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Discovery of Nucle Acids
Discovery of Nucleic Acids
Friedrich Miescher (1869)
Isolated the genetic material from white blood cell nuclei. He noted it had an acidic nature and called it nuclein -
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Oswald Avery
Canadian physican -
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Conin MacLeod
Canadian-American Geneticist -
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Discovery of DNA Components
Phoebus Levene
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 -
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Levene's Tetranucleotide
Levene proposed that there were four nucleotides per molecule
Said DNA could not store the genetic code because it was chemically far too simple -
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MacLyn McCarty
American-Genecist -
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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 -
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Avery, MacLeod and McCarty 1944
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) Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Deoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III
DNA not protein was responsible for the bacterial transformation Griffith observed! -
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Double Helix?
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 -
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DNA Discovery Timeline
Erwin Chargoff was Counting Nucleobasesm in 1952
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!!! -
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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