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Transcript
Cell Membranes Mark Mayo Cypress College Last update 9/10/13 1 Fluid Mosaic Model The cell membrane is composed of two layers of simple lipid molecules They are commonly depicted as a ball with two dangling strings 2 Fluid Mosaic Model The heads face outward – away from the middle of the lipid bilayer The heads are hydrophilic while the tails are hydrophobic 3 Fluid Mosaic Model The evidence for our model of cell membrane structure has been verified by numerous electron micrographs that show a dual layer Cell #1 Cell #2 4 Fluid Mosaic Model * Membrane components include: • Lipids (gray) • Proteins (purple) • Cholesterol (yellow) 5 Fluid Mosaic Model Membranes regulate the materials that can enter and leave the cell 6 Fluid Mosaic Model Carbohydrates are frequently attached to the proteins on the external portion 7 Membrane Proteins There are several types of proteins associated with cell membranes: • Integral – embedded in the membrane and are difficult to remove • Integral Transmembrane – spans the entire membrane from inside to the outside of the cell membrane * • Peripheral – proteins loosely attached to the cell membrane on the inside or outside of the cell 8 Membrane Proteins Important * (spans membrane) 9 Membrane Proteins 10 Membrane Proteins Membrane proteins have a variety of functions they perform • Transport proteins allow the movement of materials into and out of the cell • Receptor proteins receive a signal from outside the cell and pass it inside • Recognition proteins display “self” signals to identify foreign cells • Adhesion proteins permit cell-cell junctions 11 Membrane Transport The cell membrane is both passively and actively involved in the movement of materials into and out of the cell Transport of water, ions and other substances will be treated separately 12 Membrane Transport Phagocytosis * A form of cell eating where large particles or cells are engulfed by a white blood cell * 13 Membrane Transport Endocytosis the process where materials are brought into the cell vs. Exocytosis the process where materials are removed from the cell 14 Membrane Transport Endocytosis is a general term for the movement of substances into the cell Outside Inside 15 Membrane Transport Exocytosis is the removal of substances from within the cell to the outside This may be in the form of waste removal or the secretion of substances needed outside the cell 16 Membrane Transport Contractile vacuoles are used by protists to remove internal water 17 Membrane Transport Contractile vacuole in action Full Empty 18 Membrane Transport Passive transport • Simple diffusion • Facilitated diffusion using a carrier molecule 19 Membrane Transport Passive transport – Simple Diffusion • Diffusion is the passive movement of materials from an area of greater concentration to an area of lesser concentration * 20 Membrane Transport Another view of facilitated diffusion Membrane Protein 21 Membrane Transport Active transport* requires energy, usually in the form of ATP *, to move materials across the cell membrane Note that the pump works in the reverse of diffusion due to the added energy (from lower to higher concentration) * 22 Membrane Transport + + The sodium (Na /K ) pump 23 Isotonic, Hypotonic & Hypertonic Solutions Solute – the dissolved solids in a solution (the salt in a salt/water solution) Solvent - the liquid that dissolves the solids in a solution (the water in a salt/water solution) 24 Isotonic, Hypotonic & Hypertonic Solutions Diffusion is the passive movement of materials from an area of greater concentration to an area of lesser concentration * 25 Isotonic, Hypotonic & Hypertonic Solutions Diffusion * This animation shows the diffusion of small molecules from a concentrated source * 26 Isotonic, Hypotonic & Hypertonic Solutions A cell placed in an isotonic solution Isotonic means EQUAL SALT • In the Solution: Salt concentration that is equal to that of the cell (ie. 1.0% salt). Water concentration that is equal to that of the cell (ie. 99.0%) • In the Cell: Salt concentration is usually 1.0% Water concentration is usually 99.0% 27 Isotonic, Hypotonic & Hypertonic Solutions A cell placed in an isotonic solution What happens and why... Since the water concentration outside of the cell is exactly equal to the water concentration inside the cell, water will move in and out WITHOUT ANY NET CHANGE in the cell by simple diffusion. The cell will not change in size and is said to be in equilibrium. solution Salt = 0.9 % Water = 99.1 % cell Salt = 0.9 % 28 Water = 99.1 % Isotonic, Hypotonic & Hypertonic Solutions A cell placed in a hypotonic solution hypotonic means LESS SALT • Solution: Salt concentration that is less than that of the cell (ie. 0.1% or 0.0% salt) Water concentration that is greater than that of the cell (ie. 99.9% or 100%) • Cell: Salt concentration is usually 1.0% Water concentration is usually 99.0% 29 Isotonic, Hypotonic & Hypertonic Solutions A cell placed in a hypotonic solution What happens and why... Since the water concentration outside of the cell is greater than the water concentration inside the cell, water will enter the cell by simple diffusion. The cell will expand and possibly burst generally called cytolysis or hemolysis for red blood cells. * Cells get LARGER & HEAVIER solution Salt = 0 % Water = 100 % cell Salt = 0.9 % 30 Water = 99.1 % Isotonic, Hypotonic & Hypertonic Solutions A cell placed in a hypertonic solution hypertonic means MORE SALT • Solution: Salt concentration that is greater than that of the cell (ie. 2.0% or 10.0% salt) Water concentration that is less than that of the cell (ie. 98.0% or 90%) • Cell: Salt concentration is usually 1.0% Water concentration is usually 99.0% 31 Isotonic, Hypotonic & Hypertonic Solutions A cell placed in a hypertonic solution* What happens and why... Since the water concentration outside of the cell is less than the water concentration inside the cell, water will leave the cell* by simple diffusion. The cell will shrink and distort generally called plasmolysis or for red blood cells - crenation. Cells get SMALLER & LIGHTER solution Salt = 10 % Water = 90 % cell Salt = 0.9 % 32 Water = 99.1 %