Journey of Discovery: DNA and the Pioneers of Genetics

1. DNA Discovery Katerina Zlatkin

2. Early history • Charles Darwin and the famous book “On the Origin of the Species by Means of Natural Selection”. His book was published in 1859. • In 1865 Gregor Mendel had discovered the laws of heredity with his experiments with peas. • In 1866 Ernest Heckle suggested the idea that the nucleus of the cell contained the hereditary material which brought much attention to the nucleus which was an unexplored organelle at the time.

3. Friedrich Miescher • Born in Switzerland to a family of scientists, Miescher wanted to become a priest but the idea was turned away very quickly by his father and uncle and he went to medical school. Miescher was a very shy person and also had hearing impairments which made him turn away from patient care but instead go into medical research. • Friedrich Miescher moved to Germany where he started doing research on histochemistry. After gaining experiences working in a laboratory he joined Hoppe-Seyler’s laboratory in 1869. Miescher wanted to study the chemistry of cells, he started by studying lymphocytes which were simple and isolated cells. • Lymphocytes turned out to be hard to purify and there was not enough material to work up a full analysis. Hoppe-Seyler suggested using leukocytes instead. • He collected and worked with pus, where leukocytes were very abundant, and he found it to be the perfect base material for his research. The purity of the fresh pus he collected allowed him to achieve the most complete and purified building blocks of the cell. • Miescher focused on the proteins since those were showed the most potential to understand how a cell functions. • Under limited resources Friedrich Miescher he was able to describe the properties of those proteins. • During his test Miescher noticed a substance that precipitated in a solution when acid was added and then dissolved when alkali was added. He was the first to obtain the precipitate of DNA. The molecule he isolated was nuclein. Miescher found that the molecule consisted of oxygen hydrogen nitrogen and phosphorous and that there was a unique ratio between nitrogen and phosphorous.

4. Identifying chemical composition of nucleic acids • Albert Kossel was a German biochemist who won the noble prize in 1910 for his accomplishment in identifying the chemical composition of nucleic acids. Kossel identified adenine, thymine, guanine, cytosine and uracil which are very important in the formation and function of DNA and RNA. • Kossel studied under Hoppe-Seyler in 1872. After completing his studies at the university Kossel became Hoppe-Skeyler’s research assistant. • The focus in the lab was to further understand this new nuclein molecule, Friedrich Miescher’s finding. This substance was fascinating due to the considerable amounts of phosphorous it contained and its acidity. • Kossel was able to show that nuclein consisted of a protein component and a non-protein component, he then further isolated this substance which is now widely known as nucleic acid.

5. Nikolai kolstov • Russian biologist and pioneer of modern genetics • Kolstov was a professor in Moscow University he also established and directed the Institute of Experimental Biology. • Kolstov focused his research on cytology and vertebrate anatomy. In 1927 he proposed that hereditary material would be passed and inherited by “a giant hereditary molecule” which he said would be made up of “two mirror strands that would replicate in a semi-conservative fashion using each strand as a template”(Soyfer N. Valory 2)

6. DNA Components • Phoebus Levene was an American biochemist who characterized the different forms of nucleic acid and found that DNA contained adenine, guanine, thymine, cytosine, deoxyribose and a phosphate group. • Levene discovered ribose in 1909 and deoxyribose in 1929. • Levene was able to show that DNA components were connected in a specific order; sugar-phosphate-base to form units which themselves are linked together through the phosphate group to form the backbone of the molecule. Levene coined the name nucleotide calling each of those units a nucleotide. • Levene theorized that there were only four nucleotides per molecule, he is also known for his “tetranucleotide hypothesis” formulated in 1910 stating that DNA was made up of equal amounts of adenine, guanine, cytosine and thymine.

7. Frederick Griffith and the transforming principle

8. A+g=c+t Erwin Chargaff was a biochemist teaching at Columbia University. Throughout his research he discovered two rules that shed some light on the structure of DNA. The first rule says that in DNA there is the same amount guanine units as there are cytosine units. The same rule applies for adenine and thymine. The second rule says that the relative amount of guanine, thymine, adenine and cytosine vary among different species.

9. Picture 51 This famous x-ray diffraction image was taken by Raymond Gosling who was a PhD student who was studying under Rosalind Franklin at King’s College. James Watson was shown the picture by Maurice Wilkins without Franklins approval. James Watson was working with Francis Crick and using this image they figured out the double helix structure of DNA.Wilkins, Watson and Crick won a noble prize Rosalind Franklin did not because she had died of breast cancer at the time of the award.

10. “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material”

11. Works Cited • “Redirecting.” PLOS Biology, Public Library of Science, 21 Dec. 2004, doi.org/10.1016/j.ydbio.2004.11.028. • “Albrecht Kossel.” Wikipedia, Wikimedia Foundation, 9 Sept. 2018, en.wikipedia.org/wiki/Albrecht_Kossel. • “Concept 15 DNA and Proteins Are Key Molecules of the Cell Nucleus.” Maurice Wilkins :: DNA from the Beginning, www.dnaftb.org/15/bio.html. • “Albrecht Kossel.” Wikipedia, Wikimedia Foundation, 9 Sept. 2018, en.wikipedia.org/wiki/Albrecht_Kossel • “Nikolai Koltsov.” Wikipedia, Wikimedia Foundation, 9 Sept. 2018, en.wikipedia.org/wiki/Nikolai_Koltsov. • “Phoebus Levene.” Wikipedia, Wikimedia Foundation, 9 Sept. 2018, en.wikipedia.org/wiki/Phoebus_Levene. • “Classic Experiments: DNA as the Genetic Material.” Khan Academy, Khan Academy, www.khanacademy.org/science/biology/dna-as-the-genetic-material/dna-discovery-and-structure/a/classic-experiments-dna-as-the-genetic-material. • “The Rosalind Franklin Papers: Biographical Information.” U.S. National Library of Medicine, National Institutes of Health, profiles.nlm.nih.gov/ps/retrieve/Narrative/KR/p-nid/183.