DNA: History and discovery

Discovery of Nucleic Acids

1869

It was discovered by Friedrich Miescher. He isolated the genetic material from white blood cell nuclei. He noted it had an acidic nature and called it nuclein.

Frederick Griffith

1879

He studied the epidemiology and pathology of 2 strains of Sreptococcus pnoeumoniae. In January f 1928, he reported the first widely accepted demonstrations of bacterial transformation.

Discovery of DNA components

1895

Discovered by Phoebus Levene. He determined the following components:
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. DNA couldn't store the genetic code, because it was chemically far too simple.

Journal of Experimental Medicine

1944

The paper suggest that DNA, rather than protein, may be the hereditary material of bacteria, and perhaps in higher organisms as well.

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:
- Proteases (which destroys protein).
- DNase (which destroys DNA).

Double Helix?

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.

Hershey-Chase Experiments

1952

Alfred Hershey and Martha Chase, made experiments with bacteriophages, are the viruses that infect bacteria. They took a radioactive sulfur, and that allowed them to follow the proteins in the phage, or they used radioactive DNA to follow the movement of DNA during the infection.
Hershey and Chase concluded that DNA 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.

Triple Helix?

1952

Linus Pauling and Robert Corey proposed a triple helix structure for DNA.
Rosalind Franklin, publish a diffraction image of DNA, later King's College show to Cambridge, finally Watson J.D. and Crick F.HC. made a structure for Deoxyribose Nucleic Acid exactly with the form of the Rosalind image.

Counting Nucleobases

1952

Erwin Chargaff, used paper chromatography and UV spectroscopy to examine the abundance of the nucleobases. He investigated the % Adenine, % Thymine, % Cytosine and % Guanine.

So, it's the DNA

1953

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 is that DNA exists in two forms:
- Dry form.
- Wet form, as DNA exists in cells.

DNA is a Double-Stranded Helix

1953

Characteristics:
- 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 animo acid sequence of a protein.
- Strings of base pairs that code for a product are called genes.