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Friedrich Miescher
Year of discovery:1869
Contributions: Discovered a substance containing both phosphorus and nitrogen in the nuclei of white blood cells. It was fist named nuclein but then known as nucleic acid after 1874. It is know known as deoxyribonucleic acid (DNA)
How discovery was made: found the substances in pus, then found nucleic acid in salmon spermatozoa.
Argument used: scientist were debating the concept of cells and Miescher was given the task of researching the composition of white blood cells -
Erwin Chargaff
Year: 1944
Contributions: Created Chargaff's Rule, which led to the clarification of the DNA molecular structure. It shows that the number of adenine equals the number of thymine, cytosine equals guanine, and purines equals pyrimidines.
How: He took out nuclei from cells, isolate the DNA from the nucleic and broke it down to its nucleic acids, then separated the primes from pyrimidines.
Argument: Helped Watson and Crick show that since the bases have the same amount, they must bond together. -
Rosalind Franklin
Year of discovery:1951
Contributions: She discovered that the phosphates were on the outside of a DNA structure.
How discovery was made: She took photos of crystallized DNA fibers. She used two different fibers of DNA, one more hydrated (A) than the other. The wet form (B) showed a definite helical structure.
Argument used: Her photos contained information that Watson and Crick needed to complete an accurate DNA structure. The phosphate needed to attach DNA -
Hershey and Chase
Year of discovery:1952
Contribution: In the Hershey-Chase experiment, bacterial viruses (phage) were used to demonstrate that DNA is the genetic material. Proved that the DNA, not the protein, carries the genetic information for a new generation of phage.
How discovery was made: when Phage infect bacterium, they attach to the surface of the bacteria and inject the DNA into the cell. No radioactive label in the DNA as a result.
Argument used: For further proof after Avery's demonstration. -
Watson and Crick
Year of discovery: 1953
they showed that each strand of the DNA molecule was a template for the other and the two stands separate and the new half is built.
How discovery was made: Watson heard Wilkins talk on the molecular structure of DNA and saw his recent X-ray crystallographic photographs of DNA.
Argument: Crick learned about Chargaff's findings about base pairs in 1952 and added to the model so that matching base pairs interlocked in the middle of the double helix. -
Meselson and Stahl
Year of discovery: 1958
Contribution: They demonstrated that DNA replicated semi-conservatively, meaning that each strand in a DNA molecule serves as a template for synthesis of a new complementary strand. The Meselson-Stahl experiment showed that DNA replicates by a semi-conservative mechanism.
How discovery was made: They used E. coli as a model system for DNA replication. It produced the patterns of bands.
Argument used: How the strands of the helix might separate during replication.
