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Cell Membranes & Movement Across Them
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Cell (plasma) membrane
Cells need an inside & an outside… separate cell from its environment cell membrane is the boundary IN food - sugars - proteins - fats salts O2 H2O OUT waste - ammonia - salts - CO2 - H2O products - proteins cell needs materials in & products or waste out
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Lipids of cell membrane
Membrane is made of special kind of lipid phospholipids “split personality” Membrane is a double layer phospholipid bilayer “attracted to water” phosphate inside cell outside cell lipid “repelled by water”
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Semi-permeable membrane
Cell membrane controls what gets in or out Need to allow some materials — but not all — to pass through the membrane semi-permeable only some material can get in or out So what needs to get across the membrane? sugar lipids aa O2 H2O salt waste
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Cell membrane channels
Need to make “doors” through membrane protein channels allow substances in & out specific channels allow specific material in & out H2O channel, salt channel, sugar channel, etc. inside cell H2O aa sugar salt outside cell waste
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Protein channels Proteins act as doors in the membrane
channels to move specific molecules through cell membrane HIGH Donuts! Each transport protein is specific as to the substances that it will translocate (move). For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, its structural isomer. Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane -- simply provide corridors allowing a specific molecule or ion to cross the membrane. These channel proteins allow fast transport. For example, water channel proteins, aquaprorins, facilitate massive amounts of diffusion. LOW
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Molecules move from high to low
Diffusion move from HIGH to LOW concentration Movement from high concentration of that substance to low concentration of that substance.
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Diffusion Move from HIGH to LOW concentration diffusion of water
passive transport no energy needed diffusion of water diffusion osmosis
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Diffusion Move from HIGH to LOW concentration
directly through membrane simple diffusion no energy needed help through a protein channel facilitated diffusion (with help) HIGH LOW
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Simple vs. facilitated diffusion
simple diffusion facilitated diffusion lipid inside cell outside cell inside cell outside cell H2O protein channel H2O
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Active transport Cells may need molecules to move against concentration “hill” need to pump “uphill” from LOW to HIGH using energy protein pump requires energy ATP Plants have nitrate & phosphate pumps in their roots. Why? Nitrate for amino acids Phosphate for DNA & membranes Not coincidentally these are the main constituents of fertilizer. ATP
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Transport summary simple diffusion facilitated diffusion
ATP active transport
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Osmosis Movement of Water Across Cell Membrane
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Osmosis Water is very important, so we talk about water separately
diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane
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Keeping right amount of water in cell
1 Keeping right amount of water in cell Hypotonic condition a cell in distilled water high concentration of water around cell cell gains water problem: cells gain water, swell & can burst Plant cells- become turgid, which which is normal Animal cells-burst and die KABOOM! freshwater No problem, here
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Keeping right amount of water in cell
2 Keeping right amount of water in cell Isotonic condition no difference in concentration of water between cell & environment Water flows equally into and out of cell cell in equilibrium Plant cells: Flaccid Animal cells: Normal That’s better! balanced I could be better…
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Keeping right amount of water in cell
3 Keeping right amount of water in cell Hypertonic solution a cell in salt water low concentration of water around cell cell loses water Plant cells- shrink, can survive for a time Animal cells- shrink and die I’m shrinking, I’m shrinking! saltwater I will survive!
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Ice Fishing in Barrow
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