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Unformatted text preview: Chapter 12: Intracellular Compartments Endomembrane system Endoplasmic reticulum continuous network of flattened sacs, tubules, and associated vesicles that stretches throughout the eukaryotic cells cytoplasm (ER cisternae (sacs) and ER lumen (space enclosed by sacs))- Smooth ER absence of ribosomes attached to membrane o Involved in several different cellular processes, including drug detoxification, carbohydrate metabolism, calcium storage, steroid biosynthesis o Carbohydrate metabolism involved in the enzymatic breakdown of stored glycogen Catabolism of liver glycogen glucose-6-phosphate bound to smooth ER membrane removes phosphate group from glucose-6- phosphate Allows glucose to be moved out of liver cell by permease (glucose transporter) and into blood for transport to other cells that need energy- Rough ER ribosomes attached to cytosolic side (outer surface) of membrane, facing away from ER lumen o Ribosomes are responsible for synthesizing both membrane-bound and soluble proteins o Proteins enter endomembrane system by being inserted into rough ER lumen cotranslationally as polypeptide is synthesized on ribosome- Membrane Synthesis: Flippases mechanism for transferring phospholipids from one layer of membrane to other o Phospholipid translocators (flippases) catalyze translocation of phospholipids through ER membranes Quite specific and affect only rate of process contributes to membrane asymmetry o Phospholipid exchange proteins found in cytosol convey phospholipid molecules from ER membrane to outer mitochondrial and chloroplast membranes Golgi Complex component of endomembrane system that is closely linked, both physically and functionally to the ER- structure consists of series of flattened membrane-bounded cisternae (Golgi stack) o transport vesicles bud off membranes in one region of the cell and fuse with other membranes convey lipids and proteins from transitional elements of the ER to the Golgi complex, between Golgi stack cisternae, and from Golgi complex to various destinations in cell, including secretory granules, endosomes, and lysosomes...
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