What is the Difference Between Endosome and Lysosome

The main difference between endosome and lysosome is that the endosome is a vacuole which surrounds materials internalized during endocytosis, whereas the lysosome is a vacuole which contains hydrolytic enzymes. Furthermore, endosome forms at the transmembrane of the Golgi apparatus and at the plasma membrane. But, the proteins of the lysosomes form at the endoplasmic reticulum and the membrane forms from the Golgi apparatus. 

Endosome and lysosome are two types of membrane-bound vesicles inside the cell. Both are important in endocytosis and phagocytosis. 

Key Areas Covered 

1. What is an Endosome
     – Definition, Formation, Role
2. What is a Lysosome
     – Definition, Formation, Role
3. What are the Similarities Between Endosome and Lysosome
     – Outline of Common Features
4. What is the Difference Between Endosome and Lysosome
     – Comparison of Key Differences

Key Terms 

Endosome, Endocytosis, Golgi Apparatus, Hydrolytic Enzymes, Lysosome, Phagocytosis, Plasma Membrane 

What is an Endosome 

Endosome is the membrane-bound vesicle that forms as a result of endocytosis. Here, endocytosis is the process that takes materials into the cell by invagination of the plasma membrane, and thus, forming a vesicle. Therefore, the main function of an endosome is to serve as a temporary vesicle for transportation. Pinocytosis, phagocytosis, and receptor-mediated endocytosis are the three mechanisms of endocytosis. Pinocytosis forms a type of endosomes called pinosomes, which contain liquids with suspended substances. On the other hand, phagocytosis forms another type of endosomes called phagosomes, which contain pathogens like bacteria and virus. However, receptor-mediated endocytosis forms clathrin-coated endosomes. Proteins and lipids enter the cell through this method. 

Figure 1: Phagocytosis

The three main types of endosomes are early endosomes, recycling endosomes, and late endosomes. Early endosomes can be either narrow tubular columns or large vesicles with membrane invaginations. In the recycling endosomes, the ligands and receptors are sorted into different compartments, recycling receptors back in the plasma membrane. Ultimately, the late endosomes fuse with lysosomes. 

What is a Lysosome 

The lysosome is a membrane-enclosed vacuole in the cytoplasm, containing hydrolytic enzymes. The main function of a lysosome is to help in the digestion of biomolecules like nucleic acids, peptides, carbohydrates, lipids, etc. The hydrolytic enzymes in the lysosome come from the endoplasmic reticulum. They travel to the cis phase of the Golgi apparatus by packaging in secretory vesicles. Finally, these enzymes leave the trans phase of the Golgi apparatus as lysosomes. 

Figure 2: Formation of Lysosomes

Furthermore, the pH of the cytoplasm is around 7.2. However, the pH inside a lysosome is 4.5-5.0. That means; the internal environment of the lysosome is acidic. It is due to the requirement of an acidic pH by the action of the hydrolytic enzymes in the lysosome. 

Similarities Between Endosome and Lysosome 

• Endosome and lysosome are two types of membrane-bound vesicles inside the cell. 
• Both contain important substances for the functioning of the cell. 
• Also, both can form from the Golgi apparatus. 
• Furthermore, both play an important role in endocytosis and phagocytosis. 

Difference Between Endosome and Lysosome 

Definition 

Endosome refers to a vesicle formed by the invagination and pinching off of the cell membrane while lysosome is an organelle in the cytoplasm of eukaryotic cells containing degradative enzymes enclosed in a membrane. Hence, this is the fundamental difference between endosome and lysosome.

Formation 

Moreover, the formation is a major difference between endosome and lysosome. Endosomes, mainly, form during endocytosis while lysosomes form from Golgi apparatus.  

Components 

Another difference between endosome and lysosome is their component. Endosomes contain internalized materials including nutrients and pathogens like bacteria while lysosomes contain hydrolytic enzymes. 

Function 

Furthermore, endosomes store internalized materials till their digestion while lysosomes fuse with endosomes, aiding the digestion of materials inside the endosome. Thus, this is another difference between endosome and lysosome.

Conclusion 

Endosome is a membrane-bound vesicle which contains internalized materials during endocytosis. On the other hand, lysosome is another vesicle which contains hydrolytic enzymes. It emerges from the trans phase of the Golgi apparatus. Lysosomes fuse with endosomes to digest the materials inside the endosome. Therefore, the main difference between endosome and lysosome is their formation and functional relationship.

References:

1. Luzio, J P. “Relationship between Endosomes and Lysosomes.” Biochemical Society Transactions, vol. 29, no. 4, 1 Aug. 2001, pp. 476–480., doi:10.1042/bst0290476.

Image Courtesy:

1. “Figure 04 04 04” By CNX OpenStax –  (CC BY 4.0) via Commons Wikimedia  
2. “Endomembrane system diagram en” By Mariana Ruiz LadyofHats – I made it myself on adobe ilustrator based on the information found on this websites:[1], [2],[3],[4] and [5] (Public Domain) via Commons Wikimedia