Genetics Review
PubMed Entrez BLAST OMIM Taxonomy Structure
NCBI Site Map

Course Description



Genetics Review

Types of Databases

Format of Sequence Record



3-D Structures

Genomes and Maps

Librarian Roles

WWW Sites

Glossaries and Dictionaries


Nucleotide back to top

Source:  image from the National Human Genome Research Institute (NHGRI) Genetic Illustrations.

Definition back to top

A nucleotide is one of the structural components, or building blocks, of DNA and RNA. A nucleotide consists of a base (one of four chemicals: adenine, thymine, guanine, and cytosine) plus a molecule of sugar and one of phosphoric acid.

More:  C, T, and U are called pyrimidines and each has a single nitrogen-containing ring. A and G are called purines and each has two nitrogen-containing rings.

Source:  definition from the National Human Genome Research Institute (NHGRI) Glossary of Genetic Terms.

Help Desk NCBI NLM NIH Credits
  Revised September 29, 1999
Comments/questions about course to Renata Geer
Questions about NCBI resources to