In the DNA double helix, complementary base pairs (A with T, and G with C) are primarily held together by which type of interaction?

• A. Ionic bonds formed between the sugar-phosphate backbones of opposite strands
• B. Peptide bonds linking adjacent nucleotides within each strand
• C. Hydrogen bonds between complementary nitrogenous bases
• D. Covalent phosphodiester bonds between bases across the two strands

Answer: (C)

Verified step by step guidance

1. Identify the types of bonds mentioned in the problem and understand their roles in DNA structure: ionic bonds, peptide bonds, hydrogen bonds, and covalent phosphodiester bonds.
2. Recall that the sugar-phosphate backbone of DNA strands is held together by covalent phosphodiester bonds, which link nucleotides within the same strand, not between strands.
3. Understand that peptide bonds are specific to proteins and link amino acids, so they are not involved in DNA structure.
4. Focus on the interaction between the two strands of the DNA double helix, where complementary nitrogenous bases pair up (A with T, and G with C).
5. Recognize that these complementary bases are held together by hydrogen bonds, which are weaker than covalent bonds but strong enough to stabilize the double helix and allow strand separation during replication.