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DNA Spirals

X-ray crystal image of DNA spacer What does all that DNA look like? In the 1950s, James Watson got a look at an X-ray image, much like this one, taken from DNA crystals. From the pattern of spots on the image, he concluded that DNA must be a spiral, or helix shape.
 ribbon helix

Watson and Francis Crick figured out that DNA looks like two threads twisted around each other, held together by many bridges between the strands. You could think of it as a spiral staircase. This shape is called a double helix. There are many ways of looking at the double helix.