Question

In order to explain DNA's consistent width, Watson and Crick concluded that

Answer 1

The answer is C. Purines (A and G) have double-ring structure while pyrimidines (C and T) have single rings. The obligate complimentary base pairing between a purine and pyrimidine ensures that the width between the helix backbones are maintained at approximately 20 angstroms.

Answer 2

Answer;

C. one single ring base will always bond with one double ring base.

Explanation;

• At first, Watson and Crick thought the bases paired such that a like base pairs with its like (A with A, and so on), but such pairings did not result in a uniform width.
• Instead, pairing a purine with a pyrimidine resulted in a uniform width consistent with the X-ray data.
• Each base pair forms a different number of hydrogen bonds. Adenine and thymine form two hydrogen bonds, cytosine and guanine form three hydrogen bonds