You can, for example, pull the spark plug wires, or drain the gas tank, or fill the intake manifold with Silly Putty, and a working car will become a not-working car, even though they look pretty much the same. Inactivated viruses are a bit like not-working cars: some part of the machinery has been changed or damaged to make it not work.
You can inactivate viruses by heating them so the protein coat is damaged, or the genetic material is destroyed. You can hit them with radiation to destroy the genetic material. You can break the virus into pieces. Your body's immune system does not recognize the entire virus. It looks for and recognizes certain parts of the virus, called "antigens" or "antigen subunits. By way of comparison, if you open the hood of a car, melt the engine into slag, and then close the hood, people walking down the street will still recognize it as a car.
By Gege Li. Viruses are microscopic parasites responsible for a host of familiar — and often fatal — diseases, including the flu , Ebola , measles and HIV. They are made up of DNA or RNA encapsulated in a protein shell and can only survive and replicate inside a living host, which could be any organism on earth. This means no life form is safe from infection by a virus. Since viruses were first discovered in by Dmitri Ivanovsky, our ideas of what they are have shifted from poisons to biological chemicals.
Some years after their discovery, scientists first raised the idea that viruses were living — albeit simple — organisms because they caused diseases like bacteria, which we know to be alive. However, viruses lack the hallmarks of other living things. The only life process a virus undergoes independently is reproduction to make copies of itself, which can only happen after they have invaded the cells of another organism.
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.
We are aware of only a tiny fraction of the total genetic diversity of viruses. Moreover, their genomes evolve far more rapidly than cellular organisms. So, from the small islands of sequence data we have, it is hard to argue that a coherent phylogeny does or does not exist.
Interestingly, conservation of folds in viral proteins has begun to highlight possible common ancestries that could never be inferred from genome sequence data.
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