A Short History of DNA Technology
The History Of DNA
Miescher
1869 removed substance from pus off of old bandages had acid properties, came from nucleus called it “nucleic acid”
Griffith
Frederick Griffith Bacterial Strain Injection Results Living S cells Living R cells Heat killed S cells Heat killed S cells mixed with living R cells Living S cells in blood sample from dead mouse capsule Transformation of Streptococcus pneumoniae “Rough” colonies“Smooth” colonies
Griffith smooth and rough bacteria dead smooth could “transform” live rough cells “accidental” discovery
Avery, MacLeod, McCarty
Avery, MacLeod & McCarty Purified DNA as transforming factor Oswald Avery Work not well-received Protein more complex & better able to store information Colin MacLeodMaclyn McCarty
Avery, McLeod, McCarty separated cellular molecules tested each for “transforming” abilities carbohydrates, lipids, proteins were ineffective only nucleic acids “transformed” the cells
Hershey and Chase
Hershey & Chase Viral DNA (not protein) programs cells Martha Chase & Alfred Hershey Bacteriophages
Hershey & Chase T2 Phage Bacterium Radioactive protein ( 35 S) Radioactive phage infects bacterial cells Blender separates protein coats from bacterial surface Centrifuge and measure radioactivity in pellet and supernatant Radioactivity in supernatant, but not pellet
Hershey & Chase Radioactive DNA ( 32 P) Radioactivity in pellet, but not supernatant Therefore, it is the viral DNA, and not protein, that programs cells to make copies of the virus.
Hershey and Chase chose “organism” composed only of protein and nucleic acid infected cells with viruses tagged with radioisotopes tagged proteins were not transferred tagged nucleic acids were transferred
Chargaff
Erwin Chargoff DNA bases follow certain “rules” Base composition is species specific A = T, C = G for all species
Chargaff analyzed percentage of each base in DNA samples found adenine % = thymine% found cytosine % = guanine %
Wilkins and Franklin
Franklin & Wilkins Elucidation of the helical nature of DNA X-ray source Crystallized DNA Rosalind Franklin Maurice Wilkins Photographic film
Wilkins and Franklin X-ray crystallography on DNA to establish shape, dimensions of molecule
Watson and Crick 1953
Watson & Crick 1865 Description of the 3-D structure of DNA Francis Crick & James Watson
Watson and Crick did no original research/ relied on work of others analyzed X-ray crystallography, biochemistry hypothesized double-stranded helix in 1953
Watson & Crick 1865 What they deduced from: Franklin’s X-ray data Double helix Uniform width of 2 nm Bases stacked 0.34 nm apart Chargoff’s “rules” Adenine pairs with thymine Cytosine pairs with guanine
Watson & Crick 1865 What they came up with on their own: Bases face inward, phosphates and sugars outward Hydrogen bonding Hinted at semi-conservative model for replication
Review of Gel Electrophoresis and DNA Fingerprinting Write questions and answers in your notes 1)What section of the DNA molecule is used for DNA fingerprinting? 2)How is the DNA polymer cut? 3) What factors determine how fast a segment of DNA migrates in the gel? 4) What is the purpose of the marker?