In
cell biology, an
endosome is a membrane-bound compartment inside
eukaryotic cells. It is a compartment of the
endocytic membrane transport pathway originating from the
trans Golgi membrane. Molecules or ligands internalized from the plasma membrane can follow this pathway all the way to lysosomes for degradation, or they can be recycled back to the plasma membrane. Molecules are also transported to endosomes from the
trans-
Golgi network and either continue to lysosomes or recycle back to the Golgi. Endosomes can be classified as early, sorting, or late depending on their stage post internalization. Endosomes represent a major sorting compartment of the
endomembrane system in cells. In HeLa cells, endosomes are approximately 500
nm in diameter when fully mature.