The History of DNA Structure Discovery
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Transcript of The History of DNA Structure Discovery
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The History of DNA Structure Discovery
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1869 – Johann MiescherStudied the nuclei of white
blood cells Isolated the material using
HCl(aq) and digestive proteins
Named the substance nuclein
Found the material was rich in nitrogen and phosphorus
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1919 – Pheobus LeveneDiscovered that DNA
was made up of chains of nucleotides
ACID
RIBOSE
NITROGENRICH
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1920 – DNA vs Protein
thought that 4 nucleotides were connected in the same repeated pattern
protein have 20 amino acids which could be combined in many combinations
RNA DNA
sugar
location
bases
RNA DNA
sugar ribose deoxyribose (one less oxygen)
location
bases
RNA DNA
sugar ribose deoxyribose (one less oxygen)
location mainly outside nucleus mainly inside nucleus
bases
RNA DNA
sugar ribose deoxyribose (one less oxygen)
location mainly outside nucleus mainly inside nucleus
bases AGCU AGCT
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Levene’s Nucleotide Pattern
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1928 – Frederick Griffithstudied two strains of
pneumococcus bacteria
rough strain = nonvirulentinjection into mouse did not
result in death
smooth strain = virulentinjection caused mouse to diehttp://
www.youtube.com/watch?v=vQOdDGM5vSg
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Griffith’s Experiment
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Griffith’s Conclusionssome “factor” from the dead, virulent smooth strain
“transformed” the living, non-virulent rough strain
non-virulent rough strain picked up DNA to become virulent
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1930 – Joachim Hammerling
nucleus at bottom of stalk
Acetabularia – type of alga
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Hammerling’s Experiment
Hereditary information is stored in the nucleus.
http://www.youtube.com/watch?v=tl5KkUnH6y0
no regrowth
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1944 – Avery, McCarty & MacLeod
continued Griffith’s work with pneumococcus
Condition Tested Resultpneumococcus & proteasepneumococcus & DNAse
Condition Tested Resultpneumococcus & protease
non-virulent bacteria virulent bacteria
pneumococcus & DNAse non-virulent bacteria remained non-virulent
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1940s – Joshua Lederbergdemonstrated
bacterial conjugationbacteria can exchange
DNA
bacteria have no nucleus or chromosomes
http://www.youtube.com/watch?v=7stZk6TesKk
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1940s – Edwin Chargafffor all organisms
A = T and G = C
Chargaff’s Rule
organisms with more Gs and Cs tend to be more complex
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1952 – Hershey & Chaseconducted
experiments to definitively show that DNA is the hereditary material
bacteriophage used to infect bacteriabacterial virushttp://
www.youtube.com/watch?v=3QJ4CjFsflA
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1950s – Maurice Wilkins & Rosalind Franklin
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X-ray Crystallographyphysics approach to examining biological molecules https://www.youtube.com/watch?v=0tmNf6ec2kU Start at 14:35
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Rosalind Franklin’s X-raysThe photo indicated:1. Backbone of alternating phosphate and sugars
2. Backbone is a helical structure
3. Double helix structure (molecule is a uniform helix)
4. Nitrogenous bases are in the middle of the molecule
5. Bases are at right angles to the backbone
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Base Pairing knew that each base could pair with itself
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1953 – James Watson & Francis Crickinspired by alpha-helix model of proteins
determined how A + T and G + C bonded together
width of purine + pyrimidine bonds fit perfectly between the sugar-phosphate backbone
the double helix model offered an easy method for replication