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LECTURE 3.2

LECTURE 3.2. LECTURE OUTLINE. The Ziggurats Carbon Rosalind Franklin. CATAL HUYUK. THE ZIGGURAT AT UR. THE ZIGGURAT AT UR. OCTANE AND DECANE. A DIGRESSION ON THE CRYSTAL STRUCTURE OF GRAPHITE, AND THE STRUCTURE OF CHARCOAL.

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LECTURE 3.2

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  1. LECTURE 3.2

  2. LECTURE OUTLINE • The Ziggurats • Carbon • Rosalind Franklin

  3. CATAL HUYUK

  4. THE ZIGGURAT AT UR

  5. THE ZIGGURAT AT UR

  6. OCTANE AND DECANE

  7. A DIGRESSION ON THE CRYSTAL STRUCTURE OF GRAPHITE, AND THE STRUCTURE OF CHARCOAL • In graphite, each carbon atom strongly bonds to three other carbon atoms, to create six-membered rings

  8. THE CRYSTAL STRUCTURE OF GRAPHITE • The six-membered rings form parallel sheets

  9. THE CRYSTAL STRUCTURE OF GRAPHITE • The three-dimensional structure of graphite consists of parallel sheets of carbon atoms • Within the sheets, the carbon atoms are strongly bonded to each other. • Between the sheets, the bonding is weak. • The sheets of carbon easily slide over each other…..graphite is a good lubricant!

  10. THE STRUCTURE OF DIAMOND

  11. THE STRUCTURE OF CHARCOAL • The carbon atoms are found in a mixture of 5-, 6-, and 7-membered rings • The sheet of carbon atoms is no longer flat or planar: it is convoluted!

  12. THE STRUCTURE OF CHARCOAL • The structure of charcoal as a mixture of 5-, and 6- membered rings

  13. THE “BUCKYBALL” • When “mistakes” are made at regular intervals, some beautiful structures may result! • A regular distribution of 5-, and 6- membered rings results in a soccer ball: also called a triacontahedron: aka a “buckyball”/”fullerene” • The beast is a C60 “molecule”, with carbon atoms at the vertices of the pentagons and hexagons.

  14. THE DODECAHEDRON • Build a material with only pentagons? • The “dodecahedron” results: it is one of the five “Platonic Solids”… all faces are regular polygons, and are identical; all vertices are identical

  15. ROSALIND FRANKLIN: THE DARK LADY OF DNA • X-Ray Crystallography • ~1942-1950. The structure of coals and carbons. • 1951-1953. The structure of DNA • 1951-1958. The structure of viruses

  16. ROSALIND FRANKLIN: THE DARK LADY OF DNA • “Our dark lady is leaving us next week” • Letter from Maurice Wilkins to Francis Crick, 7th March, 1953

  17. “THE DOUBLE HELIX” • A best-selling account of the “race” to solve the structure of DNA • A less than flattering account of Rosalind Franklin’s contribution to the “race”. • Also shows the author in a less than flattering light!!

  18. “THE DARK LADY OF DNA” • A “balanced view” of Rosalind Franklin’s contribution to the “race”! • Rosalind Franklin was a superb experimentalist. • Did death cheat her of the “Nobel Prize”?

  19. ROSALIND FRANKLIN (1920-1958) • 1938. “Goes up” to Newnham College, University of Cambridge • 1941. Obtains bachelor’s degree in Chemistry • 1942-1946 Works for the British Coal Utilization Research Association, in London • 1945. Obtains a Ph.D in Physical Chemistry from Cambridge • 1947-1951. Works at the “Laboratorie Central des Services Chemique de L’Etat” in Paris

  20. ROSALIND FRANKLIN (1920-1958) • 1951-1953 King’s College, University of London • 1953-1958 Birkbeck College, University of London

  21. PUNTING ON THE RIVER CAM • Although the photograph was taken in 1983, the scene could well represent the 1940s when Rosalind was in Cambridge

  22. THE EAGLE IN CAMBRIDGE • The “Eagle” is the most famous pub in Cambridge • Crick and Watson used to lunch there most days • The ceiling of the bar still displays the signatures of hundreds of American airmen and women who visited the pub from the neighboring air-force bases, during World War II

  23. “GRAPHITIZING CARBON”, ACCORDING TO FRANKLIN • Classic papers in “Proc. Roy. Soc. Lond. • Rosalind Franklin’s schematic drawing of a “graphitizing” carbon. • The “structure consists of microcrystals of graphite-like material, all of which are of a similar orientation. • This material will easily “crystallize”

  24. “NON-GRAPHITIZING CARBON”, ACCORDING TO FRANKLIN • Rosalind Franklin’s schematic drawing of a “non-graphitizing” carbon. • The “structure consists of microcrystals of graphite-like material, but in many, very different orientations • This material will be very difficult to crystallize.

  25. X-RAY DIFFRACTIOON PATTERN OF THE B-FORM OF DNA • The most famous x-ray diffraction pattern of all time! From the pattern, Franklin, Watson and Crick were able to determine: • DNA is crystalline • The crystal structure of DNA • The presence of two interpenetrating helices: one “up” and one “down” • The “pitch” of the helices

  26. THE DOUBLE HELIX OF CRICK AND WATSON • A schematic drawing of “The Double Helix” (from Watson’s book) • Note that DNA is a polymer: each helix is a macromolecule, and the two macromolecules are linked by “hydrogen bonds”…… see later!

  27. THE DNA OF CRICK AND WATSON: REPLICATION • “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material” • Quoted from Crick and Watson’s paper in Nature, April 1953. • Image is from Watson’s book.

  28. THE TOBACCO MOSAIC VIRUS ACCORDING TO FRANKLIN • A drawing of the structure of the Tobacco Mosaic Virus (TMV). • For the last five years of her life, Rosalind Franklin worked on the structures of complex organic macromolecules, at Birkbeck College in London

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