Chapter 5 Notes: Cell Membrane
Chapter 5 Notes: Cell Membrane
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Date Created: 10/08/15
Chapter 5 Cell membranes 1 Every cell is bordered by a plasma membrane of the cell a 2layered membrane that holds the contents of a cell in place amp regulates what enters amp leaves the cell thin exible amp looks like a plastic bag 2 HOW ARE THEY TRANSPORTED regulating the cell s molecular traf c a Nonpolar molecules dissolve in the lipid bilayer amp pass through the membrane rapidly very fast i Hydrocarbons 02 C02 b Polar molecules do not cross the membrane easily i Sugars ions c The direction of traf c across a membrane I allow passage of hydrophilic substances across the membrane 1 no energy required The net movement of ionsmolecules form a region of higher concentration to a region of lower concentration The tendency for molecules to spread out evenly into the available space 1 diffusion of water across a selectively permeable membraneWATER DIFFUSES ACROSS A MEMBRANE FOMR THE REGION OF LOWER SOLUTE CONCENTRATION TO THE REGION OF HIGHER SOLUTE CONCENTRATION C the concentration difference that drives diffusion concentration of a substance form one area to another Potential energy NO WORK MUST BE DONE TO MOVE SUBSTANCES DOWN THE CONCENTRATION GRADIENT 239 b Controlled movement of speci c ions amp molecules across a membrane by proteins i one type of active transport system 1 Functions Function h 39 a Mozaic of lipids proteins are oating around 3 gquot fquot Filbers of extra cell matrix I Peripheral e e e e Integral we 1 protein M quot is QW UPLASMIC SIDE 39QF MEMBRANE 5 are the most abundant lipid in the plasma membrane polar end wphosphate group amp nonpolar uncharged w2 nonpolar fattyacid tails a Amphipathic molecules b In an medium The polar ends are located at the surfaces where they face aqueous media Nonpolar chains assemble in the membrane interior in a nonpolar region that includes H20 C In the into a semisolid gellike state when 6 dual solubility molecules nonpolar Carbon rings wa nonpolar side chain at one end amp a single polar group OH at the other a the main sterol in ANIMALS membranes keeps the membrane uid Has different effects on membrane uidity at different temp b Phytosterols C transmembrane proteins span the membrane embedded in the phospholipid bHayer d bound to the surface of the membrane held to membrane surfaces by noncovalent bonds have diverse functions b Cells recognize each other by binding to surface molecules often to carbs on the plasma membrane Membrane carbohydrates may be covalent bonded to lipids glycolipid5more common to p rotei ns glycoproteins c Carbs on the external side of the plasma membrane vary among species individuals amp even cell types in an individual 8 located on the outer surface of cell membranes oligosaccharides a the carbohydrate groups that are sometimes formed on a surface coat present in many ANIMAL cells the carb Groups of the cell surface glycolipids amp glycoproteins b Ed molecules Wcarbohydrates groups attached c protein molecules wcarbohydrate groups attached 1 Transmembrane 9 a uid phospholipid bilayer in which proteins are embedded i The membrane is a uid structure w a of various proteins embedded in it ii The membrane consists of a phospholipid bilayer in which proteins are embedded amp oat freely b quotquot phospholipid molecules move amp exchange places win the same layer unsaturated fatty acid chains in membrane phospholipids help keep membranes uid at low temp high temp the rigid rings of cholesterol help reduce membrane C e a b uidity ex like partygoers elbowing through a crowded room Viscous 0 3 X Ho 34 w4444w wrfww i llHll tails with kinks quotquot membrane proteins most oat individually in the lipid bilayer some are attached to the cytoskeleton Phospholipids in the plasma membrane can move win the bHayer Most of the lipids amp some proteins drift laterally Membrane uidity is in uenced by temperature Also is it unsaturated fatty acids more uidsaturated fatty acids Must be a uid to work properly uid as a salad oil Variations in lipid composition appear to be adaptions to speci c environmental conditions Ability to change the lipid compositions in response to temp changes has evolved in organisms that live where temp vary 14 3 Membrane proteins labeled with red uorescent dye Membrane proteins start out segregated lCell Human celll 40 minutes Membrane proteins labeled with green uorescent dye V Hybrid lulumanfmouse celll Mouse cell i the ability of a surrounding solutions to cause a cell to gainlose water ii solution solute concentration is the same as the inside the cell no net water iii solution solute concentration is greater than that inside the cell CELL LOOSES WATER iv solution solute concentration is less than that inside the cell cell gains water Passive Transport bc the solute moves down its concentration gradient a called aquaporin s facilitate the passage of water i lntegral membrane proteins that form hydrophilic channels in the membrane through which water amp ions can pass 1 channel proteins that transport water b Some are gated channels that openclose to transport ions l switch between open closed intermediate states ii Facilitate transport of ions Na K Ca2 Cl c Polar amp charged molecules through transport proteins in the hydrophobic lipid bilayer d Membrane proteins transport certain polar amp charged molecules H20 amino acids sugars amp ions but NO others 39 undergo a subtle changed in shape that translocates the solutebinding site across the membrane i Bind a speci c solute amp transport it across the lipid bia yer uniport transport ii Undergo conformational changes that moves the solute binding site from one side of the membrane to the other iii Can be saturated when there are too few transport proteins to handle all the solute molecules 16 all cells have voltages across their plasma membranes Electrical potential energy a separation of opposite charges Cytoplasm is amp the extracellular uid is c Membrane potential ranges from 50 to 200 mV UQ 17 ELECTROCHEMICAL GRADIENT a ANIMALS CELLS b Moves 3 Na out of the cell amp 2K into the cell in the same pumping cycle 18 electronegative pumps help store energy that can be used for cellular work 19 when active transport of a solute indirectly drives transport of other substances PLANTS commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell a drive diffusion of ions across a membrane i the ion s concentration gradient ii the effect of the membrane potential on the ion s movement b Two combined forces collectively called electrochemical potentiaon the ion s movement 20 Eukaryotic cells import amp export larger particles amp molecules such as proteins by exocytosis amp endocytosis a Large molecules such as polysaccharides amp proteins across the membrane in bulk via vesicles b Requires energy require energy from ATP requires energy form ATP EXTRACELLULAH CYTOPLASM FLUID vacuole a Molecules are taken up when extracellular uid is gulped into tiny vesicles Plasma membrane Vesicle a is any molecules that binds speci cally to a receptor site of another molecules b Binding of ligands to receptors triggers vesicle formation
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