Chapter 3: Transport Across Cell Membrane
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acornell8317 on July 9, 2012
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Terms | Definitions |
|---|---|
 cell membrane permeability is based on | - the amphipathic nature of phospholipid bilayer - membrane proteins (allow only certain things to pass through - specific) - gradients present on either side of the membrane (pressure, concentration, electrochemical) - nothing can cross the cell membrane unless the CM is permeable to it |
| passive transport | - utilizes existing gradients to drive movements (until equilibrium is reached) - simple diffusion - osmosis - filtration - facilitated diffusion |
| active transport | - utilized when movement of a substance must go uphill against its gradient - requires input of ATP in order to take place - primary active transport - secondary active transport - vesicular transport |
| simple diffusion | - movement of a solute through PB from an area of high concentration to an area of low concentration until substance is equal in solute concentration on either side of the membrane |
| factors that affect rate of diffusion | - steepness of gradient - the greater the difference in concentration, the faster the substance will move - temperature - the higher the temperature, the faster molecules move - mass of diffusing substance - the bigger something is, the longer it takes to move - surface area - the greater the surface area, diffusion occurs faster - distance to travel - the greater the distance, the longer it takes to diffuse |
| osmosis | - diffusion of water across a cell membrane - moves from areas of more water to areas of low water until equilibrium is reached - all cell membranes are permeable to water |
| why all cell membranes are permeable to water | - movement of phospholipids creates gaps in the PB that water sneaks through - aquaporins - integral proteins that allow water to pass through |
| tonicity | - ability of a solution to affect the volume and pressure inside a cell |
| isotonic solution | - concentration of solutes is same inside cell and in solution - solution does not affect intracellular environment - no net movement of water |
| hypertonic solution | - concentration of solute is greater in solution than in cell (lower concentration of water in solution) - water moves out of cell - cell undergoes crenation - shrivels and won't be able to carry as much oxygen |
| hypotonic solution | - concentration of solute is less in solution than is in cell - water rushes in cell - hemolysis occurs |
| filtration | - uses pressure gradient - particles and water can be driven across a permeable membrane because of pressure differences - hydrostatic pressure (pressure in our bodies based on water) - ex) glomular filtration |
| facilitated diffusion | - solute that are too polar or highly charged to move through PB can move from areas of high concentration to low concentration using specific carrier proteins - integral protein serves as a carrier or channel - proteins are specific to specific solutes |
| channel-mediated facilitated diffusion | - solute moves down gradient through integral protein that serves as a channel - allows specific, small, inorganic ions that are too hydrophilic or charged to pass - gated channel has portion that acts as a gate to open or close channel's pore |
| carrier-mediated facilitated diffusion | - moves a solute down a gradient - solute binds to a specific carrier on one side of the membrane and is released on the other side after the carrier undergoes a change in shape - solute binds to carrier on side with higher concentration of solute and moves until equilibrium is reached - ex) movement of glucose |
| primary active transport | -energy from the hydrolysis of ATP changes the shape of the carrier proteins which pumps a substance against its gradient - ex) N/K ion pump |
| sodium-potassium ion pump (n/k) | - uses primary active transport - used to drive nerve impulses - sodium ions are pumped out of a protein while potassium ions are pumped in through the same protein at the same time - 3 Na: 2 K - sodium needs to be higher outside of cell and potassium needs to be higher inside cell - constantly running in excitable cells |
| antiporter | - an integral protein that pumps 2 different substances in opposite directions at the same time |
| symporter | - an integral protein that pumps 2 different substances together at the same time |
| vesicular transport | - carry large things that can't fit through PB - uses vesicles - endocytosis - exocytosis - transcytosis |
| endocytosis | - brings substances into cell within a vesicle - receptor-mediated - phagocytosis - bulk-phase endocytosis (pinocytosis) |
| receptor-mediated endocytosis | - a ligand (specific molecule) is recognized and binds to a receptor on outside of membrane and enters within a vesicle - specific |
| phagocytosis | - cell eating - a large, solid particle is engulfed by a cell within a vesicle, enters the cell, fuses with lysosome for destruction of the engulfed particle - ex) macrophages - specific |
| bulk-phase endocytosis (pinocytosis) | - random, non-specific droplets of ECF are brought into cell within a vesicle |
| transcytosis | - substances goes into cell in vesicle on one side, travels across the cell, then is transported out the opposite side of the cell within the same vesicle - ex) how antibodies pass from mother's to baby's blood |
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