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Genetic Code Part Ii


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#1 Guest_92g_*

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Posted 30 March 2005 - 03:35 AM

During our Gitt debate, I found a couple of quotes that I thought would make interesting conversation, e.g.:

"The development of the metabolic system, which, as the primordial soup thinned, must have "learned" to mobilize chemical potential and to synthesize the cellular components, poses Herculean problems. So also does the emergence of the selectively permeable membrane without which there can be no viable cell. But the major problem is the origin of the genetic code and of its translation mechanism. Indeed, instead of a problem it ought rather to be called a riddle. The code is meaningless unless translated. The modern cell's translating machinery consists of at least fifty macromolecular components which are themselves coded in DNA: the code cannot be translated otherwise than by products of translation. It is the modern expression of omne vivum ex ovo. When and how did this circle become closed? It is exceedingly difficult to imagine." (Monod, Jaques [Biochemist, Director of Pasteur Institute, Paris], "Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology", [1971], Penguin: London, 1997, reprint, p.143. Emphasis in original). [top of page]


http://members.iinet...chcknndgggntccd

I think this aspect can provide some insightful discussion into the information aspect of DNA.

Comments?

Terry

#2 Guest_Paul C. Anagnostopoulos_*

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Posted 30 March 2005 - 06:40 AM

Well, it happened somehow. Does Monod have an alternate scenario that he finds easier to imagine?

~~ Paul

#3 Guest_Calipithecus_*

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Posted 30 March 2005 - 07:44 AM

"... it is a classic chicken-and-egg problem: Which came first, proteins or DNA?"

A similar problem occurs in architecture. The arch shape is fantastically strong and self-supporting, but the individual stones of which it is constructed cannot possibly support each other until the structure is complete. The answer to the riddle is that early stages of its construction involve a support structure -- a scaffold -- which is removed at the final stage.

What makes the protein (in particular, the enzyme) the indispensible workhorse of biological systems is its 3-dimensional shape. What makes DNA so reliable as a medium for the storage of protein templates is that it can be split down the middle, and recreated from either half (by what are know as: 'Watson-Crick pairing rules'). What makes RNA the favored candidate for 'scaffolding' is that, to a certain extent, it has properties of both.

Because RNA lacks the double-helix shape characteristic of DNA, it is less reliable as a replicator, but at the same time, because its shape is less constrained, it is free to tie itself in knots like a protein (lacking a partner chain to pair with like DNA, RNA is free to 'pair' with odd bits of itself).

The RNA World Hypothesis is a fascinating area of investigation -- at present, it is only that, but perhaps it might help to stimulate some who tend to start sentences with: "I simply cannot imagine how..."

Check out Speigelman's Monster

#4 chance

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Posted 30 March 2005 - 01:49 PM

I have often thought that a form of naked DNA roaming the early seas, would be an intermediate step to single celled life, followed by a spiky DNA (molecules attached), then spiky but smoothed out (lots of attached molecules).

It is an unknown as established life has erased the past conditions.

#5 Guest_92g_*

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Posted 02 April 2005 - 03:35 PM

The RNA World Hypothesis is a fascinating area of investigation -- at present, it is only that, but perhaps it might help to stimulate some who tend to start sentences with: "I simply cannot imagine how..."


Considering the problems with the RNA world, then its not to difficult to understand how someone would say "I simply cannot imagine how...".

http://www.arn.org/d...rnaworld171.htm

I also think its worth adding that I disagree with his statement about the information being meaningless unless its translated. It may be useless, but the information is still there, and still has meaning.

Terry

#6 Guest_Calipithecus_*

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Posted 02 April 2005 - 06:56 PM

Considering the problems with the RNA world...

I agree that the RNA World hypothesis has a long way to go (which is a lot of why it's referred to as a 'hypothesis') -- but instead of just throwing URLs around, maybe we could address specific points. In the link you offerred, what do you consider to be the most compelling argument against the hypothesis?

I also think its worth adding that I disagree with his statement about the information being meaningless unless its translated. It may be useless, but the information is still there, and still has meaning.

I wondered if you had noticed that. At some point, I think this becomes a philosophical argument -- but since that discussion is already under way in the other thread, I suggest we continue it there.




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