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Transcript
Cell boundaries Objectives: 1. Describe the functions of the cell membrane and cell wall. 2. Describe the process that occurs during diffusion. 3. Discuss how osmosis is a form of diffusion. 4. Explain the processes of facilitated diffusion and active transport. 5. Differentiate between endocytosis and exoctyosis. Cell membrane (plasma membrane) Lipid bilayer = double layer sheets of phospholipids Phosphate group (PO4-3) attached to a diglyceride Hydrophilic head on the outside and hydrophobic tails on inside Hydrophobic tails no association with water or charged molecules; lipid soluble molecules, oxygen gas molecules and carbon dioxide molecules do pass across the membrane Regulates what enters and leaves the cell while providing protection and support to the cell Membrane proteins – channel proteins create a channel to allow water, ions to move across lipid membrane Carrier proteins bind and transport solutes across plasma membrane may(active transport) or may not need (facilitated diffusion) ATP CELL WALLS Plants, fungi, algae, and most prokaryotes Provide support and protection Allows water, oxygen, carbon dioxide, other substances to pass across Cellulose = fibers of carbohydrate and protein, cell walls of plants DIFFUSION Cytoplasm = solution of dissolved solutes in water Concentration = amount of solute in a given volume of water Example: 12 grams NaCL in 3 Liters water concentration = 4g/L Solute particles and water molecules always moving Particles move until at equilibrium DIFFUSION = movement of solute molecules from areas of high concentration to areas of low concentration until equilibrium is met NO ENERGY REQUIRED OSMOSIS The diffusion of water across cell membranes ISOTONIC = concentration of water and solute molecules is equal on both sides of cell membrane : water in equals water out HYPERTONIC = High concentration of solute molecules than water molecules : water moves out of cell to achieve equilibrium – cell shrinks, dies HYPOTONIC = lower concentration of solute molecules than water molecules : water moves into cell to achieve equilibrium – cell bursts Water will move in the direction of the concentration gradient FACILITATED DIFFUSION Works with the concentration gradient Simile: you skiing downhill Cell membrane proteins act as carriers for SPECIFIC molecules: same principle as enzyme-substrate complex Binding of molecule to protein changes the shape of the protein allowing the molecule to enter into cytoplasm Cofactors present in protein transport (just like in enzyme-substrate complex)ex: hormones facilitated diffusion Does not require E Works with the concentration gradient Example: RBCcell membrane protein(GLUT1)glucose cytoplasm Glucose can’t diffuse unless Aquaporins: H2O channel proteins in both plants and animal cells – facilitate the MASSIVE amounts of H2O whereas the polarity of H2O causes the slow movement of H2O across the hydrophobic tails of membrane ACTIVE TRANSPORT Movement AGAINST concentration gradient Simile: you “skiing” uphill to retrieve your “lost”ski Requires ENERGY(ATP) Transport proteins = PUMPS o Small molecules and ions (Ca+2, Na+, K+) o Change in protein shape – pumps ions or molecules AGAINST the concentration gradient o ****Na+/K+ pump for nerve impulse o ATPase is the protein responsible for Na+/K+ pump – carries 3Na+ out and 2K+ into cell for each ATP-> ADP conversion Endocytosis o Large molecules or clumps of molecules requires MOVEMENT of portions of cell membrane to engulf molecules o Infolding – creates pockets in membrane o Pinching off of pocket vacuole cytoplasm o 2 forms of endocytosis Phagocytosisengulf solids particles Very typical of amoebas WBC destroy bacteria via phagocytosis Requires ENERGY o Pinocytosis- engulf liquids Same process as phagocytosis o EXOCYTOSIS – reverse of endocytosis o Example: contractile vacuole in paramecium(protist)