The truth about the movement of NO across cell membranes Jeffrey Garvin
AP Biology 2005-2006 Cell Membranes and Movement Across Membranes (Transport)
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Transcript of AP Biology 2005-2006 Cell Membranes and Movement Across Membranes (Transport)
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AP Biology2005-2006
Cell Membranes and Movement Across Membranes (Transport)
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AP Biology2005-2006
Cell Membrane…more than just a barrier!
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AP Biology2005-2006
Cell (plasma) membrane Cells need an inside & an outside…
separate cell from its environment cell membrane is the boundary
INfoodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2O
OUTwasteammoniasaltsCO2
H2O products
cell needs materials in & products or waste out
IN
OUT
Can it be an impenetrable boundary? NO!
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AP Biology
Lipids of cell membrane Membrane is made of phospholipids
phospholipid bilayer
phosphate
lipid
hydrophilic
hydrophobic
inside cell
outside cell
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AP Biology
Phospholipid bilayer What molecules can get through directly?
inside cell
outside cell
fats & other lipidscan slip directly through the phospholipid cell membrane, but…
what about other stuff?
lipid
salt
aa H2Osugar
NH3
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AP Biology2005-2006
Membrane Proteins Proteins determine most of membrane’s
specific functions cell membrane & organelle membranes each
have unique collections of proteins Membrane proteins:
peripheral proteins = loosely bound to surface of membrane
integral proteins = penetrate into lipid bilayer, often completely spanning the membrane =
transmembrane proteins
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AP Biology
Membrane Protein Types Channel proteins – wide open passage Ion channels – gated, only active under
specific conditions Aquaporins – move water only, found
primarily in animal kidneys and plant roots Carrier proteins – conformational change
(change in shape occurs) Transport proteins – require ATP
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AP Biology
Membrane Protein Types Recognition proteins – glycoproteins,
carbohydrates are attached (too hydrophilic to be directly on membrane)
Adhesion proteins – anchors to surrounding cells/tissues
Receptor proteins – hormones; receptors that start signal transduction pathways
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AP Biology2005-2006
A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer
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AP Biology2005-2006
Membrane Carbohydrates Play a key role in cell-cell recognition
ability of a cell to distinguish neighboring cells from another
important in organ & tissue development
basis for rejection of foreign cells by immune system
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AP Biology
Cholesterol Provides stability in animal cells Replaced with sterols in plant cells
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AP Biology
Getting through cell membrane Passive transport
No energy needed Movement down concentration gradient
high low
Active transport Movement against concentration gradient
low high requires ATP
Think: does it take more energy to move water down a waterfall (from high to low) or up a waterfall (from low to high)?
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AP Biology
Diffusion
2nd Law of Thermodynamics - Universe tends towards disorder
Diffusion movement from high low concentration
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AP Biology2005-2006
Simple diffusion across membrane
inside cell
outside cell
Which way will lipid move?
low
high
lipid
lipid
lipid
lipid
lipid
lipid lipid
lipidlipid
lipid
lipid
lipid
lipid
lipid
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AP Biology
Diffusion of 2 solutes Each substance diffuses down its own
concentration gradient, independent of concentration gradients of other substances
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AP Biology2005-2006
Facilitated diffusion Movement from HIGH to LOW
concentration through a protein channel passive transport; no energy needed facilitated = with help
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AP Biology2005-2006
Gated channels Some channel proteins open only in the
presence of stimulus (signal) stimulus usually different from
transported molecule ex: ion-gated channels
when neurotransmitters bind to a specific gated channels on a neuron, these channels open = allows Na+ ions to enter nerve cell
ex: voltage-gated channelschange in electrical charge across nerve cell membrane opens Na+ & K+ channels
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AP Biology
Active transport Cells may need molecules to move
against concentration situation need to pump against concentration protein pump requires energy
ATP
Na+/K+ pump in nerve cell membranes
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AP Biology2005-2006
Transport summary
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AP Biology2005-2006
How about large molecules? Moving large molecules into & out of cell
requires ATP! through vesicles & vacuoles Endocytosis (taking molecules in)
phagocytosis = “cellular eating” pinocytosis = “cellular drinking” receptor-mediated
endocytosis Exocytosis
Molecules exiting
Exocytosis
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AP Biology
Endocytosis
phagocytosis
pinocytosis
receptor-mediated endocytosis
fuse with lysosome for digestion
non-specificprocess
triggered byligand signal
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AP Biology2005-2006
The Special Case of Water
Movement of water across the cell membrane
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AP Biology2005-2006
Osmosis is diffusion of water Diffusion of water from
high concentration of water to low concentration of water across a
semi-permeable membrane
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AP Biology2005-2006
Concentration of water Direction of osmosis is determined by
comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water
hypotonic hypertonic
water
net movement of water
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AP Biology2005-2006
Managing water balance Cell survival depends on balancing
water uptake & loss
freshwater balanced saltwater
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AP Biology
Hypotonicity animal cell in a hypotonic
solution will gain water, swell & possibly burst (cytolysis)
Paramecium vs. pond water Paramecium is hypertonic H2O continually enters cell specialized organelle, contractile
vacuole, pumps excess H2O out of cell; requires ATP
plant cell in a hypotonic solution is turgid
Turgor pressure Cell wall exerts force
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AP Biology2005-2006
Hypertonicity animal cell in hypertonic
solution will lose water, shrivel & probably die
salt water organisms are hypotonic compared to their environment
they have to take up water & pump out salt
plant cell in a hypertonic solution experiences plasmolysis
Vacuole shrinks; cell membrane pulls away from cell wall
Wilting
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AP Biology2005-2006
Cell (compared to beaker) hypertonic or hypotonic
Beaker (compared to cell) hypertonic or hypotonic
Which way does the water flow? in or out of cell
.05 M .03 M
Osmosis…
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AP Biology
Water Potential Water moves from a place of greater
water potential to a place of lesser water potential (net).
As the concentration of a solute increases in a solution, the water potential will decrease accordingly. Which has the greater water potential:
.2M or .8M? Which has the greater water potential:
20% or 80% water?