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Transcript
Cell Membranes & Movement Across Them Regents Biology 2006-2007 Cell (plasma) membrane Cells need an inside & an outside… separate cell from its environment cell membrane is the boundary IN food sugars proteins fats salts O2 H2 O Regents Biology OUT waste ammonia salts CO2 H2 O products cell needs materials in & products or waste out Building a membrane How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? What substance do you know that doesn’t mix with water? Regents Biology FATS LIPIDS oil & water don’t mix!! Lipids of cell membrane Membrane is made of phospholipids phospholipid bilayer “attracted to water” inside cell phosphate lipid “repelled by water” outside cell Regents Biology Semi-permeable membrane Need to allow passage through the membrane But need to control what gets in or out membrane needs to be semi-permeable So what needs to get across the membrane? sugar Regents Biology aa lipid H 2O salt NH3 So how do you build a semi-permeable membrane? Phospholipid bilayer What molecules can get through directly? inside cell waste outside cell Regents Biology lipid salt sugar aa H 2O fats & other lipids can slip directly through the phospholipid cell membrane, but… what about other stuff? Permeable cell membrane Need to allow more material through membrane needs to be permeable to… all materials a cell needs to bring in all waste a cell needs excrete out all products a cell needs to export out “holes”, or channels, in cell membrane allow material in & out Regents Biology inside cell outside cell Haa sugar 2O waste salt lipid Semi-permeable cell membrane But the cell still needs control membrane needs to be semi-permeable specific channels allow specific material in & out inside cell waste Regents Biology outside cell H 2O salt aa sugar How do you build a semi-permeable cell membrane? channels are made of proteins proteins both “like” water & “like” lipids bi-lipid membrane Regents Biology protein channels in bi-lipid membrane Protein channels Proteins act as doors in the membrane channels to move specific molecules through cell membrane Regents Biology Movement through the channel Why do molecules move through membrane if you give them a channel? ? ? Regents Biology Molecules move from high to low Diffusion move from HIGH to LOW concentration Regents Biology Diffusion Move from HIGH to LOW concentration “passive transport” no energy needed Regents Biology Simple Diffusion Move from HIGH to LOW fat inside cell fat fat fat fat fat Which way will fat move? low high outside cell fat fat fat fat Regents Biology fat fat fat fat Diffusion through a channel Move from HIGH to LOW sugar sugar sugar sugar inside cell sugar sugar low Which way will sugar move? high outside cell sugar Regents Biologysugar sugar sugar sugar sugar sugar Diffusion Move from HIGH to LOW concentration through membrane simple diffusion no energy needed through a protein channel facilitated diffusion (with help) no energy needed Regents Biology high low Active transport Cells may need molecules to move against concentration difference need to pump “uphill” from LOW to HIGH using ATP protein pump requires energy ATP ATP Regents Biology Transport summary diffusion facilitated diffusion active transport Regents Biology ATP Osmosis Movement of Water Across Cell Membrane Regents Biology 2006-2007 Osmosis Water is very important, so we talk about water separately Osmosis diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane Regents Biology Keeping water balance Cell survival depends on balancing water uptake & water loss freshwater Regents Biology balanced saltwater http://www.dnatube.com/video/2775/Oni on-Cells-Plasmolysis Regents Biology Managing water balance Balanced conditions no difference between cell & environment example: blood problem: none water flows across membrane equally, in both directions volume of cell doesn’t change Regents Biology balanced Managing water balance Freshwater a cell in fresh water example: Paramecium problem: gains water, swells & can burst water continually enters Paramecium cell solution: contractile vacuole pumps water out of cell Regents Biology freshwater Controlling water Contractile vacuole in Paramecium Regents Biology Managing water balance Saltwater a cell in salt water example: shellfish problem: lose water plasmolysis in plants shrinking cell solution: take up water Regents Biology saltwater Regents Biology Active Transport Regents Biology Exocytosis Regents Biology Endocytosis Regents Biology Hypercholesterolemia Faulty LDL receptors in liver cells Liver does not remove Cholesterol builds up in blood vessels Regents Biology http://www.youtube.com/user/jchvatal1/ videos?view_as=public Go to mastering Regents Biology