History of The discovery of DNA

Johann Friedrich Mieschner 1869 Mieschner discovered large molecules in the nucleus of the cell that were acidic . He called them nucleic acids. He didn’t know what they were for.

Frederick Griffith 1928 80 years later Bacteria could share “genetic material”. It could transfer from 1 bacteria to another

Griffith’s Experiment

Frederick Griffith’s experiment There were 2 kinds of Pneumonococcus bacteria Rough strain was harmless to the mice. Smooth strain killed the mice. If he heat killed the smooth strain then the mice lived. If he mixed the heat killed smooth bacteria with the rough strain, then the mice died. Something was transferred from the dead bacteria into the live innocuous bacteria that made it deadly. .

Oswald Avery and coworkers Colin McCleod and Maclyn McCarty 1944 Common belief was protein carried the genetic information. Avery removed all the protein from the bacteria and repeated the Griffith experiment. It still transformed the Bacteria DNA was the “something” that carried the genetic information

Linus Pauling 1950 Protein chains were helical. The first twist is called the alpha helix. The 2nd twist is the beta sheets DNA was similar also helical. He won 2 Nobel prizes 1 in chemistry for protein structure. Nobel peace prize for his work vs. above ground nuclear testing.

Rosalind Franklin 1951 She perfected the technique of x-ray chrystalography Took the first photographs of DNA Identified 2 kinds Her unpublished papers inspired and supported Watson and Crick. Personality clashes with her collegue Wilkins, prevented her from getting credit.

Erwin Chargaff 1951 2 rules Using paper chromatography he found the amount of adenine = thiame And the amount of cytosine = guanine Different species had different ratios of nitrogen bases.

James Watson and Francis Crick 1953 Discovered the double helix structure of DNA. Twisted ladder (Left handed twist) Sugar phosphates sides (anti parallel) Nitrogen bases for rungs (Complimentary) As you can see they stood on the support of their collegues. Won the Nobel Prize 1962 with Maurice Wilkins. Rosalind Franklin was not included

Matthew Messelson and Franklin W. Stahl 1958 Determined the method by which DNA replicated. If it was the “Stuff of inhertance” it had to duplicate. One new strand and one old strand (Semi conservative)

Nirenberg and coworkers Crick and coworkers 1961 The triplicate code Three DNA nucleotides code for 1 amino acid Nirenberg and coworkers 1964 Supported Crick’s hypothesis

Human Genome Project 2003 identify all the approximately 20,000-25,000 genes in human DNA, determine the sequences of the 3 billion chemical base pairs that make up human DNA, 1993 NIH & Dept of Energy joined to become the National Human Genome Research Institute (NHGRI) Headed by Francis Collins. 1998 Craig Venter and Celera Genomics wanted to do it privately and get patents for the genes. This was deemed unethical in 2000 but the competition speeded up the process