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Thursday, 9/27 Discuss SA:Volume Ratio Lab
Any questions? Collect Lab sheet
Chp.6 Quiz 15 multiple choice/matching 1 short answer
Start Chp.7 Draw model of the cell membrane (plasma membrane) use
diagram in class, book fig.7.5???• Label all of the parts
• Color your diagram
• This goes in your notes Bring textbook tomorrow, HW due Monday
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Friday, 9/28
Cell Transport Notes
Homework = Chp.7 Reading Notes Due Monday
AP Lab: Diffusion & Osmosis next week Set up Monday, Lab Tues - Thursday Lab debrief/Review Friday Chp.6&7 Test will be next MONDAY!
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Chapter 7 ~ Membrane Structure & Function
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Cell Membrane (Notes)
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Is the boundary that separates the living cell from its nonliving surroundings
exhibits selective permeability It allows some substances to cross it more easily
than others
The plasma (cell) membrane:
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Cellular membranes
are fluid mosaics of lipids and proteins
Fluid Mosaic Model
Phospholipids Are the most abundant
lipid in the plasma membrane
Are amphipathic, containing both hydrophobic and hydrophilic regions
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The Fluidity of Membranes Phospholipids in the plasma membrane
Can move within the bilayer
Figure 7.5 A
Lateral movement(~107 times per second)
Flip-flop(~ once per month)
(a) Movement of phospholipids
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Membrane structure
Cholesterol~ membrane stabilization
“Mosaic” Structure~ Integral proteins~
transmembrane proteins Peripheral proteins~ surface of
membrane Membrane carbohydrates ~ cell
to cell recognition; oligosaccharides (cell markers);glycolipids; glycoproteins
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Membrane protein function:
1. transport
2. enzymatic activity
3. signal transduction
4. intercellular joining
5. cell-cell recognition
6. ECM attachment
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Membrane proteins and lipids Are synthesized in the ER and Golgi apparatus
ER
Figure 7.10
Transmembraneglycoproteins
Secretoryprotein
Glycolipid
Golgiapparatus
Vesicle
Transmembraneglycoprotein
Membrane glycolipid
Plasma membrane:
Cytoplasmic face
Extracellular face
Secretedprotein
4
1
2
3
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Membrane structure results in selective permeability A cell must exchange materials with
its surroundings, a process controlled by the plasma membrane
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The Permeability of the Lipid Bilayer
Figure 7.2
Hydrophilichead
Hydrophobictail
WATER
WATER
Hydrophobic molecules Are lipid soluble and can pass through the membrane
rapidly
Polar molecules (hydrophillic) Do not cross the membrane rapidly
Transport proteins Allow passage of hydrophilic substances across the
membrane
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Passive transport is diffusion of a substance across a membrane with no energy investment Movement of a substance from [high] to
[low] (down a concentration gradient)
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1. Diffusion~ tendency of any molecule to spread out into available space
2. Osmosis~ the diffusion of water across a selectively permeable membrane
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Water balance : Osmoregulation=control of water balance
Isotonic~ The concentration of solutes is the
same as it is inside the cell There will be no net movement of
water
Hypertonic~ The concentration of solutes is
greater than it is inside the cell The cell will lose water
Hypotonic~ The concentration of solutes is less
than it is inside the cell The cell will gain water
Hypotonic solution Isotonic solution
Hypertonic solution
H2OH2O H2O H2O
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Cells with Walls:Walls help maintain water balanceTurgid (very firm)
Flaccid (limp)
Plasmolysis~ plasma membrane pulls away from cell wall
Plant cell. Plant cells are turgid (firm) and generally healthiest ina hypotonic environ-ment, where theuptake of water iseventually balancedby the elastic wallpushing back on thecell.
H2OH2OH2OH2O
Turgid (normal) Flaccid Plasmolyzed
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Facilitated Diffusion = Passive Transport Aided by Proteins Transport proteins speed the movement of molecules across the
plasma membrane
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Channel proteins Provide corridors that allow a specific molecule or
ion to cross the membrane
Figure 7.15
EXTRACELLULARFLUID
Channel proteinSolute
CYTOPLASM
A channel protein (purple) has a channel through which water molecules or a specific solute can pass.
(a)
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Carrier proteins Undergo a subtle change in shape that translocates
the solute-binding site across the membrane
Figure 7.15
Carrier proteinSolute
A carrier protein alternates between two conformations, moving a solute across the membrane as the shape of the protein changes. The protein can transport the solute in either direction, with the net movement being down the concentration gradient of the solute.
(b)
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Active transport = uses energy to move solutes against their gradients
Moves substances against their concentration gradient Requires energy, usually in the form of ATP Example: Sodium-Potassium Pump
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Na-K Pump
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Review
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Maintenance of Membrane Potential by Ion Pumps
An electrochemical gradient Is caused by the concentration electrical gradient of ions across a membrane
An electrogenic pump Is a transport protein that generates the voltage across a membrane
EXTRACELLULARFLUID
+
H+
H+
H+
H+
H+
H+ Proton pump
ATP
CYTOPLASM
+
+
+
+–
–
–
–
–
+
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Bulk transport (Large proteins) across the plasma membrane occurs by exocytosis and endocytosis
In exocytosis Transport vesicles migrate to the plasma membrane, fuse with it, and release their
contents
In endocytosis The cell takes in macromolecules by forming new vesicles from the plasma
membrane
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EXTRACELLULARFLUID
Pseudopodium
CYTOPLASM
“Food” or other particle
Foodvacuole
1 µm
Pseudopodiumof amoeba
Bacterium
Food vacuole
An amoeba engulfing a bacterium viaphagocytosis (TEM).
PINOCYTOSIS
Pinocytosis vesiclesforming (arrows) ina cell lining a smallblood vessel (TEM).
0.5 µm
In pinocytosis, the cell “gulps” droplets of extracellular fluid into tinyvesicles. It is not the fluiditself that is needed by the cell, but the molecules dissolved in the droplet. Because any and all included solutes are taken into the cell, pinocytosisis nonspecific in the substances it transports.
Plasmamembrane
Vesicle
In phagocytosis, a cellengulfs a particle by Wrapping pseudopodia around it and packaging it within a membrane-enclosed sac large enough to be classified as a vacuole. The particle is digested after the vacuole fuses with a lysosome containing hydrolytic enzymes.
Three types of endocytosis
Figure 7.20
PHAGOCYTOSIS
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0.25 µm
RECEPTOR-MEDIATED ENDOCYTOSIS
Receptor
Ligand
Coat protein
Coatedpit
Coatedvesicle
A coated pitand a coatedvesicle formedduringreceptor-mediatedendocytosis(TEMs).
Plasmamembrane
Coatprotein
Receptor-mediated endocytosis enables the cell to acquire bulk quantities of specific substances, even though those substances may not be very concentrated in the extracellular fluid. Embedded in the membrane are proteins with specific receptor sites exposed to the extracellular fluid. The receptor proteins are usually already clustered in regions of the membrane called coated pits, which are lined on their cytoplasmic side by a fuzzy layer of coat proteins. Extracellular substances (ligands) bind to these receptors. When binding occurs, the coated pit forms a vesicle containing the ligand molecules. Notice that there are relatively more bound molecules (purple) inside the vesicle, other molecules (green) are also present. After this ingested material is liberated from the vesicle, the receptors are recycled to the plasma membrane by the same vesicle.