DNA: the story behind the molecule SBI4U Biology

We Live in an age of DNA How we got here is another story… DNA’s history can be divided into three time periods: The Age of Early Discovery The Protein vs DNA period The Era of DNA Advancement

The Age of Early Discovery 1865 Gregor Mendel Laws of Genetics Existence of discrete ‘factors’ Knew the ‘how’ but not the ‘what’.

The Age of Early Discovery Mendel’s Experiments

The Age of Early Discovery 1869 Friedrich Miescher Isolates Nuclein Impure protein + DNA mixture Knew a ‘what’ but not a ‘why’.

The Age of Early Discovery 1902 Walter Sutton Chromosomes Name based on staining properties University of Kansas Basketball Star, 1899!

The Age of Early Discovery 1910 Thomas Morgan Genes From Drosophila (Fruit fly) salivary glands Proposed coding function of chromosomes

The Age of Early Discovery 1927 Hermann J. Muller X Rays induce mutations If you change the structure of chromosomes, you change the traits of the organism. Heredity has a physical basis!

Protein vs. DNA? 1928 Frederick Griffiths Bacterial Transformation S. pneumoniae strains: S = virulent, R = nonvirulent Mice survive infection with R, but not S Heat-treated (dead) S + Live R = Mice die; autopsy reveals live S Something got passed on Protein? DNA? Not sure!

Protein vs. DNA? Griffiths Experiment

Protein vs. DNA? 1942 George Beadle & Edward Tatum One Gene, One Enzyme Hypothesis Proposed genes = ‘recipes’ for specific proteins. Disable a gene for Arginine metabolism, & cells can’t survive. DNA 1, Protein 0!

Protein vs. DNA? Beadle & Tatum Experiment

Protein vs. DNA? 1944 Avery, MacLeod, Owen & McCarthy Traits change if you destroy DNA enzymatically Repeated Griffiths experiment, + enzyme. Dead S + one of various enzymes: Protease, Carbohydrase, RNAase, DNAase Take treated S cells  add to live R cells Infect mice & wait. Only with the DNAase do you get S cells disabled

Protein vs. DNA? Avery & MacLeod Experiment

Protein vs. DNA? 1950 Edwin Chargaff DNA has predictable ratios of A, T, G, & C In any sample of DNA: [A] = [T] & [G] = [C] Within a species, [A/T] and [G/C] are within a narrow range. Alluded to possibility of pairing in the DNA molecule? Two strands?

Protein vs. DNA? Chargaff’s Ratios Organism %A %G %C %T A/T G/C Maize 26.8 22.8 23.2 27.2 0.99 0.98 Octopus 33.2 17.6 31.6 1.05 1.00 Chicken 28.0 22.0 21.6 28.4 1.02 Rat 28.6 21.4 20.5 1.01 Human 29.3 20.7 20.0 30.0 1.04 Grasshopper Wheat 27.3 22.7 27.1 Yeast 31.3 18.7 17.1 32.9 E. Coli 24.7 26.0 25.7 23.6

Protein vs. DNA? 1952 Alfred Hershey & Martha Chase Blender Experiment Bacteriophage passed on DNA to next generation, not protein Radioactive isotopes: 32P in DNA, 35S in Protein 2nd generation only had 32P present. Proves DNA as genetic material!

Protein vs. DNA? Hershey & Chase Experiment

DNA Elucidated: 1953 James Watson, Francis Crick, Rosalind Franklin DNA Structure

Nature, April 25, 1953: ‘We are much indebted to Dr. Jerry Donohue for constant advice…We have also been stimulated by a knowledge of the general nature of unpublished experimental results and ideas of Dr. M.H.F. Wilkins, Dr. R. E. Franklin, and their co-workers at King’s College, London’

Era of DNA advancement 1957 Francis Crick & George Gamov Central Dogma DNA  RNA  Protein

Era of DNA advancement 1966 Marshall Nirenberg & Severo Ochoa DNA Coding

Era of DNA advancement 1972 Paul Berg Recombinant DNA Used restriction enzymes to splice together viral & bacterial DNA samples in vitro 1973 Stanley Cohen & Herbert Boyer Recombinant Organism viral & bacterial DNA combined in vivo Gene Splicing!

Era of DNA advancement 1989 Lap-Chee Tsui Cystic Fibrosis Gene Identified Locus on Chromosome 7 Hospital for Sick Children, Toronto!

Era of DNA advancement 1993 Kary B. Mullis PCR – Polymerase Chain Reaction Used DNA Polymerase Enzyme to copy DNA & magnify limited samples. Surfin’ scientist!

Era of DNA advancement 1990 – 2003: The Human Genome Project International effort to sequence & catalogue known human genes Database created to speed research Identified 20 – 25K genes