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endocytosis

Page history last edited by Kim Cutshall 13 years ago

Endocytosis

 

Endocytosis is the process in which the cell takes in macromolecules and particulate matter by forming new vesicle from the plasma membrane.  Althought the proteins involved in the processes are different, the events of endocytosis look like the reverse of exocytosis.  A small area of teh plasma membrane sinks inward to form a pocket.  As the pocket deepens, it pinches in, forming a vesicle containing material that had been outside the cell. (Cutshall)

 

Phagocytosis – a cell engulfs a particle by wrapping pseudopodia around it an packaging it within a membrane-enclosed sac large enough to be classified as a vacuole.  The particle is digested after the vacuole fuses with a lysosome containing hydrolytic enzymes.

 

 http://fig.cox.miami.edu/~cmallery/150/memb/c8.7x20a.phagocytosis.jpg

(Cutshall)

 

Pinocytosis – the cell “gulps” droplets of extracellular fluid into tiny vesicles.  It is not the fluid itself that is needed by the cell, but the molecules dissolved in the droplet.  Because any and all included solutes are taken into the cell, pinocytosis is nonspecific in the substances it transports.

 

 http://fig.cox.miami.edu/~cmallery/150/memb/c8.7x20b.pinocytosis.jpg

(Cutshall)

 

Receptor-mediated endocytosis – enables cell to acquire bulk quantities of specific substances, even though those substances may not be very concentrated in the extracellular fluid.  Embedded in the membrane are proteins with specific receptor sites exposed to the extracellular fluid.  The receptor proteins are usually already clustered in regions of the membrane called coated pits, which are lined on their cytoplasmic side by a fuzzy layer of coat proteins.  Extracellular substances (ligands) bind to these receptors.  When binding occurs, the coated pit forms a vesicle containing the ligand molecules.  After this ingested material is liberated from the vesicle, the receptors are recycle to the plasma membrane by eh same vesicle.

 http://fig.cox.miami.edu/~cmallery/150/memb/c8.7x20c.receptor.jpg

(Cutshall)

 

Campbell, Neil A., and Reece, Jane B. AP Edition Biology. 7th. San Francisco: Pearson Benjamin Cummings, 2005.

 

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