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7 Cards in this Set

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What does an endosome do?
endocytosed macromolecules are sorted in endosomes. Endosomal compartment acts as main station in the inward endocytic pathway, just as the trans Golgi network serves this function in the outward secretory pathway.
what types of endosomes are there?
early endosomes--> just beneath the plasma membrane, mature gradually into late endosomes as the vesicles within them fuse, either with one another or with a preexisting late endosome

late endosomes-->near the nucleus, appears 5-15 minutes later.
what's an endosome like?
interior of endosome is kept acidic (pH 5-6) by an ATP-driven proton pump in the endosomal membrane that pumpts protons into the lumen from the cytosol. Acidic environment plays a crucial role in sorting process because it causes many receptors to relase bound cargo.
What is LDL?
cholesterol (a membrane lipid that does not contain a fatty acid tail) is extremely insouble and is transported into the blood protein in the form of LOW DENSITY LIPOPROTEINS (LDL). The LDL binds to receptors located on cell surfaces and the receptor-LDL complexes are ingested by receptor-mediated endocytosis and delivered to endosomes. Acidic endosome interior causes LDL to dissociate from receptor, which is returned in transport vesicles to the plasma membrane for reuse, and LDL is delivered to lysosomes.
What does LDL do in the lysosome?
LDL is broken down by hydrolytic enzymes--free cholesterol is released to the cytosol where it is available for membrane synthesis
Pinocytosis vs. receptor-mediated endocytosis
Pinocytosis is indiscriminate,

receptor-mediated is when macromolecules bind to complementary receptors on the cell surface and enter the cell as receptor-mediator macromolecule complexes in clathrin-coated vesicles. Provides a selective concentrating mechanism that increases the efficiency of internalization of specific macromolecules more than 1000-fold compared with ordinary pinocytosis.
What are lysosomes and what do they do?
lyososomes are membranous sacs of hydrolitic enzymes that carry out the controlled intracellular digestion of both extracellular materials and worn out organelles. pH is around 5. All enzymes are optimally active in the acidic conditions. Proteins in the transport membranes of lysosomes are unusually highly glycosolated on the lumen side, because the sugars protect the proteins from digestion by lysosomal proteases.