Organelle · single membrane
Endosomes
Sorting stations on the way in
In view
Incoming vesicles merge with early endosomes near the membrane. Opened up, a late endosome shows the small vesicles packed into its lumen.
Vesicles pinched in from the surface fuse with early endosomes just under the membrane: small vacuoles with thin tubules, mildly acidic at pH 6.8–5.9. The tubules send receptors back to the surface, while the cargo stays behind.
Over 8–15 minutes an early endosome matures into a late endosome, or multivesicular body: round, 250–1000 nm across, more acidic and packed with small vesicles budded into its lumen. It travels inward along microtubules and fuses with lysosomes, which digest what it carries.
- Early endosome
- ≈ 0.1–0.5 µm · pH 6.8–5.9
- Late endosome
- 0.25–1 µm · pH 6.0–4.9
- Maturation
- ≈ 8–15 min
- Inner vesicles
- 40–100 nm · often 30+
Did you know?
Some late endosomes fuse with the plasma membrane instead of a lysosome. Their inner vesicles are then released outside the cell as exosomes.
Sources
- Endosome maturation · Huotari & Helenius 2011 · EMBO J
- The complex ultrastructure of the endolysosomal system · Klumperman & Raposo 2014 · Cold Spring Harb Perspect Biol