Question For Tyler and/or others

Discussion in 'Health and medical' started by Tomhendricks474, Mar 13, 2004.

  1. I read this quote from a textbook with 2000 c.

    "Graham Cairnes-Smith (suggests that) RNA nucleotides and
    amino acids became associated in such a way that
    polypeptides were ordered by and helped synthesize
    RNA...This hypothesis suggests that both polypeptides and
    RNA arose at the same time."

    I tend to agree that they did. I did not know that Cairnes -
    Smith did too. Does anyone know exactly how he thought the
    two might arise at the same time and under what conditions?
     
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  2. Tim Tyler

    Tim Tyler Guest

    TomHendricks474 <[email protected]> wrote or quoted:

    > I read this quote from a textbook with 2000 c.
    >
    > "Graham Cairnes-Smith (suggests that) RNA nucleotides and
    > amino acids became associated in such a way that
    > polypeptides were ordered by and helped synthesize
    > RNA...This hypothesis suggests that both polypeptides and
    > RNA arose at the same time."
    >
    > I tend to agree that they did. I did not know that Cairnes
    > - Smith did too. Does anyone know exactly how he thought
    > the two might arise at the same time and under what
    > conditions?

    I don't.

    My brief search revealed that he rarely mentions
    polypeptides - and the places where he does so don't seem to
    have much to say about this issue.
    --
    __________
    |im |yler http://timtyler.org/ [email protected] Remove
    lock to reply.
     
  3. << I don't.

    My brief search revealed that he rarely mentions
    polypeptides - and the places where he does so don't seem to
    have much to say about this issue. -- >>

    I don't either. I thought that since this book's copyright
    was so recent, there might have been info I was not aware of
     
  4. Jim Menegay

    Jim Menegay Guest

    [email protected] (TomHendricks474) wrote in message news:<[email protected]>...
    > I read this quote from a textbook with 2000 c.
    >
    > "Graham Cairnes-Smith (suggests that) RNA nucleotides and
    > amino acids became associated in such a way that
    > polypeptides were ordered by and helped synthesize
    > RNA...This hypothesis suggests that both polypeptides and
    > RNA arose at the same time."
    >
    > I tend to agree that they did. I did not know that Cairnes
    > - Smith did too. Does anyone know exactly how he thought
    > the two might arise at the same time and under what
    > conditions?

    Tom, Since you found a quote from Tim's hero that kind-of
    supports your views, I thought you might be interested in a
    couple of papers from two of my FeS heros that also kind-of
    support you. Jim

    An All-Purine Precursor of Nucleic Acids Gunter
    Wachtershauser Proceedings of the National Academy of
    Sciences of the United States of America, Vol. 85, No. 4.
    (Feb. 15, 1988), pp. 1134-1135. Stable URL: http://links.jstor.org/sici?sici=0027-
    8424%2819880215%2985%3A4%3C1134%3AAAPONA%3E2.0.CO%3B2-H
    Abstract The theory is proposed that the pyrimidines in
    extant nucleic acids are postenzymatic substitutes for their
    isoelectronic and isogeometric position 3-bonded purine
    analogs xanthine and isoguanine, which were sibling products
    in a preenzymatic de novo purine pathway.

    Selection by Differential Molecular Survival: A Possible
    Mechanism of Early Chemical Evolution Christian De Duve
    Proceedings of the National Academy of Sciences of the
    United States of America, Vol. 84, No. 23. (Dec. 1, 1987),
    pp. 8253-8256. Stable URL: http://links.jstor.org/sici?sici=0027-
    8424%2819871201%2984%3A23%3C8253%3ASBDMSA%3E2.0.CO%3B2-P
    Abstract A model is proposed to account for selective
    chemical evolution, progressing from a relatively simple
    initial set of abiotic synthetic phenomena up to the
    elaborately sophisticated processes that are almost
    certainly required to produce the complex molecules, such as
    replicatable RNA-like oligonucleotides, needed for a
    Darwinian form of selection to start operating. The model
    makes the following assumptions: (i) that a small number of
    micromolecular substances were present at high
    concentration; (ii) that a random assembly mechanism
    combined these molecules into a variety of multimeric
    compounds comprising a wide repertoire of rudimentary
    catalytic activities; and (iii) that a lytic system capable
    of breaking down the assembled products existed. The model
    assumes further that catalysts supplied with substrates were
    significantly protected against breakdown. It is shown that,
    by granting these assumptions, an increasingly complex
    network of metabolic pathways would progressively be
    established. At the same time, the catalysts concerned would
    accumulate selectively to become choice substrates for
    elongation and other modifications that could enhance their
    efficiency, as well as their survival. Chemical evolution
    would thus proceed by a dual process of metabolic extension
    and catalytic innovation. Such a process should be largely
    deterministic and predictable from initial conditions.
     
  5. Thanks for both of these and their abstracts (url access
    was denied)

    << An All-Purine Precursor of Nucleic Acids Gunter
    Wachtershauser >>

    Fascinating - I continue to think there may well have been a
    'purine' world early on. RNA could well have formed without
    base pairing - at least at first. And/or with non WC base
    pairing. This seems to reinforce that idea somewhat.

    << Selection by Differential Molecular Survival: A Possible
    Mechanism of Early Chemical Evolution Christian De Duve
    (snipped) Abstract A model is proposed to account for
    selective chemical evolution, progressing from a relatively
    simple initial set of abiotic synthetic phenomena up to the
    elaborately sophisticated processes that are almost
    certainly required to produce the complex molecules, such as
    replicatable RNA-like oligonucleotides, needed for a
    Darwinian form of selection to start operating. The model
    makes the following assumptions: (i) that a small number of
    micromolecular substances were present at high
    concentration;

    TH Agreed.

    (ii) that a random assembly mechanism combined these
    molecules into a variety of multimeric compounds
    comprising a wide repertoire of rudimentary catalytic
    activities; and

    TH Disagree. How can you have such molecular randomness in a
    very nonrandom environment? Life does not pop up and then
    face selection as most current scenarios contend. It was
    that which always was chemically best suited to surviving
    that environment. There was no random assembly mechanism -
    it was temperature, and any random assembly aspects, would
    then be chemically and prebiotically 'selected' in that
    temperature cycle. The assembly mechanism was the heat cycle
    - that set up a chemically symnbiotic temperature zones
    where certain reactions worked, others did not. The most
    noticable temp zone is the range of liquid water.

    (iii) that a lytic system capable of breaking down the
    assembled products existed. The model assumes further
    that catalysts supplied with substrates were
    significantly protected against breakdown.

    TH The heat cycle would bothuild up and break down.

    It is shown that, by granting these assumptions, an
    increasingly c Zomplex network of metabolic pathways would
    progressively be established.

    TH Only if there was a nonrandom heat cycle pushing it.
    Randomness by itself could not lead to life.

    At the same time, the catalysts concerned would accumulate
    selectively to become choice substrates for elongation and
    other modifications that could enhance their efficiency, as
    well as their survival. Chemical evolution would thus
    proceed by a dual process of metabolic extension

    TH This is a leap of millions of years to say that anything
    would want, need, or profit from metabolic extension. If so
    why didn't water, salt, or gold latch on and begin to use
    energy to replicate? There must be a reason for metabolism.
    It grew as one of the novel ways to survive a heat cycle -
    specifically the high end of,

    and catalytic innovation. Such a process should be largely
    deterministic and predictable from initial conditions.
    >>

    Comment? Tom
     
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