A nucleotide is composed of a nucleobase (nitrogenous base), a five-carbon sugar (either ribose or 2-deoxyribose), and one phosphate group. Nucleotides contain either a purine or a pyrimidine base. Ribonucleotides are nucleotides in which the sugar is ribose. Deoxyribonucleotides are nucleotides in which the sugar is deoxyribose.
In DNA, the purine bases are adenine and guanine, and the pyrimidines are thymine and cytosine. RNA uses uracil in place of thymine. Adenine always pairs with thymine by 2 hydrogen bonds, while guanine pairs with cytosine through 3 hydrogen bonds, each due to their unique structures.
Nucleotides also play a central role in metabolism at a fundamental, cellular level. They provide chemical energy for the many cellular functions that need it. Examples are: amino acid, protein and cell membrane synthesis, moving the cell and cell parts (both internally and intercellularly), cell division, and so on. In addition, nucleotides work in cell signaling, and they are in important cofactors of enzymatic reactions (e.g. coenzyme A, FAD, FMN, NAD, and NADP+).
Images for kids
Showing the arrangement of nucleotides within the structure of nucleic acids: At lower left, a monophosphate nucleotide; its nitrogenous base represents one side of a base-pair. At the upper right, four nucleotides form two base-pairs: thymine and adenine (connected by double hydrogen bonds) and guanine and cytosine (connected by triple hydrogen bonds). The individual nucleotide monomers are chain-joined at their sugar and phosphate molecules, forming two 'backbones' (a double helix) of nucleic acid, shown at upper left.
Nucleotide Facts for Kids. Kiddle Encyclopedia.