Lecture 7- Types of Endocytosis

Receptors, in a coated pit, bind to the molecule that will enter the cell. The pit is reinforced by a lattice like network of proteins called clathrin. Additional clathrin molecules add to the lattice, which eventually pinches off part of the membrane and forms a coated vesicle.    Inside the cell, the vesicle soon becomes uncoated as the clathrin molecules dissociate from the vesicle and each other. The vesicle then fuses with an endosome (another vesicle) from within the cell. The receptors are released and recycled. The receptors are returned tot he plasma membrane to bind to further complementary molecules that need to undergo receptor mediated endocytosis.  The vesicle then fuses with a lysosome which carries enzymes capable of digesting the contents of the vesicle 

Receptor Mediated Endocytosis

Phagocytosis Chemotaxis and adherence of microbe to phagocyte  Ingestion of microbe by phagocyte  Formation of a phagosome (a vesicle forms around the microbe)  Fusion of the phagosome with a lysosome to form a phagolysosome Digestion of the microbe by enzymes found in the lysosome  Formation of a residual body containing indigestible material   Discharge of waste material

Pinocytosis   Small droplets of extracellular fluid are taken in (no receptors are needed). All solutes in the extracellular fluid are taken in (non-selective) Lysosomes break down the components into monomers such as amino acids  Occurs in most cells but especially in absorptive cells in the intestine and kidney

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