Question

Where did the first DNA molecule come from? What kind of information did it carry (What for and where did it get it)?

There is at least one idea that seems to be gaining recognition as a possible theory for the evolution of DNA. The idea is termed “The RNA World” and it suggests that RNA was the precursor to DNA. Sidney Altman and Thomas Cech independently determined that RNA was capable of carrying out two roles: that of DNA, a genetic information storage molecule, as well as that of proteins, the molecular workhorses of the cell responsible for catalyzing most biochemical reactions. They shared the Nobel Prize in Chemistry in 1989 for their discoveries. RNA and DNA are very similar in structure, biochemically. The difference being that RNA is single stranded while DNA is a double helix (a spiral curve) in its most natural state. Additionally, RNA is relatively unstable compared with DNA, and degrades more quickly. So while RNA may have functioned as the initial information storage molecule, there was evolutionary pressure to evolve a more stable storage molecule, such as DNA. The central dogma of modern molecular biology follows in this manner: DNA->gives rise to RNA-> gives rise to Protein. Ultimately, the information carried in the structure of the DNA molecule is a set of instructions for the cell to direct the production of proteins. Proteins are required for the structure, function and regulation of a complex organism’s cells, tissues and organs. So before complex organisms could arise, a stable information storage molecule like DNA was necessary. For more information about the RNA world, check out these web sites: http://www.nobel.se/chemistry/laureates/1989/illpres/index.html http://www.astrobio.net/articles/rna.html Madalyn Edwards, NASA Astrobiology Institute
September 12, 2002