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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.
Discovered by Friedrich Mienscher. -
Frederick Griffith
- Studied the epidemiology and pathology of 2 strains of Streptococcus pneumoniae.
- In janaury 1928 reported the first widely accepted demostrations of bacterial transformation
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Discovery of DNA Components (1869 - 1940)
Determined the components of DNA:
- Adenine, guanine, thymine, cytosine, deoxyribose phosphate.
-Defined phosphate-sugar-base units called nucleotides.
Discovered by: Phoebus Levene in period 1869-1940 -
Levene's Tetranucleotide
- Levene proposed that there were four nucleotides per molecule.
- DNA could not store the genetic code because it was chemically far too simple.
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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: Proteases wich destroys protein DNase wich destroys DNA
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Journal of experimental medicine
Studies on the chemical Nature of the Substance Inducting Transformation of pneumococcal Types: Induction of transforrmation by a Deoxybonucleic Acid Fraction Isolated from Pneumococcus Type III -
Double Helix
In, 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 Triple Helix?
Linus Pauling and Robert Corey proposed a triple helix structure for DNA -
Counting Nucleobases
Used paper chromatography and UV spectroscopy to examine the abundance of the nucleobases and he started to notice something VERY odd.
Discovered by: Erwin Chagraff -
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 -
DNA exists in 2 forms
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
A form (dry form)
B form (wet form, as DNA exists in cells) -
DNA is a Double-Stranded Helix
The backbone is made of sugar (deoxyribose) and phosphate groups
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