The RNA world hypothesis proposes that a world filled with RNA-based life predates current DNA-based lifeforms
RNA has two key qualities that would have allowed it to function in this manner:
RNA can self-replicate
- RNA is able to store information in a sequence composed of four recurring nucleotides (similar to DNA)
- Short sequences of RNA are able to be accurately duplicated to form identical RNA molecules
RNA can act as a catalyst
- Modern cells use RNA catalysts (called ribozymes) to remove introns from mRNA and help synthesise new RNA molecules
- In ribosomes, rRNA functions as the catalytic component and plays a pivotal role in peptide bond formation
RNA is the only molecule that is capable of both self-replication and catalytic functioning, but has since been superseded:
- DNA, through its superior chemical stability (double helical structure) has taken over as the data storage form
- Protein, through its greater variability (20 amino acids as opposed to 4 nucleotide bases) has taken over as the catalytic form
- RNA remains as a transitional form between DNA and protein, suggestive of its multi-faceted origins
Summary of the RNA World Hypothesis
