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Friedrich Miescher - Discovery of Nucleic Acids
Isolated the genetical material from white blood cell nuclei. He noted it had an acidic nature and called it nuclein. -
Phoebus Levene - Discovery of DNA components
He determined the components of DNA: adenine, guanine, thymine, cytosine, deoxrybose phosphate. He defined phosphate-sugar-base units in cells called nucleotides. -
Phoebus Levene - Theory of DNA
Levene proposed that there were four nucleotides per molecule. He also said DNA could not store the genetic code because it was chemically far too simple. -
Frederick Griffin
Studied the epidemology and pathology of 2 strains of Streptoccus 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.
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 -
Erwin Chargoff - Counting Nucleobasesm
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 "Chargaff's Rules"
Amounts of Adenine = Amounts of Thymine
Amounts of Cytosine = Amounts of Guanine
ALWAYS in EVERY SPECIES. -
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 So, it's the DNA
The race was on to determine the structure of DNA in cells and to determine how it codes for proteins and how it replicates
The problem: DNA exists in two forms -
Linus Pauling - Robert Corey Triple Helix
Linus Pauling and Robert Corey proposed a triple helix structure for DNA -
Watson - Crick Double helix
In Watson and Crick's model, the two strands of the DNA double helix are held together by hydrogen bonds between nitrogenous bases on opposite strands. Each pair of bases lies flat, forming a "rung" on the ladder of the DNA molecule. Base pairs aren't made up of just any combination of bases. -
Rosalind Franklin - photo 51
Photo 51 is one of the world's most important photographs, demonstrating the double-helix structure of deoxyribonucleic acid: the molecule containing the genetic instructions for the development of all living organisms.a- -
Watson - Crick Correct double Helix
Rosalind Franklin obtained images of DNA using X-ray crystallography, an idea first broached by Maurice Wilkins. Franklin's images allowed James Watson and Francis Crick to create their famous two-strand, or double-helix, model.