BIOL 101 1st Edition Lecture 8Outline of Last LectureI. Cytoplasmic MembraneII. Fluid Mosaic Modela. Proteinsb. Carbohydratesc. CholesterolIII. Small Molecules Across the Membranea. Transport ProteinsIV. DiffusionOutline of Current LectureI. Water Balance in Cellsa. Hypertonicb. Hypotonicc. IsotonicII. Facilitated DiffusionIII. Active Transporta. Ion Transportb. Co-TransportIV. Traffic of Large Moleculesa. Exocytosisb. Endocytosisi. Phagocytosisii. Pinocytosisiii. Receptor-mediated endocytosisCurrent LectureChapter 7 cont.Water Balance in CellsWhich direction will H2O diffuse- INTO or OUT OF the cellH2O is like any other substance- it will diffuse DOWN its concentration gradientMore concentrated less concentratedTRICK about H2O diffusion is that it is affected by the concentration of solutes dissolved in the waterThe more solutes dissolved, the LESS H2O that is free to DIFFUSE (ie solutes bind to H2O molecules and prevent them from diffusing)Therefore, to determine where the concentration of water that is free to diffuse is higher, just figure out where [solutes] is higher and the [free water] will be the OPPOSITE.There are 3 possibilities:1. Hypertonic (hyperosmotic) environment OUTSIDE the cell- Concentration of solutes dissolved in the water is greater OUTSIDE the cellBIOL 101 1st Edition- So, the concentration of H2O that is free to move is greater INSIDE the cell- H2O will diffuse out of the cell- cell will shrink2. Hypotonic (hypoosmotic) environment OUTSIDE the cell- Concentration of solutes dissolved in the water is greater INSIDE the cell- So, the concentration of water that is free to move is greater OUTSIDE thecell- H2O will diffuse INTO the cell- cell will swell upAnimal cell- cell explodes (cell lysis)Plant cell- swells up, but doesn’t explode because cell wall protects it Turgor pressure builds up= optimal condition for a plant cell3. Isotonic (isosmotic)= concentration of solutes OUTSIDE the cell=concentration of solutes INSIDE the cellNO NET movement of H2O into or out of the cellAnimal cell- best condition, anything else is potentially lethalPlant cell- no turgor pressure, plant weltsFacilitated Diffusion- another example of passive transport, diffusion of solutes across a membrane with the help of a transport protein- Solute moves DOWN its concentration gradient - No energy input is required from cell (energy comes from concentration gradient)- Cell must provide a transport protein for the solute Active Transport= solute is moved AGAINST its concentration gradient- Requires a transport protein for that particular solute- Requires energy input from the cell (moving solute the wrong direction takes work)BIOL 101 1st EditionIon TransportWhen considering the movement of CHARGED atoms or molecules across the membrane, the membrane potential must be considered(voltage across the membrane)- All cells have voltage across their membranes- Voltage= potential energy (electric) due to separation of charges across the membrane- Membrane potential affects the movement of all charged substances across the membraneTherefore, two forces drive the transport of ions across the membrane.1. concentration gradient of the specific ion2. membrane potential- because most cells have a net negative charge- so (+) ions are favored to go INTO the cell AND- (-) ions are favored to go OUT of the cellIons diffuse down their electrochemical gradient combines both influencesCo-TransportElectrogenic pump= transport protein that generates voltage across a membrane by moving charged atoms or moleculesEx: proton pump- moves H+ across the membrane- electrogenic pumps create an electrochemical gradient that can be used to do cellular work- example is the movement of SUCROSE into a plant cell AGAINST its concentrationgradient- first, the cell creates a H+ concentration gradient using a PROTON PUMP- the high [H+] concentration has energy- it can diffuse back into the cell- the cell provides a transport protein to let H+ back into the cell, BUT the H+ can only use the transport protein IF it brings a sucrose molecule with it= CO-TRANSPORT- in this way, the energy in the H+ gradient is used to move sucrose against its concentration gradient and get it INTO the cellBIOL 101 1st EditionTraffic of Large Molecules (and Particles)i.e. proteins, polysaccharides, etc.Exocytosis- moving OUT of the cell- transport vesicle forms around the thing- the vesicle moves to the plasma membrane- the vesicle membrane fuses with plasma membrane- the contents of vesicle are releasedEndocytosis- capture of outside molecules by the cellBasically the reverse of exocytosis- the cell engulfs the things and forms a vesicle around it 1. Phagocytosis= “cell eating”- capture of solid substances2. Pinocytosis= “cell drinking”- uptakes of liquid- all the solutes in the solution are taken in- the cell can not discriminate and take only SOME and not others3. Receptor-mediated endocytosis= region on the membrane has receptors thesecan attach to specific moleculesWhen the specific molecule attaches to the receptor, it triggers vesicleformation. This allows uptake of specific substance that may be in low
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