In the DNA double helix, what interaction primarily holds the two antiparallel strands together?

• A. Ionic bonds between the negatively charged phosphate groups of each strand
• B. Hydrogen bonds between complementary nitrogenous bases (A with T, and G with C)
• C. Peptide bonds between adjacent nucleotides across the two strands
• D. Covalent phosphodiester bonds between nucleotides on opposite strands

Answer: (B)

Verified step by step guidance

1. Understand the structure of the DNA double helix, which consists of two antiparallel strands made up of nucleotides.
2. Recall that each nucleotide contains a sugar, a phosphate group, and a nitrogenous base (A, T, G, or C).
3. Identify the types of bonds present: phosphodiester bonds link nucleotides within the same strand, while hydrogen bonds form between complementary nitrogenous bases across the two strands.
4. Recognize that ionic bonds between phosphate groups are not responsible for holding the two strands together because the phosphate groups are negatively charged and repel each other.
5. Conclude that the primary interaction holding the two antiparallel strands together is the hydrogen bonds between complementary nitrogenous bases (A pairs with T, and G pairs with C).