Final answer:
In DNA, adenine pairs with thymine and guanine pairs with cytosine. In RNA, adenine pairs with uracil and guanine pairs with cytosine.
Step-by-step explanation:
The nitrogen bases in DNA and RNA are called 'nitrogenous bases' because they contain nitrogen atoms in their structure. In DNA, the four nitrogenous bases are adenine (A), guanine (G), cytosine (C), and thymine (T). In RNA, the bases are adenine (A), guanine (G), cytosine (C), and uracil (U).
Purines and pyrimidines are two types of nitrogenous bases. Purines, such as adenine and guanine, have a double-ring structure, while pyrimidines, such as cytosine, thymine, and uracil, have a single-ring structure.
Each base pairs with a complementary base. In DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). In RNA, adenine (A) pairs with uracil (U), and guanine (G) pairs with cytosine (C).