Question

If a DNA double helix is gradually heated, which bonds in the molecule will break first (are the weakest)?

A. bonds between the nitrogenous bases
B. bonds between the bases and the sugars
C. bonds between the sugar and phosphate within a nucleotide
D. bonds between the sugar and phosphate of adjacent nucleotides

Answer 1

The answer is A. bonds between the nitrogenous bases

Answer 2

A is the correct answer. Chemical bonds can be classified as strong or weak. Van der Waals bonds (attractions) are weak and ionic or covalent bonds are strong. The bonds between bases, sugars and phosphates (answers B, C and D) are all covalent and are strong. The bonds between two bases, answer A, are weak van der Waals bonds.