05. VESICULAR TRANSPORT - Ayesha Riyaz.pptx

TRANSPORT

1. Vesicular Transport Guided by; Dr. M.M. Khan sir (H.O.D.) Dr. Indu Ma’am Dr. Pushpalata Ma’am Dr. Rashmi Ma’am Dr. Samreen Ma’am Dr. Majid Sir Dr. Sanjeev Sir Presented by; Aisha Riyaz

2. INTRODUCTION Vesicular transport is the special category of Active Transport, But is Independent of concentration gradient across the cell membrane. The substances are transported across but NOT THROUGH the Cell membrane in the form of VESICLES. CATEGORIES OF VESICULAR TRANSPORT : Endocytosis. Exocytosis. Transcytosis .

3. ENDOCYTOSIS It is defined as the transport mechanism by which the MACROMOLECULES enters the cell. Macromolecules are very large and thus can’t pass through the cell membrane either by Active or Passive Transport. Such substances are transported into the cell by Endocytosis. TYPES OF ENDOCYTOSIS : 1- Pinocytosis 2- Phagocytosis 3- Receptor-mediated endocytosis.

4. 1. PINOCYTOSIS It is a process by which Macromolecules are taken into the cell. It is also called Cell Drinking, because macromolecules are taken along with the droplets of extracellular fluid in the vesicle.

5. Events involved in pinocytosis Macromolecules attach to the surface of cell membrane. Now the cell membrane evaginates around the droplets and engulf the droplets. The engulfed droplets are converted to vesicles or vacuoles called endosomes. Endosome travel into the interior of cell. Primary lysosome in the cytoplasm fuses with the endosome to form secondary lysosome. Now the Hydrolytic enzymes in secondary lysosome active resulting in the digestion and degradation of endosomal content.

6. 2. PHAGOCYTOSIS It is the process in which, p articles larger than Macromolecules like Bacteria or Antigen, are engulf into the cell. It is also called ‘CELL EATING’. Only few cells like Neutrophils, monocytes ( WBCs) and Tissue Macrophages shows Phagocytosis

7. HOW WHITE BLOOD CELLS PERFORM PHAGOCYTOSIS? White blood cells, Neutrophils and Monocytes are the first line of Defense Mechanism of the body when any Infection occurs. So, during any Infection or injury to the tissue, these cells shows the f ollowing steps : DIAPEDESIS : leukocytes squeeze out through the narrow blood vessels to reach the site of infection. AMOEBOID MOVEMENT : Cells shows amoebic movement by bulging out of the cytoplasm and change in shape. CHEMOTAXIS: It is the attraction of these cells towards the injured tissue by the chemical substances released at the site of injury . PHAGOCYTOSIS: Neutrophils and monocytes engulf the foreign bodies by means of phagocytosis.

8. EVENTS INVOLVED IN PHAGOCYTOSIS When a microbe enters the body, first the phagocytic cell send cytoplasmic extension (pseudopodium) around bacteria. Then, these particles are engulfed and are converted into large Endosome called vacuoles or PHAGOSOMES. Phagosomes travel into the interior of the cell. Primary lysosome fuses with phagosome to form secondary lysosomes. Hydrolytic enzymes in the secondary lysosomes are activated resulting in the digestion of phagosomal content.

9. 3. RECEPTOR-MEDIATED ENDOCYTOSIS It is a transport of macromolecules with the help of a receptor protein. Surface of the cell membrane has some pits which contain a receptor protein called CLATHRIN. Each pit with receptor protein called receptor coated pits. Some receptor protein in cell membrane other than Clathrin are Caveolin which are concerned with the transport of Vitamins into the cell.

10. E vents involved in receptor-mediated endocytosis Ligand molecule bind with receptor to form ligand-receptor complex. Ligand-receptor complex get aggregated in the clathrin coated pits. This whole pit detached from the cell membrane and become coated vesicle (Endosome) in the cytoplasm. Later, receptor protein detached from the endosome Endosome fuses with the Primary lysosome to form secondary lysosome. Hydrolytic enzymes in the secondary lysosome activated resulting in the release of Ligand in cytoplasm.

11. E xocytosis It is the process by which substance are expelled from the cell by means of secretory vesicle. This is the reverse of endocytosis.

12. Mechanism of Exocytosis Secretory substances are stored in the form of secretory vesicle in the cytoplasm. When required, the vesicle approaches the cell membrane and get fused with it. Later, the content released out of the cell. ROLE OF CALCIUM IONS IN EXOCYTOSIS: Calcium ions play an important role in transmission of impulse at Neuromuscular Junction. When the action potential reaches the axon terminal, the voltage gated calcium channels open, and calcium enter from synaptic cleft into the axonal bulb This cause the exocytosis of synaptic vesicle and release of Acetyl choline (neurotransmitter) into the synaptic cleft.

13. T ranscytosis It is a transport in which extracellular substance enters the cell through one side and leaves the cell through the other. It involves the mechanisms of Receptor-mediated endocytosis and exocytosis. But here the protein involve is Caveolin and not Clathrin. EXAMPLE: Movement of protein from capillary blood into interstitial fluid across the endothelial cells.

14. REFERENCE A.K. Jain Sembulingam

15. THANK YOU