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Discovery of Nucleic Acid
It was discovered by Friederich Miescher (Swiss physician / biologist).
Isolated the genetic material from white blood cell nuclei. He noted it had an acidic nature and called it nuclein. -
Discovery of DNA Components
It was discovered by Phoebus Levene (Lithuanian-America / Biochemist).
Determined the components of DNA:
adenine, guanine, thymine, cytosine, deoxyribose phosphate.
Defined phosphate-sugar-base units called 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. -
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:
- Protease (destroys protein)
- DNase (destroys DNA) In February, is published in the Journal of Experimental Medicine some studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types and it, and it is proved that the DNA not was responsible for the bacterial transformation Griffith observed, was protein! -
Watson and Crick description of DNA
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. Also,Linus Pauling and Robert Corey proposed a triple helix structure for DNA. -
Counting Nucleobasesm
Erwin Chargaff (Austrian / biochemist) was using a paper chromatography and UV spectroscopy to examine the abundance of the nucleobases and then, 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!!! -
Hershey-Chase Experiments
Alfred Hershey (American Geneticist / Bacteriologist) and Martha Chase (American Geneticist) used phages, radiolabelled phosphorus and sulphur.
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. -
The Nobel Prize in Physiology or Medicine
The Nobel Prize in Physiology or Medicine was awarded to James Watson, Francis Crick and Maurice Wilkins for their discovery of the molecular structure of DNA, which helped solve one of the most important of all biological riddles. -
So what we know now?
- DNA is a Double-Stranded Helix.
- The backbone is made of sugar (deoxyribose) and phosphate groups.
- There's hydrogen bonds between the nucleobases: A-T and G-C.
- The sequence of nucleobases codifies the amino acid sequence of a protein.
- Strings of base pairs that code for a product are called genes.
- Finally, James Watson, Francis Crick and Maurice Wilkins won the Nobel Prize in 1962 for their discovery of the 3D molecular model of the DNA.