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Fred Griffith
Contribution: Griffith had discovered what is now called Transformation, transformation is a change in genotype caused when cells take up foreign genetic material.
Experiment: He first injected mice with a live strain of deadly bacteria, and all of those mice died. Then, he killed the deadly bacteria cells by heating them. Mice injected with these heat-killed deadly bacteria did not die. In another set of mice, Griffith injected a live non-virulent strain of bacteria, and these mice did not die, -
Oswald Avery, Maclyn McCarty, Colin MacLeod
Contribution: identify DNA as the "transforming principle" responsible for specific characteristics in bacteria
Experiment: First used heat to kill virulent bacteria. He then extracted RNA, DNA, carbohydrates, lipids, and proteins from these dead cells, all of which were considered to be possible candidates for the carriers of genetic information. Next, he added each type of molecule to a culture of live non-virulent bacteria to determine which was responsible for changing them into virulent ba -
Erwin Chargaff
Contribution: First, he noted that the nucleotide composition of DNA varies among species. In other words, the same nucleotides do not repeat in the same order, as proposed by Levene. Second, Chargaff concluded that almost all DNA--no matter what organism or tissue type it comes from--maintains certain properties, even as its composition varies. In particular, the amount of adenine (A) is usually similar to the amount of thymine (T), and the amount of guanine (G) usually approximates the amount -
Rosalind Franklin
Contribution: “The results suggest a helical structure (which must be very closely packed) containing 2, 3 or 4 co‐axial nucleic acid chains per helical unit, and having the phosphate groups near the outside.”; “X” shape that DNA had a helix shape
Experiment: DNA Crystallization -
Alfred Hershey & Martha Chase
Contribution: DNA was comprised of genetic material
Experiment: Labeled the DNA of phages with radioactive Phosphorus-32. They allowed the phages to infect E. coli, and were able to observe the transfer of P32 labeled phage DNA into the cytoplasm of the bacterium. Then, labeled the phages with radioactive Sulfur-35. Following infection of E. coli they then sheared the viral protein shells off of infected cells using a high-speed blender and separated the cells and viral coats by using a centrifu -
Meselson and Stahl
Contribution: Each strand serves as the template for new strand and that each newly formed double helix has one new and one old strand.
Experiment: They placed the bacteria in an environment which contained a selected Nitrogen isotope. They first used N14. The bacteria then integrated this isotope into their DNA. Later they used an environment that contained N15. They then looked at which of the isotopes the bacterial DNA contained. They found that it contained both isotopes of nitrogen, which -
Francis Crick and James Watson
Contribution: Watson and Crick Propose the Double Helix
Experiment: Using cardboard cutouts representing the individual chemical components of the four bases and other nucleotide subunits, Watson and Crick shifted molecules around on their desktops, as though putting together a puzzle. They were misled for a while by an erroneous understanding of how the different elements in thymine and guanine were configured. Only upon the suggestion of American scientist Jerry Donohue did Watson decide to ma
