Exam 4 Study Guide - Chapter 12 Semi-Permeable Cell...

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Chapter 12 Semi-Permeable Cell Membrane Hydrophobic molecules can easily pass Only small molecules can pass through o O 2 , CO 2 , N 2 , steroids Types of Diffusion Simple diffusion o Molecules are constantly moving to create even distribution Move from high to low concentration (concentration gradient) Osmosis = diffusion of water o Water is polar so it does not easily diffuse o Small amounts of water can pass but there is a need for other mechanisms Aquaporin = facilitated diffusion; -helix bundle Facilitation diffusion o Not simple diffusion across membrane Ex- either a polar molecule or too large o Channel mediated or transporter mediated Passive v. Active Transport Passive transport does not require energy and molecules move down concentration gradient Active transport requires an energy input and moves molecules against the concentration gradient Membrane Potential Ion concentrations are different on either side of the membrane o Creates a voltage difference across a membrane = membrane potential Resting membrane potential = potential of an unstimulated cell o Exchange of +ve and –ve charge across membrane is balanced o About -20 to -200 mV Interior of cell is more negative than the exterior of the cell Electrochemical Gradient Acts on the transport of charged molecules The concentration gradient and the membrane potential influence the movement of these molecules Osmoregulation = Water balance within the cell Contributes to cell like cytoplasm (animal) Contributes to turgor pressure (plant) Tonicity = solute concentrations inside/outside cell Hypotonic – greater concentration inside Hypertonic – greater concentration outside
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Isotonic – same concentration inside and outside of the cell Endocytosis/Exocytosis Vesicles are used to transport material o Built from one membrane and fuses to another Endocytosis = movement into the cell o Phagocytosis = cellular eating (solids) o Pinocytosis = cellular drinking (liquid) o Receptor mediated endocytosis = specific molecules binds to receptors Exocytosis = movement out of cell GLUT Family Proteins Glucose transporters Multi-pass (12) -helix bundle Uncharged only depends on concentration gradient Conformation randomly fluctuates Transmembrane Pumps Active transporters Coupled pump – links uphill transport to downhill transport ATP-driven pumps – hydrolyze ATP to drive uphill transport Light driven – energy from sunlight drives uphill transport (bacteria) Na + - K + Pump Transmembrane pump ATP driven – about 30% of cell’s ATP consumption 3Na + out; 2K + in creates negative potential inside (steep gradient) Process: o 3 sodium ion bind to the protein at specific sites (cytosolic side) o
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