Watson and Crick: Discovery of DNA structureand DNA PropertiesBrooke Noble and Serena Patel
Who are Watson and Crick?James Watson and FrancisCrick collaborated touncover DNA structureJames 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
Previous research that contributed to Watsonand Crick’s Discovery Friedrich Miescher- (1869) Swiss PhysiologicalChemistDiscovered the Nucleic Acid
Phoebus Levene- (1905) Russian BiochemistDiscovered the order of aNucleotide: Phosphate-sugar-basePrevious research that contributed to Watson andCrick’s Discovery
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
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?
Base CompositionAnswer: 17% A, 23% T, 40%C, and 20% G
Previous research that contributed to Watsonand Crick’s Discovery Rosalind Franklin- Biophysicist and X-rayCrystallographerX-Ray diffraction images of DNA structure
Watson and Crick in 1953 uncovered the three dimensional,double helical structure of DNAWatson and Crick’s Discovery: Helical DNAStructure
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
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 axisEach chain made up of phospodiesterbondsPhosphate groups are on outside ofhelix and bases are insideTwo chains held together by purine andpyrimidine pairsChains run in opposite directions andare complementary
Building Blocks of Deoxyribonucleic AcidsNucleotides are madeup of 3 maincomponents: Five-carbon sugar Phosphate groups Nitrogen containingbase (adenine,thymine, cytosine, orguanine)
What Holds Bases Together?Two hydrogenbonds formbetween A-TpairsThreehydrogenbonds formbetween C-Gpairs
Which DNA Helix will require more energy toseparate?A. 5’-ATGATCATCATTA-3’3’-TACTAGTAGTAAT-5’ORB. 5’-CCGAGCTGCCAT-3’3’-GGCTCGACGGTA-5’http://www.basic.northwestern.edu/biotools/OligoCalc.html
Which DNA Helix will require more energy toseparate?A. 5’-ATGATCATCATTA-3’3’-TACTAGTAGTAAT-5’ORB. 5’-CCGAGCTGCCAT-3’3’-GGCTCGACGGTA-5’
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
If we know the base sequence of this strand,what is the sequence of the other strand?DNA strand: 5’-ATCGTACCATAGC-3’
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
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
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
What’s next?? DNA Replication DNARNA RNAProtein
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