Difference Between Endosome and Lysosome

Key Difference – Endosome vs Lysosome
 

The key difference between the Endosome and the Lysosome is based upon its formation and its function in the cell. Endosome is formed by endocytosis, whereas the lysosome is a membrane bound vesicle containing degrading hydrolytic enzymes.

The endosomal and the lysosomal systems are important in cellular degradation. When a molecule is captured by endocytosis, they form the endosome. Endosome is a membrane bound compartment in eukaryotic cells. The endosome then fuses with the lysosome to degrade the molecule by lysosomal hydrolytic enzymes.

CONTENTS

1. Overview and Key Difference
2. What is Endosome
3. What is Lysosome
4. Similarities Between Endosome and Lysosome
5. Side by Side Comparison – Endosome vs Lysosome in Tabular Form
6. Summary

What is an Endosome?

Endosomes are membrane bound compartments derived from plasma membrane due to the process of endocytosis. Endocytosis is the process by which fluid matter, solutes, different macromolecules, plasma membrane components and various other particles are internalized. The plasma membrane forms invaginations, and they form vesicles through membrane fission. These vesicles are called Endosomes. Endosomes are primarily involved in regulating the trafficking of proteins and lipids in the cell.

Endosomes can be categorized as early endosomes, late endosomes, and recycling endosomes. Early endosomes are the first to be formed. Upon maturation by the release of different substances such as acids, they convert into late endosomes. Late endosomes then fuse with lysosomes to form endolysosomes. This fusion will then result in the degradation of the molecule.

Recycling endosomes contain a fine tubular network and are involved in re-shuttling the molecules back to the plasma membrane. This is vital in protein recycling.

What is Lysosome?

Lysosomes are membrane bound organelles present in eukaryotic cells. Lysosomes contain acid hydrolases that have the ability to degrade biomolecules. These enzymes function only at the acidic pH.

When molecules are captured via endocytosis, they form endosomes. Thus the endosomes then fuse with the lysosomes to initiate degradation. Endolysosomes are formed as a result of this fusion. Precisely, the late endosomes that have an acidic pH fuse with the lysosomes. Thus, the lowered acidic pH will, in turn, activate the hydrolases that would degrade the molecules.

In addition to endocytosis, phagocytosis and autophagy can also activate lysosomal systems. Phagocytic cells can fuse with lysosomes forming Phagolysosomes which then undergoes degradation. During autophagy, the intracellular components are compartmentalized into autophagosomes. These autophagosomes fuse with lysosomes to undergo degradation of the compounds resulting in gradual cell death.

What are the Similarities Between Endosome and Lysosome?

• Both endosomes and lysosomes are present in eukaryotic cells.
• Both are membrane bound structures and found in the cell cytoplasm.
• Both participate in the degradation of compounds.

What is the Difference Between Endosome and Lysosome?

Endosome vs Lysosome
Endosomes are plasma membrane based invaginations formed by the process of endocytosis.	Lysosomes are membrane bound organelles that contain hydrolytic enzymes.
Formation
Endosomes are formed as a result of endocytosis, where the plasma membrane formed invaginations by capturing a molecule. The plasma membrane fission results in endosomes.	Lysosomes are naturally present as membrane bound organelles in the cell cytoplasm.
Types
Early endosome, late endosome, recycling endosomes are the three types of endosomes.	Endolysosome, Phagolysosome, Autophagolysosome are the three types of lysosomes.
Function
Capture of biomolecules, fluids, and solutes and direct them for degradation, protein recycling is the functions of endosomes.	Degradation of molecules taken up by endosomes and phagocytes, degradation or intracellular matter taken up by autophagy are the functions of lysosomes.
pH Conditions
Early endosomes – neutral pH. Late endosomes – acidic pH.	Non – fused lysosomes – neutral pH. Fused with late endosomes/phagocytes – acidic pH.

Summary – Endosome vs Lysosome

Endosomes and Lysosomes are found in eukaryotes. Endosomes are formed as a result of endocytosis which engulfs components such as proteins and lipids to form plasma membrane based vesicles known as endosomes. Lysosomes, in contrast, are organelles containing acid hydrolases and participate in the degradation of biomolecules when fused with endosomes, phagosomes or autophagosomes. This is the difference between endosomes and lysosomes.

Reference:

1.Marisa Otegui, and Francisca C. Reyes. “Endosomes in Plants.” Nature News, Nature Publishing Group. Available here  
2.Cooper, Geoffrey M. “Lysosomes.” The Cell: A Molecular Approach. 2nd Edition., U.S. National Library of Medicine, 1 Jan. 1970. Available here 

Image Courtesy:

1.’Endocytic pathway of animal cells showing EGF receptors, transferrin receptors and mannose-6-phosphate receptors’By Matthew R G Russell – Own work, (CC BY-SA 3.0) via Commons Wikimedia
2.’Lysosome’By lumoreno – Own work, (CC BY-SA 3.0) via Commons Wikimedia