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Transcript
The Cell Membrane AP Biology Fluid Mosaic Model Time to learn about 7.3 and 7.4 AP Biology Arranged as a Phospholipid bilayer Serves as a cellular barrier / border, Selective Permeability sugar H 2O salt polar hydrophilic heads nonpolar hydrophobic tails impermeable to polar molecules polar hydrophilic heads waste AP Biology lipids Cell membrane is more than lipids… Transmembrane proteins embedded in phospholipid bilayer create semi-permeabe channels lipid bilayer membrane AP Biology protein channels in lipid bilyer membrane Membrane Proteins Proteins determine membrane’s specific functions cell membrane & organelle membranes each have unique collections of proteins Classes of membrane proteins: peripheral proteins loosely bound to surface of membrane ex: cell surface identity marker (antigens) integral proteins penetrate lipid bilayer, usually across whole membrane transmembrane protein ex: transport proteins channels, permeases (pumps) AP Biology Many Functions of Membrane Proteins “Channel” Outside Plasma membrane Inside Transporter Cell surface identity marker aka Cell-cell AP Biology recognition Enzyme activity Cell adhesionIntercellular joining Cell surface receptor aka Signal Transduction Attachment to the cytoskeleton Movement across the Cell Membrane AP Biology 2007-2008 Two Types of Transport 1) Passive Transport- 2) Active TransportNO ENERGY ENERGY AP Biology 8 Three Types of Passive Transport 1) Diffusion 2) Facilitated Diffusion 3) Osmosis AP Biology 9 Simple Diffusion Particles move from HIGH to LOW concentration “passive transport” movement of water no energy needed diffusion AP Biology osmosis Diffusion of Liquids AP Biology 11 Cell membrane -Solute moves DOWN concentration gradient (HIGH to LOW) until reaches equilibrium AP Biology 12 Diffusion through phospholipid bilayer What molecules can get through directly? fats & other lipids, hydrocarbons, CO2, Oxygen, hydrophobic molecules inside cell NH3 What molecules can lipid salt NOT get through directly? polar molecules H 2O outside cell sugar aa ions (charged) salts, ammonia H 2O large molecules starches, proteins AP Biology Facilitated Diffusion Diffusion through protein channels channels move specific molecules (ex.glucose) across cell membrane facilitated = with help open channel = fast transport no energy needed Channel proteins are embedded in the cell membrane & have a pore for materials to cross Carrier proteins can change shape to move material from one side of the membrane to the other AP Biology Osmosis is just diffusion of water Water is very important to life, so we talk about water separately Diffusion of water from HIGH concentration of water to LOW concentration of water AP Biology across a semi-permeable membrane Diffusion of H2O Across A Membrane High H2O potential Low solute concentration AP Biology Low H2O potential High solute concentration 16 Three Types of Solutions AP Biology 17 Concentration of water Direction of osmosis is determined by comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water water AP Biology hypotonic hypertonic net movement of water Managing water balance Cell survival depends on balancing water uptake & loss AP Biology freshwater balanced saltwater 1 Managing water balance Hypotonic a cell in fresh water high concentration of water around cell problem: cell gains water, swells & can burst (cytolysis) KABOOM! example: Paramecium ex: water continually enters Paramecium cell solution: contractile vacuole pumps water out of cell ATP Requires ATP plant cells No problem, here turgid = full (turgor pressure) cell wall protects from bursting AP Biology freshwater Cell in Hypotonic Solution 10% NaCL 90% H2O CELL 20% NaCL 80% H2O -HYPOtonic – water moves inside of cell -Turgor pressure- pressure that builds up, gives plant shape -Contractile Vacuole- forces out excess water AP Biology 21 2 Managing water balance Hypertonic I’m shrinking, a cell in salt water I’m shrinking! low concentration of water around cell problem: cell loses water & can die solution: take up water or pump out salt plant cells plasmolysis = wilt can recover AP Biology I will survive! saltwater Cell in Hypertonic Solution 15% NaCL 85% H2O ENVIRONMENT CELL 5% NaCL 95% H2O -Hypertonic- water moves OUT -plasmolysis- loss of water, decreasing turgor pressure causing wilting -Crenation- animal cell shrivels up AP Biology 23 3 Managing water balance Isotonic That’s perfect! animal cell immersed in mild salt solution no difference in concentration of water between cell & environment problem: none no net movement of water flows across membrane equally, in both directions I could cell in equilibrium be better… volume of cell is stable example: blood cells in blood plasma slightly salty IV solution in hospital AP Biology balanced Cell in Isotonic Solution 10% NaCL 90% H2O ENVIRONMENT CELL 10% NaCL 90% H2O NO NET MOVEMENT -Isotonic- amount of solute is equal on both sides, there is no net movement - Cell has reached EQULIBRIUM AP Biology 25 1991 | 2003 Aquaporins Water moves rapidly into & out of cells evidence that there were water channels protein channels allowing flow of water across cell membrane AP Biology Peter Agre Roderick MacKinnon John Hopkins Rockefeller Three Types of Solutions 90% H2O 10% solute 85% H2O 15% solute 95% H2O 5% solute 90% H2O 10% solute 90% H2O 10% solute 90% H2O 10% solute Isotonic (no net movement of water) Hypotonic Hypertonic AP Biology 27 Fig. 7-UN4 AP Biology Three Types of Passive Transport 1) Diffusion 2) Facilitated Diffusion 3) Osmosis AP Biology 29 Active Transport Cells may need to move molecules against concentration gradient conformational shape change transports solute from one side of membrane to other protein “pump” “costs” energy = ATP LOW conformational change ATP HIGH AP Biology “The Doorman” Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential http://www.youtube.com/watch?v=yz7EHJFDEJs http://www.youtube.com/watch?v=7EyhsOewnH4 AP Biology 31 How about large molecules? Moving large molecules into & out of cell through vesicles & vacuoles Endocytosis- bulk transport of materials into the cell phagocytosis = “cellular eating” pinocytosis = “cellular drinking” Exocytosis- bulk transport of materials out of the cell. AP Biology http://www.youtube.com/watch?v=kfy92hdaAH0 Transport summary simple diffusion facilitated diffusion active transport AP Biology ATP Getting through cell membrane Passive Transport Simple diffusion diffusion of nonpolar, hydrophobic molecules lipids HIGH LOW concentration gradient Facilitated transport diffusion of polar, hydrophilic molecules through a protein channel HIGH LOW concentration gradient Active transport diffusion against concentration gradient LOW HIGH AP Biology uses a protein pump requires ATP ATP