A Closer Look at Cell Membranes. BOZEMAN VIDEO—CELL MEMBRANES .
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Transcript of A Closer Look at Cell Membranes. BOZEMAN VIDEO—CELL MEMBRANES .
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A Closer Look at Cell Membranes
CH. 5 CELL MEMBRANE AND TRANSPORT
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BOZEMAN VIDEO—CELL MEMBRANEShttp://www.youtube.com/watch?v=y31DlJ6uGgE
http://www.youtube.com/watch?v=S7CJ7xZOjm0
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http://www.youtube.com/watch?v=y31DlJ6uGgE
http://www.youtube.com/watch?v=S7CJ7xZOjm0
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Lipid BilayerCell membranes consist of a lipid bilayer
containing different proteinsMembrane is a continuous boundary layer
that selectively controls the flow of substances across it
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hydrophilicparts
hydrophobicparts
b
a
fluid
fluid
one layer of lipids
one layer of lipids
cross-sectionthrough lipid bilayer
Fig. 5.3, pg. 76
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Fluid Mosaic ModelEvery cell membrane has a mixed
composition of phospholipids, glycolipids, sterols, and proteins
KNOW THE CAMPBELL DIAGRAM “CELL MEMBRANE MOSAIC”
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Fluid Mosaic Model
adhesionprotein
cytoskeletal proteins just beneath the plasma
membrane
active transporter(calcium pump)
passivetransporter
active transporter(ATPase pump)
recognitionprotein
receptor
phospholipid
Cytoplasm
PlasmaMembrane
Lipid bilayer
cholesterol
Fig. 5.4, pg. 77
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Studying Membranes
Fig. 5.5a, pg. 77
Stepped Art
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Overview of Membrane Proteins
AdhesionProteins
CommunicationProteins
Fig. 5.6, p.78
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Overview of Membrane Proteins
ReceptorProteins
RecognitionProteins
PassiveTransporters
ActiveTransporters
Fig. 5.6, p.79
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Transport ProteinsSpan the lipid bilayerInterior is able to open to both sidesChange shape when they interact with solute Play roles in active and passive transport
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Concentration Gradient Means the number of molecules or ions in
one region is different than the number in another region
In the absence of other forces, a substance moves from a region where it is more concentrated to one one where it’s less concentrated - “down” gradient
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DiffusionThe net movement of like molecules or ions
down a concentration gradient
Although molecules collide randomly, the net movement is away from the place with the most collisions (down gradient)
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Diffusion
Fig. 5.7a, p.80
Stepped Art
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Factors Affecting Diffusion Rate
Steepness of concentration gradientSteeper gradient, faster diffusion
Molecular sizeSmaller molecules, faster diffusion
TemperatureHigher temperature, faster diffusion
Electrical or pressure gradients
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Membrane Crossing MechanismsDiffusion across lipid bilayer
Passive transport
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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Fig. 5-9, p.81
Membrane Crossing: Overview IHigh
Concentrationgradient acrosscell membrane
Low
Diffusion oflipid-solubleSubstancesacross bilayer
Passive transport of water-soluble substancesthrough channel protein;no energy input needed
Active transportthrough ATPase;requires energyinput from ATP
ATP
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Passive Transport Flow of solutes through the interior of
passive transport proteins down their concentration gradients
Passive transport proteins allow solutes to move both ways
Does not require any energy input
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TYPES OF PASSIVE TRANSPORTDIFFUSION
FACILITATED DIFFUSION—diffusion that is “helped out” by membrane transport proteins (such as helping larger molecules pass)
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Passive Transport
Stepped Art
glucose transporter
solute (glucose)
high
low
Fig. 5.10, p.80
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Active TransportNet diffusion of solute is against
concentration gradientTransport protein must be activated (requires
an integral membrane protein)ATP gives up phosphate to activate proteinBinding of ATP changes protein shape and
affinity for solute
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TYPES OF ACTIVE TRANSPORTSODIUM-POTASSIUM PUMP—3 Na move out
and allow 2 K to enter; needs net 1 ATP molecule to dothis
PROTON PUMP– pushes H ions out of the membrane allowing them to eventually diffuse back in; generates ATP for the cell; used in cell respiration
This uses ATP synthase enzymeCOTRANSPORT– when molecules travel
together across the membrane
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Types of active transport ContinuedEndocytosis—”engulfing “things into cell
membrane; difficult for plants to do Ex: white blood cells engulfing bacteria—to fight
infectionsphagocytosis (large food)
pinocytosis (small things) Receptor-mediated endocytosis—use of receptor
proteins to help pull things into cell
Exocytosis—”spitting” things out of cell
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Osmosis Diffusion of water molecules across a
selectively permeable membrane
water molecules protein molecules
semipermeable membranebetween two compartments
• Direction of net flow is determined by water concentration gradient
• Side with the most solute molecules has the lowest water concentration
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Osmosis
p.84
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Tonicity Refers to relative solute concentration of two fluids
Hypotonic - having fewer solutes
Hypertonic - having more solutes
Isotonic - having same amount
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2% sucrose solutio
n
1 liter of distilled
water
1 liter of 10% sucrose
solution
1 liter of 2%
sucrose solution
HypotonicConditions
HypertonicConditions
IsotonicConditions
Fig. 5-13, p.85
Tonicity and
Osmosis
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DIALYSIS BAG % MASS CHANGE
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Pressure and OsmosisHydrostatic 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 pressureAmount of pressure necessary to prevent
further increase of a solution’s volume
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Increase in Fluid Volume
hypotonic solution
membrane permeable towater but not to solutes
hypertonicsolution
fluid volume rises in second compartment
second compartment
first compartme
nt
Fig. 5.14, p.85
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ENDOCYTOSIS AND EXOCYTOSIS VIDEOhttp://www.youtube.com/watch?v=DuDmvlbpjHQ
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Endocytosis and ExocytosisExocytosis: A cytoplasmic vesicle fuses with the
plasma membrane and contents are released outside the cell
3 types: phagocytosis—engulfs large molecules; difficult for plant cells to do (WHY??)
pinocytosis—engulfs small molecules receptor-mediated—uses receptor membrane
proteins to pull things inEndocytosis: A small patch of plasma membrane
sinks inward and seals back on itself, forming a vesicle inside the cytoplasm – membrane receptors often mediate this process
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Fig 5.17, p.87
Macrophage engulfing Leishmania mexicana
parasite macrophage
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bacterium phagocytic vesicle
Fig. 5-17b, p.87
Phagocytosis
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Contractile Vacuole
contractile vacuole filled
contractile vacuole emptied
Fig. 5.21, pg. 89
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Plasmolysis
Plasmolysis
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cytoskeletal
proteins
adhesion protein
lipid bilayer
recognition
protein
receptor protein
cytoplasm
active transporter
(calcium pump)
active transporter
(ATPase pump)
passive transporter
Fig. 5-19, p.88
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BOZEMAN VIDEO—CELL TRANSPORT ACROSS MEMBRANES AND ANIMATIONhttp://www.youtube.com/watch?v=RPAZvs4hvGA
http://www.youtube.com/watch?v=RPAZvs4hvGA