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- Newsgroups: sci.space
- Path: sparky!uunet!mcsun!ieunet!tcdcs!unix1.tcd.ie!rwallace
- From: rwallace@unix1.tcd.ie (russell wallace)
- Subject: Re: Biogenesis (was: ETs and Radio)
- Message-ID: <rwallace.712535154@unix1.tcd.ie>
- Sender: usenet@cs.tcd.ie (NN required at ashe.cs.tcd.ie)
- Nntp-Posting-Host: unix1.tcd.ie
- Organization: Trinity College, Dublin
- References: <a7327850@Kralizec.fido.zeta.org.au> <1992Jul28.105743.29096@news.Hawaii.Edu> <rwallace.712328556@unix1.tcd.ie> <1992Jul29.162909.3574@ke4zv.uucp> <rwallace.712441800@unix1.tcd.ie> <SJE.92Jul29183135@xylos.ma30.bull.com> <rwallace.712483849@unix1.tcd <SJE.92Jul30115800@xylos.ma30.bull.com>
- Date: Thu, 30 Jul 1992 22:25:54 GMT
- Lines: 99
-
- In <SJE.92Jul30115800@xylos.ma30.bull.com> sje@xylos.ma30.bull.com (Steven J. Edwards) writes:
-
- >#> 4) At some point an rRNA replicating cluster using amino acids becomes
- >#> capable of partial synthesis of useful amino acids. This replicator
- >#> gains a tremendous advantage over imperfect and less efficient
- >#> replicators who must compete for the limited spontaneous amino acid
- >#> production.
- >#
- ># Why would it gain an advantage, given that without a cell membrane, the
- ># amino acids it synthesizes would float away to benefit the other
- ># clusters just as much as the synthesizer?
-
- >This is trivally answered: first, the synthesized products do not
- >merely float away because they have assorted polar regions that can
- >interact with the synthesizer, and second, other similar or identical
- >replicators nearby would share in the benefit of peptide production
- >from other than themselves.
-
- I don't think polar regions by themselves are enough to stop the amino
- acids floating away pretty quickly. And why should nearby pieces of RNA
- be similar or identical? If you answer, because the original piece of
- RNA used amino acids to replicate itself, then this is begging the
- question, because the point at issue is can you get something capable of
- non-trivial self-replication.
-
- ># As a matter of interest, just how could an RNA cluster synthesize amino
- ># acids? From what raw materials? I thought synthesizing amino acids
- ># required energy, and therefore a complex set of enzymes to extract that
- ># energy from something.
-
- >All chemical reactions require energy to start; this is called the
- >"activation energy" of a reaction. There are several natural sources,
- >some of these are: photons from the Sun, ambient kinetic energy
- >(heat), stored chemical energy from previously producted compounds,
- >and lightning.
-
- Sure. Now how is an RNA cluster actually going to go about tapping this
- energy to synthesize amino acids, without already having a complex set
- of enzymes?
-
- >#> 5) The protein making rRNA clusters become self sufficient and the
- >#> first true ribosomes are the result. This is a good candidate for
- >#> "first life".
- >#
- ># Yes, it certainly would be, except the problems again arise:
- >#
- ># without a cell membrane, how would the "first life" cluster gain an
- ># advantage, when all its carefully synthesized enzymes floated away to
- ># benefit other replicators?
-
- >Again, the peptides do not just "float away"; peptides that did get
- >loose would benefit similar (or identical) replicators. These
- >secondary replicators would likely be physically close anyway.
-
- Again, why are nearby replicators similar, unless you previously assume
- that the RNA cluster is capable of non-trivial self-reproduction?
-
- ># you *still* need the full machinery for non-trivial self-reproduction.
-
- >No. Simple RNA replicator molecules can do it with only naturally
- >occuring amino acid molecules. Complex RNA replicators may synthesize
- >some to all of the needed amino acids (and other molecules).
-
- Has an RNA cluster unsupported by enzymes been demonstrated to
- synthesize amino acids or peptide chains (actually, stringing amino
- acids together into proteins is more important, because there would be
- plenty of amino acid molecules already floating around)?
-
- ># This means that the RNA must serve as a blueprint carrying the
- ># information to synthesize the proteins which assist with the synthesis
- ># of proteins and the replication of the RNA. What is the simplest system
- ># capable of doing all this, and is it simple enough to have a reasonable
- ># probability of falling together by chance? I don't think so. Why would
- ># you not require the full transcription apparatus?
-
- >Information necessary for early replication does not need the "full
- >transcription apparatus" because it is not based on any genetic code.
- >Early RNA replicators had their replication information stored in
- >their three dimensional structure, not in any one dimensional coded
- >strand. RNA chains act as sort of a "poor man's emzymes": there are
- >only four bases instead of dozens of amino acids, but there still is a
- >lot that can be accomplished. Laboratory results show that: both RNA
- >and amino acids form under natural conditions, complex RNA structures
- >form spontaneously, some these structures have the power of
- >replication and peptide synthesis. Of course, none of the early
- >replicators had the efficiency and fidelity of today's genetic
- >apparatus. But they didn't need it either.
-
- Hmmm... this is interesting; you're saying that an RNA cluster could
- double as blueprint *and* machinery, thereby making things a lot easier.
- However, you would still seem to have the problem that the RNA cluster
- must eventually get around to synthesizing some proteins that are going
- to assist it in replication, and these would tend to drift away before
- being much use. How much of this has been demonstrated so far?
-
- --
- "To summarize the summary of the summary: people are a problem"
- Russell Wallace, Trinity College, Dublin
- rwallace@unix1.tcd.ie
-