Viruses: Living or Non-living organisms

[Biosyn]

Do you consider a virus living or non-living organism?

In middle school, I was taught that a virus was the smallest living organism.
However, I see viruses as packages of genes coated in protein and that they are inert on their own. I think of viruses as stuck in a "Twilight Zone" between living and non living.

I don't think that viruses are true living organisms because they do not grow by dividing, generate energy, creating protein, etc. Yet, some scientists believe they are living because they contain genes necessary for their replication.

And there are some bacteria that are like viruses, unable to reproduce outside a host cell, such as Chlamydia or Rickettsia that are classified as living organisms. But they have the same limitations as viruses.



p.s. I think there was a similar topic for some research paper that was posted in 2009. I can't seem to find it.

 

[bfman]

Viruses are not considered to be "living" organisms in the fullest sense of the word. They replicate inside other living beings, but themselves are not living.

 

[Dasarath Sai]

bfman is exactly right.

 

[Ryan_m_b]

To be honest I don't think I've ever heard a solid definition of "life". Instead I've heard lists of attributes that if something has (or at least has some of them) it can be said to be alive. I would not class viruses as alive because they are not metabolically active and cannot reproduce themselves. The latter is different to needing a host to replicate because the distinction is that viruses literally are assembled by the host rather than growing in it.

I also find it bewildering that people have voted "both" for a question that is essentially "A" or "Not-A"

 

[Pythagorean]

"Towards a Mathematical Theory of Complex Biological Systems" by C. Bianca, 2011:

my paraphrasing and comments in the parenthesis

1. Wide range of participating entities (e.g. functional molecular groups)
2. Nonlinear interactions between entities (characterized by feedback and dispersion)
3. Heterogeneity (not sure how this is different form 1 given the paragraph on this)
4. Self-Organization / ability to develop specific strategies (I don't think these should be the same)
5. Active entities "play a game" at each interaction. (not really clear, but the author's paragraph talks about basically, changing internally as a result of external interacitons.
6. System is not in equilibirum (I agree that would be bad for a living system)
7. Entities belong to a wide variety of components (the entities have diverse functions)
8. Time is a key variable (this seems irrelevant/obvious to me. It uses the words Darwinian evolution, but we've already established that implicitly with 4 and 5)
9. multiscale approach (multi-scale optimization).
10. small changes lead to large effects (an extension of 2: form nonlinearity to chaos)

I think some of these are important and the idea develops a good framework for mathematical biology (which allows you to more concretely define things) but I think the number "10" was reached for. There's maybe four or five basic quantifiable principles here.

We could lump:

1, 3 and 7 together
4, 5, 8 and 9 together
2, 6 and 10 together

(wow, that would bring it down to 3!)

So far it seems that viruses would pass the test on these little quantifiers (but probably only in the presence of a "host"?), but then I have the feeling like they're life junk: amalgamates that must inevitably result from an ecology diverse degeneracy.

But I also have another thought. In the spatiotemporal limit, we are all part of one system (we all came from the same ancestor, we're all driven by and interact with the same chemical and physical gradients). So the boundaries we define between "organisms" can often be fuzzier than we imagine it is. At some point, a transitions from a colony of single celled organism to a single multi-celled organism must have occurred.

So my thought with viruses is then.. maybe they're just an extension of living things, more so than a living thing themselves. An example of where the phenomena of "organism" leaks into and out of the environment through these fuzzy boundaries that define the organism.

 

[Antiphon]

Seems like we need to make finer distinctions. I propose that a virus is dead until it contacts a cell and begins working. I'd further propose that it's not alive at that point either; that it has merely transformed the host cell into a new entity.

In a very real way the infected cell is like a Zombie. It's no longer the cell it was and the mutated cell has to be considered the true organism with the virus particle as a mere "seed" or spore.

 

[Biosyn]

Seems like we need to make finer distinctions. I propose that a virus is dead until it contacts a cell and begins working. I'd further propose that it's not alive at that point either; that it has merely transformed the host cell into a new entity.

In a very real way the infected cell is like a Zombie. It's no longer the cell it was and the mutated cell has to be considered the true organism with the virus particle as a mere "seed" or spore.

Same, I personally don't think a virus is living or non living.

A friend of mine said that saying that a virus is a living organism inside a host is almost like saying DNA nanobots are living organisms once inside a human body.

http://www.sciencedaily.com/releases/2012/02/120216144238.htm

 

[Borek]

Trying to classify a virus as living or not is a futile effort. We (Homo sapiens) have a tendency to try to classify everything, even if the classification doesn't make sense and is based on a questionable definitions.

 

[Ryan_m_b]

Same, I personally don't think a virus is living or non living.

A friend of mine said that saying that a virus is a living organism inside a host is almost like saying DNA nanobots are living organisms once inside a human body.

http://www.sciencedaily.com/releases/2012/02/120216144238.htm

I fail to see how a virus could be inside once in a host cell as often they have broken apart to shed their protein coat and release RNA. This RNA is then read by ribosomes that assemble more virus proteins, with the RNA is replicated by other processes, then the viral components self assemble. I don't think it is fair to say that any of that counts a virus as alive considering that when a virus replicates there is no whole virus at all.

Trying to classify a virus as living or not is a futile effort. We (Homo sapiens) have a tendency to try to classify everything, even if the classification doesn't make sense and is based on a questionable definitions.

Agreed.

 

[r-j]

What about Prions?

 

[DarioC]

But I also have another thought. In the spatiotemporal limit, we are all part of one system (we all came from the same ancestor, we're all driven by and interact with the same chemical and physical gradients). So the boundaries we define between "organisms" can often be fuzzier than we imagine it is. At some point, a transitions from a colony of single celled organism to a single multi-celled organism must have occurred.

So my thought with viruses is then.. maybe they're just an extension of living things, more so than a living thing themselves. An example of where the phenomena of "organism" leaks into and out of the environment through these fuzzy boundaries that define the organism.[/QUOTE]

Well written, I like it. A fuzzy line of almost life. Lots of grey areas in this universe.
DC

 

[tmcphd]

A a College Biology professor, the debate about a virus being living or non-living is ongoing. The reproduction is the complicated issue, because all viruses use the host's cell DNA/RNA replication machinery, ie, enzymes, nucleotides. Even the enzyme itself is incorporated into the virus' envelop. They therefor are not self sufficient for the own reproduction, which is a characteristic for living things. They also do not carry out all the cool little processes that eukaryotic cells do to produce energy. They lead a "borrowed" life, so to speak.

Prions, on the other hand, are nonliving particles. They are proteins that are capable of misshaping others simply by their contact with them.

 

[bobze]

Trying to classify a virus as living or not is a futile effort. We (Homo sapiens) have a tendency to try to classify everything, even if the classification doesn't make sense and is based on a questionable definitions.

I'd like to second this as well. Whether they are "living" or "non-living" isn't important. We like to shove things in boxes, which sometimes let's us loose sight of the big picture.

People do it when trying to ponder the origins of life as well. Evolution doesn't have a requirement that something be "alive" to evolve--Viruses get by just fine in their niche and evolving without meeting what we deem necessary for something to be alive.

 

[Moonbear]

Viruses fit perfectly in the gray area. I also agree that defining them into living or non-living really has no impact on studying them and what they do. That discussion is mainly useful in the high school biology setting to introduce students to the idea that not everything can be easily categorized and that biological molecules to organisms exist on a continuum.

 

[Pythagorean]

I see it the other way around. Theoretically, if life is ever formally defined a (i.e. a quantitative set of measurements on a system) it would be interesting to see where viruses fall on the test.

 

[Nik_2213]

I'd class viruses as 'living' because they are obligate parasites. Also, IIRC, viruses do range from stripped-down, minimal monsters to much larger whatsits...

 

[bobze]

I see it the other way around. Theoretically, if life is ever formally defined a (i.e. a quantitative set of measurements on a system) it would be interesting to see where viruses fall on the test.

That's the point though Pythagorean--Life isn't amenable to "definitions", it occurs across a spectrum. Its not binary, its shades of gray.

Probably the most simple and inclusive definition for life we could come up with is something capable of biological evolution.

 

[Ryan_m_b]

Probably the most simple and inclusive definition for life we could come up with is something capable of biological evolution.

Hmm however by this definition products of genetic algorithms would be classed as alive.

 

[Moonbear]

That's the point though Pythagorean--Life isn't amenable to "definitions", it occurs across a spectrum. Its not binary, its shades of gray.

Probably the most simple and inclusive definition for life we could come up with is something capable of biological evolution.

It's sort of like when I assign final grades in a course, and someone emails me that they are only some smidgen of a percentage point from the cut-off for the next letter grade and pleads for a grade bump. The answer is that wherever the cut-off is set, there will be someone with a grade close to that cut-off, especially in a large course. The same holds for how we define life. In a way, the definitions try to take into account things we have a gut feeling are "alive" but no matter how we define it, something will just miss the cut off and be the topic of this same debate.

The only potential value in defining a cut off for what is alive would be to foist some topics over onto the chemists that the biologists don't want to deal with. Biology is the study of life, so if it's not alive, and it involves chemical reactions of some sort, maybe we can make it the problem of the chemists instead. Of course, in reality, that's why fields like biochemistry exist, and why chemists work on biological problems and biologists work on chemical problems, because again, there's a range of topics that bridge the two subjects and are not easily defined as one or the other, nor do I think they should be.

 

[Pythagorean]

That's the point though Pythagorean--Life isn't amenable to "definitions", it occurs across a spectrum. Its not binary, its shades of gray.

Probably the most simple and inclusive definition for life we could come up with is something capable of biological evolution.

Yes! I'm glad you agree with my point! This is not something special about life (or else we would have a clear cut distinction, right? :)

This is the same problem with, say, conductors vs. insulators. There is no perfect conductor or insulator. Everything exists in between (i.e. they are two ideals we have invented for studying them). But we can still identify regions where we say "oh that's definitely not a conductor" (even though electrons do actually move across the substance).

So life will have the same kind of spectrum... but the point is we still have yet to quantify it mathematically; and once we do, we would expect a rock to be at one end, animals to be at the other, and viruses to be somewhere in between.

But the point I was discussing, was whether the measure would be useful or not:

I also agree that defining them into living or non-living really has no impact on studying them and what they do.

...and I am contending that it would be useful to have a quantitative test for living things. Quantitative classification is always useful to prediction, even if we accept that near the boundaries between regions (living/non-living or conductor/insulator) there are some problems with a rigid definition.

Even in Moonbear's example above, she outlines how the distinctions are useful, even though the boundaries are fuzzy. That's the nature of EVERYTHING we study! Not just life!

 

[fuzzyfelt]

Probability?

 

[Ryan_m_b]

Virus comes under both the category of living or non living organism. When virus present inside the human body or any living things body,it is said to be that virus is living organism,But When virus present outside the human body or any living things body,it is called as non-living organism.

I addressed this above and I think the point still stands:

I fail to see how a virus could be inside once in a host cell as often they have broken apart to shed their protein coat and release RNA. This RNA is then read by ribosomes that assemble more virus proteins, with the RNA is replicated by other processes, then the viral components self assemble. I don't think it is fair to say that any of that counts a virus as alive considering that when a virus replicates there is no whole virus at all..

 

[dpsguy]

I think a mention of Mimivirus would be relevant here.

From the Wikipedia page on mimivirus:

Mimivirus possesses many characteristics which place it at the boundary of living and non-living. It is as large as several bacterial species, such as Rickettsia conorii and Tropheryma whipplei, possesses a genome of comparable size to several bacteria, including those above, and codes for products previously not thought to be encoded by viruses. In addition, mimivirus possesses genes coding for nucleotide and amino acid synthesis, which even some small obligate intracellular bacteria lack. This means that unlike these bacteria, mimivirus is not dependent on the host cell genome for coding the metabolic pathways for these products. They do however, lack genes for ribosomal proteins, making mimivirus dependent on a host cell for protein translation and energy metabolism. These factors combined have thrown scientists into debate over whether mimivirus is a distinct form of life, comparable on a domain scale to Eukarya, Archaea and Bacteria. Nevertheless, mimivirus does not exhibit the following characteristics, all of which are part of many conventional definitions of life: homeostasis, response to stimuli, growth in the normal sense of the term (instead replicating via self-assembly of individual components) or undergoing cellular division.

See also the Nature Education article on this topic.

 

[Ryan_m_b]

I think a mention of Mimivirus would be relevant here.

From the Wikipedia page on mimivirus:

See also the Nature Education article on this topic.

Good thing to bring up, though this would be the relevant part for me:

Nevertheless, mimivirus does not exhibit the following characteristics, all of which are part of many conventional definitions of life: homeostasis, response to stimuli, growth in the normal sense of the term (instead replicating via self-assembly of individual components) or undergoing cellular division.

 

[apeiron]

So life will have the same kind of spectrum... but the point is we still have yet to quantify it mathematically; and once we do, we would expect a rock to be at one end, animals to be at the other, and viruses to be somewhere in between.

Robert Rosen did argue a mathematical definition of life based on category theory - see his M/R systems, or metabolism-replication, work.

http://planetmath.org/encyclopedia/MRSystem.html [Broken]

On that score, a virus has the replication but it has to borrow the metabolism - so "borrowed life" is a good way to put it.

This also fits with an evo-devo approach to evolution as clearly a virus evolves quite happily. It has that aspect of life. But it has to borrow its development, the metabolic processes.

This M/R systems definition at least allows you to more sharply separate virus fragments as genetic information from "mere" physico-chemical potentials, the self-organising metabolic cycles that life harnesses.

So maybe rather than being in the middle of the living spectrum, a virus comes from way over one side, an extreme, as a naked stripped down replicator which only evolves.

There are still grey areas of course. Like the 8% of our genome which is retroviral contamination apparently. The line between parasite and host is really getting blurred once the DNA become part of the host's genetic diversity!

http://www.uta.edu/ucomm/mediarelations/press/2010/01/genome-biologist-reports.php

 

[Pythagorean]

Interesting metric by Rosen. I can see how a virus would be an extreme by a particular metric; One point to keep in mind is that life probably won't be measured by the dimensionality of one variable, so while an extreme is hit in one dimension by viruses, the landscape across the whole n-dimensional space may have maxima at places other then the extrema of each abscissa.

 

[Pythagorean]

Probability?

Sorry, I missed the context of this. While probability is an important example, even deterministic models have behavior that eludes definitions. In stability analysis, we eventually have to ignore anything beyond first order terms if we want to move forward with conceptual discussion and theory. We can define the behavior for which the eigenvalues of a nonlinear system are positive (repellor) or negative (attractor). But we can't easily talk about what happens when one of the eigenvalues is 0, because those second order terms become important. For each system, we'd have to do the second order analysis (and if that's 0 too, we have to do third-order.. and if that's zero...) and for sufficiently high-dimensional systems, there will be no generalizing of the behavior.

 

[apeiron]

Interesting metric by Rosen. I can see how a virus would be an extreme by a particular metric; One point to keep in mind is that life probably won't be measured by the dimensionality of one variable, so while an extreme is hit in one dimension by viruses, the landscape across the whole n-dimensional space may have maxima at places other then the extrema of each abscissa.

Except it is explicitly a two variable model - a dichotomy. So you would have a pair of orthogonal axes. The virus might land entirely on the x-axis (or Replication axis), while an H2O molecule lands entirely on the y-axis (or Metabolism axis). Then living systems would have some co-ordinate on the plane created.

Instead of M-R, I might suggest we use entropy and meaning as purer descriptions. So a virus is all meaning (no entropy, just the constraints), while water is all entropy (no meaning, just the unconstrained material potential).

So a virus would be high in meaning, low if not zero in entropy measured in this two-variable space. Only a handful of base pairs can control a lot of cellular activity. And there is no wasted fat in information terms.

While water is maximally entropic on its own. Or within some cell, it then takes on a distinct temperature and pressure at least. It gains information by becoming part of a cell's organised metabolic economy.

On the other hand, your idea of an n-dimensional phase space doesn't capture the essential distinction Rosen was making. That would be just modelling a system's degrees of freedom, creating as many axes as you think there are degrees of freedom.

The systems approach is instead to measure both the degrees of freedom and their constraints. And Rosen was offering a maximally general model in terms of metabolism and replication, which I am suggesting becomes even more generalised as entropy and meaning.

I've got to say Rosen's scheme never stuck me as fully worked out. In fact, he called it metabolism-repair more than metabolism-replication. He also tried to make a strong connection to anticipation, his anticipatory systems papers. So his was a work in progress, and I'm now thinking that entropy-meaning (the kind of division now being made in biosemiosis) is sharper yet.

This means we still need a metric to define meaning. Another mathematical biologist who I believe is doing good work on this angle is Bob Ulanowicz - http://en.wikipedia.org/wiki/Ascendency

 

[fuzzyfelt]

Sorry, I missed the context of this. While probability is an important example, even deterministic models have behavior that eludes definitions. In stability analysis, we eventually have to ignore anything beyond first order terms if we want to move forward with conceptual discussion and theory. We can define the behavior for which the eigenvalues of a nonlinear system are positive (repellor) or negative (attractor). But we can't easily talk about what happens when one of the eigenvalues is 0, because those second order terms become important. For each system, we'd have to do the second order analysis (and if that's 0 too, we have to do third-order.. and if that's zero...) and for sufficiently high-dimensional systems, there will be no generalizing of the behavior.

Thank you very much for replying, Pythagorean. I'm very sorry, I thought I had deleted the question, as I was thinking of a different one about subjective probability and multi-valued categories, but hadn't managed to do so, but thanks so much for your help.

 

[Flatland]

Perhaps we need a new classification that exists between life and non-life?

 

[Biosyn]

Perhaps we need a new classification that exists between life and non-life?

Gene Creatures

 

[Amiri Daudi]

Viruses are of botanical and zoological enigma.There some facts which shows that they are living and some facts that they are non-living.This is the reason why diseases cause by viruses are difficult to treat the only remedial measure is using the vaccines.The viruses replicate in this respect this is one characteristic of a living thing that of reproduction.On the other hand viruses can be crystalised and kept in a bottle and close even for 300yrs but when release and found their substrate organ they start to replicate again this charactiristic is not in living organisms.Viruses do not respire,digest or excrete as living organisms do.

 

[Ryan_m_b]

There some facts which shows that they are living and some facts that they are non-living.

It's more a case of we don't have a definition that can adequately deal with viruses rather than us not having enough facts about them.

This is the reason why diseases cause by viruses are difficult to treat the only remedial measure is using the vaccines.

Vaccines are not the only measure and for some diseases there is no vaccine but there are treatments (like interferon or anti-retrovirals). I'm not sure what you mean by difficult to treat as I am unsure what you are comparing it to.

The viruses replicate in this respect this is one characteristic of a living thing that of reproduction.On the other hand viruses can be crystalised and kept in a bottle and close even for 300yrs but when release and found their substrate organ they start to replicate again this charactiristic is not in living organisms.Viruses do not respire,digest or excrete as living organisms do.

You can also put the component parts of viruses into a vial and they self assemble, in that respect they are complex biological nanoparticles capable of self assembly.

 

[ViewsofMars]

The American Society of Microbiology states:

1. A virus is basically a tiny bundle of genetic material—either DNA or RNA—carried in a shell called the viral coat, or capsid, which is made up of bits of protein called capsomeres. Some viruses have an additional layer around this coat called an envelope. That's basically all there is to viruses.

2. Viruses are the simplest and tiniest of microbes; they can be as much as 10,000 times smaller than bacteria. Viruses consist of a small collection of genetic material (DNA or RNA) encased in a protective protein coat called a capsid. (Retroviruses are among the infectious particles that use RNA as their hereditary material. Probably the most famous retrovirus is human immunodeficiency virus, the cause of AIDS.) In some viruses, the capsid is covered by a viral envelope made of proteins, lipids and carbohydrates. The envelopes may be studded by spikes made of carbohydrates and proteins that help the virus particles attach to host cells. Outside of a host, viruses are inert, just mere microbial particles drifting aimlessly.

http://www.microbeworld.org/index.php?option=com_content&view=category&layout=blog&id=77&Itemid=72