Wilkins X-ray diffraction showed the diameter of the DNA helix as ________?

Correct answer: B. 20A

  • A. 10A
  • B. 20A
  • C. 30A
  • D. 40A

Explanation

Wilkins's X-ray diffraction data supported a DNA helix diameter of about 20 Å, which is 2 nm because 10 Å = 1 nm and 20 Å ÷ 10 = 2 nm. Students may choose 10 Å by confusing the helix diameter with the approximate spacing between stacked base pairs, which is about 3.4 Å.

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