Chapter_5_Outline_Part_I_

Chapter_5_Outline_Part_I_ - Chapter 5 - Part I Cell...

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Chapter 5 - Part I Cell Membrane Biol 1001 Spring 2012
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Fluid Mosaic Model Cell membranes consist of a patchwork (=mosaic) of different proteins that constantly shift & flow within a viscous fluid formed by the phospholipid bilayer Membrane components remain relatively constant Distribution of proteins & phospholipids within membrane change over time
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extracellular fluid cytoplasm cholesterol phospholipid bilayer phospholipid enzyme cytoskeleton Fig 5-1
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Fluidity of Membrane no bonds between individual phospholipids Hydrophilic heads Orient towards intracellular & extracellular watery environments Form hydrogen bonds with water molecules Hydrophobic tails Orient towards center of membrane Some with unsaturated fatty acids in tail double bonds in tail -> kinks more double bonds=more fluid membrane Fig 5-2
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More unsaturated fatty acids More double bonds More kinks Fewer unsaturated fatty acids Fewer double bonds Fewer kinks Fig 5-4
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Degree of Membrane Fluidity Based on: Level of fatty acid saturation (more kink=more fluid) Amount of cholesterol stabilizes bilayer Make membrane less permeable to water-soluble substances varies between cells Allows cells to perform different functions Allows cells to function in different environments Ex: Cells in low temperatures tend to be less fluid Solution: more unsaturated fatty acids & less cholestrol
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Why is Fluidity of Bilayer Important? Cells need to be able to change shape stiff cells would break apart->cell death Eukaryotic cell membranes need to be in constant motion Membrane-enclosed compartments bring materials into cell (e.g. food vacuole) Membrane bound organelles move materials throughout cell (e.g. lysosomes) Membrane bound organelles merge with membranes of other organelles (e.g. ER, Golgi)
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Cell membranes Surround cells & organelles within eukaryotic cells Functions Phospholipid bilayer Isolate cell contents from environment Embedded proteins Allow communication between cells Create attachments in & between cells Regulate biochemical reactions Transport essential substances Between organelles & cytoplasm
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Isolation of Cell Contents Phospholipid bilayer: Separates cytoplasm from extracellular environment Maintains integrity of cytoplasm Cannot pass through nonpolar, hydrophobic region of phospholipid bilayer Ex: salts, sugars, amino acids Small molecules Can pass through phospholipid bilayer Ex: water, oxygen, carbon dioxide Larger, uncharged, lipid-soluble molecules Can pass through phospholipid bilayer
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Embedded Proteins 1000s of different proteins possible Many are glycoproteins (=protein with carbohydrate group)
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This note was uploaded on 02/24/2012 for the course BIOL 1001 taught by Professor Minor during the Spring '08 term at LSU.

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Chapter_5_Outline_Part_I_ - Chapter 5 - Part I Cell...

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