Are Viruses Considered Living or Nonliving?

[Cowkilla]

[SOLVED] Viruses - Dead or Alive?

Hi guys. I got a paper due in a week or so on viruses. I have to write an argumentative essay on whether viruses are considered as living or nonliving. i believe they are nonliving, based on the characteristics of life, etc, etc. but can u guys give me more resources? i really need more information...

Right now, my arguments are:
Viruses can't , use metabolism, reproduce, respond to stimuli, etc. on their own
they don't satisfy the criteria of the characteristics of living things.

right now my paper has less than 100 words and it looks pretty lame. and i can't find any more interesting info on google.


Thanks.

 

[Hootenanny]

http://en.wikipedia.org/wiki/Virus

 

[Cowkilla]

Well, there seems to be a really annoying problem. I couldn't access the wikipedia site for some reason.

 

[bomba923]

Well, there seems to be a really annoying problem. I couldn't access the wikipedia site for some reason.

Alright...

It has been argued extensively whether viruses are living organisms. They are considered non-living by the majority of virologists as they do not meet all the criteria of the generally accepted definition of life. Among other factors, viruses do not possesses a cell membrane or metabolise on their own. A definitive answer is still elusive due to the fact that some organisms considered to be living exhibit characteristics of both living and non-living particles, as viruses do. For those that consider viruses living, viruses are an exception to the cell theory proposed by Theodore Schwann, as viruses are not made up of cells.

Argument continues over whether viruses are truly alive or not. According to the United States Code, they are considered to be micro-organisms in the sense of biological weaponry and malicious use. Scientists however are more divided. They have no trouble classifying a horse as living and can see evolutionary relationships between it and other animals, but things become complicated as they look at the more simple viruses, viroids and prions. In the case of viruses, they resemble life in that they possesses nucleic acid and can respond to their environment in a limited fashion. They can also reproduce by creating multiple copies of themselves through simple self-assembly.

However, unlike all other forms of established lifeforms, they do not possesses a cell structure, regarded as the basic unit of life. Viruses are also absent in the fossil record, making phylogenic relationships difficult to infer. Additionally, although they reproduce they do not metabolise on their own and therefore require a host cell to replicate and synthesise new products. However, confounding this previous statement is the fact that bacterial species such as Rickettsia and Chlamydia, while living organisms, are also unable to reproduce outside of a host cell.

A powerful argument can be made that all accepted forms of life divide at the cell level via cell division to reproduce, whereas all viruses simply assemble spontaneously within cells. What then prevents the comparison to be drawn that viral self-assembly is no different than the autonomous growth of non-living crystals? Virus self-assembly within host cells also has implications for the study of the origin of life, as it lends credence to the hypothesis that life could have started as self-assembling organic molecules.

Other questions involve the classification of viruses within the Tree of Life and its implications – if viruses are considered alive, then the criteria specifying life will have been permanently changed, leading scientists to question what the basic prerequisite of life is. If they are considered living then the prospect of creating artificial life is enhanced, or at least the standards required to call something artificially alive are reduced. Whether or not other infectious particles, such as viroids and prions, would next be considered forms of life could follow if viruses are said to be alive.

 

[Mk]

Well, there seems to be a really annoying problem. I couldn't access the wikipedia site for some reason.

You can always access the cached version on Google though.
http://72.14.209.104/search?q=cache...irus+virus+wikipedia&hl=en&gl=us&ct=clnk&cd=1

 

[jpop287]

Scientific American; Dec2004, Vol. 291 Issue 6, p100-105, 6p, 1 diagram, 4c

"Impact on Evolution DEBATES OVER WHETHER to label viruses as living lead naturally to another question: Is pondering the status of viruses as living or nonliving more than a philosophical exercise, the basis of a lively and heated rhetorical debate but with little real consequence ? I think the issue is important, because how scientists regard this question influences their thinking about the mechanisms of evolution.

Viruses have their own, ancient evolutionary history, dating to the very origin of cellular life. For example, some viral-repair enzymes which excise and resynthesize damaged DNA, mend oxygen radical damage, and so on [see box below] are unique to certain viruses and have existed almost unchanged probably for billions of years.

Nevertheless, most evolutionary biologists hold that because viruses are not alive, they are unworthy of serious consideration when trying to understand evolution. They also look on viruses as coming from host genes that somehow escaped the host and acquired a protein coat. In this view, viruses are fugitive host genes that have degenerated into parasites. And with viruses thus dismissed from the web of life, important contributions they may have made to the origin of species and the maintenance of life may go unrecognized. (Indeed, only four of the 1,205 pages of the 2002 volume The Encyclopedia of Evolution are devoted to viruses.)

Of course, evolutionary biologists do not deny that viruses have had some role in evolution. But by viewing viruses as inanimate, these investigators place them in the same category of influences as, say, climate change. Such external influences select among individuals having varied, genetically controlled traits; those individuals most able to survive and thrive when faced with these challenges go on to reproduce most successfully and hence spread their genes to future generations.

But viruses directly exchange genetic information with living organisms--that is, within the web of life itself. A possible surprise to most physicians, and perhaps to most evolutionary biologists as well, is that most known viruses are persistent and innocuous, not pathogenic. They take up residence in cells, where they may remain dormant for long periods or take advantage of the cells' replication apparatus to reproduce at a slow and steady rate. These viruses have developed many clever ways to avoid detection by the host immune system-essentially every step in the immune process can be altered or controlled by various genes found in one virus or another.

Furthermore, a virus genome (the entire complement of DNA or RNA) can permanently colonize its host, adding viral genes to host lineages and ultimately becoming a critical part of the host species' genome. Viruses therefore surely have effects that are faster and more direct than those of external forces that simply select among more slowly generated, internal genetic variations. The huge population of viruses, combined with their rapid rates of replication and mutation, makes them the world's leading source of genetic innovation: they constantly "invent" new genes. And unique genes of viral origin may travel, finding their way into other organisms and contributing to evolutionary change.

Data published by the International Human Genome Sequencing Consortium indicate that somewhere between 113 and 223 genes present in bacteria and in the human genome are absent in well-studied organisms--such as the yeast Saccharomyces cerevisiae, the fruit fly Drosophila melanogaster and the nematode Caenorhabditis elegans--that lie in between those two evolutionary extremes. Some researchers thought that these organisms, which arose after bacteria but before vertebrates, simply lost the genes in question at some point in their evolutionary history. Others suggested that these genes had been transferred directly to the human lineage by invading bacteria.

My colleague Victor DeFilippis of the Vaccine and Gene Therapy Institute of the Oregon Health and Science University and I suggested a third alternative: viruses may originate genes, then colonize two different lineages--for example, bacteria and vertebrates. A gene apparently bestowed on humanity by bacteria may have been given to both by a virus.

In fact, along with other researchers, Philip Bell of Macquarie University in Sydney, Australia, and I contend that the cell nucleus itself is of viral origin. The advent of the nucleus-which differentiates eukaryotes (organisms whose cells contain a true nucleus), including humans, from prokaryotes, such as bacteria--cannot be satisfactorily explained solely by the gradual adaptation of prokaryotic cells until they became eukaryotic. Rather the nucleus may have evolved from a persisting large DNA virus that made a permanent home within prokaryotes. Some support for this idea comes from sequence data showing that the gene for a DNA polymerase (a DNA copying enzyme) in the virus called T4, which infects bacteria, is closely related to other DNA polymerase genes in both eukaryotes and the viruses that infect them. Patrick Forterre of the University of Paris-Sud has also analyzed enzymes responsible for DNA replication and has concluded that the genes for such enzymes in eukaryotes probably have a viral origin.

From single-celled organisms to human populations, viruses affect all life on earth, often determining what will survive. But viruses themselves also evolve. New viruses, such as the AIDS-causing HIV-1, may be the only biological entities that researchers can actually witness come into being, providing a real-time example of evolution in action.

Viruses matter to life. They are the constantly changing boundary between the worlds of biology and biochemistry. As we continue to unravel the genomes of more and more organisms, the contributions from this dynamic and ancient gene pool should become apparent. Nobel laureate Salvador Luria mused about the viral influence on evolution in 1959. "May we not feel," he wrote, "that in the virus, in their merging with the cellular genome and reemerging from them, we observe the units and process which, in the course of evolution, have created the successful genetic patterns that underlie all living cells?" Regardless of whether or not we consider viruses to be alive, it is time to acknowledge and study them in their natural context--within the web of life."

My micro professor told us that the debate whether or not they are alive is a waste of time, but we should focus more on their obligately parasitic lifestyle.

I hope that helps somewhat...I couldn't find a journal article.

 

[lordmetal2]

viruses are in my opinion living. i had a biology class today when i first heard that ,,viruses are not alive''. I almost freaked. I have some arguments that they are alive.

- my teacher said that they are considered to be dead because they can't move on their own. Well DUH! if their only a small piece of DNA an a protein how on Earth could they move?

-it is said that they are dead DESPITE the fact that they REPRODUCE! A tiny rock in your blood stream wouldn't reproduce now wouldn't it!

-Another argument that they are not alive is that they arent even made of a cell. So? They are built in a way that they can function. If they were made out of a cell they couldn't reproduce by infecting another cell with their DNA.

-and theyr to simple to be alive. Jeez! Its like comparing an ant to an elephant in terms of complexty. They reproduce according to their size, or their size is determined by their reproductive way... Dunno , don't care.

-they arent alive due to the fact that they don't eat or breathe- An organism made only of DNA and protein wouldn't really need oxygen and nutrients... again due to its size.

It is in my opinion that viruses should not be included in any of the five reigns , but instead have one of their own : micro cellular bio-entities.

I hope I've shed some light on the subject... and i know my arguments are a bit childish but I am 15 years old so i have the right... AND IM NOT A NERD , I am just expressing my opinion