RNA world – The origin of life?

Описание: OTHER VIDEOS YOU MIGHT LIKE:
• Capillary coup! The birth of the Southern blot -    • Capillary coup! The birth of the Southern ...  
• Immunity genes also control a dog’s coat colour? -    • Immunity genes also control a dog’s coat c...  
• The history and mechanism of photolyase: How bacteria recover after sunburn -    • The history and mechanism of photolyase: H...  

How did life first start? How did simple organic molecules evolve into today’s complex cells? Understanding this may help to search for life on other planets. Early thoughts on the origin of life were that RNA and proteins worked together to form the first self-replicating systems. However, if RNA is needed for protein synthesis, and proteins needed for RNA replication, which evolved first?

In 1986, Walter Gilbert gave life to the “RNA world”, a hypothetical prebiotic existence where RNA was both the information carrier and catalytic molecule. These RNA enzymes (ribozymes) eliminate the need for proteins in the beginning of life. Multiple ribozymes were found over time, including in the ribonuclease-P of Escherichia coli, the self-splicing introns in Tetrahymena thermophila, cross-replicating ribozymes that synthesise each other from oligonucleotides, and possibly the 50S ribosomal subunit of Thermophilus aquaticus. Self-splicing introns, capable of splicing themselves out of and into RNA, may have acted as transposons to carry exons within and between RNA molecules. These provided recombination to the RNA world, enhancing RNA’s ability to gain beneficial sequences and evolve. Recombining exons and excising introns formed varieties of ribozymes, enabling RNA to be both the information carrier and catalytic molecule.

The RNA world evolution possibly began from the formation of many different RNA molecules, some capable of self-replication. RNA gained new enzymatic functions through intron-based recombination and random mutations, and the evolution of tRNA- and ribosome-like RNA molecules enabled the start of protein synthesis. The proteins may have performed better as enzymes than the ribozymes. Double-stranded DNA possibly evolved through reverse transcription of RNA, storing genetic information better. Thus, due to the superior performance of DNA and proteins, RNA was relegated to mediating the transition from nucleotides to amino acids.

Other hypothetical prebiotic worlds include a protein-first or RNA-protein coevolution. However, almost 40 years since its first proposal, Gilbert’s RNA world is still one of the most supported hypotheses of the origin of life.

Creator: Ashleah Williams

References:
The origin of genetic information. Eigen M, Gardiner W, Schuster P, Winkler-Oswatitsch R. Scientific American. 1981 Apr;244(4):88-92, 96, et passim. doi: 10.1038/scientificamerican0481-88.
Origin of life: The RNA world. Gilbert W. Nature. 1986 Feb 20;319(6055):23. doi: 10.1038/319618a0.
On the problems of evolution and biochemical information transfer. Rich A. In: Horizons in Biochemistry. 1962:103-126. Academic Press.
The RNA moiety of ribonuclease P is the catalytic subunit of the enzyme. Guerrier-Takada C, Gardiner K, Marsh T, Pace N, Altman S. Cell. 1983 Dec;35(3 Pt 2):849-57. doi: 10.1016/0092-8674(83)90117-4.
Catalytic activity of an RNA molecule prepared by transcription in vitro. Guerrier-Takada C, Altman S. Science. 1984 Jan 20;223(4633):285-6. doi: 10.1126/science.6199841.
Self-splicing RNA: autoexcision and autocyclization of the ribosomal RNA intervening sequence of Tetrahymena. Kruger K, Grabowski PJ, Zaug AJ, Sands J, Gottschling DE, Cech TR. Cell. 1982 Nov;31(1):147-57. doi: 10.1016/0092-8674(82)90414-7.
The intervening sequence RNA of Tetrahymena is an enzyme. Zaug AJ, Cech TR. Science. 1986 Jan 31;231(4737):470-5. doi: 10.1126/science.3941911.
Self-sustained replication of an RNA enzyme. Lincoln TA, Joyce GF. Science. 2009 Feb 27;323(5918):1229-32. doi: 10.1126/science.1167856.
Reverse self-splicing of the tetrahymena group I intron: implication for the directionality of splicing and for intron transposition. Woodson SA, Cech TR. Cell. 1989 Apr 21;57(2):335-45. doi: 10.1016/0092-8674(89)90971-9.
Exon shuffling by recombination between self-splicing introns of bacteriophage T4. Hall DH, Liu Y, Shub DA. Nature. 1989 Aug 17;340(6234):575-6. doi: 10.1038/340574a0.
Unusual resistance of peptidyl transferase to protein extraction procedures. Noller HF, Hoffarth V, Zimniak L. Science. 1992 Jun 5;256(5062):1416-9. doi: 10.1126/science.1604315.
The RNA world hypothesis: the worst theory of the early evolution of life (except for all the others). Bernhardt HS. Biology Direct. 2012 Jul 13;7;23. doi: 10.1186/1745-6150-7-23.