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Whats the difference between a dead virus and a live one?

  1. Dec 11, 2008 #1
    I have been wondering about life. Not the origins of life or the philosophical implications of life. just what is life. whats the difference between dead and alive.

    I know no one has the answer, but it would seem to me that a place to start would be to study the simplest form of life we know, apparently that is a virus. I have even read some consider it not to be alive. but I know thats crackpot stuff because in the same paragraph they said a particular form of virus can only 'survive' outside a host for x hours. Thus it must require some form of nourishment to replace depleted resources and without those resources it 'dies' it also is self duplicating which I believe is one of the most basic requirements of life.

    Anyway that diversion aside. The question is what physical difference is there between a living virus and a dead one? is it measurable?

    Is it a missing molecule, a lack of electrical activity, or lack of some other chemical activity?

    If we replaced it could we re-animate the virus. If not why not, does it mean something else is missing?

    This to me is a logical place of investigation for any scientist interested in the origins of life, it also seems to me to be more in the realms of physics than medical science. Is it some sort of quantum effect?

    It would appear to me if its some sort of physical effect, in other words the loss of some attribute, then reanimation is entirely probable. When a car runs out of petrol we fill it up again. If a piston breaks replacing it gets it working again. Nothing in a car is so important it is irreplaceable (though it might be too costly) that it can't be replaced to fix it.

    But for life my intuition says otherwise, something goes after death that can't be replaced no matter what.

    Please read that last sentence in reference to a single cell life form, not human or other higher (multi cell) life form.

    To put it in terms a physicist may understand. When death occurs there is a loss of information that cannot be reclaimed. Like the death of a black hole ( yes I know Stephen Hawking recanted and lost the bet).

    The last paragraph was to pique physicists interest because apparently you cannot lose information, eh I don't understand why but you can't. Therefore permanent death is a physical impossibility, which is the way I read it.

    So to re ask the original question, has anyone been able to catalogue the difference between a live virus and a dead one?

  2. jcsd
  3. Dec 11, 2008 #2

    Andy Resnick

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    I wonder if it's no coincidence that some vaccines contain 'deactivated' virii ( as opposed to 'dead' virii).
  4. Dec 11, 2008 #3
    probably just semantics but deactivated implies reactivation is possible
  5. Dec 12, 2008 #4
    Actually no. It means that they are biological inactive. Dead is rarely used simply because viruses are generally not considered to be living organisms in the first place. This shows the ambiguity regarding whether viruses are actually organisms or merely mobile genetic elements. It should be noted that in biological contexts one does not usually talk about death with regards to viruses, only inactivation, whereas in medical context at least the term live vaccine is sometimes used.

    You have got a faulty understanding here. A virus has no metabolic activity per se. "Death" in this case means that it loses its ability to replicate within a host. In other words, it has been inactivated.
    What we can argue is what really should be defined as living. Essentially there is no clear-cut definition. This is mostly because nature itself is not set within distinct boundaries but generally within continua.

    For example, if we take the ability to reproduce as the single defining aspect of live, we would have to consider other mobile genetic elements like plasmids or transposons and even prions as living entities, too.

    Back to the question: an inactive virus is characterized by its loss of ability to infect cells and reproduce (as viruses cannot replicate by themselves either). This can e.g. be achieved by heat inactivation, radiation, or chemical treatment. The problem is that if the process is too aggressive and the whole protein component of the virus gets denatured too much, it may not be antigenic enough for a vaccine. The basic tests for inactivation are mostly standardized assays which show that the virus is not infectious anymore.
    Last edited: Dec 12, 2008
  6. Dec 12, 2008 #5


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    Dearly Missed

    And that has already been done, if my hazy memory does not betray me.

    Didn't Craig Venter accomplish such a thing?
  7. Dec 12, 2008 #6


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    You should NOT start with viri, or prions for that matter!
    Apart from not being alive (rather, they might be called undeads), they are specialized parasitical genetic matter that represents the triumphant end result of the process of natural selection, whereby a set of genes finally maximizes its own reproductive potential by not bothering to create a living organism to further its cause, but let other organisms reproduce it.
  8. Dec 12, 2008 #7
    I would be surprised if Craig Venter was actually involved in that kind of stuff. It is not newsworthy enough. In any case the reversibility of virus inactivation depends on the means of inactivation. Extreme conditions like autoclaving or radiation are usually not reversible, for example (as the nucleic acids are also destroyed). Chemical inactivation might be, though.
  9. Dec 13, 2008 #8
    Ok so a virus is not alive, I wont argue the point. We will ignore the Mimivirus for this discussion then. Perhaps most virii are more like a crystal which can grow given the right conditions. Hmmm interesting I was always of the belief a virus is alive.

    Surely though the original question is still pertinent.

    What physical/chemical/electrical/? difference is there between a dead basic organism and a live one.

    Why can't we reanimate by re introducing the "missing element" what irreplaceable information is lost when an organism dies?

    I ask this on a physics forum because it seems to me at the basic level its a physics problem. If life arose from inanimate molecules (and virii now seem to me an excellent precursor or building block towards life) then what is it over and above their molecular structure that makes life?

    Surely a close examination of two identical organisms one alive and one dead from an nondestructive form of death could provide the clues.

    My question still remains.

    If anyone can point me towards studies that follow that reasoning I'd be appreciative.
  10. Dec 14, 2008 #9
    The answer is homeostasis. Even the simplest life requires incredibly precise regulation between all of its components to continue to function. The balance between components is so precise that, once lost, it is essentially impossible to recreate it.

    If you take a car's engine out, repair it, and put it back in, the car will still be functional because all of its other parts remained in much the same way while you removed the engine. If you tried to the same in a living being, you will get very different results. As soon as you remove or damage a component that is needed for life, all other components rapidly start degrading. If an hour later you put back the component you removed, the cell will not be the same; proteins, DNA and RNA will have all been degraded as a result of the loss of homeostasis. Thus, even if you put the "missing component" back in after a while, everything else is already inoperable. It's as if your car started rapidly evaporating as soon as you removed any part for repairs.
  11. Dec 14, 2008 #10
    Thats very interesting Proggle.

    You have given me something to research. I am reading about homeostasis on wikipedia at the moment.

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