Viruses aren't living things but

[Math Is Hard]

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]

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

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]

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]

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]

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 || Viral life || Non-LIVING

 

[Math Is Hard]

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

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]

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

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

 

[pattylou]

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]

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]

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

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.

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?

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]

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." I'll put it on my list.

 

[matthyaouw]

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

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]

Danish Kings Play Cards On Fat Girls' Stomachs.

Reclining.

 

[honestrosewater]

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?

Reclining

What is that for?

 

[matthyaouw]

Crackers on seaweed? Wouldn't you put the seaweed on the crackers?

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

 

[iansmith]

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]

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

 

[Math Is Hard]

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

 

[iansmith]

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

Yes, there is people that exclusively study viruses. There a few people in my department that are virologists.

 

[Renge Ishyo]

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?

What sucks about trying to define things is that nature is quite disagreeable when it comes to drawing straight clear cut lines. Viruses are in that "grey area" between living and non-living things. They are like a rock in a sense that they lack cellular structure and can't go through life processes all on their own. At the same time they are like a "biological entity" in the sense that they *function* inside biological lifeforms in many of the ways that we use to distinguish a living from a non living thing.

So we say it's non living because it does not meet the minimum criteria, at the same time it is NOT inorganic because it shares structures and functions that are characteristic of biological lifeforms. It's in one of those areas of science where if you try to define it based on overly general groupings you are dammed either way (sort of like trying to describe light as either a particle or a wave when it shares characteristics of both).

I don't think that show has an agenda so much as they are struggling with how they should describe it to someone that (presumably?) doesn't know what a virus is yet. I mean, they aren't part of the lithosphere or the biosphere technically...so where DO they fit into the picture?

 

[hitssquad]

Danish Kings Play Cards On Fat Girls' Stomachs.

Reclining

What is that for?

Race.

More mnemonics:
http://en.wikiquote.org/wiki/English_mnemonics#Biology

 

[nipwoni]

The most important difference between classification of viruses and classification of living things is that living things are classified based on their phylogenies (what they evolved from and their relatedness to other living things). Viruses are classified based on their properties, such as whether they have a membrane and whether they use DNA or RNA. Viruses can't be classified based on phylogeny because they don't evolve in the same way we do. All living things have a common ancestor way back in time, but that's not true for viruses. Viral DNA is derived from the DNA of host organisms. So each viruses' closest "relative" is its host (or its initial host, in the case of viruses that can infect multiple species). Viruses are really bits of DNA or RNA that have gotten out of control and have started to evolve on their own.