Sunday, February 18, 2007

The Origin of Life : RNA Hypothesis

Of late I have been reading books by great scientists. The best one as I found out, is one from James Watson, named as DNA : The secret of Life. I have gone through first three chapters of the book only. It has given me a lot of knowledge on how the life has been evolved on the earth.

The basic mystery that I had prior to reading the book was on the relation between protein and life. The explanation tha I got is really interesting. It's the DNA that replicates a part of it (transcribes) to messenger RNA. The messenger RNA then comes to Ribosome and gets translated to amino acids with the help of transfer RNAs present there. Amino acids are catalyzed by RNAs to build polypeptide bonds among them to generate Protein. But, DNA, RNA and the Proteins are built on nucleotides.

Here the RNA World hypothesis comes into picture. It's now obvious that RNA has a property to store, transmit and duplicate the genetic information as DNA. It can also produce proteins - the building block of life. According to this hypothesis, RNA was independent initially and later evolved a barrier outside to form later form of life - like bacteria and Amoeba. Carl Zimmer, who's working on this for long, believes that RNA Viruses are the last common ancestors of life. They evolved into DNA based viruses and since then, the superior system of DNA based life exists.

The most interesting part to me was the role of Natural Selection in the process of forming RNAs. Initially nucleotides (purely chemical substance) were free floating. They were often formed bonds to bind together. but certain sequence of bonds had properties to bind and go to more stable state. As each chain grew longer it attracted more matching nucleotides faster. RNA is one of these giant nucleotide chains. In an RNA world, different forms of RNA compete with each other for free nucleotides and are subject to natural selection. The most efficient molecules of RNA, the ones able to efficiently catalyze their own reproduction, survived and evolved, forming modern RNA. The competition grew and resulted in co-operation between separate RNA chains to produce more and more different proteins. DNA came later and so lipids, carbohydrates and other materials since a collaboration of such materials were more 'sustainable' and 'replicable'.

The main problem of this thesis was the instability of RNA while being exposed to UV Rays. Recent experiments also suggest that the original estimates of the size of an RNA molecule capable of self-replication were most probably vast underestimated, the size can be smaller than one have thought of. More-modern forms of the RNA World theory propose that a simpler molecule was capable of self-replication (that other "World" then evolved over time to produce the RNA World). There are many more hypothesis surrounding this RNA and life but the lack of undisturbed sedimentary rock from that early in Earth's history leaves few opportunities to test any of these hypothesis robustly.

The idea of RNA world was first proposed in Carl Woese's The Genetic Code. The term was coined in 1986, by Walter Gilbert.

The origin of life on earth is a mystery that Humankind ought to solve. The proper understanding might give us several advantages over the natural world. We may create our own microbes to fight against the diseases caused by virus and bacteria. We will have much better understanding of each of the building blocks of our own body.

News Reference from BBC :
Creation of Viral life by researchers.

DNA, RNA, Evolution, Origin of Life

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