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Structure of DNA

98 questions found

Practice Questions

7. The total diameter of the standard B-form DNA double helix as determined by Watson and Crick is exactly

A. 1 nanometer

B. 2 nanometers ✓

C. 3.4 nanometers

D. 0.34 nanometers

The double helix maintains a constant width of 2 nm (20 A˚) because a double-ringed purine always pairs with a single-ringed pyrimidine.

8. The chemical linkage that holds the sugar-phosphate backbone of a single DNA strand together is the

A. Hydrogen bond

B. Phosphodiester bond ✓

C. Peptide bond

D. Glycosidic bond

Phosphodiester bonds covalently link the 3' carbon of one deoxyribose sugar to the 5' carbon of the adjacent sugar via a phosphate group.

9. The scientific data that directly provided Watson and Crick with the structural dimensions and helical nature of DNA was derived from

A. Protein sequencing

B. X-ray diffraction images ✓

C. Paper chromatography

D. Electron microscopy

Rosalind Franklin’s famous "Photo 51" obtained via X-ray crystallography revealed the helical configuration and dimensions of the DNA molecule.

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