History and discovery of DNA

Discovery of Nucleic Acids

1869

Friedrich Miescher was the person who discovered the Nucleic Acids. He was a Swiss physician and a biologist.
What he did was isolate the generic material from the white blood cells.

Discovery of all DNA components

1895

Phoebus Levene was who discovered all the DNA components. He was a Lithuanian-American Biochemist. The components that he found out are:
- Adenine
- Guanine
- Thymine
- Cytosine
- Deoxyribose phosphate
He also defined phosphate-sugar-base units called nucleotides.

Levene´s Tetranucleotide

1910

Levene thought that there were four nucleotides per molecule. He was unfortunetay wrong and he died just before the correct answer was given.

Frederick Griffith

1928

He was a british bacteriologist that studied epidamiology and pathology of 2 strains Streptococcus pneumoniae. He reported the first widely accepted demostrations of bacterial transformation.

Griffith's Transformation Experiment

1928

Griffith used two strains of Streptococcus;
- Type S: virulent (deadly)
- Type R: non-virulent (harmless)
Griffith's did not figured out why was this happening to his experiment so he left the project and start focusing with other things.

Avery, MacLeod and McCarty

1944

They finally determined the cause of the transformation in Griffith's Experiment.
They figure this out by taking the 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.

Chargaff's Rules

1952

Erwin Chargaff didn't realize how much important was this descovery.
Chargaff's rules are basically that he amount of adenine and thymine were always in balance, and the amount of cytosine and guanine, always in balance.

Counting Nucleobases

1952

Erwin Chargaff was an Austrian Biochemist that loved counting things in percentage. He used paper chromatography and UV spectroscopy to exime the abundance of nucleobases and he started to notice something weird. He mesured the amounts of the four bases and no matter what, all the organism were about the same.

Photo 51

1952

Rosalind Franklin took a lot of photos of the B form of DNA. She figured out how to see the wet form in cells. They call it photo 51. The photo is perfect because it shows very clearly the x in the middle that is the sign of a double helix.
She didn't want to publish it because she wasn't sure about her calculation, but, somehow, Maurice Wilkins got the photo 51 and get it to Watson and crick in cambrige. When they saw the image, they knew what it meant.

Hershey-Chase Experiments

1952

They 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.
DNA exists in two forms
A form
B form

Triple Helix

1953

Linus Pauling and Robert Corey proposed a triple helix structure for DNA. But it was also incorrect.

The Nobel Prize in Physiology or Medicine

1962

The reason why Rosalind did not share in the nobel prize was because, unfortunately, she past away.