Which two bases pair together in DNA and form two hydrogen bonds?

In DNA, the pairing of nitrogenous bases is fundamental to its structure and function. Adenine and thymine pair together specifically through the formation of two hydrogen bonds. This pairing is a key feature of the double helix structure of DNA, stabilizing the molecule and ensuring that the genetic information can be faithfully replicated and transcribed.

Adenine is a purine, while thymine is a pyrimidine, and they complement each other in size and structure, allowing for proper alignment and bonding. The two hydrogen bonds that form between adenine and thymine are crucial because they contribute to the overall stability of DNA while still allowing for the necessary flexibility for replication.

In contrast, other pairings such as adenine with cytosine and guanine with cytosine involve different bonding mechanisms. Guanine and cytosine, for instance, form three hydrogen bonds, making their pairing stronger than that of adenine and thymine. Pairing with uracil occurs in RNA, not DNA, and thymine specifically replaces uracil in DNA. Understanding the specific base pair interactions is essential for grasping fundamental concepts in genetics and molecular biology.