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 TransportDiffusion

Concentration difference or chemical

gradient

Random motion of particles in solution

Net diffusion

Steady state

http://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/Scheme_simple_diffusion_in_cell_membrane-en.svg/626px-Scheme_simple_diffusion_in_cell_membrane-en.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 IonsChannels

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.gifhttp://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/8/81/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+, A-

Concentration 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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