RNA perfect for the Origin

[email hidden] wrote in message news:<[email hidden]>...

Quoted message said:

Reading about RNA, the thing that stuck me is how perfect
RNA is for the start of life.

You have single strands alternating with realtively short
double helical segnments.

RNA offers stability in the double helical parts and
coding or variation in the single stranded bubbles.

It has two pairs or sets of bases that nicely fit this
purpose - the GC as extra stable in double helical parts
with its 3 h-bonds and base stacking, and AU in the single
stranded bubbles - augmented by GC and others - as the
variant or coding, or ribozyme part.

But for all RNA's pluses at this earliest stage - DNA
would be much better for coding using all double helix
structure, and protein for enzymes.

But that would come later.

I agree with every word in this post except one. You write
"how perfect RNA is for the start of life". I would change
that to "the start of genetics". For the start of life, I
would like to have a mechanism for producing chiral sugars
and high energy phosphate bonds within the emergent biology,
rather than outside of it. Do that, and I will concede you
the purines and pyrimidines, and replicase ribozymes.

Jim Menegay <[email hidden]> wrote or quoted:

Quoted message said:

I agree with every word in this post except one. You write
"how perfect RNA is for the start of life". I would change
that to "the start of genetics". For the start of life, I
would like to have a mechanism for producing chiral sugars
and high energy phosphate bonds within the emergent
biology, rather than outside of it. Do that, and I will
concede you the purines and pyrimidines, and replicase
ribozymes.

There's no life without genetics - IMO.

Not if you use "life" to refer to evolving systems - and use
"genetics" to describe however such systems transmit
heritable information, anyway.

You only need chirality if you are building complex
machinery.

First life was probably not that complex - and need not have
been chiral.

Of course once you have a self-replicating system, the
origin of chirality becomes a non-problem - since it can be
explained by variation and common descent.
--
__________
|im |yler timtyler.orgtimtyler.orgOpen ↗ [email hidden] Remove
lock to reply.

<< I agree with every word in this post except one. You
write "how perfect RNA is for the start of life". I would
change that to "the start of genetics". For the start of
life, I would like to have a mechanism for producing chiral
sugars and high energy phosphate bonds within the emergent
biology, rather than outside of it. Do that, and I will
concede you the purines and pyrimidines, and replicase
ribozymes.

Quoted message said:

Quoted message said:

Fair enough, and well said.

[email hidden] (Jim Menegay) wrote in message news:<[email hidden]>...

Quoted message said:

[email hidden] wrote in message
news:<[email hidden]>...

Quoted message said:

Reading about RNA, the thing that stuck me is how
perfect RNA is for the start of life.

You have single strands alternating with realtively
short double helical segnments.

RNA offers stability in the double helical parts and
coding or variation in the single stranded bubbles.

It has two pairs or sets of bases that nicely fit this
purpose - the GC as extra stable in double helical parts
with its 3 h-bonds and base stacking, and AU in the
single stranded bubbles - augmented by GC and others -
as the variant or coding, or ribozyme part.

But for all RNA's pluses at this earliest stage - DNA
would be much better for coding using all double helix
structure, and protein for enzymes.

But that would come later.

I agree with every word in this post except one. You write
"how perfect RNA is for the start of life". I would change
that to "the start of genetics". For the start of life, I
would like to have a mechanism for producing chiral sugars
and high energy phosphate bonds within the emergent
biology, rather than outside of it. Do that, and I will
concede you the purines and pyrimidines, and replicase
ribozymes.

But it appears that Shapiro is not so ready to concede the
purines and pyrimidines. He has written a series of articles
critiquing the evidence for prebiotic synthesis of the
bases. Here is a link to the one for Cytodine. Note that he
has nice things to say about both Cairns-Smith and
Wachtershauser. ;-) But he also mentions Kauffman. ;-(

Robert Shapiro Prebiotic cytosine synthesis: A critical
analysis and implications for the origin of life PNAS 1999;
96: 4396-4401. pnas.org4396Open ↗

Excerpt from Conclusion: The evidence that is available at
the present time does not support the idea that RNA, or an
alternative replicator that uses the current set of RNA
bases, was present at the start of life. This conclusion
could be reversed if a prebiotic simulation were devised
that produced all of the bases in good yield under a single
set of conditions, by using a plausible combination of
water, atmospheric components, and minerals. In the absence
of such a demonstration, more attention should be given to
origin-of-life theories that do not require the four RNA
bases: (i) The first living system used a replicator
constructed of more accessible and stable components. A
number of possibilities may exist, with the clay system of
A.G. Cairns-Smith (*) perhaps the best known. (ii) Life
began with cycles of autocatalytic reactions. Storage and
transfer of information at the polymer level came later. A
number of writers have discussed this possibility, including
F. Dyson (*) and S. Kauffman (*). One possible system has
been described in detail by G. Wächtershäuser (*).

References: Cairns-Smith, A. G. (1982) Genetic Takeover and
the Mineral Origins of Life (Cambridge Univ. Press, New
York). Dyson, F. (1985) Origins of Life (Cambridge Univ.
Press, Cambridge). Kauffman, S. (1993) The Origins of Order.
Self-Organization and Selection in Evolution (Oxford Univ.
Press, New York). Wächtershäuser, G. (1992) Prog. Biophys.
Mol. Biol. 58, 85-201