2.6 DNA’s Double Helix Structure
After DNA was found to be the material for genes, scientists around the world
competed to elucidate its molecular structure. In 1950, E. Chargaff analyzed the
formation of DNA bases in various organisms and found that while it differed from
one organism to the next, the amount of adenine was always equal to the amount of
thymine and the amount of guanine to the amount of cytosine (Chargaff 1950).
Around the same time, Wilkins learned that DNA extracted from different organisms showed similar X-ray diffraction, and that DNA was a very long, thin
molecule that coiled into a spiral. He also discovered that all DNA molecules
showed a rod-like structure measuring around 2 nm across, and that consisted of
Fig. 2.7 Hershey and Chase’s experiment. When E. coli were infected with T2 phages bearing
DNA marked with
32
P and proteins marked with
35
S, only the DNA marked with
32 P entered the
bacterium, while the
35
S-marked proteins did not
34
2 Introduction to Molecular Biology
After DNA was found to be the material for genes, scientists around the world
competed to elucidate its molecular structure. In 1950, E. Chargaff analyzed the
formation of DNA bases in various organisms and found that while it differed from
one organism to the next, the amount of adenine was always equal to the amount of
thymine and the amount of guanine to the amount of cytosine (Chargaff 1950).
Around the same time, Wilkins learned that DNA extracted from different organisms showed similar X-ray diffraction, and that DNA was a very long, thin
molecule that coiled into a spiral. He also discovered that all DNA molecules
showed a rod-like structure measuring around 2 nm across, and that consisted of
Fig. 2.7 Hershey and Chase’s experiment. When E. coli were infected with T2 phages bearing
DNA marked with
32
P and proteins marked with
35
S, only the DNA marked with
32 P entered the
bacterium, while the
35
S-marked proteins did not
34
2 Introduction to Molecular Biology