A nucleotide is a building block of nucleic acids, which are the molecules that store and transmit genetic information in living organisms.
A nucleotide is composed of three parts: a nitrogen-containing base, a five-carbon sugar molecule, and a phosphate group. 1
The nitrogen-containing base can be one of four types: adenine (A), cytosine (C), guanine (G), or thymine (T) in DNA, or uracil (U) in RNA.
The five-carbon sugar molecule is either deoxyribose in DNA or ribose in RNA. The phosphate group is a molecule containing one phosphorus atom and four oxygen atoms.
Nucleotides are linked together through covalent bonds between the phosphate group of one nucleotide and the sugar molecule of another nucleotide, forming a long chain called a polynucleotide. The sequence of the nitrogen-containing bases in the polynucleotide chain determines the information that the nucleic acid molecule carries.