In the DNA double helix, the two antiparallel strands are primarily held together by which type of interaction?

• A. Hydrogen bonds between complementary nitrogenous bases (A with T, and G with C)
• B. Covalent peptide bonds between adjacent nucleotides on opposite strands
• C. Ionic bonds between the sugar-phosphate backbones of the two strands
• D. Phosphodiester bonds linking the bases to each other across the helix

Answer: (A)

Verified step by step guidance

1. Recall the structure of the DNA double helix, which consists of two antiparallel strands made up of nucleotides.
2. Understand that each nucleotide contains a sugar, a phosphate group, and a nitrogenous base (A, T, G, or C).
3. Recognize that the sugar-phosphate backbone of each strand is held together by covalent phosphodiester bonds, but these bonds do not connect the two strands to each other.
4. Identify that the two strands are held together by interactions between the nitrogenous bases on opposite strands, specifically through hydrogen bonds.
5. Remember that adenine (A) pairs with thymine (T) via two hydrogen bonds, and guanine (G) pairs with cytosine (C) via three hydrogen bonds, stabilizing the double helix.