By Abdallah Muhammed Youssof, M.sc. Department of pharmaceutics, college of pharmacy, King Saud University

1. Bulk Transport Across
Biomembrane
Prepared by:
Abdallah M. Youssof
PhD Student, College of
Pharmacy, KSU
ayoussof@ksu.edu.sa

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3. OUTLINES
I. Goals
II. Introduction
III. Endocytosis
IV. Exocytosis
V. Conclusions
VII. Questions
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4. I. Goals of the this lecture
By the end of this lecture you will be able to:
1. Define endocytosis and exocytosis
2. Compare between different endocytosis processes
3. Explain with examples some diseases associated with
malfunction of bulk transport
4. Answer MCQs on bulk transport
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5. I. Introduction
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6. II. Endocytosis
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Endocytosis occurs when the
plasma membrane envelops
food particles and liquids into
a vesicle to take into the cell.
• It involves the pinching in of
a portion of the cell
membrane to form a vesicle
inside the cytoplasm which
then travels to the needed
location within the cell.

7. II. Endocytosis:
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Types:

8. II. Endocytosis
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A. Phagocytosis (Cell
eating)
• The bulk transport of large
molecules or whole cells into the
cell
• Involves the use of pseudopods
to engulf particles
• i.e. macrophages WBC engulf
entire bacteria; which eventually
encloses them in a vesicle within
the cell’s cytoplasm
• Lysosomes containing digestive

9. II. Endocytosis
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A. Phagocytosis (Cell
eating)
Electron Micrograph of Macrophage Phagocytosis of E.
coli

10. II. Endocytosis
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B. Pinocytosis (Cell
drinking)
• The bulk transport of large
amount of small solutes or
(liquid) extracellular fluid into
vesicles in the cell, forming a
pinocytic vesicle

11. II. Endocytosis
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C. Receptor-mediated
endocytosismolecule binds to receptor
protein on cell membrane
exterior
 Receptor-molecule
complexes move within
membrane
 Vesicles form when
enough accumulate

12. II. Endocytosis
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• Hypercholesterolemia is
a condition in which
receptor proteins on liver
cells used to remove
excess cholesterol is
absent or reduced in
number
• This leads to heart and
artery disease
Hypercholesterole
mia
C. Receptor-mediated endocytosis

13. III. Exocytosis
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Exocytosis occurs to move large amounts
of a material out of the cell in a process
which is the reverse of endocytosis
• Some cells produce substances for export like
proteins (i.e. hormones, enzymes)

14. III. Exocytosis
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Vesicles form around proteins
produced in the endoplasmic
reticulum
vesicles merge with the Golgi body
where the protein is modified and
packaged for export
new vesicles are formed by the Golgi
body which move to and fuse with
the plasm membrane, expelling the
protein from the cell (i.e. hormones
expelled into blood, digestive
enzymes into lumen of small
intestine)
 Insulin leaves insulin-secreting

15. IV. Conclusions
• Bulk transport occurs for large molecules/quantities need
to be transported into/out of the cell (i.e. proteins,
bacteria, viruses, liposomes and micelles)
• Phagocytosis is known as cell eating, while pinocytosis as
cell drinking
• Exocytosis is the reverse of endocytosis
• Insulin and cholesterol are transported by receptor-
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16. V. Questions
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17. 1. What is vesicle transport?
a. The transport of very large molecules in and out of the cell
b. The transport of very small molecules in and out of the cell
c. The transport of proteins in and out of the cell
d. Both a and c
2. How is bulk transport accomplished?
a. Via vesicles only
b. Via vesicles and receptors
c. Both a and b
d. None of the above
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18. 3. What are the types of endocytosis?
a. Phagocytosis and exocytosis
b. Phagocytosis, and receptor-mediated endocytosis
c. Phagocytosis, pinocytosis, and receptor-mediated endocytosis
d. None of the above
4. This statement "cell eating"; large particles/cells are engulfed; could be used to
describe
a. Phagocytosis
b. Exocytosis
c. Both a and b
d. None of the above
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19. 5. Which of the following best describes pinocytosis?
a. The ingestion of only liquid into a cell by the budding of small vesicles from the cell membrane
b. “Cell drinking"; cell engulfs water/solutes
c. A process by which water/solutes are transported into the outside of the cell
d. None of the ab
6. What is the receptor in receptor-mediated endocytosis?
a. Integral protein in the membrane
b. Proteins exist in the extracellular fluid
c. All of the above
d. None of the above
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20. 7. An example (s) of receptor-mediated endocytosis
a. Insulin
b. Cholesterol
c. Low density lipoproteins
d. All of the above
8. Why is bulk transport a form of active transport? Because
a. Energy is not needed for breaking and reforming of the membrane
b. Energy is needed for breaking and reforming of the membrane
c. Molecules move from area of high concentration to area of low concentration
d. None of the above
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21. 9. Regarding exocytosis, which of the following is/are correct?
a. The process by which a substance is released from the cell
b. Vesicles transport the substance to the cell surface and then fuses with the cell membrane
c. To transport substances into the cell
d. Both a and b
10. Bulk transport can be defined as
a. A para-cellular transport
b. A transcellular transport
c. All of the above
d. None of the above
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