Bare with me, Im young Please Register or Log in to view the hidden image! Why are viruses not considered alive? The typical answer I get to that question is that they cant survive on their own and are too dependent upon host cells, so they cant be alive. But how does that differ them from parasites? Tape worms cant survive unless they have a host organism, we consider them alive. In fact, there aren't many organisms, if any, that CAN survive without depending upon other organisms. So why do we single out viruses? I've also read that they aren't alive because they cant respond to stimulus. If it cant respond to stimulus, then how does it know to reproduce when it finds a cell? If it has a different reaction when it is next to a cell that it can use to reproduce than when its alone and as no opportunities to do so, isn't that a reaction?
Sorry, I don't know the answer to your question; and sorry, I can't PM you because you are new. I just want to point out that you should say, "Bear with me; I'm young." Please Register or Log in to view the hidden image!
Viruses aren't parasitic since parasites attempt to live as Symbiont, relying upon their host to survive. Viruses are destructive, their process of reproduction means wiping out the host cell. From a philosophical angle I guess you could say they are as destructive as any species that wages war, however that's not so much proof of intelligence or life but the inability to understand how to live.
unorthodox Viruses are not considered alive because they carry out none of the functions we associate with life. They do not use energy, digest food or reproduce themselves(all things that tapeworms and other parasites do). A virus attaches itself to a living cell, injects a snipet of DNA into the cell and that DNA snipet highjacks the mechanisms in the cell to construct many copies of the virus, which kills the cell and as it ruptures in death it releases these viruses to infect other cells. They are more Von Neuman like biological machines than they are life. The line between chemistry and biology is really fuzzy. GrumpyPlease Register or Log in to view the hidden image!
If they're not alive, then what are they? I dont understand how they can be nonliving when they have DNA and evolve.
They can't do work which I believe is why they aren't considered to be alive and dead cells contain DNA and technically that DNA could evolve if exposed to radiation and yes that DNA could be implanted in a cell and thrive
Welcome to the forum and nice starting topic. I found the following Scientific American article which adds some additional dimension to this question. In the article the following comment caught my eye. So a virus is somewhere between what is recognized as life and a rock (non-life). It's more than non-life but doesn't meet the full requirements of life. Very good article, it may be a bit long 4 pages, but worth the read.
One observation is the cell body of a cell can continue most functions, even without DNA or genetic material. One example are red blood cells. These can exists for months without any DNA. The red blood cells cannot reproduce and they function is limited, but it is alive. The extruded DNA from the red blood cell, on the other hand, is dead in the water, since it only has life in the context of a cell body. The cell body is needed to provide logistics. The extruded DNA is analogous to a huge virus. The normal virus differs in that it has better protein packaging to help preserve it. The virus, like the DNA is dead in the water, until finds a cell body actively supporting DNA. A good analogy is the DNA is like a hardrive, while a virus is like a thumbnail drive. The cell body is the motherboard abnd rest of the computer, which can function in limited capacity even without either drive; DOS. An interesting evolutionary modification would be when the red blood cells extrude their DNA, they do so in a way that generates preservative protein packaging like virus. Currently the extrude is goes to recycle. The extra preservation step would allow archiving of the DNA (hardrive). Later the protected and archived DNA can be used to swap out DNA within damaged or old DNA with cells, to an earlier version; system restore. The virus is like a thumnail drive containing functions and data. It needs to be plugged in to make use of it.
unorthodox The meaning of the word life is an arbitrary invention of human language. Nature is not so definite, to it life is part of a continuum from simple chemistry to active lifeform, viruses are actually closer to chemistry than to life. Prions are simply snips of genetic material, actual chemical molecules that enter cells by accident, find themselves among chemicals that they can make copies of themselves from directly(without using enzymes, proteins or any of the replication mecanisms of the cell, which viruses do use), very close to the very first life in it's simplicity and it is a single, dead, chemical molecule with one ability, it can assemble another molecule identical(more or less, mutations and additions occur)to itself if it happens to be in an environment that has all the chemical constituents(amino acids, etc.)it needs. If that's not the border between life and chemistry, you can at least see it from there. DNA is a molecule, it is chemistry, extremely complex, self organizing chemistry. GrumpyPlease Register or Log in to view the hidden image!
Yes. The perennial internet forum argument as to whether or not a virus can be considered to be alive is a purely semantic exercise. It depends purely on artificial definitions imposed on Nature by humans. Different people use different definitions and, thus, come up with different answers to the question. No, prions are proteins.
But your point remains valid. Prions blur the distinction between living and non-living even more than viruses do. Some people feel the need to modify definitions of “life” to include them, others don’t. It makes no difference with respect to our understanding of their mechanisms of action.
As other posters have noted, there is no standard definition of "life." An extremely good reason for that is that we are only familiar with life on this one tiny little planet. We have no idea what it could be like anywhere else in the universe. Chances are good that when we see it we might not even realize it. So we have to be a bit humble about it. Nonetheless, there is a consensus on the meaning. The following list is probably accepted by a majority of biologists, and note that they are not ALL required, just MOST of them. From Wikipedia, with a few edits to generalize for non-earth life: 1. Homeostasis: Regulation of the internal environment to maintain a constant state; for example, electrolyte concentration or sweating to reduce temperature. 2. Organization: For example, being structurally composed of one or more cells, which are the basic units of life [on this planet]. 3. Metabolism: Transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life. [This can also be reworded as "a local reversal of entropy"; see below. I'd suspect this is one characteristic that will be universal for all life everywhere.] 4. Growth: Maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts [or some of them], rather than simply accumulating matter. 5. Adaptation: The ability to change over a period of time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism's heredity as well as the composition of metabolized substances, and external factors present. 6. Response to stimuli: A response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often expressed by motion, for example, the leaves of a plant turning toward the sun (phototropism) and by chemotaxis. [Or by thought, in the more complex organisms like ourselves.] 7. Reproduction: The ability to produce new individual organisms, either asexually from a single parent organism, or sexually from two parent organisms. [I think this is one of the weakest points and may not prove to be universal. After all, the very first living thing formed out of non-living matter. So it's possible to envision an environment in which living things routinely form out of non-living matter, rather than reproducing themselves.] Biophysicists have a much more concise definition of life: a local reversal of entropy. In other words, within an organism disorder is constantly being replaced by more and more organization. And the way we do this is by increasing the entropy (reducing the level of organization) in the parts of the universe immediately adjacent to us. We animals do this by taking the organic tissue of other organisms and rendering it into its basic chemicals, in other words, by tearing them apart and eating them to build more cells in our own bodies. The increase in entropy in our surroundings is of much greater magnitude than the decrease of entropy within our own bodies, so the net effect on the universe of the existence of life is accelerated entropy. The universe will degrade into complete disorder sooner, because of us. Please Register or Log in to view the hidden image! If we find something that has most of these characteristics but not quite all of them, we'd probably argue a lot among ourselves and then decide that it's alive. But viruses don't have most of them. 2. They have organization. They are complex organic cells, more-or-less like the ones that make up the bodies of all living things. 5. They are capable of adaptation. When they find themselves inside the body of a living organism they are able to form a symbiotic or parasitic relationship with that organism, and become part of a living structure. Two out of seven? Not good enough. So we agree that viruses are not alive. Even when they're inside us, it is not the virus that is alive, but a complicated structure comprised of the virus and a little bit of us.
In fact, not only that's a weird definition of "parasite" (with the criterion of "intention"/"attempt" from the organism), but for organisms who necessarely destroy their hosts in order to reproduce (which is not the case with viruses in general), the term is "parasitoid". I don't know of any virus classified as a parasitoid. Nor about viruses that "wipe out" the host cell - which implies in their own premature "death"/redused reproduction, by the way, so unless it does it only after infecting a very large number of other cells, such virulent agency would tend to be selected against. I've read once in a non-technical book that it's possible that most of the more perceptible damage that common viruses cause are more an overreaction from the immune system than damage caused by the virus itself. It makes some sense since viruses in a way are nothing but a few extra genes, just like those we have in our chromosomes -- in fact, quite a bit of our nuclear DNA is made out of incorporated viruses. Not that they would be completely harmless were not by immune "overreaction", they are stealing their own building blocks from the cell and also borrwowing cell's machinery and energy in order to build themselves, and perhaps sometimes they may have collateral products that interfere more negatively with the cell processes. So the're at least a waste of material and energy to some degree. Perhaps not so much for macroorganisms (if they could be somewhat analogues to the vast amount differences in non-coding DNA that does not seem to affect fitness at all), but proportionally much larger for unicellular organisms or even tinier organisms. My personal guess is that this immune overreaction is perhaps partly inherited from our unicellular/early multicellular ancestors. But they would also be selected even if they're very virulent, as long such virulence favors their own reproductive advantage, so that could play an important role as well. Perhaps the immune system can't quite tell whether a virus will be nearly harmless like just a bit more of junk DNA or something that will take over the organism and make it die sooner/reproduce less, so it makes the safest bet, so to speak.
Complementing Fraggle Rocker's last post without even reading it completely with a sort of analogy (or maybe not an analogy at all). Viruses are just a bunch of genes with a few proteins attached to it, and they reproduce when they're in an adequate environment/host, usually a biological cell. If that suffices for a concept of "being alive", then we'd have the weird situation of having chromosomes as "living beings", rather than component structures of the "basic living unit", the cell. Not that this would be necessarily altogether wrong, anyway, it's a matter of how one decides to attribute meaning to variables/words in order to convey a larger meaning in a series of words. As long as one makes clear their different acceptions of words at the beginning of a text to avoid confusion, that will... generally avoid confusion. Except for quotes without enough context.
Even if what you say is true, in order to cause the body's immune system to over react to a particular virus, the virus would have to be reproducing itself at an alarming rate. So I would have to wonder if nothing was done by the immune system, how long would we be able to survive the mounting viral damage to our bodies? Also, not all parasites are created equal in that the more successful of them does not kill there host or they take their time killing slowly, which allows them to reproduce and spread to other host, before the original host dies. Parasitism is a type of non mutual relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. I have heard that most human death is a result of inflammation. But I would still place the blame on what caused that inflammation in the first place, be it a virus, bacteria or some other infectious agent.
If you look at a living cell, the lions share of its energy goes into the membrane. This creates potential energy within the membrane via ion pumping/segregation. This potential energy is used for transport through the membrane. If we added no ATP energy to the membrane, so no potential was created, very little would enter the cell, including virus. The cell would come to a crawl due to the lack of food in the light of restricted transport with no energy source. Once you add energy back into the membrane everything in the cell quickens as transport returns with plenty of food. Besides helping to animate the cell, by allowing an energy source for restricted input, the membrane potential also makes the inside of the cell membrane negative. Negative is also the charge on the DNA; phosphate. This double negative creates a potential between the DNA and the membrane, with the rest of the cell finding equilibrium within this potentiated grid. Again, if we stopped adding energy to the membrane and loss the potential, the grid would change as the negative repulsive potential to the DNA is lost. Without the negative charge of the membrane the DNA could escape like a huge virus. But once we add the potential to the membrane, the DNA is stuck inside. We can tweak the negative charge of the DNA pole of the grid by adding packing protein. This will neutralize the negative change and lower the gradient. As we unpack the DNA the potential of the grid increases. A virus does not generate its own membrane potential and therefore lacks the amplifying and configurational grid qualities associated with life. The virus will however, define a configurational potential and when introduced into a cell, will migrate to its place in the active grid. Not every virus attacks every cell because each cell and virus has a different set of equilibria. Once inside the virus loses its protective coat. It then becomes a different configuration (genetic) with a different place in the grid; near the DNA. The protective coat got the virus past the bouncer (cell membrane). Once the coat is gone, it is inside and is able to sneak back stage. An analogy is a small hollow ball suspended in a viscous liquid. If we squeeze the bottle of liquid this will increase pressure and the balls sinks. If we lower the pressure it floats. It will find its equilibrium spot depending on the conditions we place on the bottle. When the virus enters the cell it is like the floating ball working its way to the DNA. As it multiplies it puts on the squeeze and starts to sink back to the membrane so it can exit the cell. If the cell could tweak its membrane potential it might be able to mess up departure by placing them in equilibrium digestive spots in the grid.
Wrong, the majority of energy goes into the Na+/K+ pump NOT the membrane itself and without it the cell swells and bursts so viruses are irrelivent at that point
Buckaroo Banzai Viruses like Ebolla and Influenza certainly do destroy the host cells, becoming contaigious as the virus is expelled with the fluids that build up from ruptured cells. The virus hijacks the cell's apparatus to manufacture copies of the virus which are released when the host cell dies. GrumpyPlease Register or Log in to view the hidden image!
