mitochondrion

GO:0005739 · Membrane organelle · Membrane bounded organelle · Proposed

A semiautonomous, self replicating organelle that occurs in varying numbers, shapes, and sizes in the cytoplasm of virtually all eukaryotic cells. It is notably the site of tissue respiration. [GO:0005739]

Synonyms: mitochondria

Has part: mitochondrial envelope (GO:0005740); mitochondrial outer membrane (GO:0005741); mitochondrial inner membrane (GO:0005743); mitochondrial matrix (GO:0005759); mitochondrial outer membrane translocase complex (GO:0005742)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Essential	Role
mitochondrial outer membrane	Lipid	part of	`GO:0005741`	UNKNOWN	Cytoplasm-facing lipid bilayer of the mitochondrial envelope and outer-membrane platform for the TOM import complex. `GO:0005741` GO:0005741 defines the mitochondrial outer membrane as the cytoplasm-facing lipid bilayer of the envelope.
mitochondrial inner membrane	Lipid	part of	`GO:0005743`	UNKNOWN	Lumen-facing lipid bilayer of the mitochondrial envelope that folds into cristae and separates the matrix from the intermembrane space. `GO:0005743` GO:0005743 defines the mitochondrial inner membrane as the lumen-facing folded bilayer of the envelope.
mitochondrial outer membrane translocase complex	Protein complex	part of	`GO:0005742`	UNKNOWN	Outer-membrane protein translocase that imports most nuclear-encoded mitochondrial precursor proteins into or across the mitochondrial outer membrane. `GO:0005742` GO:0005742 defines the TOM complex as a large outer membrane complex that mediates protein transport into mitochondrial compartments. `DOI:10.1016/j.cell.2009.08.005` Chacinska et al. 2009 review mitochondrial protein import through TOM and downstream sorting machineries.

Taxonomic distribution

NCBITaxon:2759 Eukaryota — VARIABLE: Canonical mitochondria are widespread in eukaryotes, while some anaerobic lineages carry reduced mitochondrion-related organelles such as mitosomes or hydrogenosomes. [GO:0005739]
NCBITaxon:4932 Saccharomyces cerevisiae — COMMON: Budding yeast has mitochondria whose proteome includes oxidative-phosphorylation, tricarboxylic-acid-cycle, and stable mitochondrially encoded proteins. [DOI:10.1073/pnas.2135385100]

Canonical examples

NCBITaxon:4932 Saccharomyces cerevisiae — Budding-yeast example with purified mitochondrial proteomes used to inventory matrix and membrane-associated mitochondrial machinery. [DOI:10.1073/pnas.2135385100]

Functions

oxidative phosphorylation GO:0006119 — Mitochondrial respiratory-chain activity across the inner membrane contributes to ATP synthesis by oxidative phosphorylation.
- GO:0006119 GO:0006119 defines oxidative phosphorylation as ATP formation coupled to respiratory-chain oxidation and membrane-gradient formation.
- DOI:10.1073/pnas.2135385100 Sickmann et al. 2003 recovered known oxidative phosphorylation machinery from purified budding-yeast mitochondria.
protein import into mitochondrial matrix GO:0030150 — TOM and downstream inner-membrane and matrix machinery import precursor proteins from the cytosol into the mitochondrial matrix.
- GO:0030150 GO:0030150 defines matrix protein import from the cytosol via TOM-TIM23-PAM.
- DOI:10.1016/j.cell.2009.08.005 Chacinska et al. 2009 review TOM entry and downstream TIM/PAM mitochondrial protein-import pathways.

Mechanism graphs

Mitochondrial envelope gates protein import (FUNCTION)

In budding yeast, inner and outer mitochondrial envelope membranes delimit the matrix, and the TOM complex provides the outer-membrane entry point for imported proteins.

Subject	Predicate	Object	Evidence
mitochondrial envelope	encloses	mitochondrion	`GO:0005740` GO:0005740 defines the mitochondrial envelope as the double lipid bilayer enclosing the mitochondrion.
mitochondrial outer membrane	is part of	mitochondrial envelope	`GO:0005741` GO:0005741 places the mitochondrial outer membrane in the envelope.
mitochondrial inner membrane	is part of	mitochondrial envelope	`GO:0005743` GO:0005743 places the mitochondrial inner membrane in the envelope.
mitochondrial inner membrane	bounds	mitochondrial matrix	`GO:0005759` GO:0005759 defines the matrix as the gel-like material in the mitochondrial matrix space or lumen.
mitochondrial outer membrane translocase complex	spans	mitochondrial outer membrane	`GO:0005742` GO:0005742 defines TOM as a large complex of the mitochondrial outer membrane.
mitochondrial outer membrane translocase complex	provides entry for	protein import into mitochondrial matrix	`DOI:10.1016/j.cell.2009.08.005` Chacinska et al. 2009 review TOM entry and downstream TIM23-PAM presequence import into the mitochondrial matrix.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral component boundaries and groundings for mitochondrial respiratory-chain complexes, ATP synthase, TIM/PAM import machinery, mitochondrial DNA, and mitoribosomal components. This first mitochondrion record grounds envelope membranes and the TOM complex but avoids treating every respiratory-chain or protein-import factor as a single exact component.

Evidence

GO:0005739 Gene Ontology cellular-component term for mitochondrion.
GO:0005740 Gene Ontology cellular-component term for the mitochondrial envelope.
GO:0005741 Gene Ontology cellular-component term for the mitochondrial outer membrane.
GO:0005743 Gene Ontology cellular-component term for the mitochondrial inner membrane.
GO:0005759 Gene Ontology cellular-component term for the mitochondrial matrix.
GO:0005742 Gene Ontology cellular-component term for the mitochondrial outer membrane translocase complex.
GO:0006119 Gene Ontology biological-process term for oxidative phosphorylation.
GO:0030150 Gene Ontology biological-process term for protein import into the mitochondrial matrix.
DOI:10.1073/pnas.2135385100 Sickmann et al. 2003, 'The proteome of Saccharomyces cerevisiae mitochondria', Proceedings of the National Academy of Sciences.
DOI:10.1016/j.cell.2009.08.005 Chacinska et al. 2009, 'Importing mitochondrial proteins: machineries and mechanisms', Cell.
DOI:10.1038/nature12985 Friedman and Nunnari 2014, 'Mitochondrial form and function', Nature.

Curation history

2026-09-11T17:53:04Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-11T17:53:47Z codex · EXPANDED_RECORD — Added mitochondrion parentage, envelope part terms, exact synonymy, outer/inner membrane and TOM components, Saccharomyces scope, oxidative-phosphorylation and matrix-import functions, a nonmechanistic envelope-and-import graph, and a respiratory/import subcomplex grounding TODO.
2026-09-11T18:02:02Z codex · REVIEW_FIXES — Connected the top-level mitochondrion graph node to the mitochondrial envelope and broadened the TOM graph edge to the general mitochondrial protein import pathway.
2026-09-11T18:05:16Z codex · REVIEW_FIXES — Kept the TOM graph process on adapter-backed GO:0030150 and clarified that TOM provides the outer-membrane entry step for matrix import.
2026-09-20T21:55:39Z codex · ADDRESSED_REVIEW — Retyped the TOM complex graph node from GENE_OR_PROTEIN to STRUCTURE.

Source: data/structures/membrane_organelle/mitochondrion.yaml