1. By: Waleedullah Jan BSc Human Biology
Endosomal system
By: Waleedullah Jan
BSc Human Biology

2. Introduction
Cells have the ability to maintain homeostasis
Temperature PH
Salt
Glucose concentration
Endosomal system is essential in carrying out intracellular vesicular transport which is involved in maintaining the cells’ environment at steady state.

3. Bulk transport Cells use bulk transport of Exocytosis Endocytosis
is the process in which cells secrete most of their useful contents such as proteins.
Cells use the reverse process of
Endocytosis:
to take up certain molecules e.g.
Unicellular organisms e.g. amoeba use endocytosis to take up food.

4. Other mechanisms
Phagocytosis (cell eating)
macro pinocytosis ( cell drinking)
Most of the white blood cells
For example Macrophages use the mechanism of phagocytosis to ingest and digest other invading foreign bodies such as bacteria.

5. Local Transport Mediators
Vesicles are the most important components of mostly all the transport mechanisms that cells carry out.
There is a huge number of vesicles however, they are classified into three main categories.
1- Clathrin-coated vesicles.
2- COP I coated vesicles.
3- COP II coated vesicles.
Vesicles are mainly covered by protein coats remarking their specificity for specific destinations.
Vesicles remove their coats allowing more direct interactions with membrane compartments.

6. TRANSPORT FROM TGN TO LYSOSOMAL LUMEN
The transport from Golgi trans is essential in sending proteins to lysosomal lumen for degradation.
Lysosomal lumen is acidic and it contains specialised hydrolytic enzymes.
Specific hydrolytic enzymes for degradation of specific macromolecules.

7. AUTOPHAGY
Lysosome is an important organelle in carrying out autophagocytosis (autophagy)
Autophagy is important in self destruction.
It is also important when cells starve because lysosome can digest the cytosolic nutrients and provide enough food for cells.

8. Endosome
Most of the time the molecules which are taken up by endocytosis are sent to
early endosomes to confront hydrolytic enzymes.
Macromolecules are then sent to late endosomes where most of the recycling and
destruction occurs here.
Late endosomal lumen is acidic , the PH is maintained at 6.

9. Delivery Of Hydrolytic Enzymes.
The delivery of hydrolytic enzymes to late endosomes takes place with the help of
different organelles.
TGN send proteins.
Receptors in TGN.
M6P receptors for proteins.
Complementary shape.
Proteins bind to receptors.
TGN use vesicles for the transport of proteins.

10. Any questions ?