Critical pairing( How did life originate on Earth? Until...)

How did life originate on Earth? Until now, there have only been theories to answer this question. One of the fundamental steps leading to living organisms is the development of molecules that can replicate and multiply themselves--the first genetic material. A team led by Ramanarayanan Krishnamurthy and Albert Eschenmoser at The Scripps Research Institute in La Jolla, California, is researching how this molecule might have looked.

Our own genetic material is DNA. Its backbone is made of sugar and phosphate building blocks. Like a strand of pearls, the four "letters" of the genetic code are arranged along this backbone. Two complementary strands of DNA form a double helix because the purine bases adenine (A) and guanine (G) form specific pairs with the pyrimidine bases thymine (T) and cytosine (C), attaching to each other through two or three docking sites. This type of structure could also be the basis for the first genetic material. However, it is doubtful that its backbone consisted of sugar and phosphate; it may have consisted of peptide-like building blocks. Amino acids, from which peptides are made, were already present in the "primordial soup". However, the bases may also have looked different in their primitive form.

To find the right track in searching for the origins of life, the team is trying to put together groups of potential building blocks from which primitive molecular information transmitters could have been made. The researchers have taken a pragmatic approach to their experiments. Compounds that they test do not need to fulfill specific chemical criteria; instead, they must pass their "genetic information" on to subsequent generations just as simply as the genetic molecules we know today--and their formation must have been possible under prebiotic conditions. Experiments with molecules related to the usual pyrimidine bases (pyrimidine is a six-membered aromatic ring containing four carbon and two nitrogen atoms), among others, seem
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Contact: R. Krishnamurthy
rkrishna@scripps.edu
John Wiley & Sons, Inc.
17-Nov-2006