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DNA Creation Timeline
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Fredrick Griffith
Fredrick studied two strains of the same bacteria and found that one could be changed into the form of the other. One strain (called the smooth strain) was sugar coated and the other (called the rough strain) was not. Griffith found that a mixture of live R cells and dead S cells also killed a mouse. He isolated and cultured the bacteria, and discovered the smooth trait visible in the cells. He concluded that a transformation had occured between the R strain and the S strain. -
P. A. Levene
Levene determined the structure of the nucleotides that make up DNA. Nucleotides are subunits of nucleic acids and consist of a 5-carbon sugar, a phosphate group and a nitrogenous base. DNA nucleotides contain sugar deoxyribose, a phosphate, and contain of the following- adenine, guanine, cytosine, and thymine. RNA nucleotides consist of sugar ribose, a phosphate, and one of the following- adenine, guanine, cytosine and uracil. -
Oswald Avery
Oswald performed a series of experiments with strains of pneumonia bacteria. Instead he lysed the dead S strain cells with detergent. When the lysed cells were mixed with live R cells, the new cells became S strain cells. Avery started to test each of the lysate components separately. While doing this, he had set aside the nucleic acids and precipitated them wiith alcohol. He separated the DNA and RNA, and tested them. He found that DNA was causing the transformation. -
Erwin Chargaff
Erwin Chargaff analyzed the amounts of adenine, guanine, cytosine and thymine in the DNA of various animals. He found that the amounts of cytosine and guanine in a species are the same, as well as the amounts of adenine and thymine. Chargaff published this as a rule- C=G and A=T. -
Rosalind Franklin
Franklin was hired to x-ray crystallography at King's College in London. She x-rayed two different DNA fibers, and concentrated her focus on one of them. Franklin calculated the basic dimensions and submitted the calculations. They were eventually used to create the first 3-D model of DNA. -
Hershey and Chase
They were studying bacteriophage genetics and wanted to know what caused the change of bacteria into a phage-producing factory. They used sulfer to selectively label phage DNA and protein. Then they combined the phage with bacteria and waited for the phages to attach before disengaging them and mixing culture in a Waring blender. Next, they spun the mix in a centrifuge to separate the phage and the bacteria. They found that the phage DNA was used to make new phage particles. -
Maurice Wilkins
He worked with Rosalind Franklin on the x-ray diffraction. -
Linus Pauling
Pauling proposed a triple-stranded helix model for DNA. He organized the phosphates facing the helical core; the nitrogenous bases facing out. However he had forgotten the negative charges of every oxygen atom in the phosphate group. They would repel and bust the model apart. -
Watson and Crick
While Rosalind Franklin worked on the other picture of DNA fiber, Watson and Crick worked on the simpler one. Crick noticed that the 'x' shape was very similar to that of a double helix. The horizontal bars corresponded to helical turns, and the vertical bars measured the height of one helical turn. They figured out that there must be 10 nucleotides per helical repeat. In the end, they deduced that the DNA model should be a double helix with phosphates on the outside and bases on the inside.
