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Endocytosis & Exocytosis

Endocytosis & Exocytosis. Pooja Patel Elizabeth Pemberton. Water and small molecules enter and exit cells through active transport and diffusion. 

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Endocytosis & Exocytosis

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  1. Endocytosis & Exocytosis Pooja Patel Elizabeth Pemberton

  2. Water and small molecules enter and exit cells through active transport and diffusion.  • Large molecules, however, (proteins and polysaccharides) as well as larger particles are transported in and out of the cell after being packaged in vesicles.  • Endo- and exo- cytosis require energy. Introduction

  3. Cellsecretes biological molecules by the fusion of vesicles with the plasma membrane.  • Steps:  • Transport vesicles that buds off Golgi body moves along microtubules of the cytoskeleton to the plasma membrane.  • Lipid molecules of from the vesicles and the plasma membrane rearrange, forming a fused membrane.  • The contents spill outside of the cell.  • The vesicle membrane becomes part of the plasma membrane.  Exocytosis: 

  4. Examples:  • Pancreas secretes insulin into extracellular fluid by exocytosis.  • Neurons release neurotransmitters that signal other neurons or muscle cells.  • Plant cells ( when making walls) deliver proteins and carbs from Golgi vesicles to outside of cell.  Exocytosis:

  5. Cell takes in biological molecules by forming new vesicles from plasma membrane. • 3 types:  • Phagocytosis : (cell eats)  • Pinocytosis : (cell drinks)  • Receptor-Mediated Endocytosis (RME)  Endocytosis:

  6. Steps:  • Small area of the plasma membrane sinks inward. • The pocket deepens and pinches into a vesicle containing materials from the outside of the cell.  • Becomes a vacuole (for food or water)  Endocytosis:

  7. Enables cell to acquire bulk quantities of specific substances, even though those substances may not be in high concentration outside the cell.  • Steps:  • The ligands (molecule that binds to a specific receptor) attach to protein receptors that are on the outside of the cell.  • A “fuzzy” layer of coat proteins are on the opposite side of the receptors on the inside of the cell.  • Once the ligands bind to the receptors pocket forms and pinches into the cell. (The vesicle is coated by the “fuzzy” coat proteins. • Once the ligands are released, the receptor proteins are recycled back to the plasma membrane.  RME:

  8. Examples :  • Cholesterols travel in blood in particles called low density lipoproteins (LDLs) • the LDLs act as ligands • When the LDLs are defective or missing, cholesterol builds up in blood vessels and can lead to arteriosclerosis. RME:

  9. If pieces of the plasma membrane break off every time exocytosis occurs, how does the cell remain enclosed? Apparently, endo- and exo- cytosis offset each other. While one removes membrane, the other replenishes.  

  10. http://www.youtube.com/watch?v=1w10R9lv7eQ

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