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Discovery of Nucleic Acids
Isolated the genetic material from white blood cell nuclei. He noted it had an acidic nature and called it nuclein -
Discovery of DNA Components
Determined the components of DNA:
· adenine, guanine, thymine, cytosine, deoxyribose phosphate
· defined phosphate-sugar-base units celled nucleotides -
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 -
Griffith's Transformation Experiment
Frederick Griffith was a british bacteriologist, in 1928 experiment with bacterium was the first to reveal the “transforming principle,” which led to the discovery that DNA acts as the carrier of genetic information. 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 -
Double Hellix?
Watson and Crick wrote a paper where they described DNA as a double helix with sugars and phospates at the center and the nucleobases facing the outside. It was proven incorrect because all the negative charges would make it explode. -
Hershey and Chase
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 -
Counting nucleobases and Chargaff's rules
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!!! -
Actual structure, Noble Prize and Rosalind Franklin
Rosalind took photo 51 of the actual structure of DNA that proved that there were just two helix but placed in the oposite way that Watson and Crick thought. Wilkins took the picture from Rosalind and gave it to them so they could publish it and get the credit as well as finish their papers. The three of them; Watson, Crick and Wilkins, got the Noble prize. -
Triple Helix?
Linus Pauling and Robert Corey proposed a triple helix structure for DNA. But it was proven wrong, what they probably saw were the two helix but not clearly so they thought there was a third one.