Which intermolecular force is primarily responsible for holding the two strands of DNA together?

• A. Covalent bonding
• B. Hydrogen bonding
• C. Van der Waals forces
• D. Ionic bonding

Answer: (B)

Verified step by step guidance

1. Understand the structure of DNA: DNA is composed of two strands that form a double helix. These strands are held together by interactions between the nitrogenous bases of the nucleotides.
2. Identify the types of intermolecular forces: Intermolecular forces include hydrogen bonding, Van der Waals forces, ionic bonding, and covalent bonding. Each has distinct characteristics and roles in molecular interactions.
3. Focus on the nitrogenous bases: The nitrogenous bases (adenine, thymine, cytosine, and guanine) pair specifically (A with T, and C with G) through complementary base pairing. This pairing involves specific interactions between the bases.
4. Recognize the role of hydrogen bonding: Hydrogen bonds are weak intermolecular forces that occur between a hydrogen atom covalently bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom. In DNA, hydrogen bonds form between the complementary bases (A-T has 2 hydrogen bonds, C-G has 3 hydrogen bonds).
5. Conclude that hydrogen bonding is the primary force: Hydrogen bonding is responsible for the stability and specificity of the base pairing, which holds the two strands of DNA together in the double helix structure.