Final answer:
The four nitrogen bases of DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). Adenine pairs with thymine, and cytosine pairs with guanine. These base pairings, between a purine and a pyrimidine, maintain the DNA helix's structure and enable DNA replication.
Step-by-step explanation:
The four nitrogen bases of DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). These bases are called nitrogenous bases because they contain nitrogen atoms that are crucial for their structure and function in DNA. Adenine and guanine are categorized as purines, which are double-ringed structures, while cytosine and thymine are categorized as pyrimidines, which are single-ringed structures.
In DNA, the base pairing rules dictate that adenine (A) pairs with thymine (T) via two hydrogen bonds, and cytosine (C) pairs with guanine (G) via three hydrogen bonds. This pairing occurs between one purine and one pyrimidine. For example, an adenine on one strand of DNA will always pair with a thymine on the complementary strand, and similarly, a cytosine will pair with a guanine.
It's important to note that these base pairings are consistent due to their molecular structure, allowing for the DNA double helix structure to be maintained. The purine-pyrimidine pairings are critical because they ensure a uniform width of the DNA helix and allow for the accurate replication of DNA during cell division.