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Thread: I'm having a hard time understanding endogenous retroviruses

  1. #1 I'm having a hard time understanding endogenous retroviruses 
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    I'm kind of drawing a blank. Could someone be so kind and explain it like your talking to a 8 year old? Please. Filix.


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  3. #2  
    Forum Professor Zwirko's Avatar
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    One group of viruses, known as retroviruses, are able to integrate their genomes into that of their hosts. Sometimes they get stuck there (due to a mutation) and become defective, unable to replicate on their own or form new virus particles. Sometimes a retorvirus may enter the genome of a cell that is a precursor to sperm or egg cells. When this happens - and if the virus becomes defective - the virus is said to have become endogenised. In this state it can be passed from parent to offspring, inherited like a regular gene, for millions of years.

    They are the remnants of ancient retroviral infections and comprise a substantial part of our genomes. They have no known cellular functions and so tend to classed as "junk". They play roles in certain diseases and have helped shaped our own evolution.

    If there's anything you don't understand in that short story, just ask.


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    Retro means 'going backwards'. A retrovirus does the DNA/RNA thing backwards. In a normal cell, the DNA in the nucleus is used to make an equivalent RNA molecule (for making proteins). The retrovirus, though, starts with an RNA molecule, and goes backwards - making a DNA molecule, which it inserts in the nucleus of the cell it is invading.

    That new DNA molecule then does the normal thing, which is DNA making RNA. The RNA it makes, though, is virus RNA. The virus RNA is formed into new virus particles. In this way, a single virus RNA ends up making dozens of new virus RNA molecules. That is how retroviruses reproduce.

    Endogenous means (roughly) 'inside us'. As Zwirko said, it is a DNA molecule made by the retrovirus that stays inside us. Or at least inside the nucleus of the host cell.

    If the host cell with the new DNA becomes a sperm or egg cell, and then that sperm or egg becomes a new individual being, every cell in that new being will have DNA from a retrovirus.

    In this way, retrovirus 'genes' have become part of human genetic make up. Mostly it does not seem to matter much. But we are starting to discover some of these genes from retroviruses may have developed a function - good or bad - inside us.
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    Have they been implicated in the transmission of autoimmune disorders?

    Harry Harrison wrote a story called "I See You" about a dystopian future in which a huge computer runs the criminal justice system and surveillance is universal- except inside the computer. Evidently the only place for foreign genes to hide out is inside the cellular "computer".
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  6. #5  
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    Thankyou very much. My brain still hurts. It sounds like That these retroviruses Sneak in ? By doing the backwards thing? Are these retroviruses proof positive that humans have been here hunderds of thousands of years? Is a virus considered alive? Is M.S. a retrovirus? If they helped evolution, then in some ways they are good? Filix.
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    Forum Professor Zwirko's Avatar
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    Nothing is proof positive in science. ERV's do however provide a compelling argument for the common ancestry of certain groups of organisms, such as vertebrates. It's exceedingly difficult to think of any other sensible argument that could account for them, other than an evolutionary based one. They don't themselves say anything directly about timescales; combined with knowledge of other things such as mutation rates and geological/fossil evidence they show that ourselves and our ancestors have been around for quite some time. A body of evidence tends to be like a jigsaw and ERV's are just one piece; one that fits snugly.

    Most people would say that viruses are not alive.

    It's not known for certain about the MS-endogenous retroviruses connection. That some workers have seen a strong correlation is about all you can say for sure.


    I wouldn't call them "good" as such. Once infected, and if you don't go extinct, evolution can make use of them. Put them to work, so to speak. They seem to have important roles in the origin and functioning of the placenta, for example.
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  8. #7  
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    Smart stuff. I should have payed more attention when we touched on biology in science class. I think I was looking out the window. If I could go back there, I would be a retrogranddad The human Genome Is another hard one for me. I don't even understand the definition. Thanks for your patience with me. All of you. Filix.
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