How diD the First Cell get Genes to Live and Breed?
Most recent answer: 04/23/2015
- raja (age 29)
madurai, tamilnadu, india
The answer might be astonishing at first, but the contemporary theories say it did not get any genes somehow at all. The ancestor organisms are believed to be totally primitive, without any organelles, nuclei, extensive enzymatic pathways or even DNA. There is otherwise a chicken and a egg problem: the life as we know of requires transcription from DNA to get RNA, which needs to be translated into proteins. But all these machinery as well as DNA replication highly depends on protein-based enzymes. So which came first, DNA or proteins?
The key to the question is catalytic activity of RNA. Called ribozymes, RNA can catalyze certain simple reactions themselves, and RNA can be propagated. So without any need for DNA based genes or protein machinery, a single RNA can manage to execute some functions as well as providing means of replicating itself. Proteins are structurally and chemically more versatile, which favored organisms synthesizing them using their RNAs. Being chemically more stable and also providing a way to correcting the occasional mistakes, DNA-organisms was also favored, resulting in RNA/DNA/protein framework observed in most organisms today.
So how was the first organism get an RNA in this ? The first organism was very primitive, not consisting of cells but just some functional molecules. The required ingredients were not biochemically synthesized, but rather formed spontaneously in the primordial soup in the water masses containing some dissolved gases and molecules. Although it may sound unrealistic, it in laboratory and some simple organic molecules can be identified. The evolution had billions of years and virtually unlimited resources to perform this prebiotic evolution, which served as the precursors for later reactions.
I'll add that our ability to reconstruct what happened in the very early phases of evolution is pretty limited. So don't be too surprised if this picture changes. The argument about RNA playing a key role, however, is fairly compelling. One piece of supporting evidence is that a key part of the RNA of those ribosomes is shared by all organisms, indicating that it was present very early on. /mw
(published on 04/23/2015)