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slade19

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About slade19

  • Rank
    Veteran Member

Personality

  • MBTI
    INTJ
  • Astrology Sign
    How rational.

Converted

  • Biography
    not much
  • Location
    France, but been in Egypt most of my life
  • Interests
    cellular biology, system biology, microbiology, neurosciences...
  • Gender
    Male

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  1. Some additional information: More and more people now know about Rosalind Franklin and her work. What they are usually told is that she made the picture of the DNA crystal that confirmed W&C's model, but what actually happened is she figured out that the way we extracted DNA before was putting it in a mix of the A and B form while crystallography of viruses gave different results because it was moist, so she prepared a way to isolate and analyze the B form specifically since it's the main one in biological systems and then took the right pure pictures that unlocked everything (how it organized into crystals=how the strands looped around eachothers, that the phosphates are on the outside, and a few other crucial development). She was extremely close to cracking the structure but she was a perfectionist, and tried to analyze everything mathematically, while W&C were amateur chemists, extracted the main insights (believed it was a helix without a doubt) and tinkered with a cardboard model until it fit. She died before the Nobel prize was awarded to W, C, and her collaborator, Wilkins.
  2. This week, I am putting forward 5 pages by Watson and Crick detailing the first accurate structure of DNA, and a discussion of the biological significance their model had in genetic inheritance. https://tetrad.ucsf.edu/sites/tetrad.ucsf.edu/files/media/Watson and Crick- Molecular Structure of Nucleic Acids (1953) Nature 171- 737-738..pdf https://tetrad.ucsf.edu/sites/tetrad.ucsf.edu/files/media/Watson and Crick- Genetical Implications of the Structure of Deoxyribonucleic Acid (1953) Nature 171- 964-967..pdf There are other unrelated articles on the side because that's a scan of the 1953 Nature issue. Some observations on the significance of their work: most of the groundwork had already been done, it had been close to a hundred years since Miescher first isolated DNA, we already knew the chemical composition (nucleotides, made of a sugar, a phosphate, and a purine or pyrimidine), and we already knew how they joined together (so we knew they formed strands=polynucleotides thanks to Levene) and we had a series of observations (Chargaff's rules) detailing some constants like ratios of A/T and G/C very close to unity. We also, as you may read, already knew it was forming a helix, but not the details. We had also figured out the genetic nature of DNA (that it was the support to heredity) just 10 years prior. You should know that for a very long time, DNA was considered boring and having a mere structural role in the cell. That was due to the high amount of fast-moving research on proteins, their catalytic abilities, and their chemical versatility (so we thought they held the genetic information since they were so versatile and complex) while DNA was an extremely monotonous compound, so difficult to work on precisely, and held to contain little to no information (how could such a dull molecule hold the key to such complexity). It required different techniques of investigation and information theory to figure out that may not be the case. We may go back to the 1944 paper that proved DNA to be the support of heredity later. So what Watson and Crick put together, was just a synthesis of all the previous work and getting their hands on the cleanest X-ray diffraction pattern of DNA by Rosalind Franklin and Wilkins to figure out it was a double-helix and not a triple helix like most models at the time. They also used a recent development in model building by Pauling (they were even afraid Pauling might get to their conclusions before them) that allowed them to predict the structure from angles and distances between atoms. And that's how they came to their final prediction detailing the structure of B-DNA (the major form of DNA, in addition there is A-DNA, Z-DNA, and B'-DNA). They also gave an account of how information is then encoded and replicated, and how mutations may arise (by incorporating tautomeric forms of bases that can bind to the wrong base, therefor corrupting the information) which, in a large sense, is true. They made a mistake by forgetting about a hydrogen bond between G and C which is physiologically important in gene regulation using the GC box, and correctly figured out that methylated cytosine is equivalent to regular cytosine information wise (genetically that is, epigenetically, it's another story). Finally, We now know that triplexes and quadruplexes of DNA can exist in cells, and can have some function, so three strand models were not false in essence, just not molecularly accurate (as far as I know). ...... added to this post 33 minutes later: Oh, almost forgot, they say ribonucletide (RNA) can't form a double helix, but that is only true of the B-form, RNA can form a double helix of the A-form.
  3. A couillard (a terbuchet with one stem and two counterweights) which in french refers to testicles. Some sieges were literally a dick sizing contest.
  4. If anyone is willing to read the book for March, it might be a good idea to vote quickly so that we may choose the book, and those who need to get it can get it. We will have to know in a week (21th). Since there is no obligation to read it, you don't have to be committed to reading all of it to vote.
  5. Ok I finished what I was doing with it, so here are the results for anyone to prove if he wants, in addition to what I put in spoilers: You can make whatever path you want on a grid with even surface, and you can always come back to the beginning. It's very easy to make a general strategy to fill them however you want in that case. You can always make a loop on an odd grid if you take out one square (not any square will do). You can, again, make a general strategy to fill them (in fact, with that general strategy, you can make two independent loops in one go). I explored the case of making more holes in the grid but I became bored after figuring that the position of the first may or may not allow you to punch other holes afterwards and exploring the diagonal pattern it made. Have fun.
  6. Nice. Though in a realistic case, we should take into account that other ions in the water may impact the results.
  7. The standard model, and gauge theories in general.
  8. So there are no dicks in a way.
  9. I am one over the limit to being a dick, how does it work?
  10. That's interesting, how do you even do such calculations with what he gave us?
  11. Which is?