At a basic level, viruses are proteins and genetic material that survive and replicate within their environment, inside another life form. In the absence of their host, viruses are unable to replicate and many are unable to survive for long in the extracellular environment.
In many ways whether viruses are living or non-living entities is a moot philosophical point. There can be few organisms other than humans that have caused such devastation of human, animal and plant life. Smallpox, polio, rinderpest and foot-and-mouth viruses are all well-known for their disastrous effect on humans and animals.
Less well known is the huge number of plant viruses that can cause total failure of staple crops. The gift-wrapping is virtually always a virus-encoded protein capsid and may or may not also include a lipid coat from the host. In many cases the virus also encodes some of the enzymes required for its replication, a well-known example being reverse transcriptase in RNA viruses. Over the last 15 years or so, giant viruses found in amoebae have complicated our picture of viruses as simple non-living structures.
Mimiviruses and megaviruses can contain more genes than a simple bacterium and may encode genes for information storage and processing. Genes common to the domains Archaea, Bacteria and Eukarya can be found in different giant viruses, and some researchers argue on this basis that they constitute a fourth domain of life. However, a crucial point is that viruses are not capable of independent replication.
They have to replicate within a host cell and they use or usurp the host cell machinery for this. They do not contain the full range of required metabolic processes and are dependent on their host to provide many of the requirements for their replication.
To my mind there is a crucial difference between viruses and other obligate intracellular parasites, such as bacteria; namely, viruses have to utilise the host metabolic and replication machinery. Intracellular bacteria may merely use the host as the environment in which they can supplement their limited metabolic capacity and they usually have their own replication machinery. Organisms such as Chlamydia spp.
They further claim that this means that viruses are indeed living organisms. This is not an argument I am comfortable with. If a virus is alive, should we not also consider a DNA molecule to be alive? Plasmids can transfer as conjugative molecules, or be passively transferred, between cells, and they may carry genes obtained from the host.
What about prions? The argument reductio ad absurdum is that any biologically produced mineral that can act as a crystallisation seed for further mineralisation hence meeting the criterion of reproducibility might also be classified as living!
This questioner currently considers viruses to be non-living. Where we draw the line between chemistry and life can seem a philosophical, or even theological argument. Are viruses able to claim a similar ancestry? The contention that viruses have no place in the tree of life is often supported by the assertion that viruses do not have a comparable history — viruses are polyphyletic.
Viruses are at a terrible disadvantage in this comparison, however. They'll see it and say "yep, that's a car," even though the engine is totally destroyed. You can take the wheels off and people will still say "yep, that thing I'm looking at is a car. Your body will look at the outer shell of a virus and say "yep, that's a virus," even if the genetic material is completely destroyed or entirely removed altogether.
You can take parts of the virus off and your body will still say "yep, that thing I'm looking at is a virus. This post originally appeared on Quora. Click here to view. BY Quora. Franklin Veaux : There is none, because viruses aren't alive.
However, none of these proccess can occur independent of a host. Therefore, in my opinion,viruses are dead. At the start of reading chapter 19, I was convinced that viruses were alive. They replicate to infect their host, and they contain a genetic code, which only living things are said to contain. However, it is hard to believe that viruses are alive, considering they depend on a host cell to carry out their functions of producing proteins etc. I believe that once viruses attach to a host cell, they act as though they are alive, replicating themselves and sometimes killing the host cell in an attempt to infect the host.
I would do this very simply and I presume swiftly too, simply by adding on to one of the professors claims as follows:. Although in the absence of a host cell, viruses lack MOST perhaps not all of the properties of a living thing, they do exhibit those basic properties of life such as reproduction within a host cell.
Whether stolen or not, viruses, at one point, do exhibit the properties of life which I believe only living things are SAID to demonstrate! After reading chapter 19, I would say that viruses are alive. My main reasoning for this is that they contain a genetic code. And although they do depend on another host cell to reproduce, a virus does have a unique genetic code. To me, viruses are one of the simplest living beings in this respect. I would have to agree with you in saying that viruses are not living.
They do show some characteristics of living organisms, but they are also missing too many other characteristics of being a living organism to be considered alive. In Chapter 1 of our reading, I took special attention to Figure 1. Though they reproduce, they are entirely dependent on a host; they are also known to respond to their environments, but not in the ways that other living organisms do; they are capable of adapting on an evolutionary standpoint, but still they require another organism for this evolution to take place; etc.
Viruses definitely walk the thin line in being considered a living organism, but as of right now, I think that they have yet to make the leap into being considered alive. I agree that a virus, itself, is not alive. It can only survive via host cells otherwise it cannot function or spread. They are unknown and not alive.
But once in the host cell, they come to life and can cause harm, spreading diseases evolving into even more complex forms of viruses. The host cell carries the properties of life, not the virus itself. It would be nothing without the host cell. Viruses share many characteristics with living things. Viruses respond to stimuli, have genetic makeup, and even evolve. However, to be truly scientific, we must apply the rigid definition of life, and if one or more of the criterion of life is not met, viruses are not alive.
Since viruses lack the ability to thrive and reproduce autonomously, they cannot be called alive. I also do not think we can consider viruses to be living. For example, the heart, an organ that is vital, cannot reproduce among other things , and therefore is not alive. However, when the heart is placed in the context of the body with other non-living organs, life emerges. Similarly, a virus alone is not living, but when it interacts with a host cell, life can emerge.
My opinion is that viruses are not alive. They do not react to stimuli, undergo internal regulation, or undergo other life processes without a host. Though they do reproduce, there are many other non-living things which do in a sense reproduce: waves and crystal, for instance. Viruses differ from living parasites in that unlike tape worms which can carry out metabolic processes while living outside a host, they owe all their life properties to their hosts.
This separates them from parasites that rely on their hosts for nutrition or shelter.
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