Outline - Membranes Membranes 178 Fall 2007/B178F07... · Copyright © The McGraw-Hill Companies,...
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1 Outline - Membranes 1. Fluid Mosaic Model of Membrane Structure 2. Membrane Proteins 1. Kinds of membrane proteins 2. Membrane protein structure Single pass Multi-pass: Channels, Pores & Carriers 3. Transport Mechanisms Passive: Diffusion & Facilitated Diffusion Active: Molecular & Bulk Membranes Fig. 6.2 (TEArt) Fatty acid Phosphorylated alcohol Polar (hydrophilic) region Nonpolar (hydrophobic) region Fatty acid G L Y C E R O L Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 6.3 (TEArt) Polar hydrophilic heads Nonpolar hydrophobic tails Polar hydrophilic heads Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Transcript of Outline - Membranes Membranes 178 Fall 2007/B178F07... · Copyright © The McGraw-Hill Companies,...
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Outline - Membranes
1. Fluid Mosaic Model of Membrane Structure2. Membrane Proteins
1. Kinds of membrane proteins2. Membrane protein structure
Single passMulti-pass: Channels, Pores & Carriers
3. Transport MechanismsPassive: Diffusion & Facilitated DiffusionActive: Molecular & Bulk
Membranes
Fig. 6.2 (TEArt)
Fatty acidPhosphorylated
alcohol
Polar(hydrophilic) region
Nonpolar (hydrophobic) region
Fatty acidGLYCEROL
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 6.3 (TEArt)
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 Structure
1. Phospholipid bilayer2. Proteins3. Carbohydrates
Attached to lipids GlycolipidsAttached to proteins Glycoproteins
4. Cholesterol
Outside
Plasmamembrane
InsideTransporter Cell surface
receptorEnzyme
Cell surface identitymarker
Attachment to thecytoskeleton
Cell adhesion
Membrane Protein Functions
Phospholipids
Polar areasof protein
Nonpolar areas of
protein
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Anchoring Proteins in the Phospholipid
Bilayer
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1. Single-Pass… Anchors
2. Multi-Pass
Channels & Pores
Carriers
Structure of Membrane ProteinsFig. 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
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
Hyperosmoticsolution
Isoosmoticsolution
Hypoosmoticsolution
Direction of Water Diffusion
Water diffuses out Water diffuses out and in = equilibrium
Water diffuses in
External environment of a cell can vary
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Fig. 6.15c (TEArt)
PlasmolysisCell body shrinks
from cell wall
Normal cellTurgor Pressure
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HyperosmoticExternal Solution
Water Diffusion in Plant CellsIsoosmotic
External Solution
HypoosmoticExternal Solution
Life in a osmotic environment1. Extrusion
e.g. Contractile Vacuoles in Paramecium
2. Isoosmotic solutionse.g. Blood Protein
3. Live with ite.g. Turgor pressure
Maintaining Osmotic Balance
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
1. Multi-pass proteins create openings in the membrane
Moving Molecules into or out of Cells- Passive Transport
Passive TransportPassive Transport1. Channels1. Channels2. Carriers2. Carriers3. Pores3. Pores
Solutemolecule
Transportprotein
Multi-PassProtein
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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 Cells- Passive 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 Cells- Passive Transport – Pores
Pleated folds
Porin Protein
Production of tearsLacrimal glandsProduction of salivaSalivary glands
Aquaporin-5
Bronchial fluid secretionLung: bronchial epitheliumOsmosensing function?Brain: hypothalamusCSF fluid balanceBrain: ependymal cellsReabsorbtion of waterKidney: collecting ducts
Aquaporin-4
Secretion of water into tracheaTrachea: epithelial cellsReabsorbtion of water into bloodKidney: collecting ducts
Aquaporin-3 *
Mediates antidiuretic hormone activityKidney: collecting ductsAquaporin-2Alveolar hydration stateLung: alveolar epithelial cellsProduction of cerebrospinal fluidBrain: choriod plexus
Production of aqueous humorEye: ciliary epithelium
Concentration of urineKidney: proximal tubuleOsmotic protectionRed blood cells
Aquaporin-1
Fluid balance within the lensEye: lens fiber cellsAquaporin-0
CommentsMajor Sites of ExpressionAquaporins are Water Channels
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1. Proteins allow transport2. Mechanisms of movement through proteins1. Passive Transport – “down” concentration gradient
Channels, carriers & poresDiffusion
SimpleFacilitated
2. Active Transport – “up” concentration gradientMolecular TransportBulk Transport
ExocytosisEndocytosis
How do molecules move across membranes?
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
Example of Glucose Transport From Intestine to Blood
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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
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Example of Neurotransmitter Movement from Cell to Cell
Reuptake transporter
END
Membranes & Transport
