The History of DNA

Early Work Friedrich Miescher, 1869, first isolates a non- protein substance from the nucleus of pus cells that he calls “nuclein.” Video (1:15-2:40) Montage showing (from left to right) Friedrich Miescher, a vial containing DNA isolated by Miescher, his original publication describing his discovery of DNA and his laboratory in Tübingen castle.

Hammerling (1930’s) Worked with a one-celled green algae called Acetabularia

Conclusion The hereditary information (which we now know is DNA), driving regeneration is found within the foot of the organism, and possibly in the nucleus

In 1928, Frederick Griffith carried out experiments on bacteria (Streptococcus pneumonia) in mice. VIDEO (2:02- 4:50) Frederick Griffith

Griffith’s Experiment

Conclusion Griffith concluded that the harmless R strain bacteria had been "transformed" (changed) into the lethal S strain by a "transforming principle" that was somehow part of the dead S strain bacteria. (Today, we know that the "transforming principle" Griffith observed was the DNA of the S strain bacteria).

Oswald Avery et al.. Avery continued working with Griffith’s findings in hope of discovering what “factor” in bacteria carried the trait of virulence. Isolated proteins, lipids, carbohydrates, and nucleic acids (DNA and RNA) from dead S strain and mixed them with live R bacteria. When only DNA was destroyed, transformation DID NOT happen

Avery’s Work

Conclusion Transformation cannot occur unless DNA is present, therefore DNA must be the hereditary material

Worked with a bacteriophage virus that infects E.coli bacteria Hershey and Chase Worked with a bacteriophage virus that infects E.coli bacteria

Experiment

Conclusion Phosphorous rich DNA was injected into the bacterial cells DNA entering host bacterial cells carries all the genetic information Therefore, DNA must be the hereditary material…FINALLY CONFIRMED! VIDEO (4:50-7:00)

Erwin Chargaff Chargaff studied DNA itself (of many organisms), in hopes of providing some clues about its structure. Discovered that there are always equal amounts of the bases Adenine and Thymine, and equal amounts of Cytosine and Guanine. Also discovered the total amount of purines equals the total amount of pyrimidines in an organism’s genome Chargaff proposed that these bases pair with one another in some way. VIDEO (7:00- end)

His most famous work was determining the structure of proteins Linus Pauling His most famous work was determining the structure of proteins He proposed a 3 stranded DNA molecule with phosphates on the inside-WRONG!

Rosalind Franklin and Maurice Wilkins worked with X-ray crystallography to find more clues about the structure of DNA. Franklin’s X-ray images suggested a helical structure. Wilkins and Franklin

Franklin and Wilkins

Watson and Crick James Watson and Francis Crick were also working on discovering the structure of DNA. Applied Chargaff’s rule, assumed that A always pairs with T, C with G. Watson was not entirely convinced of the helical structure that Franklin had suggested, and his critique of her work led her to doubt herself.

Watson and Crick Wilkins consulted with Watson and Crick. Without Franklin’s knowledge, he handed them the data that he and Franklin had worked on. Watson immediately recognized the significance. He and Crick went to work on a model of DNA.

The First DNA Model