Nucleotide - GCSE Biology Definition

A nucleotide is a small molecule that acts as the basic building block of DNA and RNA, which are essential for storing and transmitting genetic information in living organisms. Each nucleotide is made up of three parts: a sugar, a phosphate group, and a nitrogenous base. In DNA, the bases are adenine (A), thymine (T), cytosine (C), and guanine (G), while in RNA, thymine is replaced by uracil (U). These bases pair in specific ways (A with T, and C with G in DNA) to form the rungs of the DNA ladder. Nucleotides are essential for heredity and play a key role in the coding, decoding, and expression of genes.