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Miescher
Friedrich Miescher is credited with discovering nuclein while studying the composition of lymphoid cells. The lymph cells were too difficult to extract from lymph glands, so Miescher used pus and salmon sperm to retrieve his samples. Miescher was the first person to recognize DNA as a distinct molecule. -
Chargaff
Erwin Chargaff studied the composition of DNA. From his studies Chargaff came up with three fundamental rules of the molecular structure of DNA, known as Chargaff's Rules. The rules state that the number of Adenine (A) always equals the number of Thymine (T), and the number Guanine (G) always equals the number of Cytosine (C). Chargaff's Rules also state that the number of purines always equal the number of pyrimidines. -
Franklin
Rosalind Franklin studied the structure of DNA molecules using X-ray crystallography. Franklin was able to acquire high resolution photos of DNA fibers. While studying two different fibers, she noticed that one was more hydrated than the other. From this evidence Franklin concluded that the basic structure of DNA consists of phosphates on the outside of a helical structure. She did not receive credit for this discovery due to Watson and Crick publishing their findings before she was able to. -
Hershey & Chase
Alfred Hershey and Martha Chase demonstrated that DNA carries genetic information. They were able to prove this by revealing that DNA is passed from bacteriophages to bacteria. Bacteriophages are viruses that attack bacteria and Hershey and Chase proved that DNA could be passed from a virus to a bacteria in order to infect the bacteria, then it became evident that DNA could pass genetic information. -
Watson and Crick
Biologists James Watson and Francis Crick examined the structure of DNA molecules. They discovered that DNA was a double helix structure, meaning it contains two rows of nitrogenous bases. Watson and Crick discovered that the nitrogenous bases always pair in the same configuration, meaning Adenine always pairs with Thymine etc. This discovery helped scientists understand how DNA is able to copy itself, and that is due to the simple pairing of the complementary bases. -
Meselson & Stahl
Matthew Meselson Franklin Stahl attempted to expand on Watson and Cricks discovery of the DNA double helix. Meselson and Stahl believed that the double helix structure of the DNA meant that during replication two strands of RNA separated allowing for two new, complementary strands of RNA to connect with one of the original strands. Meselson and Stahl's theory suggested that DNA replication is only semi-conservative, meaning the DNA is replicated as two separate strands rather than as a whole.
