Notes on Membrane Structure and Function

*Exocytosis occurs when the cell secretes macromolecules by the fusion of vesicles with the plasma membrane; a transport vesicle that has budded from the Golgi apparatus moves along fibers of the cytoskeleton to the plasma membrane; when the vesicle membrane and plasma membrane come into contact, the lipid molecules of the two bilayers rearrange themselves so that the two membranes fuse; the contents of the vesicle then spill to the outside of the cell; exportation; release chemical signals that stimulate other cells
*Endocytosis is the importation of macromolecules by forming new vesicles with the plasma membrane
*Phagocytosis occurs when a cell engulfs a particle by wrapping pseudopodia around it and packaging it within a membrane-enclosed sac large enough to be classified as a vacuole
*Pinocytosis is when the cell "gulps" droplets of extracellular fluid and its dissolved solutes into tiny vesicles
*Receptor-mediated endocytosis occurs when ligands (extracellular substances that bind to specific receptor sites) cluster into regions of the membrane called coated pits; a fuzzy layer of proteins deepen the pit and form the vesicle; enables the cell to acquire bulk quantities of specific substances; take in cholesteroil for use in the synthesis of membranes and as a precursor for the synthesis of other steroids
*cholesterol travels in the blood in particles called low-density lipoproteins (LDLs)
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