Some integral proteins form ion channels, pores or holes that specific ions, such as potassium, can flow through to get into or out of the cellOther integral proteins act as carriers (transporters), selectively moving a polar substance or ion from one side of the membrane to the otherIntegral proteins called receptors serve as cellular recognition sitesEach receptor recognizes and binds a specific type of moleculeA specific molecule that binds to a receptor is called a ligandSome integral proteins are enzymes that catalyze specific chemical reactions at the inside or outside surface of the cellIntegral proteins also serve as linkers that anchor proteins in the plasma membranes of neighboring cells to one another or to protein filaments inside and outside the cellMembrane glycoproteins and glycolipids often serve as cell-identity markersMay enable cell to recognize other cells of the same kind during tissue formationMay recognize and respond to potentially dangerous foreign cellsPassive transportSubstance moves “downhill” its concentration/electrical gradient to cross membrane using only its own kinetic energy; no energyEx. simple diffusionActive transportATP is used to drive substance “uphill” against its concentration gradientVesicles: spherical membrane sacs for transport; requires energyEndocytosisMaterials move into a cell in a vesicle formed from the plasma membraneExocytosisMaterials move out of a cell by the fusion with the plasma membrane of vesicles formed inside the cellSecretory cells and nerve cellsPinocytosis (‘drinking’)A form of endocytosis in which tiny droplets of extracellular fluid are taken upPlasma membrane folds inward and forms a vesicle containing a droplet of extracellular fluid. The vesicle “pinches off” from the plasma membrane and enters the cytosolVesicle fuses with lysosome, where enzymes degrade the engulfed solutesPhagocytosis (‘eating’)A form of endocytosis in which the cell engulfs large solid particles such as bacteriaBegins when particle binds to a plasma membrane receptor causing it to extend pseudopods, projections of its plasma membrane and cytoplasmPseudopods surround the particle outside the cell and membranes fuse to form a vesicle called a phagosome, which enters the cytoplasmPhagosome fuses with one or more lysosomes and enzymes break down ingested materialSimple diffusionPassive process where substances move freely through the lipid bilayer of the plasma membranes of cells without the help of membrane transport proteinsEx. nonpolar, hydrophobic molecules, oxygen, carbon dioxide, nitrogen gasesFacilitated diffusionPassive process where integral protein assists a specific substance across the membrane when solutes are too polar or highly chargedChannel-mediated facilitated diffusionWhen a solute moves down its concentration gradient across the lipid bilayer through a membrane channel (potassium ions through ion channel)Carrier-mediated facilitated diffusionWhen a carrier moves a solute down its concentration gradient across the plasma membraneSolute binds more often to the carrier on the side of the membrane with a higher concentration of soluteEx. glucose, fructoseOsmosisWhen there is a net movement of a solvent through a selectively permeable membrane; passive processMoving from areas of higher water concentration to areas of lower water concentrationMoving from areas of lower solute concentration to areas of higher solute concentrationWater molecules pass through the plasma membrane either by moving between neighboring phospholipid molecules in the lipid bilayer via simple diffusion or by moving through aquaporins, integral membrane proteins that function as water channelsHydrostatic pressurePressure exerted by a liquid that forces water molecules to move back and forth when equilibrium is reachedOsmotic pressureThe force exerted by the solution with the impermeable soluteThe higher the solute concentration, the higher the osmotic pressureTonicityA measure of the solutions ability to change the volume of cells by altering their water contentIsotonic solutionRed blood cell maintaining normal shape and volumeHypotonic solutionA solution that has a lower concentration of solutes than the cytosol inside the red blood cellsWater enters the cells faster than they leave causing it to burst (hemolysis of red blood cells)Hypertonic solutionA solution that has a higher concentration of solutes than does the cytosol inside red blood cellsWater moves outside the cells faster than they enter causing it to shrink (crenation)Active transportRequires energy for carrier proteins to move solutes across the membrane against a concentration gradientPrimary active transportEnergy derived from hydrolysis of ATP changes the shape of a carrier protein, which “pumps” a substance across a plasma membrane against its concentration gradientSodium-potassium pumpMost prevalent mechanism that expels sodium ions from cells and brings potassium ions inPump maintains a low concentration of Na+ in the cytosol by pumping these ions into the extracellular fluid against the Na+ concentration gradient, while also moving K+ into cells against the K+ concentration gradientWorks nonstop to maintain a low concentration of Na+ and a high concentration of K+ in the cytosolMaintains normal tonicity on each side of the plasma membraneSecondary active transportIndirectly uses energy obtained from hydrolysis of ATPThe energy stored in a Na+ or H+ concentration gradient is used to drive other substances across the membrane against their concentration gradientSecondary active transport proteins harness the energy in the Na+ concentration gradient by providing routes for Na+ to leak into cellsA carrier protein simultaneously binds to Na+ and another substance and then changed its shape so that both substances cross the membrane at the same timeIf these transporters move 2 substances in the same direction they are called symportersWhereas, antiporters move 2 substances in opposite directions across the membraneTranscription: messenger RNA copies genetic info from DNATakes place in the nucleus, where the genetic code is transcribed into mRNACytosine pairs with GuanineAdenine pairs with ThyminemRNA leaves the nucleus via nuclear pore and travels to cytoplasmmRNA then binds to ribosome via rRNA, the code on the mRNA is translated into instructions for specific order of amino acidsThe segment of DNA where transcription begins is the promoterThis is where RNA
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