2 15 12 Diffusion Types 1 Simple Diffusion 2 Facilitated diffusion a Substances that are polar hydrophilic or charged can not traverse the lipid bilayer of the plasma membrane b Such substances are facilitated by transmembrane proteins to cross the plasma membrane Still goes down concentration gradient c These transmembrane proteins transport or carrier proteins each substance has its own carrier protein Carrier proteins bind to a specific substance d Substances that use facilitated diffusion include glucose amino acids and water Facilitated diffusion exhibits specificity When all carrier proteins are engaged in transporting the substance saturation is observed A maximum of transportation will be reached 3 osmosis a movement of water from area of low solute concentration to an area of high solute concentration Active Process Vesicular Transport Movement of bulky substances enclosed in vesicles These vesicles have a similar structure to the plasma membrane but without a glycocalyx Exocytosis looking at movement of substances from the interior of the cell to the exterior of the cell Substances such as hormones and neurotransmitters are released from cells via exocytosis Substance to be released is enclosed in a vesicle The vesicle moves to the plasma membrane and fuses with it The area of the plasma membrane ruptures to release the substance to the exterior of the cell Endocytosis 3 types phagocytosis pinocytosis receptor mediated phagocytosis Phagocytosis Bacteria and cell debris are enclosed in vesicles Vesicles are made by the involution of the plasma membrane The vesicle detaches into the cytoplasm of the cell such a vesicle is referred to as a phagosome The phagosome coalesces with the lysosome that contains powerful digestive enzymes called lysozymes The lysozymes digest the contents of the phagosome Then the contents are destroyed Hence phagocytes contain high levels of lysosomes Pinocytosis movement of solution into cells by enclosing the solution in vesicles all cells can undergo pinocytosis not all cells can undergo phagocytosis Pinocytosis is also referred to as bulk fluid endocytosis Looking at movement of fluid a solution enclosed in a pinocytic vesicle into the cell the pinocytic vesicle coalesces with the lysosome to digest the vesicles and release the fluid Receptor mediated phagocytosis LDL is taken into steriodogenic cells via receptor mediated endocytosis LDL binds to LDL receptors integral proteins on the surface of the plasma membrane of the steroidogenic cells
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