Question

The two polynucleotide strands of DNA are held together by

• A. Hydrogen bonds
• B. Covalent bonds
• C. Metallic bonds
• D. Ionic bonds
• E. Polar covalent bonds

Answer 1

The correct option is A Hydrogen bonds

Two polynucleotide chains of DNA are wound around the same axis and are held together by complementary base pairing between nitrogenous bases of two strands in the same plane. Adenine of one strand forms two hydrogen bonds with thymine of other strand and guanine forms three hydrogen bonds with cytosine. The two bases forming hydrogen bonds to joins the polynucleotide strands together are present in the same plane. Thus, the correct answer is A.