV has approved 3 orders, 56 families, 9 subfamilies, 233 genera and 1550 virus species. Descriptions of virus satellites, viroids and the agents of spongiform encephalopathies (prions) of humans and several animal and fungal species are included. Finally, a list of unassigned viruses is provided with a pertinent reference for each.
I don't know much about taxonomy but it looks like they are following the same classifications that are used for living things. I'm curious about that 'unassigned' list, and why some of them haven't been classified yet.

honestrosewater Sep4-05 05:13 PM

Danish Kings Play Cards On Fat Girls' Stomachs. :blushing:
Domain Kingdom Phylum Class Order Family Genus Species. :approve:

Sorry, I want to play along, but I know nothing about viruses. I must sneak in stuff where I can.

pattylou Sep4-05 05:19 PM

Quote:

Quote by Math Is Hard
I'm curious about that 'unassigned' list, and why some of them haven't been classified yet.

The vast majority of viruses haven't been isolated yet.* The unnassigned list probably has numerous viruses that have been described functionally in one or two papers, and not picked up by anyone interested in taxonomy.

* In a teaspoon of sewage treatment effluent, you can isolate viruses that infect almost any bacterium you'd like. In other words, the diversity is likely far greater than we appreciate. It might not be unreasonable to suggest that there is an order of magnitude more diversity/variety among viruses, than among bacteria. And bacteria put eukaryotes to shame in terms of diversity.

Renge Ishyo Sep4-05 08:46 PM

Viruses aren't grouped as part of the "phylums" of life because they lack certain key characteristics that all the things we consider lifeforms share. For example, viruses do not have cells of their own. They use the machinery in the cells of the host they infect in order to replicate their DNA code. As far as I know, viruses can't replicate unless they first invade a body and use it's cells.

Of course, none of this will stop people from grouping viruses together based on similiarities or differences and studying their functions. This will inevitably lead to organizational (taxonomic) structures that are very similar to those we have for living things, chemical compounds, etc. Nevertheless, viruses still are not considered "living" if only because they do not meet the minimum criteria for how we define "life."

Math Is Hard Sep5-05 01:50 AM

Quote:

Quote by honestrosewater
Danish Kings Play Cards On Fat Girls' Stomachs. :blushing: Domain Kingdom Phylum Class Order Family Genus Species. :approve:

That will come in handy!! It's unforgettable! Actually, HRW, I was thinking you might (being the mathophile) enjoy this article I am reading: American Scientist, September-October 2005, "Cheating Viruses and Game Theory". It's all about the role of "cheaters" in the evolutionary process, and the hypothesis that the author came up with is based on mathematical game theory.
Quote:

Quote by pattylou
It might not be unreasonable to suggest that there is an order of magnitude more diversity/variety among viruses, than among bacteria. And bacteria put eukaryotes to shame in terms of diversity.

From what I have been reading that sure seems entirely plausible. I wonder what the rate of virus mutation is compared with both prokaryotes and eukaryotes?
Quote:

Quote by Renge Ishyo
Nevertheless, viruses still are not considered "living" if only because they do not meet the minimum criteria for how we define "life."

Agreed. Without a host cell to infect, viruses could be seen as nothing more than a jar of chemicals on a shelf. But what fascinates me is that the ICTV group refers to them as a "biological entity" and even lays out a "virosphere". I am surprised that there hasn't been something like a "pseudo-life" domain created for viruses. Perhaps there is a surreptitious agenda here to create such a thing?

honestrosewater Sep5-05 02:31 AM

Quote:

Quote by Math Is Hard
That will come in handy!! It's unforgettable! Actually, HRW, I was thinking you might (being the mathophile) enjoy this article I am reading: American Scientist, September-October 2005, "Cheating Viruses and Game Theory". It's all about the role of "cheaters" in the evolutionary process, and the hypothesis that the author came up with is based on mathematical game theory.

Thanks. I'm not sure what they mean by "The study is the first to demonstrate the evolution of irrational, selfish behavior in a biological system." :surprised I'll put it on my list. :smile:

matthyaouw Sep5-05 04:25 AM

Quote:

Quote by honestrosewater
Danish Kings Play Cards On Fat Girls' Stomachs. :blushing:
Domain Kingdom Phylum Class Order Family Genus Species. :approve:

King prawn crackers on fried green seaweed
Kingdom, phylum etc...

I had chinese food cravings all the way through my taxonomy lessons. It was terrible!

hitssquad Sep5-05 05:09 AM

Quote:

Quote by honestrosewater
Danish Kings Play Cards On Fat Girls' Stomachs.

Reclining.

honestrosewater Sep5-05 05:24 AM

Quote:

Quote by matthyaouw
King prawn crackers on fried green seaweed
Kingdom, phylum etc...

I had chinese food cravings all the way through my taxonomy lessons. It was terrible!

Crackers on seaweed? Wouldn't you put the seaweed on the crackers? :rofl:
Quote:

Quote by hitssquad
Reclining

What is that for?

matthyaouw Sep5-05 05:39 AM

Quote:

Quote by honestrosewater
Crackers on seaweed? Wouldn't you put the seaweed on the crackers? :rofl:

Only if you want to fail your taxonomy exam :biggrin:
(Here come the chinese food cravings again...)

iansmith Sep5-05 06:37 AM

Quote:

Quote by Math Is Hard
From what I have been reading that sure seems entirely plausible. I wonder what the rate of virus mutation is compared with both prokaryotes and eukaryotes?

It will depend on the type of viruses. DNA viruses have a mutation rate that compares to their host, so bacterial and archea viruse will have a mutation rate around 10-6 and eukaryote viruses will have a rate around 10-9. RNA viruses have the highest rate of mutation with a frequency of 10-2 to 10-4. The enzyme responsible for synthesising RNA to DNA (Reverse transcriptase) does not have a proofreading mechanism. Hence, higher error rate compare to DNA viruses.

Math Is Hard Sep5-05 10:46 AM

That's very interesting, Ian. Do some microbiologists study viruses exclusively - or is that an entirely different field of study?

Math Is Hard Sep5-05 10:48 AM

Matthaeiouw has made me hungry for Dim Sum now. I doubt the buses to Chinatown are running today. Darn.


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