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PowerLecture: Chapter 5
A Closer Look at Cell Membranes
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Lipid Bilayer hydrophilic parts hydrophobic parts fluid fluid
one layer of lipids one layer of lipids b cross-section through lipid bilayer a Fig. 5.3, pg. 76
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cytoskeletal proteins just beneath the plasma membrane
Fluid Mosaic Model passive transporter recognition protein phospholipid adhesion protein cholesterol receptor Lipid bilayer active transporter (ATPase pump) active transporter (calcium pump) Cytoplasm Plasma Membrane cytoskeletal proteins just beneath the plasma membrane Fig. 5.4, pg. 77
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Studying Membranes Stepped Art Fig. 5.5a, pg. 77
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Overview of Membrane Proteins
Adhesion Proteins Communication Proteins Fig. 5.6, p.78
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Overview of Membrane Proteins
Receptor Proteins Recognition Proteins Passive Transporters Active Transporters Fig. 5.6, p.79
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Transport Proteins Span lipid bilayer
Change shape when they interact with solute active and passive transport
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Concentration Gradient
Movement - “down” gradient ( high concentration to low concentration)
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Diffusion Stepped Art Fig. 5.7a, p.80
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Diffusion Stepped Art Fig. 5.7b, p.80
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Diffusion Rate depends upon…
Steepness of c gradient Molecular size Temp Electrical or pressure gradients
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Membrane Crossing Mechanisms
Diffusion across bilayer Facilitated Diffusion Passive & Active transport Endocytosis Exocytosis
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Cell Membranes Show Selective Permeability
oxygen, carbon dioxide, and other small, nonpolar molecules; some water molecules glucose and other large, polar, water-soluble molecules; ions (e.g., H+, Na+, K+, Ca++, Cl–); water molecules Fig. 5-8, p.80
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Membrane Crossing: Overview I
High Concentration gradient across cell membrane ATP Low Diffusion of lipid-soluble Substances across bilayer Passive transport of water- soluble substances through channel protein; no energy input needed Active transport through ATPase; requires energy input from ATP Fig. 5-9, p.81
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Membrane Crossing: Overview II
Endocytosis (vesicles in) Exocytosis (vesicles out) Fig. 5-9, p.81
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Passive Transport glucose transporter solute (glucose) high low
Stepped Art Fig. 5.10, p.80
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Active Transport against concentration gradient
ATP gives up phosphate to activate protein Binding of ATP changes protein shape and affinity for solute
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Active Transport higher calcium concentration ATP Pi ADP Stepped Art
Fig. 5-11, p.83
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Osmosis p.84
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Tonicity Relative solute concentration of two fluids
Hypotonic - having fewer solutes Hypertonic - having more solutes Isotonic - having same amount
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1 liter of 10% sucrose solution 1 liter of 2% sucrose solution
Tonicity and Osmosis 2% sucrose solution 1 liter of distilled water 1 liter of 10% sucrose solution 1 liter of 2% sucrose solution
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1 liter of distilled water
Tonicity and Osmosis 2% sucrose solution 1 liter of 10% sucrose solution 1 liter of 2% sucrose solution 1 liter of distilled water Hypotonic Conditions Hypertonic Conditions Isotonic Conditions Fig. 5-13, p.85
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Pressure and Osmosis Hydrostatic pressure Osmotic pressure
Pressure exerted by fluid on the walls that contain it The greater the solute concentration of the fluid, the greater the hydrostatic pressure Osmotic pressure Amount of pressure necessary to prevent further increase of a solution’s volume
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Increase in Fluid Volume
first compartment second compartment hypotonic solution hypertonic solution membrane permeable to water but not to solutes fluid volume rises in second compartment Fig. 5.14, p.85
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Endocytosis and Exocytosis
Exocytosis: A cytoplasmic vesicle fuses with plasma membrane - contents released outside cell Endocytosis: patch of plasma membrane sinks inward, seals back on self, forming vesicle inside cytoplasm – (membrane receptors often mediate this)
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Endocytosis and Exocytosis
coated pit b c d f e Fig. 5-15, p.86
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Endocytosis of cholesterol
plasma membrane cholesterol
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Macrophage engulfing Leishmania mexicana
parasite macrophage Fig 5.17, p.87
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Phagocytosis bacterium phagocytic vesicle Fig. 5-17b, p.87
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How Proteins Get to the Surface
vesicle membrane fuses with plasma membrane Golgi body endoplasmic reticulum Fig. 5.18, pg. 87
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Contractile Vacuole contractile vacuole filled
contractile vacuole emptied Fig. 5.21, pg. 89
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active transporter (calcium pump) active transporter (ATPase pump)
adhesion protein passive transporter recognition protein receptor protein lipid bilayer cytoskeletal proteins cytoplasm active transporter (calcium pump) active transporter (ATPase pump) Fig. 5-19, p.88
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Fig. 5-20, p.89
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extracellular fluid cytoplasm
Fig. 5-22, p.89
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