History and discovery of DNA

History and discovery of DNA

From Nucleic Acids to the Double Helix: key milestones in DNA research

1951

1928

1910

1944

1869

1909

Watson and Crick - Inside-Out Double Helix

Frederick Griffith's - Transformation experiment

Phoebus Levene - Tetranucleotide structure

Phoebus Levene - Discovery of DNA Components

Avery, MacLeod and McCarty - Proving DNA as the transforming principle

Friedrich Miescher - Discovery of Nucleic Acids

Discovered DNA's components: adenine, thymine, guanine, cytosine, deoxyribose sugar and phosphate, defining the nucleotide structure.

Demonstrated bacterial transformation, suggesting the existence of a "transforming principle."

Proved that DNA, not proteins, is the "transforming principle" responsible for hereditary information.

Proposed an incorrect double-helix DNA model with sugars and phosphates inside.

Isolated genetic material from nuclei, naming it nuclein due to its acidic properties.

Incorrectly proposed a tetranucleotide structure for DNA, influencing future genetics research.

History and discovery of DNA

From Nucleic Acids to the Double Helix: key milestones in DNA research

1962

1952

1953

1952

1953

1952

Nobel Prize for DNA structure

Hershey and Chase - Proof that DNA carries genetic information

Watson, Crick, Wilkins and Franklin - Correct Double Helix

Erwin Chargaff’s - Counting Nucelobases and Chargaff’s Rules

Linus Pauling and Robert Corey - Triple Helix

Rosalind Franklin - Photo 51

Watson, Crick and Wilkins were awarded the Nobel Prize for discovering DNA's structure, though Franklin was not recognized due to her death.

Proved definitively that DNA, not protein, carries genetic information using bacteriophages.

Discovered Chargaff’s Rules, showing equal ratios of A-T and C-G bases.

Incorrectly proposed a triple-helix DNA structure.

Captured Photo 51, revealing the double-helix structure of DNA.

Built the correct double-helix model of DNA using Franklin’s X-ray data.

191O

PHOEBUS LEVENE - TETRANUCLEOTIDE STRUCTURE

Phoebus Levene incorrectly suggested that DNA had a simple tetranucleotide structure, with four nucleotides per molecule, which was wrong. This idea led to the belief that DNA was too simple to carry genetic information. His research provided a lot of important information for future genetics and DNA researchers.

1928

Frederick Griffith's - Transformation experiment

Frederick Griffith conducted experiments with two strains of Streptococcus pneumoniae, one harmful (smooth, type S) and one harmless (rough, type R). And he applied both strains to mice. With the S they died and with the R they remained alive. He then heated the S, killing the

bacteria, so it was no longer deadly to the mice. His key discovery was bacterial transformation: he mixed heat-killed harmful bacteria with live harmless bacteria and surprisingly the mixed became harmful! It killed the mice. Griffith didn’t know what caused the transformation, but it hinted that there was a “transforming principle” in cells.

1952

Rosalind Franklin - Photo 51

Rosalind Franklin, an expert in X-ray crystallography, took an important photo known as Photo 51 showing the clear double-helix structure of DNA, the wet form which is the real one. Her work was key to understanding DNA’s structure, though she wasn’t immediately credited.

1952

Erwin Chargaff’s - Counting Nucleobases and Chargaff’s Rules

Erwin Chargaff discovered that in any given organism, the amount of adenine (A) was always almost the same as thymine (T), and the amount of cytosine (C) was always almost the same as guanine (G). This observation, known as Chargaff's rules, hinted at the way DNA bases pair with each other (A with T, and C with G). It was a great discovery that he was not aware of and was never publicly acknowledged.

1953

Watson, Crick, Wilkins and Franklin - Correct Double Helix

Using Franklin’s Photo 51 without her direct knowledge, Watson and Crick, along with Maurice Wilkins, created the first accurate model of DNA as a double helix. The backbone of the helix was made of sugar and phosphate, with the bases (A, T, C, G) pairing inside (A with T, C with G). This discovery explained how DNA stores genetic information and how it can replicate. This model was the opposite of what they had said in 1951. Publication in the Nature magazine of their various articles.

1951

Watson and Crick - Inside-Out Double Helix

Watson and Crick stated that DNA was a double helix structure with sugars and phosphates in the core and the nucleobases facing outside. But it was an incorrect approximation without any chemical sense.

1953

Linus Pauling and Robert Corey - Triple Helix

The triple helix structure (shown in the picture) proposed by Linus Pauling and Robert Corey was again wrong because chemically it was not possible under normal cellular conditions.

1952

Hershey and Chase - Definitive proof that DNA carries genetic information

Martha Chase and Alfred Hershey conducted experiments with viruses called bacteriophages (phages) that infect bacteria. They used proteins and DNA. They labeled the proteins and DNA parts of the viruses with different radioactive markers to watch their movement as they infected the bacteria. They observed (using the

centrifugation method) that only DNA entered the bacterial cells during infection while proteins remained outside. This reconfirmed that DNA, not protein, contained the genetic material. Now the goal was to discover its real structure because DNA existed in two forms (the dry one and the wet one, which is the real.)

1869

FRIEDRICH MIESCHER - DISCOVERY OF NUCLEIC ACIDS

Friedrich Miescher isolated the genetic material from the nuclei of white blood cells. He observed that it had acidic properties and named it nuclein.

1962

Nobel Prize for DNA structure

James Watson, Francis Crick and Maurice Wilkins were awarded the Nobel Prize in Physiology or Medicine for discovering the structure of DNA. Rosalind Franklin had passed away when she was 37 years old of ovarian cancer and it is believed that the exposure to X-rays during all this time was probably a contributing factor. And was not included in the Nobel recognition, as it is only awarded to living individuals.

1909

Phoebus Levene - Discovery of DNA Components

Levene discovered that DNA is composed of several components: adenine (A), thymine (T), guanine (G), cytosine (C), a sugar known as deoxyribose, and a phosphate group. He also defined the fundamental unit of DNA, known as a nucleotide, which consists of a phosphate-sugar-base structure.

1944

Avery, MacLeod and McCarty - Proving DNA as the transforming principle

These three scientists followed up on Griffith's experiment, showing that the "transforming principle" was DNA, not proteins.

They took live R and heat-treated S and they did two different mixes. The first with proteases (enzymes that destroy proteins) and the other with DNase (enzymes that destroy DNA). They used these enzymes to destroy the proteins or DNA of the bacteria and showed that only when the DNA was destroyed did the transformation stop, as the mouse lived, confirming that the DNA is what contains the material hereditary of bacteria and perhaps also of more evolved beings.