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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About Structure of DNA
DNA structure includes nucleotides made of deoxyribose, phosphate and nitrogenous bases, arranged in two antiparallel polynucleotide strands. Questions cover the double helix, phosphodiester and hydrogen bonds, complementary base pairing between adenine and thymine and between guanine and cytosine, and the significance of major and minor grooves.
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