Utghtfnggy

1. CELL BIOLOGY
COURSE CODE:ZOOL-304
Topic :Exocytosis And Endocytosis
Submitted to:Mam Iqra Jabeen
Prepared by:Saman Hayat
Degree :BS Zoology (2nd semester )

2. Contents :
• Introduction
• Exocytosis
• Mechanism
• Types
• Example
• Endocytosis
• Mechanism
• Types
• Example
• Summary

3. Introduction :
• Endocytosis and Exocytosis are the bulk transport mechanisms used in
eukaryotes .
• As these processes require energy they are termed as active transport
processes .
• Endocytosis and Exocytosis are the processes by which cell moves
materials into and out of the cell that are too large to directly pass
through the lipid bilayer of the cell membrane.

5. Exocytosis :
• Exocytosis is the process by which cell moves materials from within the cell into
extracellular fluid .
• Exocytosis occur when a vesicle fuses with the plasma membrane ,allowing its
contents to be released outside the cell.
• It is a vital process of plant and animal cell because it perform opposite of
endocytosis. Cell create waste or toxins that must be removed from the cell to
maintain the homeostasis.

7. Mechanism :
.Exocytosis involves the following mechanism :
A vesicle is formed ,typically within the endosplasmic reticulum and the Golgi
apparatus or early endosome.
The vesicle travels to the cell membrane .
The vesicle fuses to plasma membrane ,during which the two bilayers merge.
The vesicle ‘contents are released into the extracellular space.
The vesicle either fuses with or separates from the cell membrane.

8. Types :
There are three types of Exocytosis :
Regulated Exocytosis
Constituted Exocytosis
Lysosome Mediated Exocytosis

9. Regulated Exocytosis :
• The process of fusion of membrane of cytoplasmic organelles with the
plasma membrane which occurs in response to stimulation is regulated
exocytosis.
• Released molecules are known as regulated exocytosis because the
released molecules are regulated by extracellular signals and cause
membrane depolarization.

10. Constitutive Exocytosis :
• Constitutive exocytosis is the most common pathway performed by
the body cells which do not require extracellular signaling .
• Some exocytotic vesicle remains in the plasma membrane even after
exocytosis but other releases their content and returns to the interior of
the cell.
• This mechanism is termed as the “kiss -and -run”pathway.

11. Lysosome Mediated Exocytosis :
• Lysosome mediated exocytosis is a process of fusion of cell vesicles
and cell lysosome .
• An enzyme contained in the lysosome breaks down the molecules and
carries them into the cell membrane where it fuses and clear out.

13. Example :
• The white blood cells engulfed a foreign pathogen.
 Certain parts of the pathogen are no needed more, so they are excrete
out through exocytosis.
 Releasing a neurotransmitter for cellular communication is another
example of exocytosis.

14. Endocytosis :
• The process by which cell takes in the actively transporting molecules
from the external surrounding into the vesicles by engulfment process.
• It occurs when the cell membrane folds engulfing the molecules with
extracellular fluid which breaks off vesicles facilitating to transport inside
the cell.

16. Mechanism :
• Following steps are followed during phagocytosis :
A particle binds to the receptor on the cell‘s surface ,stimulating the
release of pseidopodia .
Pseidopodia surrounds the object untill there membrane fuse,forming
a phagocytic vesicle
The phagocytic vesicle pinches off the cell membrane ,entering the
cell membrane
The phagocytic vesicle fuses with the lysosomes ,which recycle or
destroy the vesicle contents.

17. Mechanism :
• Following steps are followed during pinocytosis.:
• Molecules bind with receptors located along the surface of the
cellular membrane.
• The plasma membrane folds in forming the pinocytic vesicle
that contains the molecules and the extracellular fluid.
• The vesicle detaches from the cell membrane inside the cell .
• The vesicle fuses with early endosome where the contents
found within are sorted.

18. Types :
• There are three types of endocytosis :
• Phagocytosis
• Pinocytosis
• Receptor mediated endocytosis

19. Phagocytosis :
• Phagocytosis is the process by which cell targets the large
molecules that are not particularly specific .
• It is also known as the cell eating process and how the immune
cells and white blood cells like macrophage and neutrophil
engulfs and destroy pathogen and toxic ccompounds.

20. Pinocytosis :
• In the pinocytosis process, the cell takes in small substances
like water and nutrients from the extracellular fluid and is non -
specific.
• It is also known as cell drinking process which is common in
plant and animal cells.

21. Receptor Mediated Endocytosis :
• Another specialized type of endocytosis is receptor mediated
endocytosis where macromolecules require specific receptors
to bind on the cell membrane surface.
• One of the common example of receptor mediated endocytosis
is cholesterol uptake in body.

23. Examples :
• White blood cells engulfing a virus and eliminating it is an
example of endocytosis.
• Cholesterol uptake in body is also an example of endocytosis.

24. Summary :
• Endocytosis is the process of capturing a substance or particle
from outside the cell by engulfing it with the cell membrane and
bringing it into the cell.
• Exocytosis is the process of fusion of vesicles with plasma
membrane and releasing the contents outside the cell.
• Both Endocytosis and Exocytosis are the processes of active
transport.