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BIOL 331 (1)
Chapter 13

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BIOL 331
Moira Glerum

Chapter 13 Intracellular Vesicular TransportThe overall organization of membranes in a eukaryotic cell is better thought as a system of membranes Cells need to eat communicate and respond to changes in its environmento They do most of these things through the membrane system Adjusting the composition of the plasma membrane Use of an internal membrane system to addremove cellsurface proteins embedded in the membrane Exocytosis biosyntheticsecretory pathway delivers newly synthesized proteins carbohydrates and lipids to either the plasma membrane or the extracellular spaceEndocytosis o Cells removeexcise plasma membrane components and deliver them to internal compartments called endosomes from where they can be recycled to the same or different regions of the plasma membrane or can be delivered to lysosomes for degradationo Capture nutrients such as vitamins lipids cholesterol and iron taken up together with the macromolecules to which they bind and then released in endosomes or lysosomes and transported into the cytosol where they are used in various biosynthetic processes Interior space or lumen of each membraneenclosed compartment along the biosyntheticsecretory and endocytic pathways is topologically equivalent to the lumen of most other membraneenclosed compartments and to the cell exterioro Proteins travelled in this space without having to cross a membrane being passed from one compartment to another by transport vesicles Transport Vesicles membrane enclosed containers that can be small spherical vesicles or large irregular vesicles or tubules formed from the donor compartment Transport vesicles continually bud off from one membrane and fuse with another carrying membrane components and soluble molecules which are referred to as cargoBiosyntheticsecretory pathwayo Leads outward from the ER toward the Golgi apparatus and cell surface with a side route leading to lysosomesEndocytic Pathway o Leads inward from the plasma membrane Retrieval Pathway o Balances the flow of membrane between compartments in the opposite direction o Brings membrane and selected proteins back to the compartments of origin Transport vesicles are highly selective must take up only the appropriate molecules and must fuse only with the appropriate target membrane The Molecular Mechanisms of Membrane Transport and the Maintenance of Compartmental Diversity
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