Cellular Transport Endocytosis Exocytosis LS 3 http users

Cellular Transport Endocytosis Exocytosis LS. 3

http: //users. rcn. com/jkimball. ma. ultranet/Biology. Pages/E/Endocytosis. html • Endocytosis • In endocytosis, the cell engulfs some of its extracellular fluid (ECF) including material dissolved or suspended in it. A portion of the plasma membrane is invaginated and pinched off forming a membrane-bounded vesicle called an endosome.

• Endocytosis removes portions of the plasma membrane and takes them inside the cell. To keep in balance, membrane must be returned to the plasma membrane. This occurs by exocytosis.

• Exocytosis is the reverse of endocytosis. • And that is just as well. In 30 minutes an active cell like a macrophage (right) can endocytose an amount of plasma membrane equal to its complete plasma membrane. • This electron micrograph (courtesy of Dr. Robert J. North) shows a guinea phagocyte ingesting polystyrene beads. Several beads are already enclosed in vacuoles while the others are in the process of being engulfed. • So the cell must have a mechanism to restore the normal amount of plasma membrane. Exocytosis is that mechanism.

More Resources • • • http: //academic. brooklyn. cuny. edu/biology/bio 4 fv/page/endocyta. htm (endocytosis and exocytosis) http: //personal. tmlp. com/Jimr 57/textbook/chapter 3/cmf 4 a. htm The Virtual Cell Web Page (endocytosis and exocytosis) http: //www. bbc. co. uk/education/asguru/biology/01 cellbiology/05 pathways/09 endoexo/ index. shtml (endocytosis and exocytosis) http: //www. wisc-online. com/objects/index_tj. asp? obj. ID=AP 11403 – Typical Animal Cell---Interactive http: //www. wiley. com/legacy/college/boyer/0470003790/animations/cell_structure/cell _structure. htm – Cell Structure—Interactive