Multiple Choice
In the structure of DNA, what molecules form the sugar-phosphate backbone of each strand?
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7. DNA and Chromosome Structure
DNA Structure
Multiple Choice
In the DNA double helix, what type of interaction holds complementary bases together across the two strands?
A
Covalent bonds between complementary bases across the helix
B
Phosphodiester bonds between the nitrogenous bases
C
Hydrogen bonds between complementary base pairs (A–T and G–C)
D
Ionic bonds between the sugar-phosphate backbones
Verified step by step guidance1
Understand the structure of the DNA double helix: it consists of two strands running in opposite directions, each made up of a sugar-phosphate backbone and nitrogenous bases extending inward.
Recall that the sugar-phosphate backbone of each strand is held together by phosphodiester bonds, which are covalent bonds linking the sugar of one nucleotide to the phosphate of the next.
Focus on the interaction between the two strands: the nitrogenous bases on one strand pair specifically with complementary bases on the opposite strand (A pairs with T, and G pairs with C).
Identify the type of bond that holds these complementary bases together across the two strands. These are hydrogen bonds, which are weaker than covalent bonds but strong enough to stabilize the double helix while allowing strand separation during replication.
Conclude that the correct interaction holding complementary bases together across the two strands of DNA is hydrogen bonding between the base pairs (A–T and G–C).
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