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Transcript
II. Movement across the Cell Membrane A. Simple Diffusion 1. Movement for high concentration [ ] to low concentration [ ] a. “passive transport” b. no energy needed Diffusion Animation 2. Diffusion across cell membrane a. Cell membrane is the boundary between inside & outside… separates cell from its environment OUT IN food carbohydrates sugars, proteins amino acids lipids salts, O2, H2O OUT IN waste ammonia salts CO2 H2O products cell needs materials in & products or waste out 3. Diffusion through phospholipid bilayer a. What molecules can get through directly? fats & other lipids inside cell NH3 lipid salt b. What molecules can NOT get through directly? i. polar molecules H 2O ii. ions outside cell sugar aa H 2O salts, ammonia iii. large molecules starches, proteins 4. Channels through cell membrane a. Membrane becomes semi-permeable with protein channels . specific channels allow specific material across cell membrane Called TRANSPORT or CARRIER PROTEINS inside cell NH3 salt H 2O aa sugar outside cell B. Facilitated Diffusion Facilitated Diffusion Animation 1. Diffusion through protein channels a. channels move specific molecules across cell membrane facilitated = with help b. NO energy needed open channel = fast transport high low “The Bouncer” C. Active Transport 1. Cells may need to move molecules against concentration gradient a. shape change transports solute from one side of membrane to other b. protein “pump” c. “costs” energy = ATP low conformational change ATP high “The Doorman” Active Transport Example: Nerve Impulse 1. Neurons, nerve cells, have a charge, or electrical potential, across their cell membranes. 2. Sodium (Na+) is on the outside of the cell and Potassium (K+) is on the inside 3. The neuron is at rest when the inside of the cell is at -70mV 4. An “action potential” occurs when the nerve is stimulated and sodium moves INTO the cell. The positive Na+ moving into the cell turns the inside positive. Facilitated diffusion 5. After the Na+ channels open, K+ channels open and K+ moves OUT of the cell to reset the negative charge inside the cell. Facilitated diffusion The Nerve Impulse 6. Eventually Na+ must move back OUT of the cell and K+ must move back IN against their concentration gradients. This occurs by Active transport. A Na+/K+ pump is used to move these ions back to their original sides of the cell membrane. Neuron: Na+/K+ Pump Na+/K+ pump D. Review of Membrane Transport 1. Passive Transport Simple diffusion diffusion of nonpolar, hydrophobic molecules lipids High to low concentration gradient Facilitated transport diffusion of polar, hydrophilic molecules through a protein channel High to low concentration gradient 2. Active transport diffusion against concentration gradient Low to high uses a protein pump requires ATP ATP Transport summary simple diffusion facilitated diffusion active transport ATP E. Moving large molecules in & out of cell Large molecules are IMPERMEABLE to the cell membrane (can’t get through) There is a way… through vesicles & vacuoles 1. Endocytosis (moving in to cell) phagocytosis = “cellular eating” Phagocytosis Animation pinocytosis = “cellular drinking” Exocytosis (moving out of cell) Endo and Exocytosis Animation 2. Endocytosis phagocytosis pinocytosis fuse with lysosome for digestion non-specific process EXOCYTOSIS Cellular Transport Interactive animation http://www.wiley.com/college/boyer/0470003790/animations/ membrane_transport/membrane_transport.htm