Nucleotides are made up of a phosphate group, a nitrogen base and a pentose sugar. These structural units serve as the fundamental building blocks of nucleic acids, such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA and RNA are named after the type of sugar molecule present in their nucleotides. The five-carbon sugar component in DNA is called deoxyribose, while the pentose sugar in RNA is referred to as ribose.
In a DNA nucleotide, the nitrogen-containing base may be one of four types: adenine, thymine, cytosine and guanine. Adenine and guanine, which are characterized by their double-ring configuration, are classified as purine bases. Cytosine and thymine, which contain a single ring structure, are categorized as pyrimidine bases. In RNA, thymine is replaced with uracil.