RNA world
Hypothetical stage in the early evolutionary history of life on Earth / From Wikipedia, the free encyclopedia
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The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins.[1] The term also refers to the hypothesis that posits the existence of this stage.
Alexander Rich first proposed the concept of the RNA world in 1962,[2] and Walter Gilbert coined the term in 1986.[3] Alternative chemical paths to life have been proposed,[4] and RNA-based life may not have been the first life to exist.[3][5] Even so, the evidence for an RNA world is strong enough that the hypothesis has gained wide acceptance.[2][6][7] The concurrent formation of all four RNA building blocks further strengthened the hypothesis.[8] Regardless of its plausibility in a prebiotic scenario, the RNA world can serve as a model system for studying the origin of life.[9]
- Like DNA, RNA can store and replicate genetic information.
- Like protein enzymes, RNA enzymes (ribozymes) can catalyze (start or accelerate) chemical reactions that are critical for life.[10]
One of the most critical components of cells, the ribosome, is composed primarily of RNA. Ribonucleotide moieties in many coenzymes, such as acetyl-CoA, NADH, FADH, and F420, may be surviving remnants of covalently bound coenzymes in an RNA world.[11]
Although RNA is fragile, some ancient RNAs may have evolved the ability to methylate other RNAs to protect them.[12]
If the RNA world existed, it was probably followed by an age characterized by the evolution of ribonucleoproteins (RNP world),[3] which in turn ushered in the era of DNA and longer proteins. DNA has greater stability and durability than RNA; this may explain why it became the predominant information storage molecule.[13] Protein enzymes may have come to replace RNA-based ribozymes as biocatalysts because their greater abundance and diversity of monomers makes them more versatile. As some cofactors contain both nucleotide and amino-acid characteristics, it may be that amino acids, peptides and finally proteins initially were cofactors for ribozymes.[11]