Endoszóma

Endoszóma is a membrane-bound organelle found in animal cells. It is a key component of the endocytic pathway, which is responsible for the uptake of extracellular materials into the cell. Endocytosis is a process by which the cell membrane invaginates, enclosing a portion of the extracellular fluid and any dissolved substances or particles within it, forming a vesicle. This vesicle then buds off from the plasma membrane and becomes an early endosome.

Early endosomes are characterized by their slightly acidic internal pH, which is maintained by proton pumps embedded in their membrane. This acidity plays a crucial role in sorting and processing internalized molecules. Receptors that have bound to their ligands on the cell surface are often transported to the early endosome. Within the early endosome, the acidic environment can cause ligands to detach from their receptors.

From the early endosome, molecules and receptors are directed to different destinations. Some receptors are recycled back to the plasma membrane, while others, along with their bound cargo, are sent to late endosomes. Late endosomes have a more acidic internal pH than early endosomes and are the precursors to lysosomes. Within late endosomes, internalized material is further degraded by hydrolytic enzymes delivered from the Golgi apparatus. The ultimate fate of the endosomal content can be degradation in lysosomes, recycling back to the cell surface, or transport to other cellular compartments. Endosomes are therefore central to cellular homeostasis, nutrient uptake, and pathogen clearance.