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Miescher
The molecule of life was isolated for the first time in 1869 by the Swiss biologist and physician Johan Friedrich Miesche. -
Discovery of DNA Components
Determined the components of DNA:
adenine, guanine, thymine, cytosine, deoxyribose phosphate
defined phosphate-sugar-base units called nucleotides
Levene's Tetranucleotide (1910)
Levene proposed that there were four nucleotides per molecule
Said DNA could not store the genetic code because it was chemically far too simple -
Frederick Griffith and his Transformation Experiment
Studied the epidemiology and pathology of 2 strains of Streptococcus pneumoniae
In January 1928 reported the first widely accepted demonstrations of bacterial transformation
Griffith used two strains of Streptococcus:
Type S: virulent (deadly)
Type R: non-virulent (harmless)
Observed bacterial transformation but did not understand the mechanism -
Avery MacLeod and McCarty
Determined the cause of the transformation in Griffith's Experiment
They took live R and heat-treated S and mixed it with one of two enzymes:
a protease (destroys protein)
a DNAse (destroys DNA)
Published in the Journal of Experimental Medicine
February, 1944
Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types. -
watson and crick
In 1951, Watson and Crick wrote a paper in which they described DNA as a double helix with sugars and phosphates at the center and the nucleobases facing the outside
This model was quickly shown to be incorrect and in fact it made no chemical sense -
Hershey-Chase Experiments
Used phages and radiolabeled phosphorus and sulfur
Hershey and Chase concluded that DNA, not protein, was the genetic material.
A protective protein coat was formed around the bacteriophage, but the internal DNA is what conferred its ability to produce progeny inside bacteria -
Erwin Chargoff
Used paper chromatography and UV spectroscopy to examine the abundance of the nucleobases and he started to notice something VERY odd...
Came to be known as "Chargoff's Rules"
Amounts of Adenine = Amounts of Thymine
Amounts of Cytosine = Amounts of Guanine
ALWAYS in EVERY SPECIES!!! -
Eureka
Triple Helix?
Linus Pauling and Robert Corey proposed a triple helix structure for DNA Eureka
James Watson and Francis Crick 1953 BUT now the story of thieves and lies...
Francis Crick, James Watson, Maurice Wilkins, Rosalind Franklin Papers in sequence in Nature April 25, 1953 (THREE papers, not 1) DNA Discovery Timeline So now we have it.
DNA is a Double-Stranded Helix
The backbone is made of sugar (deoxyribose) and phosphate groups