DNA

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  • * The proteins in DNA are involved in turning genes on and off, and in the strength of expression… so not completely true.
  • Knew 15 languages fluentlyOriginally from Austria, became American citizen in 1940, fleeing nazi regimes
  • * Pieces are left off! That’s where telomeres come in – TTAGGG – Prokaryotes no problem, circular DNA.
  • Each new strand is ½ old and ½ newWhy does this occur when the DNA is in the chromatin form, and not chromosome?
  • Transposons - BarbaraMcClintock, Cold Spring Harbor Lab, 1950’s. Received Nobel Prize 1983.
  • DNA

    1. 1. Structure of DNA<br /><ul><li>Deoxyribonucleic Acid is a type of nucleic acid.
    2. 2. Nucleic acids are polymers of nucleotides.
    3. 3. DNA was discovered in 1868, but the significance of what it was used for was unknown.
    4. 4. Even when chromosomes were discovered, it was controversial whether it was the DNA or the proteins that transmitted hereditary traits.</li></li></ul><li>Oswald Avery<br />1877-1955<br />In 1944, Avery discovered<br />that it was the DNA, and<br />not the proteins in <br />chromosomes that were<br />involved in transmitting<br />traits.<br />*is this completely true???<br />
    5. 5. Nucleotides: <br />
    6. 6. There are four nitrogen bases:<br />Pyrimidineshave one ring. Purineshave two rings<br />
    7. 7. Erwin Chargaff<br />(1905-2002)<br />Studied the chemistry of<br />DNA structure. Discovered:<br />% Adenine = % Thymine<br />% Guanine = % Cytosine<br />(1:1 purines:pyrimidines)<br />At the time, the structure<br />of DNA was unknown, so the significance of this<br />discovery was minimal at the time.<br />
    8. 8. Maurice Wilkens& Rosalind Franklin<br />In the early 1950’s, Wilkens hired<br />Franklin to work in his lab at<br />King’s College in London. Her<br />work was to do X-ray <br />crystallography on DNA in order<br />to figure out it’s structure. <br />She made many images, the<br />most famous being “Photo 51”<br />
    9. 9. Francis Crick & James Watson<br />Were both working at<br />Cambridge University in <br />1951. Using information from Avery, Chargaff, and <br />Franklin, they eventually built a model of DNA that<br />combined the ideas of all the other scientists working on the structure of DNA.<br />Crick, Watson, and Wilkens shared the Nobel Prize in Medicine in 1962.<br />
    10. 10. Their model is still on display in London<br />
    11. 11. Here’s what the structure is like:<br />Sugar – Phosphate “backbone”<br />Nitrogen bases pairing in the middle<br />Entire molecule is twisted into a double helix<br />
    12. 12. The nitrogen bases follow “Chargaff’s Rules”<br />Adenine bonds to Thymine<br />Cytosine bonds to Guanine<br />Because of this, if we know the sequence of bases on one strand of DNA, we can predict the sequence of bases on the complementary strand.<br /> A C G G C T A C T A C<br /> T G C C G A T G A T G<br />
    13. 13. Now…. about the strands: They are running “anti-parallel”…Each deoxyribose looks like this:<br />The carbons are numbered 1-5<br />The 1’ carbon bonds to a Nitrogen base<br />The 5’ and 3’ end attach to phosphate groups<br />
    14. 14. eukaryotic DNA has “ends”<br />The 5’ end will attach to a<br />phosphate group and then end.<br />The 3’ end will attach to an<br />-OH group (no phosphate) and then <br />end.<br />On one end there will be a 3’ and a 5’ end<br />The other end will be a 5’ and a 3’ end<br />
    15. 15. A picture to make it make sense:<br />These arecalled <br />“Anti-parallel”<br />strands<br />
    16. 16. DNA REPLICATION<br />Begins at “origins of replication” – numerous places all at the same time.<br />Helicase (an enzyme) untwists the DNA at each origin of replication.<br />(there’s a lot of other steps in here I’m leaving out for the sake of time and complexity…)<br />“free” nitrogen bases form new hydrogen bonds<br />DNA polymerase (an enzyme) will finish new nucleotidesbut only to the 3’ end of both strands.<br />Since nucleotides are only added to the 3’ end, what happens at the 5’ end???<br />
    17. 17.
    18. 18. End result of replication:<br />How do we know both new strands are identical?<br />
    19. 19. Genes<br />A gene is a segment of DNA that codes for the production of a polypeptide.<br />Genes are not always continuous (introns and exons)<br />Genes may overlap<br />You may have multiple copies (multigene families)<br />Some genes are silent, some are turned on or off<br />Some genes can “jump” from one chromosome to another (transposons)<br />Some genes cause apoptosis (self-destruction) of cells that are damaged or mutated<br />

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