Download Membrane Structure and Function

Membrane Structure and Function
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Enduring Understanding:
Activities of the cell are regulated
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Essential Question:
How does the plasma membrane regulate cell activity?
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Phospholipid = amphipathic molecule (hydrophilic/hydrophobic regions)
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membranes are made up of phospholipid molecules and proteins
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History of membrane model
1925 ­ Gorter and Grendal ­ cell membranes are two phospholipid bilayers
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1935 ­ Davison and Danielli ­ figured out where proteins fit in bilayer, accepted until early 1970's
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1972 ­ Singer and Nicolson ­ proteins are dispersed throughout phospholipids
­proteins have both hydrophilic and hydrophobic regions
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freeze fracture technique to look at bilayer membranes
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Membranes are fluid­fluid mosaic model
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Membrane proteins tend to move sideways within the plasma membrane
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Integral proteins penetrate the hydrophobic core
Transmembrane proteins go all the way through the membrane
peripheral proteins ­ not imbedded in bilayer at all ­ loosely bound to surface
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structure of transmembrane protein
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functions of membrane proteins
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role of carbohydrates in membranes
cell to cell recognition
­glycolipids
­glycoproteins
carbohydrates on external side of membrane vary from species to species, within same species and even between cells
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synthesis of membrane components and their orientation on the resulting membrane
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Contractile vacuole
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Facilitated diffusion ­ passive transport using diffusion and a transport protein
­no energy
­used for polar molecules and ions Uses:
1. Channel proteins ­ pore that allows molecule to pass (hydrophilic passageways in proteins)
­ Ex. aquaporins for water
2. ion channels ­ open or close due to stimulus (electrical or chemical)
­ Ex. gated channels
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Cystinuria ­ disease of kidneys
­absence of carrier protein that transports cysteine and other amino acids across cell membranes in kidneys
­normal cells reabsorb these amino acids and put it into
bloodstream
­abnormal cells ­ develop stones of amino acids ­accumulate and crystalize
kidney stones
http://www.google.com/imgres?imgurl=http://1.bp.blogspot.com/_
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Active Transport ­ uses energy to move solutes against a gradient
­ ATP transfers terminal phosphate to a transport protein.
­causes protein to change its shape to move solute across membrane
1. sodium­potassium pump
­ generates a voltage across the membrane= electrogenic pump
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Ion pumps maintain Membrane potential
membrane potential = voltage across the membrane (mV)
­50 to ­200 mV (minus sign = inside of cell is neg.)
­this favors passive transport of cations into the cell and anions out of the cell
so: chemical force due to ion concentration gradient
electrical force affects movement of ion due to membrane potential
= electrochemical gradient
if down gradient = passive if against gradient = active
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2. proton pump ­ also an electrogenic pump
­transports hydrogen ions (protons) out of the cell
­used in ATP synthesis (cell respiration)
3. Cotransport
­uses ATP
­transport of a specific solute drives the active transport of other solutes
­driven by a concentration gradient
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Use of cotransport: diarrhea
• patient given a solution of high glucose and salt. • taken up by transport proteins of intestinal cell membranes and passed into blood
• increase in solutes of blood causes flow of water from the intestine into the blood = rehydration
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4. Bulk Transport
­ for large molecules ex. proteins, polysaccharides
a. Exocytosis ­ secretion by fusing vesicles to cell membrane and expelling contents
Ex. insulin excreted by pancreas this way
neurotransmitters in neurons
b. Endocytosis ­ brings substances into the cell by forming new vesicles from cell membrane
1. phagocytosis ­ if particulates
2. pinocytosis ­ if liquids
3. receptor­mediated endocytosis­ if use binding sites
­use of ligands ­ any molecule that binds specifically to receptor site of another molecule
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So:
How does the plasma membrane regulate cell activity?
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