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Watsonand crick 4


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Watsonand crick 4

  1. 1. Watson and Crick: Discovery of DNA structureand DNA PropertiesBrooke Noble and Serena Patel
  2. 2. Who are Watson and Crick?James Watson and FrancisCrick collaborated touncover DNA structureJames Watson-Bornin 1928, Earned a PhDin Zoology, thenpursued his researchin molecular biology atthe CavendishLaboratory inCambridge.Francis Crick-(1916-2004) Earned adegree in Physics andlater a PhD inmolecular biology
  3. 3. Previous research that contributed to Watsonand Crick’s Discovery Friedrich Miescher- (1869) Swiss PhysiologicalChemistDiscovered the Nucleic Acid
  4. 4.  Phoebus Levene- (1905) Russian BiochemistDiscovered the order of aNucleotide: Phosphate-sugar-basePrevious research that contributed to Watson andCrick’s Discovery
  5. 5. Previous research that contributed to Watsonand Crick’s discovery Erwin Chargaff- (1950) Austrian BiochemistDiscovered the Total amountof Purines and Total Amountof Pyrimidines are equalPurines: Adenine and GuaninePyrimidines: Thymine andCytosine
  6. 6. Base CompositionIf one DNA strand is made up of 23%A, 17%T, 40%G,and 20%C, what is the other strand’s basecomposition?
  7. 7. Base CompositionAnswer: 17% A, 23% T, 40%C, and 20% G
  8. 8. Previous research that contributed to Watsonand Crick’s Discovery Rosalind Franklin- Biophysicist and X-rayCrystallographerX-Ray diffraction images of DNA structure
  9. 9. Watson and Crick in 1953 uncovered the three dimensional,double helical structure of DNAWatson and Crick’s Discovery: Helical DNAStructure
  10. 10. X-Ray Crystallography X-Ray Crystallography is an experimental techniquethat exploits the fact that X-rays are diffracted fromcrystals A 3-D structure can be determined by examining thediffraction patterns created by X-rays beamedthrough a crystal DNA= two strands wound togetherThe diffracted (X)pattern that RosalindFranklin found in herresearch
  11. 11. Overview of Major FindingsWatson and Crick’s predicted structure. The twistedribbons are the sugar-phosphate backbone. Theyare held by the horizontal bars which are the bases.Two helical chains coiled around axisEach chain made up of phospodiesterbondsPhosphate groups are on outside ofhelix and bases are insideTwo chains held together by purine andpyrimidine pairsChains run in opposite directions andare complementary
  12. 12. Building Blocks of Deoxyribonucleic AcidsNucleotides are madeup of 3 maincomponents: Five-carbon sugar Phosphate groups Nitrogen containingbase (adenine,thymine, cytosine, orguanine)
  13. 13. What Holds Bases Together?Two hydrogenbonds formbetween A-TpairsThreehydrogenbonds formbetween C-Gpairs
  14. 14. Which DNA Helix will require more energy toseparate?A. 5’-ATGATCATCATTA-3’3’-TACTAGTAGTAAT-5’ORB. 5’-CCGAGCTGCCAT-3’3’-GGCTCGACGGTA-5’
  15. 15. Which DNA Helix will require more energy toseparate?A. 5’-ATGATCATCATTA-3’3’-TACTAGTAGTAAT-5’ORB. 5’-CCGAGCTGCCAT-3’3’-GGCTCGACGGTA-5’
  16. 16. Complementary Base Pairing Purines are made up of tworings (adenine and guanine) Pyrimidines consist of onering (thymine and cytosine) Two chains held together bypairs of purines andpyrimidines
  17. 17. If we know the base sequence of this strand,what is the sequence of the other strand?DNA strand: 5’-ATCGTACCATAGC-3’
  18. 18. AnswerDNA strand: 5’-ATCGTACCATAGC-3’Complementary strand: 3’-TAGCATGGTATCG-5’
  19. 19. Alternating Sugar Phosphate Backbone Remember thephosphates arenegatively charged… Hydrophilic, surroundedby water Can the sugar-phosphatebackbone be on theinside while the bases areon the outside? NO! The negativecharges will repel eachother
  20. 20. Antiparallel Strands and Polarity Nitrogenous base pairing requires two DNA strands torun in opposite directions The phosphate group is the 5’ end and the –OH group isthe 3’ end
  21. 21. What is the significance of complementary DNAbase pairing and polarity? There must be a way toreplicate (copy) DNA If strands can be pulled apart,then each original strand maybe copied knowing whichbases go together and thedirection of the strand Enzymes yet to bediscovered… DNA polymerase DNA topoisomerase DNA helicase
  22. 22. What’s next?? DNA Replication DNARNA RNAProtein