History of genetic material

In 1869, the Swiss surgeon Friedrich Miescher first extracted from pus a combination of nucleic acid and protein, which was called nuclein, and in 1871 he published the first paper on nucleic acids.

In 1880, the German biochemist Albrecht Kossel isolated five nitrogenous compounds from nucleic acids: adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U). These are the compounds known in modern biology as nucleobase.

In 1889, the German pathologist Richard Altmann obtained from yeast tissue fluid the acidic nucleus without proteins and coined the term nucleic acid which replaced Nuclein.

In 1909, a Russian-American physician and chemist, Phoebus Aaron Theodore Levene, discovered that the sugar contained in nucleic acids consisted of five carbon atoms and named this sugar "ribose". In later years, he discovered that the sugar in yeast nucleic acid lacks an oxygen atom and named this sugar "deoxyribose". He also discovered that nucleic acids could be broken down into fragments containing purine, pyrimidine, ribose or deoxyribose and phosphate and their combination are called nucleotide. Since the quantitative analysis of nucleobase was not precise enough at that time, the tetranucleotide hypothesis was proposed by Levin: nucleic acids contain approximately equal amount of adenine (A), cytosine (C), guanine (G), thymine (T), and the nucleic acids structure is just a simple repetition of them. This made a mismatch between nucleic acid and complex genetic material, so protein became the first choice for the study of genetic material at that time. This false hypothesis was popular for decades and served as a hindrance to scientific research, which someone called a scientific catastrophe.

In 1928 Frederick Griffith discovered that two forms of pneumoniae, S form (with polysaccharide coat) and R form (without polysaccharide coat) could transform each other. He believed that some kind of transforming factor was at work.

In 1944 Oswald Theodore Avery crushed S-type pneumoniae and extracted sugars, lipids, proteins and DNA in order to study the composition of this transforming factor. He found that only R-type pneumoniae cultured with DNA could be transformed into S-type bacteria. If DNA was broken down by DNAase, no transformation occurred. He considered DNA as the genetic material. However, the dominance of the tetranucleotide hypothesis and a little protein made his conclusion doubtful.

In 1952 Alfred Hershey experimented with phage, radioactive elements (³²P and ³⁵S) labeled E. coli to further confirm DNA as genetic material.

In 1950 Erwin Chargaff accurately measured the nucleobase content in DNA. He discovered the law of DNA composition or the Chargaff's rules: the number of purines equals the number of pyrimidines. This means A is paired with T and C is paired with G.

Wilkins and Rosalind Franklin used X-ray crystallography to study the structure of DNA. In 1952, they produced the now-famous "Photo 51," which was a high-quality X-ray diffraction image of DNA. This image provided key information about DNA structure.
Watson and Crick proposed the double helix structure of DNA in 1953. They were awarded the 1962 Nobel Prize with Wilkins.

Frequently Asked Questions

How did Crick and Watson discover the double helix structure of DNA?

Watson and Crick's discovery of DNA double helix structure is considered one of the most significant scientific breakthroughs in 20th century. Their work was based on a combination of existing knowledge and new experimental data.

In the early 1950s, many scientists were trying to determine the structure of DNA and one of them is Linus Pauling. He published a triple helix structure, but was proven wrong. Crick and Watson were encouraged by Pauling's recent discovery of protein single-stranded alpha helix structure and modeling method used in chemical research.

Watson and Crick started their work by building models of DNA using metal rods and cardboard. They used X-ray crystallography data produced by Rosalind Franklin and Maurice Wilkins to help them refine their models.

The breakthrough was achieved when they realized that nucleobase A paired with T, and C paired with G. Then they propose the double helix structure that is perfectly matched to the X-ray image: the two nucleotide chains wound around each other in a spiral; They were held together by hydrogen bonds between pairs of nucleobase.

Watson and Crick's double helix model provided a simple and elegant solution to the problem of how genetic information is stored and transmitted. Their discovery has been praised as a new milestone and opened the door of molecular biology