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kc Group Title

How does a universal genetic code relate to the hypotheses about the origin of life on Earth?

  • 2 years ago
  • 2 years ago

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  1. Eshpelin Group Title
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    I guess you are talking about the RNS world hypothesis. here is an exerpt from wikipedia related to this that should clear it: 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, a special type of enzyme. Because it can perform the tasks of both DNA and enzymes, RNA is believed to have once been capable of supporting independent life forms.[6] In fact, some viruses still use RNA as their genetic material, rather than DNA.[27] Further, while nucleotides were not found in Miller-Urey's origins of life experiments, their formation in prebiotically plausible conditions has now been reported, as noted above;[8] the purine base known as adenine is merely a pentamer of hydrogen cyanide. Experiments with basic ribozymes, like Bacteriophage Qβ RNA, have shown that simple self-replicating RNA structures can withstand even strong selective pressures (e.g., opposite-chirality chain terminators).[28] Additionally, a given RNA molecule in the past might have survived longer than it can today. Ultraviolet light can cause RNA to polymerize while at the same time breaking down other types of organic molecules that could have the potential of causing the breakdown of RNA, suggesting that RNA may have been a relatively common substance on early Earth.[citation needed] This aspect of the theory is still untested and is based on a constant concentration of sugar-phosphate molecules. Since there were no known chemical pathways for the abiogenic synthesis of nucleotides from pyrimidine nucleobases cytosine and uracil under prebiotic conditions, it is thought by some that nucleic acids did not contain these nucleobases seen in life's nucleic acids.[29] The nucleoside cytosine has a half-life in isolation of 19 days at 100 °C (212 °F) and 17,000 years in freezing water, which has been argued to be too short on the geologic time scale for accumulation.[30] Others have questioned whether ribose and other backbone sugars could be stable enough to be found in the original genetic material,[31] and have raised the issue that ribose must all be the same enantiomer as any nucleotide of the wrong chirality acts as a chain terminator.[32] Pyrimidine ribonucleosides and their respective nucleotides have been prebiotically synthesised by a sequence of reactions which by-pass the free sugars, and is assembled in a stepwise fashion by going against the dogma that nitrogenous and oxygenous chemistries should be avoided. In a series of publications, The Sutherland Group at the School of Chemistry, University of Manchester have demonstrated high yielding routes to cytidine and uridine ribonucleotides built from small 2 and 3 carbon fragments such as glycolaldehyde, glyceraldehyde or glyceraldehyde-3-phosphate, cyanamide and cyanoacetylene. One of the steps in this sequence allows the isolation of enantiopure ribose aminooxazoline if the enantiomeric excess of glyceraldehyde is 60 % or greater, of possible interest towards biological homochirality.[33] This can be viewed as a prebiotic purification step, where the said compound spontaneously crystallised out from a mixture of the other pentose aminooxazolines. Aminooxazolines can react with cyanoacetylene in a mild and highly efficient manner, controlled by inorganic phosphate, to give the cytidine ribonucleotides. Photoanomerization with UV light allows for inversion about the 1' anomeric centre to give the correct beta stereochemistry, one problem with this chemistry is the selective phosphorylation of alpha-cytidine at the 2' position.[34] However, in 2009 they showed that the same simple building blocks allow access, via phosphate controlled nucleobase elaboration, to 2',3'-cyclic pyrimidine nucleotides directly, which are known to be able to polymerise into RNA.[35] This was hailed as strong evidence for the RNA world.[36] The paper also highlighted the possibility for the photo-sanitization of the pyrimidine-2',3'-cyclic phosphates.[35] A potential weakness of these routes is the generation of enantioenriched glyceraldehyde, or its 3-phosphate derivative (glyceraldehyde prefers to exist as its keto tautomer dihydroxyacetone). On August 8, 2011, a report, based on NASA studies with meteorites found on Earth, was published suggesting building blocks of RNA (adenine, guanine and related organic molecules) may have been formed extraterrestrially in outer space.[37][38][39]

    • 2 years ago
  2. blues Group Title
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    @ Eshpelin, copying and pasting a huge answer which doesn't really apply to the question anyway is not helpful. That the genetic code is universal - that it is shared by all life forms on earth - suggests that life evolved once and only once and that all contemporary life forms descended from that same ancestor.

    • 2 years ago
  3. Eshpelin Group Title
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    Dear blues, if you had the brains, you would know that it completely applies.

    • 2 years ago
  4. shanice Group Title
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    thank u all for your answers

    • 2 years ago
  5. Grama-Pimpsta Group Title
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    I like raisins. Bum bum!

    • 6 months ago
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