Cytosine is one of the four main building blocks of DNA and RNA, which are essential molecules for life. It is a type of nitrogenous base, and its chemical structure allows it to pair with another base called guanine in DNA. This pairing is crucial for the formation of the double helix structure of DNA, which carries genetic information. In addition to its role in DNA, cytosine is also important in the process of protein synthesis. When DNA is transcribed into messenger RNA, cytosine helps code for specific amino acids, which are the building blocks of proteins. This makes cytosine vital for the proper functioning of cells and the overall health of an organism.