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fluid mosaic model |
the membrane is a mosaic of protein molecules bobbing in a fluid layer of phospholipids |
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phospholipids |
phospholipids are arranged in 2 layers in the membrane |
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steroids |
steroid cholesterol reduces membrane fluidity at moderate temp, but stops solidifcation at low temps |
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integral proteins |
are embedded in the membrane and have a hydrophobic middle and hydrophilic ends (transport proteins) |
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peripheral proteins |
loosely bound to the surface of the membrane |
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glycoproteins and glycolipids |
used for cell to cell recognition |
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permeability of lipid bilayer |
the core of the membrane is hydrophobic non-polar molecules and hydrophobic molecules get through easily small, charged molecules get through fairly ok ion, polar molecules, and hydrophilic molecules don’t get through |
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passive transport |
diffusion-tendency for molecules of any substance to spread into available space; high concentration → low concentration = equilibrium facilitated diffusion- diffuse with assistance of transport proteins (either carrier or channel) osmosis- passive transport of H20 across membrane; water goes from hypotonic solution → hypertonic solution; isotonic solution is equal concentrations |
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active transport |
ion pumps: moves substances across membrane against their concentration gradient endocytosis and exocytosis: cell secretes macromolecules by fusion of vesicles with the plasma membrane (exo). vesicle from golgi apparatus comes into contact with the membrane, bilayers fuse together, and contents spill out |
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how can water molecules enter the cell so quickly? |
osmosis: water diffuses across the membrane from the region of lower solute concentration to that of higher solute concentration until the solute concentrations are nearly equal |
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why do cells need external and internal membranes? |
membranes control traffic and are the boundaries from surroundings. internal membranes are important because it allows the cell to do several different things at the same time |
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what is the voltage across a membrane called? how is it generated? |
voltage across a membrane is called membrane potential. the cytoplasm is negative and extracellular fluid is positive because of the unequal distribution of anions and cations on both sides. |
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hypertonic vs. hypotonic vs. isotonic solutions |
isotonic is where there will be no net movement of water across the plasma membrane. water diffuses at the same rate in both directions. becomes turgid. hypertonic is when there’s not enough water on the other side to diffuse. the cell will lose water, shrivel, and probably die. hypotonic is when the water will enter the cell faster than it leaves, and the cell will swell and lyse |
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