What type of bond holds the nitrogenous bases together within the DNA double helix?

What type of bond holds the nitrogenous bases together within the DNA double helix?

• A. Ionic bond
• B. Hydrogen bond
• C. Covalent bond
• D. Peptide bond

Answer: (B)

Hydrogen bonds between complementary nitrogenous bases hold the DNA double helix together. Adenine pairs with thymine using two hydrogen bonds, while cytosine pairs with guanine using three, which gives the specific A–T and G–C pairings that stabilize the two strands in the right orientation. These bonds are strong enough to keep the strands aligned but weak enough to break when DNA needs to be copied or transcribed. The backbone stability comes from covalent phosphodiester bonds within each strand, not from the base-to-base interactions. Ionic bonds aren’t the primary force here, and peptide bonds are used to link amino acids in proteins, not nucleotides in DNA.

Hydrogen bonds between complementary nitrogenous bases hold the DNA double helix together. Adenine pairs with thymine using two hydrogen bonds, while cytosine pairs with guanine using three, which gives the specific A–T and G–C pairings that stabilize the two strands in the right orientation. These bonds are strong enough to keep the strands aligned but weak enough to break when DNA needs to be copied or transcribed. The backbone stability comes from covalent phosphodiester bonds within each strand, not from the base-to-base interactions. Ionic bonds aren’t the primary force here, and peptide bonds are used to link amino acids in proteins, not nucleotides in DNA.