How do viruses designate targets?

[Frost Fang]

i know it's kind of a dumb question, but how do they designate what's a cell and what isn't?

[insane_alien]

its all to do with chemicals emitted from the cells they like to attack

kind of like how animals identify each other by "smell". then you get dumb viruses that just try to get into everything but are only successful in certain cells. it appears that those are targeted but infact they are not.

[RyanJ]

its all to do with chemicals emitted from the cells they like to attack

kind of like how animals identify each other by "smell". then you get dumb viruses that just try to get into everything but are only successful in certain cells. it appears that those are targeted but infact they are not.

 

I like the analogy -

 

Don't they do it the same way our immune system works out what type of cell its dealing with through the cells antigens?

 

Cheers,

 

Ryan Jones

[insane_alien]

dunno it was kind of just a random colation of stuff i've picked up while channel surfing and surfing.

[MattC]

Double check this (or hopefully an expert will post) because I am NOT an expert in this field, but ...

viruses are NOT alive - they do not have senses, and none, to my limited knowledge, have any mechanism of "sniffing" out cells, or even of moving - they do not have flagella or cilia or anything, they simply go where the wind takes them. A virus has a protein coat (or capsid as it is often called) and then single or double stranded DNA or RNA. It is basically a really complicated non-living chemical that just happens to have a structure that allows it to function as it does.

A virus capsid is not smooth - it has functional groups and these react in particular ways. When a virus finds an appropriate cell (or rather, when it drifts up next to one, as they do not have a "will" to "find"), the protein coat fits like a lego piece, in a sense, into the cell wall. It is all just a complex chemical reaction - a virus only infects certain organisms for a number of reasons, one of which is that the capsid will only react with a certain combination of functional groups that appears only on it's target cells.

 

So basically it's like a lego structure floating around, and when it hits something that fits it perfectly, it binds or reacts, and in the process it mechanically/chemically (as in, not via some living "will" or conscious "desire") inserts it's genetic code into the host cell, which is then reprogrammed to produce the virus.

 

This is a bit of a simplification, but I personally like the lego analogy, as it stresses how un-life-like these reactions are. They are really complicated, but really it's like a machine that has been designed to react only with certain other pieces, and it's automated in a sense.

 

So, to recap and specifically address your question:

A cell has a cell wall, and that wall has various components, some of which are proteins (for instance, to allow the cell to take food into itself, or water, or whatever). Cells are very diverse, and a particular type of cell may have a chemical (lego) strucure on it's surface that is a very particular shape, and a virus that infects that cell will have a functional region on it's capsid that is just the right shape to infect that and only that cell (basically - some viruses may infect multiple types of cells, and may even be able to break into cells that they cannot infect - I don't know about that, though). If the virus, as it floats along, bumps into something else, it won't fit in that particular way, and if it reacts it is most likely going to react (chemically) in such a way as to destroy the virus. For instance, if a virus in water bumps into the chlorine used to disinfect drinking water, it will be denatured (the shape will be ruined/changed) and it will basically be inert (unable to infect cells).

[RyanJ]

So' date=' to recap and specifically address your question:

A cell has a cell wall, and that wall has various components, some of which are proteins (for instance, to allow the cell to take food into itself, or water, or whatever). Cells are very diverse, and a particular type of cell may have a chemical (lego) strucure on it's surface that is a very particular shape, and a virus that infects that cell will have a functional region on it's capsid that is just the right shape to infect that and only that cell (basically - some viruses may infect multiple types of cells, and may even be able to break into cells that they cannot infect - I don't know about that, though). If the virus, as it floats along, bumps into something else, it won't fit in that particular way, and if it reacts it is most likely going to react (chemically) in such a way as to destroy the virus. For instance, if a virus in water bumps into the chlorine used to disinfect drinking water, it will be denatured (the shape will be ruined/changed) and it will basically be inert (unable to infect cells).[/quote']

 

Exactly, it uses the cells identifiers (Antigens) to fnd a cell that match its needs, if the cell does then it will bind with it and inject its [acr=Ribonucleic acid]RNA[/acr] strands into the cell causing it to produce lots of little viruses otherwise the thing just well, I suppose decays or is caught by the immune system and destroyed.

 

Cheers,

 

Ryan Jones

[Frost Fang]

thanks for scratching the itch in the back of my head

 

so if their protein coats are like legos, would it be possible to genetically modify a nearly harmless virus to where it'll stick to other viruses and inject it's dna/rna?

[RyanJ]

thanks for scratching the itch in the back of my head

 

so if their protein coats are like legos' date=' would it be possible to genetically modify a nearly harmless virus to where it'll stick to other viruses and inject it's dna/rna?[/quote']

 

I don't see why not, some viruses already attack bacteria so I suppose you could combat a virus with another virus shure.

 

You would have to either "edit" the antigens on the cell surface which would not be the best option because you can't do it for every one of the virus cells but the better option would be to "hack" or modify the viruses [acr=Ribonucleic acid]RNA[/acr] to attack another virus cell instead.

 

I'm shure it is possible and you'll never know it may someday be used to target other viruses like aids (Although this is harder becuas eit heeps changing the shape of the lego block or antigen). In the case of something like AIDS you'd need an adaptive system or even better kill the thing before it can mutate.

 

The same is also true for cancer cells, their antigens change thats how they can sometimes be picked out by the body and destroyed

 

Cheers,

 

Ryan Jones

[Sisyphus]

MattC, I don't see how that description makes them any less alive then, say bacteria. I think the real reason they're not classified as alive is because they have no metabolism, and are entirely dormant outside of a host cell.

 

http://serc.carleton.edu/microbelife/yellowstone/viruslive.html

[MattC]

Sounds fine to me, Sisyphus! When I think of viruses, I think of complex chemicals, not living organisms, but if you're going to define exactly why they are not "alive" the metabolism argument is an excellent one!

 

On a similar note, I think you could make the argument that, at some point, the distinction between "living" and "nonliving" is arbitrary. After all, a bacteria is simply a more complex arrangement of chemicals, and a human is simply a still more complex arrangement of molecules. I've never seen any argument to suggest that a human has a soul (no scientific arguments, anyways), and without that or some other wild card, we're really just a hugely complex chemical factory. Even language is just a pattern carried on by the interaction of differnet chemical factories over time, no more meaningful, in a sense, than the haphazard and intricate path of an individual proton as, over time, it goes through various cycles as part of various atoms and molecules.

 

But that's aside from the point.

 

Frost Fang, that's a great idea, and I would bet anything that some creative chemist will some day help engineers develop a factory for viruses or similar compounds that will attack and hopefully eradicate at least some of the many viruses and bacteria that infect humans!

Another idea in this vein that may prove interesting is modifying a virus that already exists so that it is able to infect and spread but does not cause the undesired symptoms of the original virus. If this virus is similar enough, the body could develop antibodies to it, and those antibodies may be effective against the original, more dangerous (unmodified) virus.

[ecoli]

Sounds fine to me, Sisyphus! When I think of viruses, I think of complex chemicals, not living organisms, but if you're going to define exactly why they are not "alive" the metabolism argument is an excellent one!

 

You could definately think of it that way. Dr. Wimmer from Stony Brook University (my university was the frist lab to synthesize a virus outside of the cell (polio virus, specifically)

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12114528&dopt=Citation

 

I attended a lecture from this guy mere days after this discovery. I was with a bunch of other high school kids. I didn't understand most of what Dr. Wimmer was saying, but I remember that we had a slide with the chemical formula of the virus, and it had like 10 different elements in it, or something like that.

 

edit: This is from the paper, the chemical formula of polio virus [imath]\cf{C332652H492388N98245O131196P7501S2340}[/imath]

[Frost Fang]

would you be able to create a virus in a lab, from scratch? i know this would be extremely hard to do and would take lots of time if it is possible, but, if it is possible do you guys think it'd help the world any?

[Sisyphus]

would you be able to create a virus in a lab, from scratch? i know this would be extremely hard to do and would take lots of time if it is possible, but, if it is possible do you guys think it'd help the world any?

 

Yes, you could, if you could manipulate the material precisely enough. But you could also create a bacterium, or a tree, or a human, theoretically. It would just be hellishly complicated and probably pointless.

[insane_alien]

err yeah of course it could help the world.

1. a virus is essentially an unpowered nanorobot.

2. we could make a virus from scratch to attack various bacteria/cells(cancer cells if you want an example.)

3. we could make virii to attack other virii.

4. we could make benificial virii(fix genetic defects)

5. some stuff that i haven't thought about yet.

[RyanJ]

err yeah of course it could help the world.

1. a virus is essentially an unpowered nanorobot.

2. we could make a virus from scratch to attack various bacteria/cells(cancer cells if you want an example.)

3. we could make virii to attack other virii.

4. we could make benificial virii(fix genetic defects)

5. some stuff that i haven't thought about yet.

 

Yup, all good examples

 

Most of those will be impliemnted withing a few years with any luck, you could have cures for various diseases, you could even engineer them to target special organisms such as those nasty parasitis wormc and the like.

 

The one about genetic defects is a hot topic right now as is all viral research as its applicaitons are again all but endless!

 

Cheers,

 

Ryan Jones

[zyncod]

Just a niggling point - the recognition elements for viruses are not called "antigens." Antigens are molecules that antibodies recognize, and viruses don't have antibodies. Also, viruses can use the recognition molecules to further their survival. The proteins that HIV binds to when it is entering a T cell cause the T cell to release signals that bring other T cells into the vicinity. Therefore, just by binding to the T cell, HIV can bring other hosts for it to infect.

[MattC]

You seem to know your stuff, Zyncod! Good point, you're right - while viruses do have "antigens" on them, that's really just the part, as you said, that antibodies recognize, and the functional groups that define a virus may be separate from the antigens. Furthermore, antigens can exist on bacteria and other substances, not just viruses. Correct me if I'm wrong, so I don't spread any misinformation!

[RyanJ]

Thanks for pointing that out zyncod, you know your stuff!

 

Furthermore, antigens can exist on bacteria and other substances, not just viruses. Correct me if I'm wrong, so I don't spread any misinformation!

 

As far as I know any cell has an antigen but I'm not shure on this either (I bet zyncod will have the answer!)

 

Some links from my database that may provide some information:

 

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

http://www.prosci-inc.com/FAQ/Antigen-FAQ.html

http://www.bookrags.com/sciences/genetics/antibody-and-antigen-wog.html

 

Cheers,

 

Ryan Jones

[Frost Fang]

ok, since they are similar to nanobots, is there any work going into this? i myself think that this could be more beneficial than most of the other things going on right now. the human genome project has been completed and stem cell research is promissing, but getting slapped in the face by some's hippocritical morals. this as i see it poses no real problem other than...well a new plague, but i think the chances of that are rather low.

[sunspot]

If viruses attach to specific sites on certain cells, does this imply that their origin comes from similar cells? In other words, if they originally formed from a particular cell, the viruses protein coat might be on the cell's DNA near where its complement membrane protein gene is. Both proteins, i.e., virus coat and membrane protein, both diffuse to the membrane. The virus continues to diffuse out of the cell when the concentration is high. Maybe at lower concentrations, it returns to the membrane near/at the neighboring genetic protein.

[ecoli]

If viruses attach to specific sites on certain cells, does this imply that their origin comes from similar cells? In other words, if they originally formed from a particular cell, the viruses protein coat might be on the cell's DNA near where its complement membrane protein gene is. Both proteins, i.e., virus coat and membrane protein, both diffuse to the membrane. The virus continues to diffuse out of the cell when the concentration is high. Maybe at lower concentrations, it returns to the membrane near/at the neighboring genetic protein.

 

Do you mean like they evolved together?

 

would you be able to create a virus in a lab, from scratch? i know this would be extremely hard to do and would take lots of time if it is possible, but, if it is possible do you guys think it'd help the world any?

 

I just gave an example of the first synthesise of a Polio Virus in a lab.

[Frost Fang]

sorry, my brain has been on the fritz lately

 

thanks for all the help everyone,

 

 

travis

[zyncod]

In other words, if they originally formed from a particular cell, the viruses protein coat might be on the cell's DNA near where its complement membrane protein gene is. Both proteins, i.e., virus coat and membrane protein, both diffuse to the membrane. The virus continues to diffuse out of the cell when the concentration is high. Maybe at lower concentrations, it returns to the membrane near/at the neighboring genetic protein.

 

No, probably not. The greatest consideration in virion formation is getting all the components to the right place at the right time. Additionally, the virus has a vested reason not to reinfect the same cell. Just as trees try to spread their seeds to prevent a bunch of trees competing for the same resources, viruses have a reason to try to spread preferentially to other cells and not reinfect the same cell. I'm not sure which virus it was (virology was a long time ago for me), but I know that some viruses cause cells to internalize the proteins that they use as their receptors.

 

As far as antigens go, anything can be an antigen. A very simple chemical (like a single uridine molecule) or a very complicated protein.

[treva]

No' date=' probably not. The greatest consideration in virion formation is getting all the components to the right place at the right time. Additionally, the virus has a vested reason not to reinfect the same cell. Just as trees try to spread their seeds to prevent a bunch of trees competing for the same resources, viruses have a reason to try to spread preferentially to other cells and not reinfect the same cell. I'm not sure which virus it was (virology was a long time ago for me), but I know that some viruses cause cells to internalize the proteins that they use as their receptors.

 

As far as antigens go, anything can be an antigen. A very simple chemical (like a single uridine molecule) or a very complicated protein.[/quote']

 

Just to clarify, I don't think viruses 'intend' to have their receptors endocytosed by their target cells. Virsues in the simplest sense just hijack cellular processes and use them to their own benefit. Many cells will internalize plasma membrane receptors in response to certian ligands (like growth factors) via receptor mediated endocytosis. Some virsues use receptor mediated endocytosis to enter their target cell. So its really not the 'virus' causing its receptors to be removed from the cell surface but rather a byproduct of it using a cellular pathway.

 

Also, it is possible for multiple strains of a single virus to infect one eukaryotic cell. Sometimes this is in the viruses benefit, as it could lead to a genomic recombination event that increases the fitness of the virus (for example by increasing transmission efficiency by acquiring a better receptor from a different strain). This is actually where all the bird flu anxiety comes from, everyone is afraid that if a human strain and a bird strain of the flu virus coinfect a cell that has the receptors for both (ie inside a pig) you could generate a virus with the pathogenicity of a bird strain but with human receptors.

[Goalfinder]

No viruses have hemagglutnin proteins on their surface that can bind to complementary receptors on cell, this is something like a triangle projection binding to its reverse wedge. Somwthing like a dove tail joint except that this chemical in nature. This enables virus to bind to multiple hosts for example a bird virus can bind to birds, pigs and human cells but in different areas, it can bind to ciliated epithelial cells in human mucosa and to epithlial cells in birds. Once it binds then it can enter the cells. Thus the binding does not signify origins, it just signifies matching "shapes", refer this site for more explanation on virus