What are Endosomes? Why are they present in a cell? Are they present in both animal and plant cells? How are they produced? Well, there are a myriad of questions like these. To be honest, Endosomes are not widely spoken on when we talk about cells and cell organelles. Despite not being given the attention they deserve, Endosomes play a very vital role in cellular function. Their absence can lead to disaster. In this article on Endosome facts, we are going to learn about these interesting compartments that allow our cells to perform optimally. However, in the process of understanding Endosomes, we are going to learn Endocytosis as well because it is important. Without learning Endocytosis, we cannot properly learn Endosomes. So, without further ado, let us begin…
Interesting Endosome Facts: 1-5 | Understanding Endocytosis
1. Endocytosis is a set or family of processes. These processes are very complex in nature. Endocytosis refers to the process of internalizing or taking in of material from outside the cell. In other words, materials that are outside the cell are taken inside the cell by this process. Remember that when we say cell, we are referring to eukaryotic cell (both plants and animals).
2. These eukaryotic cells are often known for internalizing various types of materials such as small and large molecules, different types of fluids and sometimes other cells. This internalization happens because it is necessary for various cellular processes including (but not limited to):
- Defence against microbes.
- Removal of damaged or dead cells from the body.
- Essential nutrients ingestion etc.
3. The process of Endocytosis is very important. What really happens during the process is that Plasma Membrane of the cell (remember that the Plasma Membrane is also known as Cell Membrane or Cytoplasmic Membrane) will fold inward. This process of folding inward is technically known as Invagination.
4. As the Plasma Membrane folds inwards, it creates a dent or pocket with two protruding arm-like structures extending outwards. These arm-like structures are called Pseudopodia (singular is Pseudopodium). As the extracellular material (material outside the cell) moves into the pit or pocket or dent the protruding arm-like structures will gradually go around the material and create an enclosed space.
5. These arm-like structures will then fuse together and completely enclose the material that gets into the pocket or pit or dent or compartment (whatever you prefer to call it). Once the foreign material is totally enclosed, that pocket or compartment will just pinch off from inner surface of the Plasma Membrane. This pinching off is known as Budding.
Interesting Endosome Facts: 6-10 | Understanding Endocytosis
6. The pinched-off compartment appears like a sac and is often known as a vesicle. This vesicle that pinches off the Plasma Membrane is then released into the Cytoplasm. The vesicle size may vary and only those vesicles that are bigger than 100 nm (nm means nanometer and one nanometer means one-billionth of a meter and in numeric terms it is written as 10-9 meters), the vesicle is known as Vacuole.
7. In our first point we said that Endocytosis is a set or family of processes. By that we mean to say that Endocytosis has different mechanisms. At least three different mechanisms have been identified so far. They are:
- Receptor Mediated Endocytosis
Let us take a look at each mechanism in brief.
8. Receptor Mediated Endocytosis: All active cells have receptor sites on their Cytoplasmic Membrane or Plasma Membrane. The receptors on these sites start from outer surface of the Plasma Membrane and extend all the way out into the extracellular fluid that surrounds each cell.
9. These receptor sites usually stay grouped together along certain pits of the Plasma Membrane. The specialty of these pits where these receptor sites are found is that the pits are coated from inside. The question is, “what kind of coating?”.
10. The coating is made of bristle-like proteins. These coat proteins are lined up on the inner surface of the Plasma Membrane.