DNA History and Structure Deoxyribonucleic Acid aka DNA

DNA History and Structure

Deoxyribonucleic Acid aka. DNA The genetic material of a cell Located within the Nucleus Bundled to form Chromosomes Contains the complete instructions for making all the proteins for an organism

History of DNA Friedrich Meischer (1869) Extracted a phosphate rich molecule from the nucleus of cells This molecule was DNA

Frederick Griffith (1928) Experiment that allowed others to determine that DNA was the molecule of inheritance Mice and two types of pneumonia Virulent (deadly) Non-virulent (not deadly)

Oswald Avery (1944) Continued with Griffith’s experiment Showed that transformation was done by the virulent strains DNA (not proteins) Concluded DNA carries the genetic code

Hershey – Chase Experiment Alfred Hershey and Martha Chase (1952) Scientists believed protein was the genetic material Used viruses that infect bacteria (T 2 bacteriophage) Protein and DNA Only the DNA entered the bacteria to form new viruses Concluded that DNA is the genetic material

Erwin Chargaff Noticed a pattern in the amounts of four bases Adenine = Thymine Cytosine = Guanine Chargaff’s Rule A is equal to T C is equal to G

Source Phi. X-174 Maize Octopus Chicken Rat Human mol % of bases Ratios %GC A G C T A/T G/C 24. 0 23. 3 21. 5 31. 2 0. 77 ¦ 1. 08 44. 8 26. 8 22. 8 17. 0 * 27. 2 0. 99 0. 98 46. 1 33. 2 17. 6 31. 6 1. 05 1. 00 35. 2 28. 0 22. 0 21. 6 28. 4 0. 99 1. 02 43. 7 28. 6 21. 4 20. 5 28. 4 1. 01 1. 00 42. 9 29. 3 20. 7 20. 0 30. 0 0. 98 1. 04 40. 7

Rosalind Franklin and Maurice Wilkins Decided to try to crystallize DNA X-rayed the crystallized DNA Pattern appeared to contain rungs between strands that were side by side X shape showed DNA had a Helix shape

James Watson and Francis Crick (1953) Trying to put together a model of DNA Saw Franklin’s x-ray and made an accurate model that has not changed much Double helix with rungs connecting the two strands Each side is a compliment to the other

DNA’s Structure Normally exists in the shape of a double helix Twisted ladder or twisted zipper Chain is made up of Nucleotides Sugar-Phosphate Backbone (sides of the ladder) Deoxyribose + phosphate group Nitrogen bases (rungs of ladder) Attach to the sugar molecules (deoxyribose) Hydrogen Bonds hold these bases together

Nitrogen Bases Adenine (A) = Purine - double ring Guanine (G) = Purine - double ring Cytosine (C) = Pyrimidine – single ring Thymine (T) = Pyrimidine – single ring

Bases form Complimentary Pairs Adenine pairs with Thymine Cytosine pairs with Guanine Chargaff was first to notice this Sequence of these pairs forms the unique genetic information of an organism