BIOL 101 1st Edition Lecture 8 Outline of Last Lecture I Cytoplasmic Membrane II Fluid Mosaic Model a Proteins b Carbohydrates c Cholesterol III Small Molecules Across the Membrane a Transport Proteins IV Diffusion Outline of Current Lecture I Water Balance in Cells a Hypertonic b Hypotonic c Isotonic II Facilitated Diffusion III Active Transport a Ion Transport b Co Transport IV Traffic of Large Molecules a Exocytosis b Endocytosis i Phagocytosis ii Pinocytosis iii Receptor mediated endocytosis Current Lecture Chapter 7 cont Water Balance in Cells Which direction will H2O diffuse INTO or OUT OF the cell H2O is like any other substance it will diffuse DOWN its concentration gradient More concentrated less concentrated TRICK about H2O diffusion is that it is affected by the concentration of solutes dissolved in the water The 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 cell BIOL 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 shrink 2 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 the cell H2O will diffuse INTO the cell cell will swell up Animal 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 cell 3 Isotonic isosmotic concentration of solutes OUTSIDE the cell concentration of solutes INSIDE the cell NO NET movement of H2O into or out of the cell Animal cell best condition anything else is potentially lethal Plant cell no turgor pressure plant welts Facilitated 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 Edition Ion Transport When 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 membrane Therefore two forces drive the transport of ions across the membrane 1 concentration gradient of the specific ion 2 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 cell Ions diffuse down their electrochemical gradient combines both influences Co Transport Electrogenic pump transport protein that generates voltage across a membrane by moving charged atoms or molecules Ex 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 concentration gradient 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 COTRANSPORT in this way the energy in the H gradient is used to move sucrose against its concentration gradient and get it INTO the cell BIOL 101 1st Edition Traffic 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 released Endocytosis capture of outside molecules by the cell Basically the reverse of exocytosis the cell engulfs the things and forms a vesicle around it 1 Phagocytosis cell eating capture of solid substances 2 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 others 3 Receptor mediated endocytosis region on the membrane has receptors these can attach to specific molecules When the specific molecule attaches to the receptor it triggers vesicle formation This allows uptake of specific substance that may be in low concentration
View Full Document
Unlocking...