History of DNA

Discover of Nucleic Acids

1869

Isoloated the genetic material from the white blood cell nuclei. He noted it had an acidic nature and called it nuclein. Friedrich Miescher (1869)

Levene's Tetranucleotide

1910

Discovery of DNA Components
Phoebus Levene
Determined the components of DNA:

adenine, guanine, thymine, cytosine, deoxyribose phosphate
defined phosphate-sugar-base units called nucleotides Levene proposed that there were four nucleotides per molecule
Said DNA could not store the genetic code because it was chemically far too simple Levene's Tetranucleotide (1910)

Frederick Griffith

1928

Frederick Griffith was a british bacteriologist, in 1928 experiment with bacterium was the first to reveal the “transforming principle,” which led to the discovery that DNA acts as the carrier of genetic information. Griffith used two strains of Streptococcus:
Type S: virulent (deadly)
Type R: non-virulent (harmless)
Observed bacterial transformation but did not understand the mechanism

Griffith's Transformation Experiment

1928

Griffith used two strains of Streptococcus:
Type S: virulent (deadly)
Type R: non-virulent (harmless)

Oswald Avery

1937

Oswald Avery was a famous researcher in medicine, the Canadian gave his working life to the Rockefeller Hospital University, he was a pioneer in chemical immunology and one of the first molecular biologists, but he was best known for the Avery experiment- Macleod-McCarty on DNA

Colin MacLeod

1942

Colin MacLeod was a Canadian geneticist, MacLeod studied at McGill University, and together with Avery and McCarthy he also contributed to the experiment on DNA and after being with that experiment he dedicated himself to health issues.

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 oneof 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

Journal of Experimental Medicine

1944

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
DNA not protein was responsible for the bacterial transformation Griffith observed!

Maclyn McCarty

1944

Maclyn McCarty devoted his life to medical science by studying infectious disease organisms, he is well known for his important part in the discovery that DNA, rather than proteins, is the constituent of the chemical nature of a gene

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

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

Couting Nucleobases

1952

Erwin Chargoff was Counting Nucleobasesm in 1952
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 "Chargoff's Rules"
Amounts of Adenine = Amounts of Thymine
Amounts of Cytosine = Amounts of Guanine
ALWAYS in EVERY SPECIES!!!

Triple Helix

1953

Linus Pauling and Robert Corey proposed a triple helix structure for DNA Eureka
James Watson and Francis Crick 1953 BUT now the story of thieves and lies...
Francis Crick, James Watson, Maurice Wilkins, Rosalind Franklin

DNA is a Double-Stranded Helix

1960

So now we have it.

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