Download Transport and Membrane Potential

1. The Plasma Membrane
And Membrane Potential
2. Plasma Membrane Functions
Forms cell boundary, enclosing intracellular
contents
Determines composition of the cell
Entry of nutrients
Exit of wastes
Exit of secretory products
Maintain differences in ion concentration
Joins cells together
Ability to respond to environmental signals
3-4. Membrane Transport
Semipermeable/selectively permeable
Permeability
Solubility in lipids
Size
Charge
Polar vs. nonpolar
Passive
No energy expended
Active
ATP required
5-11. Passive Transport
Diffusion
Concentration difference or chemical
gradient
Random motion of particles in solution
Net diffusion
Steady state
http://upload.wikimedia.org/wikipedia/commons/thu
mb/c/cc/Scheme_simple_diffusion_in_cell_membra
ne-en.svg/626pxScheme_simple_diffusion_in_cell_membraneen.svg.png
http://www.williamsclass.com/SeventhScienceWork
/ImagesCellBricks/Diffusion.gif
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12-13. What Can Diffuse Through the Phopholipid
Bilayer?
Small molecules
Nonpolar molecules
Uncharged particles
14. Diffusion
Rate of diffusion of a substance depends on:
Magnitude of its concentration gradient
Permeability of membrane to that substance
Temperature
Surface area of membrane
Also
Molecular weight of substance
Thickness of membrane
15. Fick’s Law of Diffusion
16.Movement of Ions
Electrical gradient
Chemical gradient
Electrochemical gradient
17. Electrochemical Gradient
18. Diffusion of Ions
Channels
Specific
Size
Charge
# present determined permeability
Leak – always open
Gated – sometimes open, sometimes closed
Chemical
Stretch
Voltage
http://www.biologycorner.com/resources/cell
_membrane.jpg
20 - 24. Osmosis
Diffusion of water through selectively permeable
membrane
Through bilayer
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Aquaporins
H2O diffuses down its concentration gradient
H2O concentration is less when there are more
solutes
Solutes have to be osmotically active
cannot freely move across membrane
H2O diffuses down its concentration gradient
until its concentration is equal on both sides of a
membrane
Some cells have water channels called
aquaporins to facilitate osmosis
25 - 30. Osmotic Pressure
Force that would have to be exerted to stop
osmosis
How strongly H2O “wants” to diffuse
Proportional to solute concentration
31-32. Molarity and Molality
1 molar solution (1.0M)
1 mole of solute dissolved in enough water
to make 1L of solution
Doesn't specify exact amount of H2O
1 molal solution (1.0m)
1 mole of solute dissolved in 1 kg H2O
Molarity and Molality
Osmolality (Osm)
is total molality of a solution
1mole of NaCl yields a 2 Osm solution
1 mole of glucose yields a 1 Osm solution
33-37. Tonicity
Effect on cell volume via osmotic movement of
H20
Isotonic
No change in volume
Solutions have same osmotic pressure
Hypertonic
Have higher osmotic pressure
Cells shrink/crenate
Hypotonic
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Have lower osmotic pressure
Cells swell/lyse
http://www.medicine.mcgill.ca/physio/vlab/bloodlab
/images/crenate.gif
http://www.medicine.mcgill.ca/physio/vlab/bloodlab
/eryfrag1_n.htm
38-9. Carrier-Mediated Transport
Molecules too large and polar to diffuse
Protein carriers
Specificity
Saturation
Transport maximum
Competition
Passive or active
Facilitated diffusion
Active transport
40. Facilitated Diffusion
Carriers bind with passenger molecule on either
side of membrane
Binding induces conformational change
41. Transport of Glucose
42. Channel vs Carrier Proteins
http://www.bio.miami.edu/~cmallery/150/memb/c8.
7x15.facilitated.diffusion.jpg
43. Active Transport
Is transport of molecules against a concentration
gradient
ATP is required
44. Primary Active Transport
Substance binds to recognition site
Bonding stimulates phosphorylation of the
carrier protein
Carrier undergoes conformational change
Transported molecule released on opposite side
of membrane
45-47. Na+/K+ Pump
3 Na+ out
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2 K+ in
Against their gradients
Uses ATP
Energy for coupled transport of other molecules
Electrochemical impulses
Osmotic reasons
49-52. Secondary Active Transport
Requires ATP to first move Na+ uphill to create
a gradient
Secondary active transport then uses energy
from “downhill” movement of Na+ to drive “uphill”
transport of another molecule
Cotransport or symport
Molecule moves in same direction as Na+
Countertransport or antiport
Molecule moves in opposite direction to Na+
Secondary Active Transport
53-76. Vesicular Transport
A.k.a. bulk transport
Large polar molecules
Multimolecular materials
Membrane-enclosed vesicle
Endocytosis
Pinocytosis
Receptor-mediated endocytosis
Phagocytosis
Exocytosis
http://upload.wikimedia.org/wikipedia/commons/8/8
1/FAGOCITOSI_BY_RAFF_.gif
Pinocytosis
“cell drinking”
ECF into cell
Retrieve extra membrane
Receptor-mediated endocytosis
Selective
Import specific large molecules
Receptors on cell surface
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Cholesterol, B12, insulin, iron
59-60. Transport Summary
61-5. Membrane Potential
All living cells
Separation of charges across membrane or
difference in relative # of cations and anions in
the ICF and ECF
Millivolts (mV)
Negative inside/positive outside
Magnitude depends on degree of separation of
charges
66. The Membrane Potential
Na+/K+ pump
Negatively charged proteins inside of cell
Membrane more permeable to K+ than amy
other cation
67. Equilibrium Potential
Membrane potential at which net movement of
ion across membrane ceases
K+
-90mV
Na+
+66mV
68-69. Ion Concentrations
70. Resting Membrane Potential
Differences in concentration and permeability of
key ions
K+, Na+, AConcentration gradient
Na+ - into cell
K+ - out of cell
Electrical gradient for both K+ and Na+ is
toward the negatively charged side of
membrane
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