Nucleobases are the building blocks of DNA and RNA, which are essential molecules for life. There are five main nucleobases: adenine (A), thymine (T), cytosine (C), guanine (G), and uracil (U). In DNA, adenine pairs with thymine, while cytosine pairs with guanine. In RNA, uracil replaces thymine. These pairings help store and transmit genetic information. Each nucleobase has a unique structure and plays a crucial role in coding for proteins. The sequence of nucleobases in a DNA strand determines the genetic instructions for an organism, influencing traits and functions. This sequence is often referred to as the genetic code.