DNA Discovery

Based on other people's data and Chargaff's rules made a model:

• Two polynucleotide chains in a double helix
• 2 strands are antiparralell but forms a right hand helix
• Bases in the core and phosphate group on outside - minimises repulsions in phosphate
• Bases hydrogen bonded 
• Complementary A-T and C-G base pairing
• 2 hydrogen bonds between A-T
• 3 hydrogen bonds between C-G

• Used acid to break down and purify DNA
• Seperated it with chromatography 
• Determined percentage of each bases in DNA pieces with UV absorbance
• % A = % T and % C = % G except for in bacteriophages (single strand DNA)
• Must be complementary base pairing here

• X-ray diffraction - where DNA is bombarded with x-rays that bounce off atoms and diffract
• The X - laws of diffaction say x-rays moving through helix diffract perpendicular to helix = HELICAL STRUCTURE
• The diamonds - shows helix repeats above and below X shape = HELIX CONTINUATION
• The smears - organised along layer lines and are parallel to helix's central axis. Placement helps determine distance between bases and helical twist = BASES
• Missing smears - when two strands cross diffraction cancelled out = DOUBLE HELIX WITH MAJOR AND MINOR GROOVES

• X-ray diffraction - where DNA is bombarded with x-rays that bounce off atoms and diffract
• The X - laws of diffaction say x-rays moving through helix diffract perpendicular to helix = HELICAL STRUCTURE
• The diamonds - shows helix repeats above and below X shape = HELIX CONTINUATION
• The smears - organised along layer lines and are parallel to helix's central axis. Placement helps determine distance between bases and helical twist = BASES
• Missing smears - when two strands cross diffraction cancelled out = DOUBLE HELIX WITH MAJOR AND MINOR GROOVES