Unit 3 Key Questions.docx - Unit 3 Key Questions Lesson 9...

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Unit 3 Key Questions Lesson 9 28. a) Watson and Crick used cardboard models of the nucleotides of DNA and used them to assemble various configurations to narrow down the possibilities of creating an accurate picture of the molecule. Watson and Crick were experimenting with many potential models of DNA having one, two and even three strands. Watson made an unexpected visit to Franklin’s lab where she had taken X-ray diffraction images of wet form DNA crystals. Once Watson saw the images, he knew the model with 2 strands was the correct one. Watson and Crick reworked their model based on Franklin’s images, creating a structure that was made of two chains of nucleotides, each in a twisted helix, with each chain running anti-parallel to each other. b) Franklin’s research was essential for Watson to confirm the structure of DNA. Franklin used X-ray diffraction images of a salt crystal form of the molecule. The images showed that wet form DNA (which is found in most cells) has a double helix shape. This confirmed that the two-
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