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Movement across the cell membrane Diffusion • Movement of molecules from high low concentration • 2nd Law of Thermodynamics • Governs biological systems • Universe tends towards disorder (entropy) Simple diffusion • Movement from high low concentration • “passive transport” • No energy needed X ATP movement of water diffusion osmosis Facilitated diffusion • Diffusion through protein channels • Channels move specific molecules across the cell membrane • Movement from high low concentration X ATP • “passive transport” • No energy needed facilitated = with help open channel = fast transport HIGH LOW “The Bouncer” Active transport • Movement through a protein pump • Movement from low high concentration • AGAINST the concentration gradient • Requires energy ATP LOW HIGH Active transport • Antiport • Molecules move in opposite directions • Symport • Molecules move in the same direction antiport symport Let’s review … • Passive transport • Simple diffusion • Diffusion of nonpolar, hydrophobic molecules • Lipids • HIGH LOW concentration gradient • Facilitated diffusion • Diffusion of polar, hydrophilic molecules • Through a protein channel • HIGH LOW • Active transport • Diffusion AGAINST the concentration gradient • LOW HIGH • Uses a protein pump • Required ATP Transport summary simple diffusion Who’s WATER! facilitated missing? diffusion active transport ATP ATP Osmosis • Diffusion of WATER • Move from HIGH concentration of water to LOW concentration of water • Across a semi-permeable membrane Water concentration • 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 Maintaining water balance • Cell survival depends on balancing water uptake & loss freshwater balanced saltwater Maintaining water balance • Hypotonic • A cell in fresh (or distilled) water • High conc of water outside cell • Animal cell • Cell gains water, swells, & can burst • Ex. Paramecium KABOOM! Water continually enters cell • Soluton: contractile vacuole Pumps water out of cell • Plant cell No problem, here • Turgid = full • Cell wall protects from bursting freshwater Contractile vacuole • Pumping out water in a paraecium ATP Maintaining water balance • Hypertonic I’m shrinking, I’m shrinking! • A cell in salt water • Low conc of water outside cell • Animal cell • Cell loses water & can die • Ex. Shellfish • Soluton: take up water or pump out salt • Plant cell • Plasmolysis = wilt • Cell can recover I will survive! saltwater Maintaining water balance • Isotonic • Cell is in slightly salty solution • No difference in That’s perfect! concentration of water between cell & environment • Problem: none No net movement of water • Example: blood cells in plasma IV solution is slightly salty I could be better… balanced Maintaining water balance • Aquaporins • Water moves rapidly into & out of cells • Protein channels allowing flow of water across the cell membrane Some quick practice … .05 M .03 M Cell (compared to beaker) hypertonic or hypotonic Beaker (compared to cell) hypertonic or hypotonic Which way does the water flow? in or out of cell What about large molecules? What about large molecules? • Large molecules move through vesicles & vacuoles • Endocytosis = movement INTO the cell • Phagocytosis = “cellular eating” • Pinocytosis = “cellular drinking” • Exocytosis = movement OUT of the cell Endocytosis phagocytosis fuse with lysosome for digestion pinocytosis non-specific process receptor-mediated endocytosis triggered by molecular signal Any Questions??
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