Hydrogen bonds in DNA occur between the nitrogenous bases of the two antiparallel strands, specifically where adenine pairs with thymine and guanine pairs with cytosine inside the double helix.

Key locations of hydrogen bonds

  • Between complementary base pairs:
    • Adenine (A) forms two hydrogen bonds with thymine (T).
* Guanine (G) forms three hydrogen bonds with cytosine (C).
  • These bonds are located in the interior of the DNA double helix, holding the two strands together while the sugar‑phosphate backbones run along the outside.

What they bond between

  • Hydrogen bonds form between specific atoms on the bases: typically hydrogen donors (N–H groups) on one base and electronegative atoms (N or O) on the complementary base.
  • This pattern of hydrogen donors and acceptors is what enforces complementary base pairing (A with T, G with C) rather than random pairing.

Why their position matters

  • Because the hydrogen bonds are in the center between bases, they:
    • Stabilize the double helix while still being weak enough individually to allow strand separation during replication and transcription.
* Help maintain a uniform distance between the two sugar‑phosphate backbones, which is crucial for the regular helical shape of DNA.

TL;DR: Hydrogen bonds in DNA are found between the complementary base pairs (A–T and G–C) in the middle of the double helix, connecting the two strands and stabilizing the structure.