What holds the complementary bases of two DNA strands together?

What holds the complementary bases of two DNA strands together?

• A. Covalent bonds (strong) hold the complementary bases together.
• B. Hydrogen bonds (weak) hold the complementary bases together.
• C. Ionic bonds hold the complementary bases together.
• D. Disulfide bonds hold the complementary bases together.

Answer: (B)

Base pairing in DNA is stabilized by hydrogen bonds between complementary bases across the two strands. Adenine pairs with thymine using two hydrogen bonds, and guanine pairs with cytosine using three hydrogen bonds. These bonds are weaker than covalent bonds, which is important because it allows the two strands to come apart during replication and transcription and then rejoin. The backbone of each strand is held together by covalent phosphodiester bonds, not by base pairing. Ionic or disulfide bonds don’t hold the base pairs together in DNA.

Base pairing in DNA is stabilized by hydrogen bonds between complementary bases across the two strands. Adenine pairs with thymine using two hydrogen bonds, and guanine pairs with cytosine using three hydrogen bonds. These bonds are weaker than covalent bonds, which is important because it allows the two strands to come apart during replication and transcription and then rejoin. The backbone of each strand is held together by covalent phosphodiester bonds, not by base pairing. Ionic or disulfide bonds don’t hold the base pairs together in DNA.