Why aren't viruses considered to be "alive"?

Originally posted by junglelord
what came first living cells (bacteria) or virsus?
Anyone know?
Either way they seem part of life!
And they are not inanimate, just dormant, big difference.

It would have to be the virus, I think. The virus is parasitic and therefore needs a host (the bacteria).

[edit on 27-5-2007 by Johnmike]

If we think in Darwinian evolution terms - does virus sustain itself as a 'spices'?

1. A virus particle attaches to a host cell.
2. The particle releases its genetic instructions into the host cell.
3. The injected genetic material recruits the host cell's enzymes.
4. The enzymes make parts for more new virus particles.
5. The new particles assemble the parts into new viruses.
6. The new particles break free from the host cell.


All of the those bolded words indicate a proactive approach. In a chemical reaction, things simply react to one another, whereas a virus seems to "bully" its
"partner."

A virus seems to take some sort of initiative; it acts; it "does.

How is it not alive, then?

[edit on 5-27-2007 by Cutwolf]

Originally posted by Cutwolf
1. A virus particle attaches to a host cell.
2. The particle releases its genetic instructions into the host cell.
3. The injected genetic material recruits the host cell's enzymes.
4. The enzymes make parts for more new virus particles.
5. The new particles assemble the parts into new viruses.
6. The new particles break free from the host cell.

Well everything after 2 isn't done by the virus. The genetic material doesn't really recruit the host cell's enzymes - the host cell's enzymes just do their job. Some viruses, I think, have their own enzymes if something has to be done that isn't normally part of the cell cycle (certain functions with DNA... I think an RNA virus is one type that needs it). The CELL's enzymes then make the parts for the new viruses.

Basically, the virus just hijacks the cell so that it makes more viruses instead of whatever it normally makes.

Now attaching to the host cell can be considered chemistry, not life - like how two ions of opposite charges are attracted to one another. Not all viruses actually inject like a phage (HIV actually merges with the membrane of the host cell, I think), but this also could be a simple mechanism caused by the binding of molecules.

But then, a cell can be seen like that as well...just a series of chemical reactions, without any definite will.

Oh boy.

Exactly.

Also...

the virus just hijacks

An action. It DOES something to something else.

Also, the fact that viruses can "die" implies they were once alive, does it not?

[edit on 5-27-2007 by Cutwolf]

[edit on 5-27-2007 by Cutwolf]

Here's a good resource if you want to learn more:
www.ummz.lsa.umich.edu/molsys/MRV04.pdf

In general, life must contain the following characteristics:
1) Must be capable of replication (both genomic information/intructions pertaining to building & maintaining structure and the containing structure itself to facilitate reactant recruitment and concentration)
2) Must be capable of Darwinian evolution (replication sufficiently faithful so as to preserve genomic information, yet sufficiently flawed so that structural &/ functional diversity may be introduced into the population as a basis for competition under changing environmental conditions)
3) Must posess some form of metabolism (energy generation and molcular conversion/making appropriate building blocks for the maintenence and replication of structure)

Since chemistry is inherently dependent on environmental conditions, this could be construed as a viable means of responding to environmental stimuli. As far as I'm concerned, viruses are alive because they replicate, mutate and obtain their molecular building blocks through hijacked metabolic pathways. They are simple parasites.

If we are to unravel the mystery surrounding the origin of life on Earth (which may not necessarily have been cellular; see www.nordita.dk/conference/AstroBioSchool/material/Russell/Russell+Martin04.pdf ), we must first define what life is. In fact, viruses may be very important in elucidating the origins of life, particularly those with RNA genomes (search "RNA World"). RNA is a crucial part of the puzzle given it's ability to act as both a biomolecular catalyst (ribozymes are less efficient than modern protein enzymes but they DO function!) and as a carrier of genetic information. Recently, DNA enzymes have been derived from in vitro selection in the lab as well (deoxyribozymes).

Alternate genetic systems have been studied which include TNA, GNA and PNA (ribose replaced with threose, glycerol and peptides, respectively) in addition to a plethora of studies investigating unnatural amino acids, alternate genetic codes and even using mineral (inorganic) templates for polymerizing nucleic acids. Prions may eventually play a larger role and I wouldn't exclude them just yet. However, my point is that in the search for the origins of life on Earth or possibilities for life elsewhere, we must learn to diverge from what is familiar in biochemistry and adhere to the three simple traits listed above as defining characteristics of life.

By the way, the NASA Astrobiology Institute has a great website with some really cool images and research groups listed who work in this field. Investigators love questions from an eager and curious public (who wouldn't love to have people interested in their passions?).
nai.nasa.gov...

Here's the virus focus group:

www.nai.arc.nasa.gov...

I understand the definition of life. However, I feel the definition of life is flawed, especially when you have something that is clearly much more than an inanimate object (a virus) that exists in this gray area.

Ultimately, I feel our flawed definition of life ends up hurting scientific efforts to identify life in remote areas of our world and on other worlds.

Originally posted by Cutwolf
An action. It DOES something to something else.

Kind of. An oxygen molecule binds to two hydrogen molecules to make water. Is oxygen alive? Obviously not, but it's "doing" something. It's just a chemical reaction. That's all that viruses seem to be.

The difference is in a reaction like that, they're both reacting with each other. Its like a dance. Both are just "passively" and effortlessly blending into one another

A virus infecting a cell is more like a baseball bat to the face. They bully. They're dominant.

Originally posted by Cutwolf
I understand the definition of life. However, I feel the definition of life is flawed, especially when you have something that is clearly much more than an inanimate object (a virus) that exists in this gray area.

Ultimately, I feel our flawed definition of life ends up hurting scientific efforts to identify life in remote areas of our world and on other worlds.

I never accused you of not having a solid understanding of what constitutes life. I simply listed the traits researchers in the field abide by when studying systems that exhibit life-like characteristics. In fact, we share the same conclusion where viruses are concerned, leaving plenty of room for exotic, yet viable organisms we theorize and/or synthesize in the lab but have yet to observe naturally.

Being parasitic does not disqualify a macromolecular assembly from the biological world. Does anyone disagree that tapeworms are alive? Perhaps the biggest bone of contention is the level at which that parasitism occurs (molecular vs. multicellular). I see no reason why the definition of life as it is should be labeled flawed unless evidence exists which prompts us to reconsider the terms.

Chemical bonding is a purely physical process which, though crucial to biology, is not exclusive to it. Whereas evolution, synthesis and replication in sum total, cannot be anything but life, regardless of what it is composed of. Current scientific theories regarding life's origins attack the issue from 3 general starting points:

1) Minimizing a modern system (deleting parts of a simple cell until it ceases to live)

2) Building up from individual modern biomolecules that have functions necessary for life, such as encapsulating ribozymes or some other autocatalyzing (self-replicating) molecule in a liposome (fatty acid vesicle that spontaneously assembles)

3) Putting molecules likely to have been present on prebiotic Earth in a simulated Hadean environment to see what biomolecules you can make (a foundation for #2)

I'm not mentioning panspermia because it does not actually address the definition of life, let alone its origin.

#1 starts off with a living thing and it was once thought that by taking parts out, we might learn what was necessary for life. This approach has largely been abandonned in origin of life studies.

#2 is the most popular method among biochemists and generates many plausible stepping stones which could have evolved into modern biochemical pathways. Rather than taking the car apart to see how it works, so to speak, one starts with what looks like the most important part and tries to build a vehicle around it that actually runs

#3 is favored by geochemists and is by far the most difficult approach given the rarity of samples exceeding 3.8 billion years in age. Although it considers environmental processes that could have provided reaction vessels and templates for the concentration of reactants necessary for biochemistry, a huge gap remains between #'s 2 & 3. A new model is on the horizon and should appear in the next year or so but funding cuts may force it to be shelved.

As I see it, the debate surrounding life's origins, possibilities for extraterrestrial life and the definition of life are one in the same. I see no reason to restrict life to a cellular, carbon-based, DNA-containing organism. Life on Earth is ubiquitous. Everywhere you look, there it is. My issue is with people who think sending labs on a chip to Mars to perform PCR is a stringent test for life. It would find viruses if present but certainly not the other genetic systems if they ever existed there.

Originally posted by Cutwolf
The difference is in a reaction like that, they're both reacting with each other. Its like a dance. Both are just "passively" and effortlessly blending into one another

And that's how you have to see a virus and most cell activities. It's just a bunch of chemical reactions, as is most of your body. In fact, your entire body can be seen as just a bunch of chemical feedback mechanisms... It's a little scary to think about, but for all I know, you're not "alive". The only thing that isn't just a series of chemical reactions is consciousness, really.

Originally posted by djohnsto77
Viruses don't meet the scientific definition of life because they can't reproduce (or do anything else for that matter) without using a living host cell.

Well, by definition, does that not make us a virus as well? We're using Earth as a host to feed off of, and to reproduce, aren't we? Without some source of energy, nothing can reproduce. We don't just spontaneously pop out young.

So, by your assessment, we're not living. I find this line of logic at best flawed, and at worst broken.

TheBorg

Originally posted by Cutwolf
An action. It DOES something to something else.

Computer viruses also DO something to something else. But they are not alive.

I think it really just comes down to semantics. We have a particular list of characteristics that, if something has all of them, we term it 'alive', and if it is missing one or more of these, it is 'not alive'. It's just a way of classifying things based on behaviour, physical structure, and all that, just as we have animals, plants, minerals, etc.

Originally posted by TheBorg
Well, by definition, does that not make us a virus as well? We're using Earth as a host to feed off of, and to reproduce, aren't we? Without some source of energy, nothing can reproduce. We don't just spontaneously pop out young.
TheBorg

Good point! I often think of us as viral creatures living off of Earth's resources. Still, this is why parasitism never even enters the equation when determining whether something is alive or not. I asked about computer viruses once in a course I took as we were discussing this very topic and it comes down to this:

1) Yes, they replicate (genetic code of sorts; information about the code itself and how to copy/ spread it)
2) Yes, they use energy to carry out the conversions needed to propagate structure (electronic metabolism!)
3) No, they do not exhibit Darwinian evolution, therefore they are not "alive".

So if they DID mutate in response to environmental pressures from changing conditions (programming periodic mutations into the code does not provide a basis for competition against other viruses & subequent selection based on environmental pressures), then they would, by NASA's definition, be considered, "alive". This is where computer viruses fail the test.

[edit on 28-5-2007 by X-tal_Phusion]

cutwolf --

Going back to your original post, why are you so keen on the scientific world defining a virus as being "life". You seemed to inply that if a virus was considered "alive" it would increase the odds of finding life outside our planet. But a virus, by definition, needs to have a host cell to live, thus a virus could not live on a planet that does not already contain life...

...so it's safe to say that -- using the accepted scientific definition of a virus -- if a planet is found to have viruses, then it MUST have the bacterial or possibly even multi-cellular life to host those viruses.

In other words, if you find a virus, life is definitely present (although, I suspect that even a single cell bacteria will be much easier to detect that a virus, thus the bacteria will be found first, then possible viruses will be found later).

Using conventional terrestrial rules, yes cellular life would be a prerequisite for the existence of viruses. However different environmental conditions lead to different evolutionary outcomes and terrestrial trends may not apply elsewhere if life evolved in a different way. Viruses may either be the product of intracellular parasitism (abandoning cellular structure in favor of rapid replication; a more drastic form of the endosymbiont theory responsible for modern mitochondria, chloroplasts and lysosomes) or a product of some more primitive autonomy (perhaps adhered to a mineral scaffold that adsorbed organics exploited by the virus until something better came along: the cell).

It is even possible that any extraterrestrial life on Mars or wherever else we choose to search does not even use traditional genomic (DNA/RNA) or structural molecules (lipids, proteins, carbohydrates). Changes in structure are inextricably linked to changes in function. Different building blocks sets new chemical parameters leading to novel organisms unlike those familiar to us now. More likely, you are right (at least where subterranean Mars is concerned) but I think it's hasty to disqualify the possibility that what we observe here is universal where life exists.

Originally posted by X-tal_Phusion
3) No, they do not exhibit Darwinian evolution, therefore they are not "alive".


[edit on 28-5-2007 by X-tal_Phusion]

Please..

Viruses DO
1. survive
2. mutate


- DNA or RNA of virus can and evolve over time - that means that viruses increase their chance for evolutionary survival meaning adaptation to the environment........ so they stay from dawn of life till present in the game..

Originally posted by laiguana
You could probably consider a virus more like a corrupted function.

This is an interesting thread - I don’t pretend to understand much of what has been said, but if I had to pick a side of the fence, I would go with not technically alive - just a bundle of rogue DNA/RNA.

Now I've got another question now - if viruses are not alive, how the hell did they come into existence in the first place?? And what about the variety / adoption (i.e. cold virus)

I know the theory of evolution isn't perfect yet - is that a direction we should be looking at?