Final answer:
DNA contains four nitrogen bases: adenine (A), thymine (T), cytosine (C), and guanine (G). The bases form the building blocks of DNA and encode genetic information. Adenine pairs with thymine, and cytosine pairs with guanine.
Step-by-step explanation:
DNA contains four nitrogen bases: adenine (A), thymine (T), cytosine (C), and guanine (G). These bases form the building blocks of DNA and are responsible for encoding genetic information. Adenine always pairs with thymine, and cytosine always pairs with guanine, creating a double helix structure in DNA.
In RNA, uracil (U) replaces thymine, but the other three bases remain the same. The sequence of these bases in DNA carries instructions for making proteins.
This pair rule is a fundamental concept of the DNA double helix structure, ensuring precise genetic information is preserved during cell division. DNA does not include uracil (U); this base is found in RNA, where it replaces thymine.