Timeline of the DNA

Discovery of Nucleic Acids

1869

In the 19th century, Friedrich Wöhler synthesized urea from inorganic compounds, opening the door to research into organic compounds. Johannes Wislicenus discovered nucleic acid in 1868 using a technique of extraction with sulphuric acid and iron chloride. This substance was called nucleic acid, because it was formed by a molecule.

Levene's Tetranucleotide

1910

Phoebus Levene proposed the tetranucleotide theory of DNA in the early 1900s, which stated that DNA was composed of repeating units of four nitrogenous bases. DNA could not store the genetic code because it was chemically far too simple.

Frederick Griffith

1928

Frederick Griffith was a British bacteriologist who conducted a series of experiments in the 1920s that helped lay the foundation for our understanding of genetics and the nature of DNA. One of his studies was the epidemeology and pathology of 2 strains of Streptoccocus pneumoniae. In 1928, Griffith conducted an experiment to study the virulence of Streptococcus pneumoniae. He discovered that a strain of the bacterium that was virulent, or able to cause disease.

Frederick Griffith and his Transformation Experiment

1928

Frederick Griffith Transformation Experiment was based on studing 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

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:
a protease (destroys protein)
a DNAse (destroys DNA)
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!

Double Helix

1951

In 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.

Counting Nucleobases

1952

In 1952, Rosalind Franklin and Maurice Wilkins used X-ray crystallography to study the structure of DNA, which allowed them to determine the number of nucleotides (or nucleobases) in the DNA molecule. They found that the ratio of adenine to thymine, and of guanine to cytosine, was approximately 1:1. This information was very important for the development of the discovery and understanding of DNA.

Hershey and Chase

1952

Hershey and Chase were virologists who conducted an experiment in 1952 that confirmed DNA as the genetic material of viruses. 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.

Discovery of DNA components

1953

Watson and Crick's discovery in 1953 of the double-helix structure of DNA revealed that it is composed of four nitrogenous bases (adenine, guanine, cytosine, and thymine), a sugar molecule, and a phosphate group. This was a major breakthrough in our understanding of genetics and the fundamental building blocks of life.

Triple Helix

1953

Linus Pauling and Robert Corey proposed a triple helix structure for DNA. Triple helix DNA refers to a structural variation of DNA with three strands instead of two. It has been observed in certain viruses and is believed to play a role in gene regulation. Further research on this structure could have implications for various areas of biology.

Eureka!

1953

In 1953,James Watson and Francis Crick discovered the double helix structure of DNA, a major milestone in molecular biology and genetics. Based on X-ray diffraction images and data from other researchers, the double helix consists of two strands of nitrogenous bases (adenine, guanine, cytosine, and thymine) forming a twisted ladder-like structure. This discovery provided a foundation for further research into heredity and the genetic code and is referred to as a "Eureka" moment in genetics.

Journal of Experimental Medicine

1953

In February 1944, a paper in the Journal of Experimental Medicine showed that DNA is the genetic material responsible for transmitting traits. The researchers used experiments on Streptococcus pneumoniae bacteria to transfer virulence using purified DNA, providing evidence that DNA, not protein, is the genetic material. This was a key discovery in the field of molecular genetics.