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Fred Griffith
Contribution: transformation, which is a change in genotype caused when cells take up foreign genetic material.
Expirement:two strains of the bacterium Streptococcus pneumoniae; one strain was lethal to mice and the other was harmless. Griffith found that the mice with either the heat-killed virulent bacteria or the living avirulent bacteria remained free of infection, but mice inoculated with a mixture of both became infected and died.
Site of information- http://www.britannica.com/EBch -
Oswald Avery, Maclyn McCarty, Colin MacLeod
Contribution-Transforming Princliple, whichis responsible for specific characteristics in bacteria
Expirement- 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. Then he added each type of molecule to a culture of live non-virulent bacteria to determine which was responsible for changing them into virulent bacteria -
Erwin Chargaff
Contribution: Notcied differences of compostion of DNA in different species, and that all DNA is composed of certain prperties
Three Rules-1. the number of adenine (A) residues always equals the number of thymine (T) residues;
2. the number of guanine (G) residues always equals the number of cytosine (C) residues;
3. the number of purines (A+G) always equals the number of
Experiment-Investigate compostion of DNA -
Rosalind Franklin
Contribution:was close to finding out DNA structure, she did find out the following conclusion- that DNA has 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 is made of genetic materiak
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 centrifuse -
Meselson and Stahl
Contribution: Each strand serves as the template for new strand and that each new double helix has one new and one old strand.
Experiment: They placed the bacteria in an environment which contained a heavy Nitrogen isotope. They first used N15. The cells were then transferred using a new meduim containing the normal light Nitrogen isotope N14. The DNA was then extracted and dissolved in a solution of cesuim chloride. Then spun rapidly in a centrifuge until a concentrion gradient, DNA was created -
Francis Crick and James Watson
Contribution: Discoverers of double helix
Experiment: Using stick-and-ball models, Watson and Crick tested their ideas of how the DNA molecule might fit together. Their first attempt in 1951 failed, but they kept at it. They also used information from X-ray pictures to give them ideas for the structure.
