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Endocytosis
ByDr. Fatima Riaz
Transport across Cell Membrane
• Diffusion is the process of cells moving from areas of high concentration to areas of low concentration.
– This random movement causes the molecules to become evenly spread out.
Diffusion
• Cells use diffusion to get substances into and out of the cell.– Example: During photosynthesis, oxygen is
produced inside the cell. When this happens the concentration of oxygen becomes higher inside the cell than outside and oxygen diffuses out of the cell.
• Osmosis is the diffusion of water through a membrane.– Water moves into an area with low concentrations
and out of areas with high concentrations.
• Both diffusion and osmosis are forms of passive transport (they require no energy)
Transport across Cell Membrane: Active Transport
• materials move from low concentration to high concentration. requires energy!
Endocytosis
– moving a particle into the cell• Phagocytosis• Pinocytosis
– Exocytosis: moving a particle from inside the cell to outside.
• PINOCYTOSISIngestion of minute particles e.g protein molecules
• PHAGOCYTOSISIngestion of large particles, such as bacteria, whole cells or portions of degenerated tissue.
Mechanism of pinocytosis
Movement thru the Cell Membrane: Active Transport
Endocytosis Exocytosis
Cell Locomotion
• Amoeboid movement• Ciliary movement
Ameboid movement
• Movement of an entire cell in relation to its surroundings
• Involves pseudopodium and ATP• Mechanism– formation of new cell membrane & exocytosis at one
end– Attachment of pseudopodium to tissues
• Receptor proteins– Absorption of the membrane & endocytosis in mid &
rear portions– Detachment of receptor proteins
Ameboid movement
Ameboid movement
• Cells that exhibit ameboid motion– WBC– Fibroblasts– Embryonic cells
• Control of ameboid motion– Chemotaxis• Positive• Negative
Cilia and Ciliary movements
• Whiplike movement of cilia on the surfaces of cells
• A sharp pointed hair projecting 2-4micrometers from the surface of the cell.
Structure of a cilium
• Covered by an outcropping of cell membrane• Supported by 11 microtubules, 9 double
tubules at the periphery and 2 single tubules down the center.
• Each cilium is an outgrowth of a structure that lies immediately beneath the cell membrane, called basal body of the cilium
• All the tubules are linked to one another by a complex of protein cross linkages, together called the axoneme.
• Multiple protein arms composed of the protein dynein (having ATPase activity) project outward from each double tubule
• ATP and appropriate magnesium and calcium concentration required.
Mechanism of ciliary movement
• Sudden fast forward whip like stroke• Slow backward stroke• An effective way of pushing the fluid in the
direction of forward stroke.
• CELLS EXHIBITING CILIARY MOVEMENT
• 1- Respiratory airways• 2- Uterine tubes of the female reproductive
tract.
Q & A
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