"The RNAWorld hypothesis (Gilbert, 1986) makes specific predictions, as illustrated by the detection of many new RNA activities during its exploration (for review, see Yarus,1999)+ For example, succession from the RNAWorld to modern biology likely required synthesis of large, specific proteins+ Such proteins subsequently replaced many RNAfunctions, allowing the evolution of organisms with modern informational mechanisms+ Thus translation and the genetic code were required for exit from the RNAWorld+ Accordingly, one predicts that coding and other translational features originate in processes that predate this exit, that is, in RNA–amino acid chemistry+ This RNA World point of view recapitulates prior arguments + The origin of the genetic code has frequently been cast in terms of two alternatives+ One hypothesis was championed by Carl Woese (Woese 1967), who argued that there was stereochemical matching, that is, affinity, between amino acids and certain triplet sequences + Woese et al+ (1966) write: “All in all, the conclusion that the genetic code derives basically from some sort of codon–amino acid-pairing interactions is essentially unavoidable+”"
"The RNA world hypothesis is a theory which proposes that a world filled with RNA (ribonucleic acid) based life predates current DNA (deoxyribonucleic acid) based life. RNA, which can store information like DNA and catalyze reactions like proteins (enzymes), may have supported cellular or pre-cellular life. Some theories as to the origin of life present RNA-based catalysis and information storage as the first step in the evolution of cellular life."
"The RNA World hypothesis is supported by RNA's ability to store, transmit, and duplicate genetic information, as DNA does. RNA can also act as a ribozyme (an enzyme made of ribonucleic acid). Because it can reproduce on its own, performing the tasks of both DNA and proteins (enzymes), RNA is believed to have once been capable of independent life. Further, while nucleotides were not found in Miller-Urey's origins of life experiments, they were found by others' simulations, notably those of Joan Oro. Experiments with basic ribozymes, like the viral RNA Q-beta, have shown that simple self-replicating RNA structures can withstand even strong selective pressures (e.g., opposite-chirality chain terminators) (The Basics of Selection (London: Springer, 1997))."
"The RNA world hypothesis places RNA at center-stage when life originated. This has been accompanied by many studies in the last ten years demonstrating important aspects of RNA function that were not previously known, and support the idea of a critical role for RNA in the functionality of life. In 2001, the RNA world hypothesis was given a major boost with the deciphering of the 3-dimensional structure of the ribosome, which revealed the key catalytic sites of ribosomes to be composed of RNA and for the proteins to hold no major structural role, and be of peripheral functional importance. Specifically, the formation of the peptide bond, the reaction that binds amino acids together into proteins, is now known to be catalyzed by an adenine residue in the rRNA: the ribosome is a ribozyme. This finding suggests that RNA molecules were most likely capable of generating the first proteins. Other interesting discoveries demonstrating a role for RNA beyond a simple message or transfer molecule include the importance of small nuclear ribonucleoproteins (SnRNPs) in the processing of pre-mRNA and RNA editing and reverse transcription from RNA in the maintenance of telomeres in the telomerase reaction."
Walter Gilbert on Wikipedia
Saturday, June 30, 2007