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Topic: RNA World

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	RNA - Wikipedia, the free encyclopedia
		Structurally, RNA is indistinguishable from DNA except for the critical presence of a hydroxyl group attached to the pentose ring in the 2' position (DNA has a hydrogen atom rather than a hydroxyl group).
		Transfer RNA (tRNA) is a small class of RNA molecules that present specific amino acids to the ribosome during translation, the anticodon of the tRNA pairs with the codon of the mRNA.
		RNA genes (sometimes referred to as non-coding RNA or small RNA) are genes that encode RNA that is not translated into a protein.
	en.wikipedia.org /wiki/RNA (1129 words)

	"RNA world"
		Advocates of the "RNA world" hypothesis argue that RNA must have come before the first proteins, since without it there would have been no molecule of heredity — no "blueprint" molecule —; and therefore no way for other molecules to have been manufactured consistently.
		According to this idea, there was a time when RNA alone handled all of the tasks required for a cell to survive, acting as both a genetic material and a catalyst for the various reactions involved in metabolism and for its own assembly.
		Opponents of the RNA world picture point to the chemical fragility of RNA and the fact that it is difficult to synthesize abiotically.
	www.daviddarling.info /encyclopedia/R/RNAworld.html (1069 words)

	RNA World?
		In fact, it is the folded RNA in the catalytic core of the ribosome that is responsible for catalyzing the polymerization of new proteins.
		The unique properties of RNA have led many scientists to support the theory that life on earth passed through an "RNA World," a stage in the evolution of life that preceded the last common ancestor and that preceded the ensemble of encoded protein synthesis.
		The RNA World theory of the evolution of life is controversial and will likely never be definitively proven or disproven.
	www.yale.edu /breaker/tutlivemolecule.htm (402 words)

	Gibson, L. J. --- Did Life Begin in an "RNA World"?
		RNA is present in all living cells, and has a variety of uses that are central to the requirements for life.
		In the case of RNA, the sugar is ribose, the purines are adenine and guanine, and the pyrimidines are cytosine and uracil.
		The importance of RNA to the origin of life is based on the conjecture that it could act both as a source of information and as a catalyst to use that information.
	www.grisda.org /origins/20045.htm (2269 words)

	[No title] (Site not responding. Last check: 2007-10-09)
		It was suggested that catalysts made entirely of RNA are likely to have been important at this early stage in the evolution of life, but the possibility that RNA catalysts might still be present in contemporary organisms was overlooked.
		All RNA World hypotheses include three basic assumptions: (1) at some time in the evolution of life, genetic continuity was assured by the replication of RNA; (2) Watson-Crick base-pairing was the key to replication; (3) genetically encoded proteins were not involved as catalysts.
		RNA World hypotheses differ in what they assume about life that may have preceded the RNA World, about the metabolic complexity of the RNA World, and about the role of low-molecular-weight cofactors, possibly including peptides, in the chemistry of the RNA World.
	www.scripps.edu /mb/joyce/51.html (392 words)

	RNA World Introduction (Site not responding. Last check: 2007-10-09)
		The tertiary structure of a transfer RNA resembles an inverted letter L. The vertical stem is formed by coaxial stacking of the acceptor and T-stems to form one contiguous helix, and the horizontal stem is likewise formed by stacking of the D-stem and the anticodon stem.
		RNase P RNA is a ribozyme that catalyzes the cleavage of precursor transfer RNA to generate a transfer RNA with a mature 5'-end.
		According to the RNA world hypothesis, the primitive self-replicating system was composed of ribonucleic acids and the processes that are carried out by protein enzymes today must have been carried out by RNAs.
	rnaworld.bio.ku.edu /class/RNA/RNA00/RNA00.html (4863 words)

	The RNA World: A Critique - Origins & Design 17:1. Mills, Gordon and Kenyon, Dean
		As researchers broaden their focus to include the chemical plausibility of the RNA World itself, however7, these difficulties cannot be avoided.
		We take heart in noting that, despite the frequent neglect in much of the popular literature of the chemical difficulties of the RNA World scenario, many of the scientists involved with that hypothesis are quite candid in their assessment of the problems associated with it.
		RNA molecules with catalytic activity that are known today predominantly have nuclease or nucleotidyl transferase activity with some minimal esterase actitivy22.
	www.arn.org /docs/odesign/od171/rnaworld171.htm (3431 words)

	It's A small nuclear RNA World After All
		RNA was not some sort of passive carrier but could actually perform biologically relevant reactions.
		Ribonucleoproteins (RNPs) containing both RNA and protein were known since the early '70s, but the emphasis of research was more on the protein than on the RNA.
		RNA is very thermolabile but replacement of RNA processing by thermostable proteins would allow bacteria to exploit environments that eukaryotic cells could not.
	radio.weblogs.com /0100187/gems/NEWSLETTER/rna.html (1800 words)

	The RNA World: A Critique - What do Ribozyme Engineering Experiments Really Tell Us About the Origin of Life?. Origins ...
		In vitro RNA selection does not demonstrate that complex ribozymes could have arisen naturally in a prebiotic soup, because the in vitro experimental conditions are wholly unrealistic, revealing at every turn the fingerprints of intervening intelligence.
		RNA World researchers have taken their own engineering of ribozymes as analogous to plausible prebiotic processes, when in fact the two situations are profoundly different.
		This has occurred precisely because the procedures used in research on RNA catalysis reinforce the notion that intelligent design is required to produce molecular species that would not form due to the natural chemical tendencies of the reacting substances themselves, even over vast stretches of time.
	www.arn.org /docs/odesign/od171/ribo171.htm (1554 words)

	Origin of Life on Earth by Leslie E. Orgel
		We proposed that RNA might well have come first and established what is now called the RNA world - a world in which RNA catalyzed all the reactions necessary for a precursor of life's last common ancestor to survive and replicate.
		For instance, when RNA was allowed to replicate repeatedly in the presence of a ribonuclease (an enzyme that normally breaks down RNA), the RNA eventually became resistant to the degradative enzyme.
		As is true of RNA, one strand of this polymer, or peptide nucleic acid (PNA), can combine stably with a complementary strand; this result implies that, as is true of standard RNA, peptide RNA may be able to serve as a template for the construction of its complement.
	www.geocities.com /CapeCanaveral/Lab/2948/orgel.html (5055 words)

	Origin of Life - The RNA world
		The "RNA world" hypothesis suggests that the roles of proteins and enzymes were once played by curled-up RNA strands.
		However, the "RNA world" is not itself hypothesis a about the actual origin of life - since RNA is not remotely plausible in the role of the first genetic material.
		RNA world hypothesis, for example, suggests that short RNA molecules could have spontaneously formed that would then catalyze their own continuing replication.
	originoflife.net /rna_world (475 words)

	Exploring the New RNA World
		RNA – ribonucleic acid – is a copy of the DNA instructions that serves as a messenger to direct protein synthesis, which is then destroyed after it has fulfilled its function.
		On the one hand, the discovery of RNA interference (RNAi) has led to the identification of many small cellular RNAs that do not encode proteins (and therefore escaped identification in the Human Genome Project) but instead act to regulate the expression of other genes (9).
		This problem was first solved for some of the smaller self-cleaving ribozymes (10, 11), revealing unanticipated intricate folding patterns and the use of RNA bases as proton donors and acceptors to speed the chemical reactions.
	nobelprize.org /chemistry/articles/cech (1670 words)

	Non-Coding RNA Genes and the Modern RNA World.
		Various cis-antisense RNAs have been observed in prokaryotes [50], plants [51] and animals [12], and their roles are unlikely to be limited to those in imprinting and chromatin structure.
		The discovery of RNA catalysis [119, 120] and the "RNA world" hypothesis for the origin of life [26, 121] provide a seductive explanation for why rRNA and tRNA are at the core of the translation machinery: perhaps they are the frozen evolutionary relic of the invention of the ribosome by an RNA-based 'riboorganism' [122].
		Self-splicing RNA: autoexcision and autocyclization of the ribosomal RNA intervening sequence of Tetrahymena.
	www.euchromatin.org /Eddy01.htm (9521 words)

	Biology's Theme Park: RNA World :: Astrobiology Magazine :: Search for Life in the Universe
		The speculation has been that RNA preceded DNA, or at least formed the early basis for what is considered the biochemical progenitor in such an RNA world of self-reproducing molecules and enzymes.
		Because RNA replication is far simpler than protein replication, and because RNA participates in central cellular functions, researchers postulate a primitive, yet elegant, system in which RNA made RNA.
		This idea, in contrast to the RNA world's "information first" thesis, posits that a chaotic soup of small, random molecules led to chance metabolic reactions that evolved into modern cellular life.
	www.astrobio.net /news/article575.html (1469 words)

	HHMI Bulletin: A World Apart
		In the hypothetical "RNA World," a vision of the primordial Earth, precursors of modern RNA were responsible for storing genetic information and catalyzing biochemical reactions —functions primarily associated with DNA and enzymes.
		In the often rigid, paradigm-driven world of biology, it was as unexpected as stumbling upon penguins nesting in the Florida Everglades.
		Despite its obvious intellectual appeal, the RNA World was for the most part a quirky conceptual pastime in the years following the discovery of ribozymes.
	www.hhmi.org /bulletin/june2002/rna/rna2.html (2171 words)

	Lewis/Life - On-line Resource Articles
		The idea that ribonucleic acid (RNA), because of its catalytic capability and multiple roles in protein synthesis, was the chemical that led directly to life is termed the RNA world hypothesis.
		RNA viruses are another source of modern RNA that may hold clues to an RNA world.
		This RNA wraps itself in the envelope from hepatitis B. Hugh Robertson, a professor of biochemistry at New York Hospital-Cornell Medical Center in New York, hypothesizes that HDV is a viroid (an infectious RNA) that somehow "captured" an mRNA, which encodes protein (H. Robertson, Science, 274:66-9, 1996).
	www.mhhe.com /biosci/genbio/life/articles/article28.mhtml (1972 words)

	Study Offers Insights Into Evolutionary Origins Of Life
		In some of the strongest evidence yet to support the RNA world—an era in early evolution when life forms depended on RNA—scientists at the Whitehead Institute for Biomedical Research have created an RNA catalyst, or a ribozyme, that possesses some of the key properties needed to sustain life in such a world.
		These results, described in the May 18 issue of Science, suggest that RNA could have had the ability to replicate itself and sustain life in early evolution, before the advent of DNA and proteins.
		For years, scientists debated this question, some arguing that RNA molecules were the progenitors and others arguing in favor of proteins.
	www.sciencedaily.com /releases/2001/05/010518083259.htm (1187 words)

	The RNA World and Beyond: Scientific Speculation on the Origin of Life
		No RNA molecule long enough to encode an entire gene has yet been developed, however,(8) and the RNA World, although it seems to be a widely accepted account of the origin of self-replication, has its detractors.
		Another objection to the RNA World theory is that even if RNA could have formed spontaneously, extreme conditions on the primitive Earth might have led to rapid chemical degradation of it.
		As one prominent RNA World research group says, natural selection can't operate in the absence of compartmentalization because an RNA molecule that is especially efficient at replication will replicate other, less efficient types indiscriminately.
	serendip.brynmawr.edu /biology/b103/f01/web1/ginanni.html (1221 words)

	The RNA World
		The phrase "The RNA World" was coined by Walter Gilbert in 1986 in a commentary on the then recent observations of the catalytic properties of various RNAs.
		The RNA World referred to an hypothetical stage in the origin of life on Earth.
		We soon suggested that the RNA subunit of RNase P was part of the active center of the enzyme, by analogy to the then current picture of the ribosome.
	nobelprize.org /chemistry/articles/altman (855 words)

	The RNA World. by Brig Klyce (Site not responding. Last check: 2007-10-09)
		It was prescient of Crick to guess that RNA could act as an enzyme, because that was not known for sure until it was proven in the 1980s by Nobel Prize-winning researcher Thomas R. Cech (2) and others.
		RNA is then relegated to the intermediate role it has today—no longer the center of the stage, displaced by DNA and the more effective protein enzymes.
		RNA is chemically fragile and difficult to synthesize abiotically.
	www.panspermia.org /rnaworld.htm (5752 words)

	Novel Proteins Give Evidence That RNA World Existed
		The research provides significant evidence for the existence of the so-called RNA world, believed to be the evolutionary stage that predates present biological systems.
		In evolving new sequences of an RNA catalyst, the authors also have developed an efficient method of creating novel proteins built out of not just the 20 amino acids found in nature, but out of additional, so-called non-natural amino acids designed in the lab.
		The research demonstrates for the first time that a precursor to transfer RNA -- the genetic material that is responsible for synthesizing proteins -- could have acted as the catalyst for reactions that link transfer RNA (tRNA) to amino acids in a pre-biological era.
	unisci.com /stories/20012/0403011.htm (615 words)

	NAI: News Stories (Site not responding. Last check: 2007-10-09)
		To investigate potential RNA precursors, the scientists have been creating nucleic acids that are structurally similar to RNA.
		The backbone of DNA and RNA is composed of sugar molecules - ribose for RNA and deoxyribose for DNA - that contain five carbon atoms.
		One answer to this riddle is the RNA world theory, which suggests that both DNA and proteins could be descendants of RNA.
	nai.arc.nasa.gov /news_stories/news_detail.cfm?ID=189 (1268 words)

	ORIGIN OF LIFE: ON REPLICATION IN THE RNA WORLD
		A major impediment to full acceptance of an ancient "RNA world" is that, although it can easily be imagined that a pure RNA machine (a proto-ribosome) can make proteins, there is no equivalent RNA machine to make RNA (a ribopolymerase).
		All the RNA we know is made by protein, leading to perhaps the original "chicken-and-egg" problem of which came first.
		4) In a world without any other type of molecule (such as protein) to prevent these unwanted interactions, it might be concluded that a pure RNA world could not have been viable.
	scienceweek.com /2005/sw050429-1.htm (1534 words)

	IMB Jena Image Library: Index of RNA structures (Site not responding. Last check: 2007-10-09)
		If you are aware of RNA structures deposited at the PDB or NDB but not included here, let me know.
		RNA / HNA hybrids (HNA - hexitol nucleic acids are oligonucleotides with a six-membered carbohydrate moiety)
		RNA / protein complexes and complexes of RNA with peptide nucleic acids
	www.imb-jena.de /IMAGE_RNA.html (773 words)

	American Scientist Online - The Beginnings of Life on Earth (Site not responding. Last check: 2007-10-09)
		The chemical evolution leading to cellular life on earth almost four billion years ago likely passed through a stage where RNA alone performed all of the functions of the modern macromolecules RNA, DNA and protein.
		However the so-called RNA world was itself too complex to evolve directly from organic molecules found on the prebiotic earth.
		More likely, the RNA world emerged from and was supported by a primitive sort of metabolism fueled by the bonds in sulfur-containing compounds called thioesters.
	www.americanscientist.org /amsci/articles/95articles/cdeduve.html (98 words)

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