b178 - membranes - montana state university billings 20… · · 2009-01-28active: molecular...
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Outline - Membranes
1. Fluid Mosaic Model of Membrane Structure
2. Membrane Proteins1. Kinds of membrane proteins2. Membrane protein structure3. Transport MechanismsPassive: Diffusion & Facilitated DiffusionActive: Molecular & Bulk
Plasma Membrane Properties and Structure
Properties:No Free EndsInternal spaceFluid Mosaic Model of Membrane StructureFluid = Phospholipid bilayerMosaic = Embedded Proteins:
Transport proteins: channels and carriers Receptor Proteins: gates, triggers Recognition Proteins: ID Tags
Plasma Membrane Function
• Gate Keeper• Regulation• Communication• Transport• Selectively permeable• Elastic• Protection
Membranes
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Polarhydrophilicheads
Nonpolarhydrophobictails
Polarhydrophilicheads
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Outside Cell
Cytoplasm (inside cell)
Cholesterol Transmembraneproteins
Peripheralprotein
Glycoprotein
CarbohydrateGlycolipid
PhospholipidBilayer
Fluid Mosaic Model of Cell Membrane
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Cell Membrane StructureSummary
1. Phospholipid bilayer
2. ProteinsTransmembraneInterior
3. CarbohydratesAttached to lipids GlycolipidsAttached to proteins Glycoproteins
4. Cholesterol
Outside
Plasmamembrane
InsideTransporter Cell surface
receptorEnzyme
Cell surface identitymarker
Attachment to thecytoskeleton
Cell adhesion
Six Functions of Membrane Proteins
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Phospholipids
Polar areasof protein
Nonpolar areas of
protein
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Anchoring Proteins in the Phospholipid
Bilayer
Types of Transport
• Passive TransportFollows concentration gradientDoes not require energyDirect or via channels
Examples: Diffusion, Facilitated Diffusion and Osmosis
• Active Transport:Against concentration gradientRequires energy
Bulk Transport• Exocytosis and Endocytosis
Moving Molecules into or out of Cells- Overview of Types of TransportI. Passive Transport
1. Always “down” a concentration gradient2. Always involves proteins called
A. ChannelsB. CarriersC. Pores… “porins”
II. Active Transport1. Always “up” a concentration gradient2. Small molecules transported through
A. Protein Pumps3. Large molecules transported by vesicles
A. EndocytosisB. Exocytosis
Fig. 6.12 (TEArt)
Lumpof sugar Sugar
molecule
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Solute dissolves in a solvent.Solutes move from a high to a low concentration.
Diffusion
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Fig. 6.14 (TEArt)
Solutemolecule Water
molecules
Osmosis is Water Diffusion Across a Semipermeable Membrane
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Shriveled cells Normal cells Cells swell & burst
Hypertonicsolution
Isotonicsolution
Hypotonicsolution
Direction of Water Diffusion
Water diffuses out Water diffuses out and in = equilibrium
Water diffuses in
External environment of a cell can vary
Fig. 6.15c (TEArt)
PlasmolysisCell body shrinks
from cell wall
Normal cellTurgor Pressure
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HypertonicExternal Solution
Water Diffusion in Plant CellsIsotonicExternal Solution
HypotonicExternal Solution
Life in a osmotic environment1. Extrusion
e.g. Contractile Vacuoles in Paramecium
2. Isotonic solutionse.g. Blood Protein
3. Live with ite.g. Turgor pressure
Maintaining Osmotic Balance
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1. Multi-pass proteins create openings in the membrane
Moving Molecules into or out of CellsPassive Transport
Passive TransportPassive Transport1. Channels1. Channels2. Carriers2. Carriers3. Pores3. Pores
Solutemolecule
Transportprotein
Multi-PassProtein
Moving Molecules into or out of Cells- Passive Transport – Channels
Passive transport of1) Water-soluble molecules2) Ions
Selectivity filter
Inside cell
Outside cell
K+ ion
K+ ion channel
Side view Top view
Moving Molecules into or out of CellsPassive Transport – Carriers
Outside cell
Inside cell
Passive transport of1) ions2) Sugars3) amino acids
Facilitated Diffusion in Red Blood Cells1) Cl- and bicarbonate ions2) Glucose carrier Porins are transport channels
1.Allow movement of small moleculesWaterIonsOrganic Wastes
2003 Nobel Prize in ChemistryAquaporin Water Channels
Moving Molecules into or out of CellsPassive Transport – Pores
Pleated folds
Porin Protein
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PPPA
PPPANa+
Extracellular
Intracellular
ATP ATP
PPPAATP
PPA
P
ADP
1. Protein in membrane bindsintracellular sodium.
2. ATP phosphorylates proteinwith bound sodium.
3. Phosphorylation causesconformational change inprotein, allowing sodium to leave.
PPA
P
ADP
4. Extracellular potassiumbinds to exposed sites.
K+
PPA
P
ADP+Pi
5. Binding of potassium causesdephosphorylation of protein.
6. Dephosphorylation ofprotein triggers change backto original conformation,potassium moves into cell,and the cycle repeats.
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Example: Active Transport – Sodium-Potassium Pump
Animation
Fig. 6.19 (TEArt)
Outside cell
Inside cell
Na+
Coupledtransportprotein
Sugar
K+
Na/Kpump
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Active Transport - Cotransport
Animation
Bulk Transport Across Membranes• Exocytosis - discharge of material from vesicles at
the cell surface
• Endocytosis - enveloping food– phagocytosis - particulate material– pinocytosis - liquid– receptor-mediated - transport specific molecules
Animation
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Bulk Tranport: Exocytosis
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Cytoplasm
Plasmamembrane
Bulk Transport: EndocytosisCoated pit
ClathrinReceptor protein
Coated vesicle
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Carrier-Mediated Endocytosis
END
Membranes & Transport