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Friedrich Miescher PT. 1
He was the first person to identify what he called "nuclein" and would later become what we know as DNA in a cells nucleus. His plan was to isolate and characterize not the DNA but the protein components of white blood cell. He made arrangements from his local clinic to get bandages; he would wash them and filter out the white blood cells and then identify the various proteins. -
Miescher PT.2
He noticed a protein unlike any other discovered and realized he discovered a new protein with a higher phosphate content and resistance to protein digestion in the nucleus. He determined that nuclein was made up of Hydrogen, Oxygen, Nitrogen and Phosphorus. -
Rosalind Franklin
She used a technique called X-Ray crystallography to find the 3D shapes of Molecules. From this she deducted the basic dimensions of the DNA strands and that phosphates were the outside part of the structure.The technique would be used to discover the shape of DNA. That would later be used for Watson and Crick to create their model of a DNA strand. Citations:
Martine Oudenhoven. "Making Life Crystal Clear." ASU - Ask A Biologist. 19 Aug 2012. ASU - Ask A Biologist, Web. 20 Jan 2017. -
Erwin Chargaff PT. 1
At first he set out to see if DNA was different for different species. After developing a new paper chromatography method for separating and identifying small amounts of organic matter, he reached two major conclusions. First, he noted that nucleotide composition varies from one species to another. Bibliography for Image and Information:
Pray, Leslie A. "Discovery of DNA Structure and Function: Watson and Crick." Nature.com. Macmillan Publishers, 2008. Web. 23 Jan. 2017 -
Chargaff PT. 2
Secondly that all DNA has certain properties. This discovery would lead to what is now known as "Chargaff's Rule". -
Hershey and Chase PT. 1
Protein was finally excluded as a hereditary material following a series of experiments published by Hersey and Chase. The experiments involved T2 bacteriophage, a virus in the E. coli bacterium. They used radioisotopes to trace the fate of the phages proteins. During the analysis of their experiments, the scientist discovered that protein was used to form a protective coat around the bacteriophage. -
Hershey and Chase PT2
Using a high speed blender, they were able to force the bacteriophages from the cells after absorption. The presence of radioactive solution showed that the protein coat of DNA stayed outside of the cell.
The scientist stated that protein was not the hereditary but they also did not prove that DNA was the hereditary material. Bibliography:
O'Connor, C. (2008) Isolating hereditary material: Frederick Griffith, Oswald Avery, Alfred Hershey, and Martha Chase. Nature Education 1(1):105 -
Watson and Crick PT.1
They came up with the model that we use today for DNA. That DNA is a double helix with two strands connected by hydrogen bonds; A's pair with T's, and C's pair with G's, which agrees with Chargaff's rules. DNA is anti-parallel, meaning that the 5' end is paired with the 3' end. Bibliography for Image and Information:
Pray, Leslie A. "Discovery of DNA Structure and Function: Watson and Crick." Nature.com. Macmillan Publishers, 2008. Web. 23 Jan. 2017 -
Watson and Crick PT2
Most DNA is "right-handed" meaning that if you hold out your right hand and put your thumb up with your fingers curled around your thumb, your thumb would represent the axis of the DNA.
Finally, not only are DNA base pairs connected via hydrogen bonding, the outer edges are available for potential H-bonding as well.
These two scientists were the first to formulate an accurate description of the molecule's complex double-helix structure. -
Meselson and Stahl-PT.1
They began experimenting in order to discover how cells reproduced. They began by choosing two isotopes of nitrogen, N14 and N15 as their sedimentation method. They grew a colony of bacterial cells to see how DNA was made into daughter strands. At that time, there were three models for how organisms might replicate their DNA: conservative, semi-conservative and dispersive. -
Meselson-Stahl PT.2
To experiment, they grew a colony of bacterial cells to see how DNA was made into daughter strands. They found the cells midway between the two isotopes by getting rid of the conservative model and leaving the semi-conservative and the dispersive models. To find out which model was correct, they let the bacteria replicate again and sample the DNA again after the second round. -
Meselson and Stahl-PT.3
After the second round, the scientists found that the DNA separated into two distinct bands. This means that each strand of DNA molecule serves as the bases of the new complementary strand.
Other scientists would later confirm in other species that this was true. Bibliography:
Pray, L. (2008) Semi-conservative DNA replication: Meselson and Stahl. Nature Education 1(1):98
