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RNA World and the Origin of Life

13 Oct

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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