As I pointed out above, 3-4 billion years ago life may have been based on RNA.
To say that it was DNA-based is supposition. If we have no references to support a statement, then it has to be removed as it is not attributed to a reliable source. If you can find a reference that says when DNA evolved, then I will be happy to add that date.
I have been unable to find any such references. TimVickers 05:15, 11 March 2007 (UTC) The point is made well in the wiki. The presence of a hydroxyl group at the 2'-position of the ribose sugar is what separates our positions. Because of the weaker information transmission vector of RNA it seems that DNA was a stong contender from the start.
Lumping them together and dating them that way holds the best path forward. I think the wiki reads well as it has evolved. The time line link is very good and more than covers the point I was making. Thank you for your time. RoddyYoung 13:45, 12 March 2007 (UTC)[edit] Suggested editsOverall the article is excellent, congratulations.
I noted some issues in a few places. See what you think:DNA p. 2 What is meant by "act directly"? Distinguish binding from catalysis. Reworded. p. 3 Implies that a given RNA can be used either as message or structural RNA. Reworded. Physical and chemical properties p. 1 The width is 3.3 angstroms. From the reference "Combined measurement of the rotational and translational frictional coefficients of rod-like DNA molecules in dilute aqueous solution yields 22 to 26 Å for the hydrodynamic diameter and 3·34(± 0·1)
Å for the length per base-pair."p. 3 third and fifth carbon atoms in adjacent sugar rings. Reworded. p. 4 When does uracil not replace thymine in RNA? I have to check my references, but when the 5 position of uracil is modified, it is typically more elaborate than simple methylation, e.g., 5-methyl-amino-methyl-2-thio-uridine. Ribosylthymine is found in some RNAs such as tRNAs, added ref. p. 5 These grooves result from the relative position of the glycosidic bonds for a base pair, as seen in the figure. Indeed, feel free to add this if you think this would make the section clearer. Sense and antisense p. 1 The 5' to 3' copying is irrelevant to sense and antisense. It results from the nature of the substrates.
Good point, removed. Supercoiling The basic explanation is inaccurate. Although there may be some distortion at the level of the double helix, the main effect is to cause intertwining of different parts of the double helix, hence, super-coiling. I disagree, the main effect in biology is to alter the ease with which the strands can be separated. DNA damage Double strand breaks are dangerous because there is no easy way to fix them in non-replicating cells. Telliott 21:18, 15 February 2007 (UTC) Expanded. Thank you for a most though review. TimVickers 23:06, 15 February 2007 (UTC) Base StackingThis article erroneously states that the two strands of DNA are held together by H-bonds between bases on the antiparallel strands, when in fact it is more base stacking that contributes to the stability of DNA. H-bonds certainly play a part, but certainly not as much as the stacking does. I would be glad to add the edit, but unfortunately the article is still semi-protected. [3] --Redsquareblack 18:26, 24 February 2007 (UTC)Reworded the sentence to The DNA double helix is stabilized by hydrogen bonds between the bases attached to the two strands. Base stacking is discussed further in the base pairing section.. This arrangement of two nucleotides joined together across the double helix is called a base pair. In a double helix, the two strands are also held together by forces generated by the hydrophobic effect and pi stacking, but these forces are not affected by the sequence of the DNA.[14] As you are logged in, Redsquareblack, you can edit semi-protected pages. This only blocks anonymous IP editing. TimVickers 19:15, 24 February 2007 (UTC)
