chapter 7
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CHAPTER 7
MEMBRANE STRUCTURE AND FUNCTION
OVERVIEW
FLUID MOSAICS
CONCEPT 7.1
Phospholipids are amphipathic:Two regions.
Fluid mosaic model: phospholipids + various proteins embedded
Freeze-fracture supported theory.
FLUIDITY OF MEMBRANES
Movement
Drifting
Flip-flop
Temperature and type of fatty acids affect fluidity.
Cholesterol molecules help maintain fluidity.
MEMBRANE PROTEINS
Variety of proteins.
Determine most of membrane’s specific functions.
SIX MAJOR FUNCTIONS (1-3)
SIX MAJOR FUNCTIONS (4-6)
SIDEDNESS OF MEMBRANESMembranes have distinct inside and outside determined when build by ER and Golgi
SELECTIVE PERMEABILITY
CONCEPT 7.2
PERMEABILITY
Material exchange controlled by membrane.
Hydrophobic (nonpolar) dissolve in lipid bilayer and pass through rapidly.
Polar molecules (sugars) do not cross easily.
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.)
PASSIVE TRANSPORT
CONCEPT 7.2
Down concentration gradient.
OSMOSIS
Diffusion of water.
Moves from area of lower solute concentration to an area of higher solute concentration.
TONICITY
The ability of a solution to cause a cell to gain or lose water.
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
Osmoregulation, the control of water balance
Facilitated diffusion.
ACTIVE TRANSPORT
CONCEPT 7.4
ACTIVE TRANSPORT
Needs energy.
Sodium-potassium pump is an example.
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
Na+ binding stimulatesphosphorylation by ATP.
Fig. 7-16-2
Na+
Na+
Na+
ATP P
ADP
2
Fig. 7-16-3
Phosphorylation causesthe protein to change itsshape. Na+ is expelled tothe outside.
Na+
P
Na+ Na+
3
Fig. 7-16-4
K+ binds on theextracellular side andtriggers release of thephosphate group.
P P
K+
K+
4
Fig. 7-16-5
Loss of the phosphaterestores the protein’s originalshape.
K+
K+
5
Fig. 7-16-6
K+ is released, and thecycle repeats.
K+
K+
6
MEMBRANE POTENTIAL
Voltage difference of positive and negative ions.
Electrochemical gradient.
Electrogenic pump: generates voltage across membrane.
Cotransport
BULK TRANSPORT
CONCEPT 7.5
EXOCYTOSIS
Large release of materials in a transport vesicle.
ENDOCYTOSIS
Taking in large molecules by forming vesicles.
Three Types:
• Phagocytosis• Pinocytosis• Receptor-mediated endocytosis.
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