Membranes And Envelopes

Terms and structure

GO distinguishes single and double membranes surrounding organelles: an organelle envelope ; GO:0031967 is defined as two lipid bilayers plus the space, or lumen, between them, whereas an organelle membrane ; GO:0031090 is defined as a single bilayer. For double-membrane organelles, the membrane term refers to either of the lipid bilayers, but excludes the intermembrane space. The envelope is part of the organelle and is a organelle envelope ; GO:0031967; the membrane is part of the envelope, and inner membrane and outer membrane terms can be included:
  • chloroplast
    • [p] chloroplast envelope
      • [p] chloroplast membrane
        • [i] chloroplast inner membrane
        • [i] chloroplast outer membrane


  • organelle envelope
    • [i] chloroplast envelope


Prior to December 2005, nuclear envelope ; GO:0005635 was named 'nuclear membrane', with 'nuclear envelope' as a synonym; this reflected a usage fairly common in the literature. For consistency with other organelle envelope and membrane terms, GO:0005635 is now named 'nuclear envelope', consistent with its definition, and a separate term, nuclear membrane ; GO:0031965, has been added.

Standard Definitions

organelle envelope
The double lipid bilayer enclosing the organelle and separating its contents from the rest of the cytoplasm; includes the intermembrane space.
organelle membrane, organelle with a single membrane
The lipid bilayer surrounding a(n) organelle.
organelle membrane, organelle with a double membrane
Either of the lipid bilayers that enclose the organelle and form the organelle envelope.
organelle inner membrane
The inner, i.e. lumen-facing, lipid bilayer of the organelle envelope.
organelle outer membrane
The outer, i.e. cytoplasm-facing, lipid bilayer of the organelle envelope.
organelle membrane lumen
The region between the inner and outer lipid bilayers of the organelle envelope.

Standard synonyms

The following synonym can be added to terms as long as the synonym string makes sense and does not have alternative meanings. Note that the term name and synonym can be switched depending on typical usage.
organelle membrane lumen
exact_synonym: organelle intermembrane space