The RNA World Hypothesis

Hosts: Doug Sharp and Rich Geer

https://youtu.be/4mPVuPrwbDQ

The RNA World Hypothesis proposes that life could have evolved from inanimate matter through initially forming self-replicating RNA. There are immediate problems with that hypothesis. The mechanism to form RNA requires nucleotides to form. For nucleotides to form, you need amino acids, phosphates and sugars. There are already problems isolating left-handed amino acids and right-handed sugars. Then somehow, DNA has to be reverse engineered from RNA, and that process needs RNA and amino acids in their right forms. The reagents needed to form amino acids conflict with the reagents needed to form nucleotides. The synthesis of nucleotides and the components of life are considered in this video. Nineteen difficulties are presented.

Two studies from Germany have proposed ways RNA could have been the link between inanimate molecules and living microbes. Benedikt Obermayer’s Munich group has reported a computer simulation of "prebiotic RNA" in Physical Review Letters. Christopher Deck and colleagues from Stuttgart reported their work synthesizing RNA in Nature Chemistry. Both groups are trying to demonstrate how RNA molecules could have built and replicated themselves to transmit useful information.

The mystery of abiogenesis - getting life from non-life - is a major hurdle for evolution. Abiogenesis violates a basic principle of biology. Since living cells need both proteins and DNA to function and reproduce, evolutionary theorists have struggled with the problem of how one could have evolved without the other. RNA is an intermediary-of-sorts between DNA and proteins (able to carry out some enzymatic function and to transmit information), so the "RNA world hypothesis" paints a scenario in which the earliest life forms would have only required RNA. The discovery of bits of self-replicating RNA increased the popularity of the RNA world.

Efforts to synthesize self-replicating RNA strands long and varied enough to actually encode for a functional biochemical molecule have been unsuccessful. The Stuttgart group decided to immobilize an 8-base-strand of RNA and surround it with chemically-activated nucleotides and "micro-helper" pieces of RNA. They hoped such immobilized RNA strands would lengthen. Some RNA chains added 4 bases. Some, however, failed to copy correctly. Twelve bases is not long enough to code for functional molecules, but Deck considers the work a success. The group suggests that early life forms may have gotten by with simpler molecules. And although the experiment required pinning down the RNA starter strand with a bit of DNA, the group proposes early RNA got "adsorbed and immobilized on surfaces billions of years ago."

The Munich group didn’t actually grow any RNA. They performed a computer simulation proposing a "natural" hydrothermal "RNA reactor" (i.e. porous rocks on the sea floor where nucleotides can accumulate in the pores and be exposed to strong temperature gradients) in which aggregates of nucleotides can randomly bond to build RNA. During normal transcription of RNA, only certain nucleotide pairings are stable. Therefore, in this computer-simulated reactor, randomly generated bits of RNA hybridized by matching up properly with other bits of RNA, thereby outlasting improperly paired molecules.