From: johnson@offroad.chem.wisc.edu (Arthur Johnson)
Newsgroups: talk.religion.misc
Subject: Re: dawkins/_the selfish
Date: 20 Aug 92 16:39:46 GMT
Distribution: talk
Organization: Physical Sciences Lab, UW-Madison

In article <1992Aug19.937.32499@dosgate> herb.sutter@canrem.com (herb  
sutter) writes:
> 
> Someone replied privately that no one claims to know the mechanism by
> which life arose on this planet; part of my reply to that person was:
> 
> me> ...you're right:  evolutionists generally don't claim to know how  
life
> me> arose on this planet originally, and they generally will/can not 
                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
even
^^^^
> me> guess at a possible mechanism for it.  Since that is so, how can 
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
they
> me> insist that it did in fact occur??  They are in the unenviable
> me> position of claiming that something which cannot be proved to take
> me> place now (generation of life from nonliving matter) DID IN FACT  
occur
> me> sometime in the primeval past -- even though they have no probable  
or
> me> even possible mechanism to propose for it!  I must question whether
> me> that is reasonable.
>

     Actually, it appears that evolutionary biologists are closing in on  
the mechanism. Until recently, evolutionary biology could not answer the  
question of which came first, DNA or proteins. The problem is that, in  
order for a cell to generate proteins, it must have DNA, and, in order for  
a cell to have DNA, it must have proteins. Schematically, the two cases  
look like this:

1)  DNA + protein1 --> mRNA + tRNA-AA + (rRNA/protein complex) -->
                                                           proteins

2)  nucleotides + protein2/protein3 + DNA --> DNA/RNA


The reason this chicken-and-egg problem was such a puzzle was because it  
was commonly assumed that DNA and RNA had no catalytic activity, i.e. it  
was believed that the only biological catalysts were enzymes (all of which  
are proteins). In the 1980's, however, Cech and Altman showed that RNA  
molecules in fact do exhibit catalytic activity. First of all, RNA  
molecules are capable of "self-splicing", i.e. they are capable of  
removing "undesirable" parts of themselves and then splicing themselves  
back together (minus the undesirable part). Secondly, it was commonly  
believed that within the rRNA/protein complex shown in 1) (called a  
ribosome), the rRNA functioned as a "scaffold" or support for the protein,  
while the protein actually "read" the mRNA code, "translated" the code  
into the proper amino-acid (AA) sequence, and synthesized the protein  
based on the code. It now appears that the true situation is the reverse,  
i.e. the protein is the passive scaffold, and the rRNA is what's actually  
doing the work of reading, translating, and synthesizing.
     What this means is that neither DNA nor proteins (enzymes) were  
first. Rather, on the early earth, it was RNA that functioned both as the  
storage medium for the amino-acid coding sequences of proteins (now done  
by DNA) _and_ as the catalytic molecule that turned that stored code into  
proteins (a function apparently still done by RNA). In addition, it is  
plausible (though as yet not verified), that RNA molecules originally  
performed many of the catalytic functions now done by enzymes. So,  
basically, it was not necessary for all of these different parts (RNA,  
DNA, proteins, etc) to evolve simultaneously and in all their present  
complexity to generate life. All that is needed for life is that an  
"organic soup" containing amino-acids and nucleotides form from inorganic  
precursors (which was proved to be possible in the 1950's), and for some  
of the nucleotides to combine to form a simple RNA molecule. At that point  
life has begun. The RNA molecule's self-splicing abilities allow it to  
alter itself and even replicate itself without the need for any protein  
"helpers". Furthermore, the ability of some RNA molecules to synthesize  
proteins based on the nucleotide sequence of another RNA molecule provides  
the basis for the appearance of proteins, as well as the subsequent  
development of the DNA-protein world as an eventual replacement for the  
RNA world. 
     If you would like to read up on the current scientific literature  
concerning the early earth as an RNA world, and the appearance of the RNA  
world as the mechanism by which life was able to evolve to its present  
complexity, I would be happy to provide you with a list of references.

Arthur Johnson
University of Wisconsin-Madison
Department of Chemistry
johnson@offroad.chem.wisc.edu     
Newsgroups: talk.religion.misc