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Transport across membranes Syllabus reference: Candidates should be able to: This symbol in the corner of a slide indicates a picture, diagram or table taken from your text book Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated Transport across membranes Diffusion (and osmosis) Facilitated diffusion Active transport Membrane trafficking passive processes energyrequiring processes Diffusion Simple diffusion through the phospholipid bilayer Diffusion animation Fick’s Law Rate of diffusion = difference in concentrat ion x surface area thickness of the exchange surface Diffusion of water; Osmosis Diffusion of water; Osmosis Diffusion of water; Osmosis = 0 kPa Diffusion of water; Osmosis Osmosis Only free water molecules can diffuse through the membrane In an environment that is hypotonic, the water concentration is greater outside the cell and the solute concentration is higher inside (the interior of the cell is hypertonic to the hypotonic surroundings). Water goes into the cell In an isotonic environment, both the water and solute concentration are the same inside and outside the cell and water goes into and out of the cell at an equal rate. There is no net change in water concentration If the environment is hypertonic, the water concentration is greater inside the cell while the solute concentration is higher outside (the interior of the cell is hypotonic to the surrounding hypertonic environment). Water goes out of the cell Osmosis; plant cells turgid cells flaccid cells Turgor pressure in plant cells depends on osmosis Osmosis; plant cells in high water potential Osmosis; plant cells in low water potential Osmosis; animal cells Osmosis and blood cells Osmosis; summary Osmosis Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated Transport across membranes The lipid bilayer is more permeable to non- polar molecules than to polar molecules and ions. The size of a molecule also affects permeability – the lipid bilayer is more permeable to small molecules than to large molecules. Transport across membranes Therefore if larger molecules and charged ions are to be transported there must be other mechanisms involved in crossing a membrane A protein molecule providing a channel through the membrane Double layer of lipid molecules Facilitated diffusion Occurs through channel proteins These proteins act as channels for ions They can be open or closed Different conditions may have to be satisfied for the channel to open Channel protein Diffusion & facilitated diffusion Carrier protein Channel proteins Voltage gated animation Ligand gated animation Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated Active transport carrier protein The carrier protein picks up the particles from one side of the membrane The energy released from ATP causes a change in the shape of the protein and the particles are deposited on the other side of the membrane Active transport involves expenditure of energy Substances are moved against a concentration gradient Active transport Active transport animation Active transport; Ion pumps The sodium-potassium pump Active transport Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated Membrane trafficking Membrane trafficking 1 2 3 4 Membrane trafficking Endocytosis and exocytosis Endocytosis & exocytosis Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated Endocytosis Endocytosis There are three types of endocytosis pinocytosis [the endocytosis of dissolved substances and liquids] phagocytosis [the engulfing of cells or particles] receptor-mediated endocytosis [selective/ controlled endocytosis] Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated Endocytosis 1; pinocytosis pinocytosis = the endocytosis of dissolved substances and liquids Endocytosis 1; pinocytosis pinocytosis = endocytosis of dissolved substances and liquids Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated Endocytosis 2; phagocytosis Second: phagocytosis Endocytosis 2; phagocytosis Phagocytosis seen under the SEM Phagocytosis seen under the TEM Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated Endocytosis 3; receptor-mediated Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated Exocytosis 1 2 3 Exocytosis Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated Exocytosis - unregulated Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated Exocytosis - regulated Membrane transport Passive Diffusion Osmosis Facilitated diffusion Energy requiring Active transport Membrane trafficking Endocytosis Exocytosis Pinocytocis Unregulated Phagocytosis Regulated Receptor mediated
