Download - The Discovery of DNA
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The Discovery of DNA
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GREGOR MENDEL1847Austrian monk who worked
with pea plants to study genetic inheritance
“Father of Genetics”Discovered ‘factors’ are
passed down from parent to offspring
*Did NOT know what DNA was or that it was the genetic material
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FREDERICK GRIFFITH1928Griffith's experiment involved mice and two types of
pneumonia, a virulent (S) and non-virulent kind (R).S = smooth coated bacteriaR = rough (no coating) bacteria
EXPERIMENT:Injected live S = mouse diedInjected live R = mouse livedInjected heat killed S = mouse livedInjected heat killed S + live R = mouse died
Cells inside dead mouse had S bacteria CONCLUSION * genetic material must have been transferred
from heat killed S bacteria to live R bacteria changed harmless R bacteria into deadly S bacteria =
“transformation principle”
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OSWALD AVERY1942Continued Griffith’s experiment
to see what the genetic material was that was being passed on.
Experiment - he destroyed the lipids, ribonucleic acids, carbohydrates, and proteins of the virulent pneumonia. Transformation still occurred.
Next he destroyed the deoxyribonucleic acid. Transformation did not occur. DNA must be inherited material
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NOW THAT WE KNOW DNA IS THE GENETIC MATERIAL… WHAT IS IT’S STRUCTURE?
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HERSHEY AND CHASE1952Proteins or DNA = genetic
material?Worked with
bacteriophage:Infects bacteria cells Composed of protein coat
with DNA insideUsed radioactive isotopes
to “tag” DNA and proteins Helped confirm DNA is
genetic material
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ERWIN CHARGAFF1940Snoticed a pattern in the
amounts of the four bases: adenine, guanine, cytosine, and thymine.
took samples of DNA of different cells and found that the amount of adenine = amount of thymine, and that the amount of guanine = equal the amount of cytosine. CHARGAFF’S RULE: A=T and G=C
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ROSALIND FRANKLIN1952Decided to try to make a
crystal of the DNA molecule to obtain an x-ray of it
They were successful x-ray crystallography image of DNA
The image appeared to contain rungs, like those on a ladder between to strands that are side by side.
It showed DNA had a (X) helix shape.
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WATSON AND CRICK1953Co-discoverers of the
structure of DNA Used x-ray diffraction images
from Rosalind Franklin and proposed the double helix structure of DNA
Built the first 3D model of DNA