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Sunday, April 25, 2021

Happy DNA day 2021!

It was 68 years ago today that the famous Watson and Crick paper was published in Nature along with papers by Franklin & Gosling and Wilkins, Stokes, & Wilson. Threre's a great deal of misinformation circulating about this discovery so I wrote up a brief history of the events based largely on Horace Freeland Judson's book The Eighth Day of Creation. Every biochemistry and molecular biology student must read this book or they don't qualify to be an informed scientist. However, if you are not a biochemistry student then you might enjoy my short version.

Some practising scientists might also enjoy refreshing their memories so they have an accurate view of what happened in case their students ask questions.

The Story of DNA (Part 1)

Where Rosalind Franklin teaches Jim and Francis something about basic chemistry.

The Story of DNA (Part 2)

Where Jim and Francis discover the secret of life.

Here are some other posts that might interest you on DNA Day.



7 comments :



  1. CHARGAFF'S LEGACY

    We might note that, in addition to Chargaff's "first parity rule" that was so helpful to W&C in 1953, there was also his "GC rule" (that GC% was species specific). Furthermore, in later years, there appeared his "second parity rule" (that the base ratio parity of his first rule that applied to duplex DNA also applied to a close approximation to single stranded DNA). Finally, there was his cluster rule (that similar bases are significantly clustered in close proximity).

    The enormous contributions these made to today's understanding of nucleic acids parallel in importance that of W&C in 1953. For more please see our paper in Gene (2000): (https://www.queensu.ca/academia/forsdyke/bioinfo2.htm or https://wayback.archive-it.org/7641/20200423142636/http://post.queensu.ca/~forsdyke/bioinfo2.htm)

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    1. We might also note that according to Watson, Crick, and Donohue, Chargaff's ratios did not play a role in discovering the A/T and G/C base pairs. It was only after they discovered them that they found that they were consistent with some of various ratios that Chargaff had published.

      Crick recalls meeting with Chargaff the previous May (1952) and realizing that one-to-one ratios could mean complementary replication but that was something that had not occurred to Chargaff. (Chargaff was notorious for not speculating about the meaning of his data. He is accused of lacking imagination.) By the time they were building their model in February 1953 both Watson and Crick had forgotten the exact ratios and which nucleotides were involved. They only checked after they had convinced themselves that A/T and G/C base pairs were correct.

      Judson gets the story right and so do a number of other historians. Chargaff's account of that May 1952 meeting in his autobiography is a lie as judged by reputable historians who have investigated the issue. Chargaff claims that he told Watson and Crick about base complementarity and he claims that "... the double-stranded model of DNA came about as a consequence of that conversation." Judson was so upset about Chargaff's lies that he published an appendix to the 1996 edition of his book where he demonstrates conclusively that Chargaff had never mentioned complementarity and always thought of DNA as single-stranded.

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  2. We might also note that the possible significance of the Chargaff base ratios (first parity rule) was "in the air" in the early 1950s. For example, Olby's historical account (1974) features the Canadian, Gerry Wyatt, who was also studying base ratios. In particular, his 1952 conference paper in Experimental Cell Research (Wyatt 1952) and shortly thereafter in the Biochemical Journal (Wyatt and Cohen 1953), are particularly informative.

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    1. The parts of Chargaff's work that addressed differences of GC composition between species, and differences of it between different parts of the genome, are not relevant to inferring complementarity. Was Wyatt's work on that or on A:T and G:C ratios?

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    2. "The parts of Chargaff's work that addressed differences of GC composition between species, and differences of it between different parts of the genome, are not relevant to inferring complementarity."

      Not relevant? Differences in GC% have corresponding k-mer differences, which impede the recognition of complementarity that precedes recombination.

      "Was Wyatt's work on that or on A:T and G:C ratios?"

      Wyatt studied GC composition of different insect species. .

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    3. Donald Forsdyke says,

      "Not relevant? Differences in GC% have corresponding k-mer differences, which impede the recognition of complementarity that precedes recombination."

      In other words, not relevant.

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    4. In other words, not relevant.
      Larry sees clearly that the issue here is whether Wyatt's work influenced, or could have influenced, Watson and Crick's structure for DNA. Wyatt's work may have been relevant to many other issues, but it is not relevant to that discovery.

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