Bulk / Vesicle Transport

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 [email protected]

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3. Outlines I. Goals II. Introduction III. Endocytosis IV. Exocytosis V . Conclusions VII. Questions 3

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 4

5. I. Introduction 5

6. II. Endocytosis 6 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: 7 Types:

8. II. Endocytosis 8 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 enzymes may fuse with the phagocytic vesicle to digest the particles it contains

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

10. II. Endocytosis 10 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 11 C . Receptor-mediated endocytosis molecule binds to receptor protein on cell membrane exterior  Receptor-molecule complexes move within membrane  V esicles form when enough accumulate

12. II. Endocytosis 12 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 Hypercholesterolemia C. Receptor-mediated endocytosis

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

14. III. Exocytosis 14 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 cells by exocytosis

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-mediated endocytosis 15

16. V. Questions 16

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 17

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 18

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 19

20. 7 . A n 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 20

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 21

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