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Movement across the Cell Membrane 2006-2007 Diffusion Diffusion movement from HIGH LOW concentration Down the concentration gradient What did it take to make the concentration gradient? The concentration gradient stores potential energy It takes energy to generate the gradient The process is still considered passive 2006-2007 3 Facilitated Diffusion • Diffusion through protein channels – highly specific – passive process HIGH what sort of molecules will use this process? LOW “The Bouncer” 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” LOW – “costs” energy = ATP Once completed, where has the energy for the active transport gone? ATP HIGH “The Doorman” Active transport • Many models & mechanisms ATP ATP antiport symport Getting through cell membrane • Passive Transport – Simple diffusion • nonpolar, hydrophobic molecules –HIGH LOW concentration gradient – Facilitated transport • polar, hydrophilic molecules • through a protein channel –HIGH LOW concentration gradient • Active transport – against concentration gradient ATP • LOW HIGH – uses a protein pump (requires ATP) Transport summary simple diffusion facilitated diffusion active transport ATP What about large molecules? • Moving large molecules into & out of cell – through vesicles & vacuoles – endocytosis • phagocytosis = “cellular eating” • pinocytosis = “cellular drinking” – exocytosis exocytosis Endocytosis phagocytosis fuse with lysosome for digestion pinocytosis non-specific process receptor-mediated endocytosis triggered by molecular signal What about Osmosis? • Diffusion of water from HIGH concentration of water to LOW concentration of water – across a semi-permeable membrane Why does osmosis need a membrane? 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 hypotonic hypertonic net movement of water Hypotonic , Hypertonic, Isotonic How does sugar concentration lead to water movement? 13 Let’s watch the video Which way would water move if oil was added to the left side of the tube? 14 Managing water balance • Hypotonic • Animal cell/protist cell problem? • Solutions? • Plant cells.... KABOOM! • turgid = full • cell wall protects from bursting No problem, here freshwater Managing water balance • Hypertonic • Animal cells: I’m shrinking, I’m shrinking! • How can they adjust: • Take up water or pump out solutes. – plant cells • plasmolysis = wilt Why do people make beef jerky, and add syrup to preserve canned fruit? I will survive! saltwater Managing water balance Isotonic –Animal cell problems: –none –solutes are equally concentrated That’s on both sides of membranes perfect! –Plant cell problems –flaccid cells lose structure. I could be better… balanced Aquaporins • Water moves rapidly into & out of cells – evidence that there were water channels • protein channels allowing flow of water across cell membrane Peter Agre Roderick MacKinnon John Hopkins Rockefeller Which way will water move? .05 M .03 M Hey...watch this
