RNA vs DNA

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Discussion by: Roedy

Crick suggested that RNA was the original encoding for genetic information, then it was replaced by DNA.

DNA is more stable and reproduces more accurately.  This explains the strangely indirect protein synthesis using both DNA and RNA.

Viruses use RNA only.

Is there any species of virus that does not need a host?  In other words, in there any remnant around of free-standing life using the archaic scheme?

How old are the DNA molecules in my body assuming I am 65 years old?  How old are the DNA molecules in an amoeba?

11 COMMENTS

  1. There are actually several kinds of viruses. Some use just RNA, and some of those have double stranded RNA, but some use double stranded DNA while others use single stranded DNA. Retroviruses use RNA and DNA in order to replicate, producing DNA from its RNA. That DNA is then incorporated into the infected cell which then produces copies of the virus.

    Viruses aren’t cellular, so they need a host cell to replicate.

  2. Is there any species of virus that does not need a host?

    I don’t know but I would wonder if it were even possible to detect it. Or if we could, observe it replicating without a host

  3. How old are the DNA molecules in my body assuming I am 65 years old? How old are the DNA molecules in an amoeba?

    If that is the same question as the ancient Greek philosophers asked:-

    “How many planks of this ship can I replace before it becomes a different ship?”

    and you replace “plank” with “base pair”, then I assume the half life of a particular base pair is in order of hours, or days, then the answer is the same as the modern answer to the ancient question.

    If every base pair in DNA can be replaced by the same base pair, then your DNA and that of the Amoeba must be “born” when a mutation makes your genome different from the DNA it was copied from. Since PZ said in a talk that each of us has about 100 mutations, most of your DNA is about 65.75 years old, unless you have really bad cancer, or have been fried by radiation.

    If you want to ask how long a particular base pair has sat at the same location in a gene, then it could be millions of years.

  4. Sorry, i was running around and could’t put together a coherent post. Speigelman’s monster actually reproduces in test tubes. In cell free environments. It really highlights evolution because the selection pressure is for speed and the shorter the genome, that faster the generational time.

    So, Speilgelman set up a test tube system with some chemicals it it and introduced the phage (virus). After it had reproduced, he took an aliquot of the first generation and seeded it into the next test tube and he repeated this until the virus had shed all it’s “unnecessary” base pairs. It went from like 5000 base pairs to 200!

    i just looked it up on wikipedia and was really pissed to see how little is there. Richard does an expert job in taking the reader through the different chemicals and their roles. Much much better than wiki. I see from the sparse info on wiki that the monster went from 4500 bases to 218 after 74 generations.

    I know that your OP is more looking for a natural system that replicates — I do not know of one. But, I couldn’t resist posting about the monster… Maybe you are another reader will look into it and find it as stimulating as I.

  5. Viruses doesn’t just use RNA there are viruses who uses DNA as well as one stranded DNA and two stranded RNAs.
    Every virus need a host to survive because viruses aren’t living organisms so no, viruses can’t live without a host. If they do live without a host they do it in a really short time.

    I would say that the DNA in your body is millions of years old and that is also the truth about amoeba because they have also evolved just like we have done. Anyone can feel free to correct me on this one last statement.

    • In reply to #6 by Klaus:

      Viruses doesn’t just use RNA there are viruses who uses DNA as well as one stranded DNA and two stranded RNAs.
      Every virus need a host to survive because viruses aren’t living organisms so no, viruses can’t live without a host. If they do live without a host they do it in a really short time.

      I wou…

      An interesting point, I had to answer this as part of my finals for my degree and saying if a virus is alive or not, is a very difficult question. Its alive for a given value of alive, as Spock would say and I quote from my answer tbh, “Its life Jim, but not as we know it”, I loved being able to add that into a university level paper, but it holds. True it doesnt satisfy all the requirements of MRS GREN at a macro level per say but it does satisfy the biochemical requirements. Putting it simply, Its the ultimate parasite, by itself it doesn’t replicate but its nature is to replicate, it has no cell functions of its own, but it forms DNA complexes which do form the proteins etc it needs to replicate and survive. though infection it behaves as an independent life form, and creates itself a seed which is resilient for subsequent infection, even if it is in itself, like an acorn, dormant, is this not therefore life????

  6. What is our best guess on the order these appeared on earth?

    1. some sort of chain duplication
    2. RNA duplication
    3. enclosing cells
    4. addition of DNA

    What are the most complex molecules we have seen piggybacking on space debris?

    • The idea that there should still be these organisms is a bit strange. The thing is, they were outcompeted. There are a myriad of potential past organisms that may have existed but were outcompeted so early in the history of life, that they do not have any surviving descendants and remnants of them would bo microscopic and billions of years old.

      The same can be said for organisms that utilize a sugar splitting biochemical pathway that predates glycolysis (or developed contemporary to glycolysis). Every living thing runs glycolysis. If there were living things that ran it, then they were outcompeted by the ancestor of ours that first developed the pathway. Is it likely that they existed??? Well, I guess. Is it likely to find true hard evidence? No, I don’t think so.

      Also, replication of DNA is done the same by all living things. It is an ancient mechanism.

      So, the RNA to DNA split and the Glycolysis vs other pathway split (and replication of DNA) occurred when the earliest life forms were competing for supremacy. The ones that won have left descendants to this very day (every living thing!) the losers went by the wayside and their potential lineage was eradicated way way back when.

      In reply to #8 by Roedy:

      Does it seem strange that we have not found even one archaic bacteria or life form that still uses RNA without DNA. Where is our coeolocanth?

  7. In line with crookedshoes #9, please remember that millions of years have gone into evolving complex enzyme systems that provide the speed of chemical reactions used to build life. Early simple life may have taken weeks or months to do the growth modern cells can do in minutes. Not only would you expect those old forms to be eaten before being seen, they might grow so slowly as to be completely missed even if they were among us.

    (Also, the coeolocanth of today may look similar to its ancestors of many millions of years ago, but it is not the same, and its cells have continued to slowly evolve their internal structures.)

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