Pinocytosis pinocytic vesicles form from coated pits

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PinocytosisPinocytic Vesicles Form from Coated Pits in the Plasma Membrane.The endocytic part of the cycle often begins at clathrin-coated pits.
Caveolae Cells can form other types of pinocytic vesicles, such as caveolae.
MacropinocytosisMacropinocytosis is a clathrin-independent endocytic mechanism.
Cells Use Receptor-Mediated Endocytosis to Import Selected Extracellular Macromolecules.CholesterolLDLeceptor-mediated Endocytosis
The Receptor-mediated Endocytosis of LDL
Early Endosomes Vs. cis and transGolgi NetworksEarly endosomes are the main sorting station in the endocytic pathwayThe cis and trans Golgi networks serve this function in the secretory pathway.64
PhagocytosisPhagocytosis is a special form of endocytosis in which a cell uses large endocytic vesicles called phagosomes to ingest large particles such as microorganisms and dead cells.65Specialized Phagocytic Cells Can Ingest Large Particles
Specialized Phagocytic Cells Can Ingest Large Particles
67Phagosome maturation: fusion with endosomes and lysosomes needed to digest particleendosomesfusionPhagosome containing bacterialysosomesPhagolysosome degrades particlesCartoon from umb_188/1190683943Ge3P8U.jpg
Some Lysosomes Undergo ExocytosisLysosomal secretion of undigested content enables all cells to eliminate indigestible debris.Melanocytes in the skin produce and store pigments in their lysosomes called melanosomes.Melanosomes release their pigment into the extracellular space of the epidermis by exocytosis.The pigment is then taken up by keratinocytes, leading to normal skin pigmentation.Albinism68
ExocytosisTransport from the trans Golgi network to the cell exteriorThe fusion of the transport vesicles with the plasma membrane is called exocytosis69
Regulated and Constitutive Secretory Pathways
71Examples of Exocytosis FunctionsDelivery of new membrane and proteins to the plasma membraneDelivery of extracellular components like proteoglycansDelivery of signalling molecules to the extracellular medium:oProteases: remodel extracellular medium or fight infectionsoHormones and growth factors: signaling between cellsoNeurotransmitters:neuronal communicationoImmune and inflammatory factors: histamine and interleukins
72Exocytosis of secretory vesiclesSecretory vesicle fusion with the plasma membrane of a pancreatic b cell
Figure 13-68 Molecular Biology of the Cell(© Garland Science 2008)73Secretion of Histamines by Exocytosis in Mast CellsUnstimulated mast cellHistamine-containing secretory vesiclesHistamine: small molecule responsible for itching and sneezing during allergenic reactionHistamine-containing secretory vesicles fused with the PMStimulated mast cell immerse in signal results in global secretion
The Three Best-understood Pathways of Protein Sorting in the trans Golgi Network
Direct and Indirect Sorting in Polarized Cells

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