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whap2005

Retroviruses - can this be real?

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From an evolutionary viewpoint, retroviruses are fascinating because they blur the very distinction between host and parasite. Their genome often contains genetic information derived from the host DNA. And once they are integrated into the DNA of the host cell, they may take a long time to reemerge. In fact, so-called "endogenous retroviruses" can be passed down from generation to generation, indistinguishable from any other cellular gene, and evolving along with their hosts, perhaps even from species to species! It has been estimated that up to 1% of the human genome consists of endogenous retroviruses! Furthermore, not every endogenous retrovirus causes a noticeable disease. Some may even help their hosts [LA], [V'].

 

From: http://math.ucr.edu/home/baez/subcellular.html

 

Ok this is some spooky shat. This means that retroviruses are basically organisms that can survive by integrating themselves into a hosts DNA. This means that the virus can basically be passed down to your ancestors. So if your great great grandfather was exposed to “human immunodeficiency virus 1” some point in his life, you or your kids could also be infected with the same virus (which I say again is basically a parasite and a separate organism then yourself).

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Some estimate that about 10% of the human genome consists of endogenous retroviruses. However unlike the retroviral DNA from active viruses, these endogenous retroviruses are mostly inactive and have lost many of their functional elements such as the reverse transcriptase needed to make copies of itself. While there are some active endogenous retroviruses in mice, no human endogenous retroviruses capable of retrotransposition have been identified yet. So essentially, they are just junk DNA and are neither harmful nor helpful (though the fact that organisms conserve endogenous retroviral sequences in their DNA may suggest that they may be, in fact, beneficial to the organism). But, you certainly won't have to worry about an endogenous retrovirus from your ancestors making you ill.

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Retroviruses do not incorporate themselves in their entirety in the host's DNA. In fact, any incorporation is relatively rare, and consists of only a single piece of DNA. (Think of it as a single gene in size). If this is incorporated into a cell that becomes a gamete that then becomes a human, the retrovirus gene may be passed down through the generations.

Since this has been happening, even if very rarely, over billions of years, the sum total that has accumulated is substantial.

 

The term RETRO virus is due to the fact that it reverses the normal process. In our cells, DNA makes RNA which makes protein.

The virus does not have DNA, only RNA. In our cells, when it infects, it makes DNA copies of its RNA. It is this DNA copy that can be incorporated.

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there is an assay used to test for reverse transcriptase (RT) activity in cells. i have known a few scientists who thought they had found this in primary lymphocytes. however i later learnt that telomerase can also give positive results for RT assays. not sure how true this is, since i haven't done any experiments like this. i am just trying to point out that when it comes to reports of endogenous RT activity in cells, you should check that they have the right controls.

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So essentially, they are just junk DNA and are neither harmful nor helpful (though the fact that organisms conserve endogenous retroviral sequences in their DNA may suggest that they may be, in fact, beneficial to the organism)

 

They are probably not helpful to the organism itself, though their cousins (and probable ancestors), retrotransposons, are an important source of evolutionary change by shuffling the genome. Especially in plants.

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retrotransposons contribute enormously to plant evolution.

 

as i mentioned before, telomerase has reverse transcriptase (RT) activity, indeed telomerase is thought to have evolved from a RT.

 

 

Well telomerase IS (partially) an RT. There is the template for the telomeres and then the RT catalyst component.

 

 

EDIT: Sorry, i took RT to mean reverse-transcriptase. Yeah stupid me. Anyway I haven't heard that theory, what's it about?

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This means that the virus can basically be passed down to your ancestors.
Don't you mean 'from' you ancestors. Otherwise that really would be spooky shat.:D

 

Interesting thread. I've often wondered how much of our evolution depends on the evolution of all of our hosted organisms. In a sense, we exist as a species within nature, and without nature, with both an external environment, and an internal invironment, both of which we are codependant upon. I am also unsure what is evolution, what is devolution, and what is adaptation to current circumstances using pre-existing genetic material and relationships with internal and external micro-organisms and even non-organic materials in our internal and external environments.

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Prime-Evil.

It is all evolution. There is no such thing as devolution. Even a move to a simpler form is still evolution. As far as we can tell, after 200 years of serious research, all life began at the same time, and possibly from a single ancestral species, about 3 to 4.5 billion years ago. Every organism, even if described as 'primitive' has had the same period of time to evolve. Truly, there is no such thing as a 'primitive' life form. Even bacteria are enormously complex.

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