chapter 7
TRANSCRIPT
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CHAPTER 7
MEMBRANE STRUCTURE AND FUNCTION
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OVERVIEW
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FLUID MOSAICS
CONCEPT 7.1
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Phospholipids are amphipathic:Two regions.
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Fluid mosaic model: phospholipids + various proteins embedded
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Freeze-fracture supported theory.
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FLUIDITY OF MEMBRANES
Movement
Drifting
Flip-flop
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Temperature and type of fatty acids affect fluidity.
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Cholesterol molecules help maintain fluidity.
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MEMBRANE PROTEINS
Variety of proteins.
Determine most of membrane’s specific functions.
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SIX MAJOR FUNCTIONS (1-3)
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SIX MAJOR FUNCTIONS (4-6)
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SIDEDNESS OF MEMBRANESMembranes have distinct inside and outside determined when build by ER and Golgi
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SELECTIVE PERMEABILITY
CONCEPT 7.2
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PERMEABILITY
Material exchange controlled by membrane.
Hydrophobic (nonpolar) dissolve in lipid bilayer and pass through rapidly.
Polar molecules (sugars) do not cross easily.
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TRANSPORT PROTEINS
Allow passage of hydrophilic substances.
Channel proteins – hydrophilic channel used as a tunnel.
Aquaporins – facilitate passage of water.
Carrier proteins – change shape to move (specific for substance it moves.)
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PASSIVE TRANSPORT
CONCEPT 7.2
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Down concentration gradient.
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OSMOSIS
Diffusion of water.
Moves from area of lower solute concentration to an area of higher solute concentration.
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TONICITY
The ability of a solution to cause a cell to gain or lose water.
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TONICITY
Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water
Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water
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Osmoregulation, the control of water balance
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Facilitated diffusion.
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ACTIVE TRANSPORT
CONCEPT 7.4
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ACTIVE TRANSPORT
Needs energy.
Sodium-potassium pump is an example.
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Fig. 7-16-1
EXTRACELLULAR
FLUID [Na+] high [K+] low
Na+
Na+
Na+ [Na+] low[K+] high CYTOPLASM
Cytoplasmic Na+ binds to
the sodium-potassium pump. 1
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Na+ binding stimulatesphosphorylation by ATP.
Fig. 7-16-2
Na+
Na+
Na+
ATP P
ADP
2
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Fig. 7-16-3
Phosphorylation causesthe protein to change itsshape. Na+ is expelled tothe outside.
Na+
P
Na+ Na+
3
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Fig. 7-16-4
K+ binds on theextracellular side andtriggers release of thephosphate group.
P P
K+
K+
4
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Fig. 7-16-5
Loss of the phosphaterestores the protein’s originalshape.
K+
K+
5
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Fig. 7-16-6
K+ is released, and thecycle repeats.
K+
K+
6
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MEMBRANE POTENTIAL
Voltage difference of positive and negative ions.
Electrochemical gradient.
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Electrogenic pump: generates voltage across membrane.
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Cotransport
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BULK TRANSPORT
CONCEPT 7.5
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EXOCYTOSIS
Large release of materials in a transport vesicle.
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ENDOCYTOSIS
Taking in large molecules by forming vesicles.
Three Types:
• Phagocytosis• Pinocytosis• Receptor-mediated endocytosis.
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