* Adenine (A)

* Guanine (G)

* Cytosine (C)

* Thymine (T)

They pair up in a specific way:

* Adenine (A) always pairs with Thymine (T)

* Guanine (G) always pairs with Cytosine (C)

This pairing is known as complementary base pairing. It is essential for the structure and function of DNA because it ensures that the two strands of DNA are held together correctly.

The complementary base pairing also allows for the accurate replication of DNA, as each strand can be used as a template to create a new complementary strand.