Nucleotide
Biochemistry · Molecular Biology · Genetics
Say it: NOO-klee-uh-tide
A nucleotide is a single unit of DNA or RNA, made of a nitrogen-containing base, a five-carbon sugar and one or more phosphate groups.
Also: nucleotides
Definition
What is a nucleotide?
A nucleotide is a small molecule with three parts: a nitrogenous base, a five-carbon (pentose) sugar and at least one phosphate group. The bases come in two shapes. Purines, adenine (A) and guanine (G), have a double ring, while pyrimidines, cytosine (C), thymine (T) and uracil (U), have a single ring. DNA nucleotides contain the sugar deoxyribose and use thymine, whereas RNA nucleotides contain ribose and use uracil instead.
Nucleotides join into long chains through phosphodiester bonds, which link the phosphate on the 5' carbon of one sugar to the 3' carbon of the next. This gives each strand a sugar-phosphate backbone with the bases sticking out to one side, and the order of those bases carries genetic information. In DNA, bases on opposite strands pair up, A with T and G with C.
Nucleotides have jobs beyond genetic material. ATP, the cell's energy currency, is an adenine nucleotide with three phosphates, and the electron carriers NAD+ and FAD used in respiration are built from nucleotides too. A change at a single nucleotide in DNA is the basis of a SNP and of many mutations.
Word parts
Where does the word “nucleotide” come from?
- nucle-
- kernel, nucleus (from Latin nux, nut)Latin nucleus
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- DNADNA is the double-stranded molecule that carries the genetic instructions of nearly all living things, written in a code of four bases: A, T, C and G.
- RNARNA is a usually single-stranded nucleic acid, built with the sugar ribose and the base uracil, that carries and uses genetic information to make proteins.
- ATPATP (adenosine triphosphate) is the molecule cells use as their main short-term energy carrier, releasing energy when a phosphate group is removed.
- Single nucleotide polymorphismA single nucleotide polymorphism (SNP) is a position in the genome where people differ by a single DNA base, the most common kind of genetic variation.
- CodonA codon is a sequence of three nucleotides in DNA or messenger RNA that stands for one amino acid or tells the ribosome to stop.
- DNA polymeraseDNA polymerase is an enzyme that builds new DNA by adding nucleotides one at a time to a growing strand, using an existing strand as a template.
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