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Transcript
Chapter 8. Movement across the Cell Membrane AP Biology 2005-2006 Diffusion 2nd Law of Thermodynamics governs biological systems Universe tends towards disorder Diffusion AP Biology movement from high low concentration Diffusion of 2 solutes Each substance diffuses down its own concentration gradient, independent of concentration gradients of other substances AP Biology Diffusion Move for HIGH to LOW concentration “passive transport” no energy needed AP Biology diffusion osmosis Lipids of cell membrane Membrane is made of phospholipids phospholipid bilayer inside cell phosphate hydrophilic lipid hydrophobic outside cell AP Biology Phospholipids AP Biology Fluid Mosaic Model In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer AP Biology Figure 7.6 Lateral movement occurs 107 times per second. AP Biology Flip-flopping across the membrane is rare ( once per month). Figure 7.8 Fluid Viscous Unsaturated hydrocarbonSaturated hydrocarbon tails tails (a) Unsaturated versus saturated hydrocarbon tails (b) Cholesterol within the animal cell membrane AP Biology Cholesterol Phospholipid bilayer What molecules can get through directly? AP Biology 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 inside cell Haa sugar 2O “holes”, or channels, in cell membrane allow material in & out AP Biology outside cell NH salt3 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 salt outside NH3 cell AP Biology H 2O aa sugar Why proteins? Proteins are mixed molecules hydrophobic amino acids stick in the lipid membrane anchors the protein in membrane hydrophilic amino acids stick out in the watery fluid in & around cell specialized “receptor” for specific molecules AP Biology 2005-2006 Membrane Proteins Proteins determine most of membrane’s specific functions cell membrane & organelle membranes each have unique collections of proteins Membrane proteins: AP Biology peripheral proteins = loosely bound to surface of membrane integral proteins = penetrate into lipid bilayer, often completely spanning the membrane = transmembrane protein 2005-2006 Figure 7.10 Signaling molecule Enzymes ATP (a) Transport Receptor Signal transduction (b) Enzymatic activity (c) Signal transduction Glycoprotein (d) Cell-cell recognition (e) Intercellular joining AP Biology (f) Attachment to the cytoskeleton and extracellular matrix (ECM) Figure 7.11 HIV Receptor (CD4) Co-receptor (CCR5) HIV can infect a cell that has CCR5 on its surface, as in most people. AP Biology Receptor (CD4) but no CCR5 Plasma membrane HIV cannot infect a cell lacking CCR5 on its surface, as in resistant individuals. A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer AP Biology 2005-2006 Membrane Carbohydrates Play a key role in cell-cell recognition ability of a cell to distinguish neighboring cells from another important in organ & tissue development basis for rejection of foreign cells by immune system AP Biology 2005-2006 Figure 7.12 Transmembrane glycoproteins Secretory protein Golgi apparatus Vesicle ER ER lumen Glycolipid Plasma membrane: Cytoplasmic face Extracellular face Transmembrane glycoprotein Secreted protein Membrane glycolipid AP Biology Getting through cell membrane Passive transport diffusion of hydrophobic (lipids) molecules high low concentration gradient Facilitated transport diffusion of 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 Simple diffusion across membrane Which way will lipid move? lipid inside cell low lipid lipid lipid lipid lipid high outside cell lipid lipid lipid lipid AP Biology lipid lipid lipid lipid Facilitated Diffusion Globular proteins act as doors in membrane channels to move specific molecules through cell membrane open channel = fast transport high low AP Biology “The Bouncer” Facilitated diffusion Move from HIGH to LOW concentration through a protein channel passive transport no energy needed facilitated = with help AP Biology 2005-2006 Gated channels Some channel proteins open only in presence of stimulus (signal) Stimulus often different than transport molecule ex: ion-gated channels when neurotransmitters bind to a specific gated channels on a neuron, these channels open = allows Na+ ions to enter nerve cell ex: voltage-gated channels change in electrical charge across nerve cell membrane opens Na+ & K+ channels see next slide AP Biology AP Biology 2005-2006 Active Transport Globular proteins act as ferry for specific molecules shape change transports solute from one side of membrane to other protein “pump” “costs” energy low high AP Biology conformational change “The Doorman” Active transport Cells may need molecules to move against concentration situation need to pump against concentration protein pump requires energy ATP Na+/K+ pump in nerve cell membranes AP Biology 2005-2006 Active transport Many models & mechanisms using ATP AP Biology using ATP Sodium Potassium Pump Video AP Biology 2005-2006 Transport summary - Video AP Biology 2005-2006 Figure 7.19 Diffusion AP Biology Passive transport Facilitated diffusion Active transport ATP Cotransport: Coupled Transport by a Membrane Protein Cotransport occurs when active transport of a solute indirectly drives transport of other solutes Plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell AP Biology © 2011 Pearson Education, Inc. Figure 7.21 ATP H H H Proton pump H H H H H Sucrose-H cotransporter Sucrose AP Biology Diffusion of H Sucrose How about large molecules? Moving large molecules into & out of cell through vesicles & vacuoles endocytosis phagocytosis = “cellular eating” pinocytosis = “cellular drinking” receptor-mediated endocytosis AP Biology exocytosis exocytosis 2005-2006 Figure 7.22 Phagocytosis Pinocytosis Receptor-Mediated Endocytosis EXTRACELLULAR FLUID Solutes Pseudopodium Receptor Ligand Plasma membrane Coat proteins Coated pit “Food” or other particle Coated vesicle Vesicle Food vacuole CYTOPLASM AP Biology Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis AP Biology fuse with lysosome for digestion non-specific process triggered by ligand signal The Special Case of Water Movement of water across the cell membrane AP Biology 2005-2006 Osmosis is diffusion of water Water is very important, 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 2005-2006 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 AP Biology Managing water balance Cell survival depends on balancing water uptake & loss AP Biology freshwater balanced saltwater Managing water balance Isotonic AP Biology animal cell immersed in isotonic solution blood cells in blood no net movement of water across plasma membrane water flows across membrane, at same rate in both directions volume of cell is stable Managing water balance Hypotonic animal cell in hypotonic solution will gain water, swell & burst Paramecium vs. pond water Paramecium is hypertonic H2O continually enters cell to solve problem, specialized organelle, contractile vacuole pumps H2O out of cell = ATP plant cell turgid AP Biology Water regulation Contractile vacuole in Paramecium AP Biology Managing water balance Hypertonic animal cell in hypertonic solution will loose water, shrivel & probably die salt water organisms are hypotonic compared to their environment they have to take up water & pump out salt plant cells plasmolysis = wilt AP Biology Figure 7.15 (a) Animal cell Hypotonic solution H2O (b) Plant cell Isotonic solution H2O Lysed Normal H2OCell wall H2O H2O Turgid (normal) Flaccid Osmosis AP Biology H2O Hypertonic solution H2O Shriveled H2O Plasmolyzed Water Balance of Cells Without Walls Tonicity is the ability of a surrounding solution to cause a cell to gain or lose water Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water AP Biology © 2011 Pearson Education, Inc. 1991 | 2003 Aquaporins Water moves rapidly into & out of cells AP Biology evidence that there were water channels Peter Agre Roderick MacKinnon John Hopkins Rockefeller Figure 7.UN03 “Cell” 0.03 M sucrose 0.02 M glucose AP Biology “Environment” 0.01 M sucrose 0.01 M glucose 0.01 M fructose Osmosis… .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 of2005-2006 cell AP Biology