The nitrogen base pairing rule in biology is also known as Chargaff's rule. It states that in DNA, adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C).

This pairing is based on the hydrogen bonding between the nitrogenous bases:

* Adenine (A) forms two hydrogen bonds with thymine (T).

* Guanine (G) forms three hydrogen bonds with cytosine (C).

Key points:

* This pairing is essential for the accurate replication of DNA.

* The specific pairing ensures that the two strands of DNA are complementary to each other.

* This complementarity allows for the accurate transcription of genetic information into RNA.

In RNA, uracil (U) replaces thymine (T), so the pairing rule becomes:

* Adenine (A) pairs with uracil (U)

* Guanine (G) pairs with cytosine (C)