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.
Bulk transport
•
•
•
•

•
•

•
Cells use bulk transport of
Exocytosis
Endocytosis
Exocytosis:
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.
•
•
•
•
•
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.
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.
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.
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.
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.
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.
Any questions ?