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RNA World and the Origin of Life

In 2011  Martin Hanczyc delivered a TED talk in London on the topic of the origin of life, “The Line Between Life and Not-Life” that discussed some of his work with proto-cells. I participated in some online commenting on the TED page including a conversation about the origin of genetic material.

I wanted to point to the talk itself and include some of the posts below.

ImageFrom Ted Mozer III: ” Two questions about life and the origin of same on earth:
Is all know life on earth related and DNA (or even RNA) based?
If life was created on earth (and not from a seed that either arrived via an comet or the like or from an alien visit), why is the creation process a not a contining process. Did the creation process occur and then stop once life awoke? If so, why??”

My Reply: “You’re asking a very good question, Ted.
Think of it this way, imagine that life first originated by self-replicating molecules (probably RNAs) that found a nice safe home in some protocells that were floating around in the neighborhood – it doesn’t matter if this is absolutely true or not, just consider the abstract idea. The ‘food’ that these cells need is more RNA and cell membrane material, right? So, the things that these cells will ‘eat’ are exactly the same stuff that they, themselves, once were. If our new cells are successful, they are probably gobbling up all the other pro to-life material around them.
This does not mean that life could not have happened more than once, but if it’s a rare enough event, then the first things to get there are going to probably stay at the top of the heap.

It would be really cool to find organisms that use different genetic material – this would support multiple origin events, but so far, the universality of DNA argues that it was a one-off thing.”

A Comment by an unknown person: “Self replicating RNA? RNA and its components are difficult to synthesize in a laboratory under the best of conditions, much less out in a primordial mud puddle. This is highly unlikely. Yes, this was a miraculous “one-off thing.””

My Reply: “Yes, I agree, it is difficult to conceive of RNA as a self-replicating genetic material that also acts as an enzyme. Although RNA does currently act as genetic material, this role is restricted to viruses while DNA plays the major role of genetic material in all other organisms (including some viruses). Also, much of the enzymatic work in biological systems is currently carried out by enzyme proteins. However, there are still some RNA enzymes (ribozymes) extant, one of note is the ribosome – a protein / ribozyme complex with deep phylogenetic roots.

The idea of an RNA world as life’s origin has been around for some time, with suggestions of such an origin being proposed by Francis Crick, Alexander Rich and Harold White (among others) in the 1960s and 1970s.

Over the years, data has emerged supporting such a possibility including:

“The system, created by Gerald Joyce and Tracey Lincoln at the Scripps research institute in La Jolla, California, involves a cross-replicating pair of ribozymes (RNA enzymes), each about 70 nucleotides long, which catalyse each other’s synthesis.  So the ‘left’ ribozyme templates the synthesis of the ‘right’, which in turn templates the ‘left’ and so on, building each other via Watson-Crick base pairing. “

discussed in “Chemists edge closer to recreating early life”, Royal Society of Chemistry 2009.

also,

“Clemens Richert and colleagues at the University of Karlsruhe have now shown that, without the use of enzymes, an RNA strand bound to a longer template strand of RNA can grow more than one order of magnitude faster than previously believed. This growth occurs in single nucleotide steps according to the base pairing rules of Watson and Crick.”

-From “Accelerating non-enzymatic RNA replication“, Royal Society of Chemistry 2005.

However, support is not proof. There will never be proof of what actually happened, but, then again, I might just be a brain floating in a jar somewhere…

 
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Posted by on October 13, 2013 in Uncategorized

 

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“Life is nothing but an electron looking for a place to rest”

ImagePhysics -> Chemistry -> Biology

The Smithsonian Magazine has an article this week proposing that we consider Mars as the origin of Terrestrial Life. This notion stems from Steven Benner’s Four Paradoxes: The Tar Paradox, The Water Paradox, The Single Biopolymer Paradox and The Probability Paradox. Each of these is described in the abstract of his work, and do add up to a possible alternative for life’s origin. However, as compelling as his arguments may be, the origin of life will always be a mystery veiled in time. Even if we were to find evidence of life on Mars that is very much like that on Earth, it would be difficult to say whether Terrestrial life was the origin of Martian life, or vice versa.

Another problem I have with tracing the origins of life off-planet is that it does not solve anything, but merely relocates the source. So it’s not that I feel that Benner’s work is uninteresting or unworthy of consideration, but presently, Ockham’s razor precludes Imageseriously considering extra-terrestrial origins without a good deal more hard evidence. Further,  relocating the source or life’s origin does little to change how we think about  origins. Regardless or where life started, it is still highly probably that it began with RNA, a unique molecule in that even today it serves dual roles as an information-carrying molecule and a structural one that often has enzymatic function. And, that the addition of the more stable , DNA molecule as the primary source of information happened later – as adding protein synthesis also did for providing an alternative structural / functional molecule. 

Evolution of the Central Dogma?

                                                              RNA

                        DNA -> RNA                                                  RNA -> Protein

                                                  DNA -> RNA -> Protein

 
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Posted by on August 31, 2013 in Uncategorized

 

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A cute video about the beginning of time

From the Ted Ed site:

“How did the universe begin — and how is it expanding? CERN physicist Tom Whyntie shows how cosmologists and particle physicists explore these questions by replicating the heat, energy, and activity of the first few seconds of our universe, from right after the Big Bang.”

Lesson by Tom Whyntie, animation by Hornet Inc

 
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Posted by on June 24, 2013 in Uncategorized

 

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