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Author Topic:   Could RNA start life?
Dr Jack
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Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
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Message 18 of 105 (682741)
12-05-2012 6:47 AM
Reply to: Message 15 by RAZD
12-04-2012 4:48 PM


Re: abiogenesis - last stages?
Both replication and metabolism -- replication needs raw materials being consumed to make the next (imperfect) copy. This would likely be enclosed in a lipid shell, so we have a ways to go before getting back to the "first" system\aspect of life.
How are you going to have replication without catalysis?

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Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 9.0


(1)
Message 19 of 105 (682742)
12-05-2012 6:59 AM
Reply to: Message 1 by dayalanand roy
12-04-2012 12:50 AM


Life is chemicals, not purposes
As we know, still majority of evolutionists believe in an RNA world hypothesis.
I wouldn't go as far as 'believe in' but, yes, most relevant scientists consider RNA world a probable step in the origin of life.
However, I have a problem in imbibing this theory. Nucleic acids are the information storage system of life.
Here, I'm afraid, you've fallen for the mistake of thinking that the simplified version presented to school children is the reality. The description of DNA as a "storage system" is poor enough, but for RNA it's simply wrong.
DNA is, in a sense, structurally boring. For the most part, it forms double strands that twist into helices. These helices are largely chemically uninteresting. There are no known occurrences of DNA acting enzymatically, and it's hard to think that it could do so. RNA is different, being single stranded it is free to twist into complex three-dimensional shapes. These three dimensional shapes are diverse enough to act as enzymes (biological catalysts) for a wide range of biologically important reactions. We know this to be the case because key roles in modern cells are still carried out by RNA enzymes (aka 'ribozymes').
This is why scientists think RNA world is so compelling an idea. In RNA world there is no dichotomy between "storage" and "enzyme" molecules; the two are one and the same: RNA. RNA shares the relative ease of copying that DNA has but combines it with much of the enzymatic capability of proteins.
Properly understood then, RNA world explains the objection you've raised.

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Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 9.0


Message 23 of 105 (682817)
12-05-2012 2:45 PM
Reply to: Message 20 by Genomicus
12-05-2012 10:08 AM


Re: Life is chemicals, not purposes
One of the cool things about biology is that it's unpredictable. Deoxyribozymes have, in fact, been discovered. See, e.g., "In vitro selection, characterization, and application of deoxyribozymes that cleave RNA."
Excellent! Thank you, Genomicus (Link for the interested)
No naturally occurring deoxyribozymes yet discovered, though, and the process under which they were identified and determined to catalytically is quite artificial. None the less: I was wrong; always good to learn new things.

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