The Gene Ontology project provides controlled vocabularies of defined terms representing gene product properties. These cover three domains:
Cellular Component, the parts of a cell or its extracellular environment;Molecular Function, the elemental activities of a gene product at the molecular level, such as binding or catalysis;Biological Process, operations or sets of molecular events with a defined beginning and end, pertinent to the functioning of integrated living units: cells, tissues, organs, and organisms.
The GO ontology Is structured As a directed acyclic graph where Each term has defined relationships To one Or more other terms In the same domain, And sometimes To other domains. The GO vocabulary Is designed To be species-agnostic, And includes terms applicable To prokaryotes And eukaryotes, And Single And multicellular organisms.
In an example of GO annotation, the gene product cytochrome c can be described by the Molecular Function term oxidoreductase activity, the Biological Process terms oxidative phosphorylation And induction of cell death, And the Cellular Component terms mitochondrial matrix And mitochondrial inner membrane.