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Cell Membranes
&
Movement Across Them

Regents Biology

2006-2007
Cell (plasma) membrane
 Cells need an inside & an outside…


separate cell from its environment



cell membrane is the...
Building a membrane
 How do you build a barrier that keeps
the watery contents of the cell separate
from the watery envir...
Lipids of cell membrane
 Membrane is made of special kind of lipid



phospholipids
“split personality”

“attracted to ...
Semi-permeable membrane
 Cell membrane controls what gets in or out
 Need to allow some materials — but not all
— to pas...
Crossing the cell membrane
 What molecules can get through the cell
membrane directly?


fats and oils can pass directly...
Cell membrane channels
 Need to make “doors” through membrane


protein channels allow substances in & out
 specific ch...
How do you build a semi-permeable
cell membrane?
 Channels are made of proteins


proteins both “like” water & “like” li...
Protein channels

 Proteins act as doors in the membrane


channels to move specific molecules
through cell membrane
HIG...
Movement through the channel
 Why do molecules move through
membrane if you give them a channel?
HIGH
?

LOW
?
Regents Bi...
Molecules move from high to low
 Diffusion


move from HIGH to LOW concentration

Regents Biology
Diffusion
 Move from HIGH to LOW concentration
passive transport
 no energy needed


Regents Biology

diffusion

diffus...
Simple Diffusion
 Move from HIGH to LOW
fat
inside cell

LOW

fat
fat

fat
fat

fat

Which way
will fat move?

HIGH
outsi...
Facilitated Diffusion
 Move from HIGH to LOW through a channel
sugar sugar
sugar
sugar
inside cell sugar
sugar

LOW

Whic...
Diffusion
 Move from HIGH to LOW concentration


directly through membrane
 simple diffusion
 no energy needed



hel...
Simple vs. facilitated diffusion
simple diffusion
inside cell

lipid

facilitated diffusion
inside cell

H2O

protein chan...
Active transport

 Cells may need molecules to move
against concentration “hill”


need to pump “uphill”
 from LOW to H...
Transport summary
simple
diffusion
facilitated
diffusion

active
transport
Regents Biology

ATP
Osmosis
Movement of Water Across
Cell Membrane

Regents Biology

2006-2007
Osmosis
 Water is very important, so we talk about


water separately
Osmosis


diffusion of water from HIGH concentrat...
Keeping water balance
 Cell survival depends on balancing
water uptake & water loss
freshwater

Regents Biology

balanced...
1

Keeping right amount of water in cell
 Freshwater

KABOOM!

freshwater

a cell in fresh water
 high concentration of ...
Controlling water
 Contractile vacuole in Paramecium

Regents Biology
2

Keeping right amount of water in cell

 Saltwater

I’m shrinking,
I’m shrinking!

a cell in salt water
 low concentra...
3

Keeping right amount of water in cell

 Balanced conditions


That’s
better!

no difference in
concentration of water...
Ice Fishing in Barrow

QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.

Regents Biology
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08 cellmembranes2009

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  • Donuts!
    Each transport protein is specific as to the substances that it will translocate (move).
    For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, its structural isomer.
    Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane -- simply provide corridors allowing a specific molecule or ion to cross the membrane.
    These channel proteins allow fast transport.
    For example, water channel proteins, aquaprorins, facilitate massive amounts of diffusion.
  • Movement from high concentration of that substance to low concentration of that substance.
  • Plants have nitrate & phosphate pumps in their roots.
    Why?
    Nitrate for amino acids
    Phosphate for DNA & membranes
    Not coincidentally these are the main constituents of fertilizer.
  • Transcript of "08 cellmembranes2009"

    1. 1. Cell Membranes & Movement Across Them Regents Biology 2006-2007
    2. 2. Cell (plasma) membrane  Cells need an inside & an outside…  separate cell from its environment  cell membrane is the boundary IN food - sugars - proteins - fats salts O2 H2O Regents Biology OUT waste - ammonia - salts - CO2 - H2O products - proteins cell needs materials in & products or waste out
    3. 3. Building a membrane  How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? → FATS ← → LIPIDS ← Remember: oil & water don’t mix!! What substance do you know that doesn’t mix with water? Regents Biology
    4. 4. Lipids of cell membrane  Membrane is made of special kind of lipid   phospholipids “split personality” “attracted to water”  Membrane is a double layer  phospholipid bilayer phosphate inside cell lipid outside cell Regents Biology “repelled by water”
    5. 5. Semi-permeable membrane  Cell membrane controls what gets in or out  Need to allow some materials — but not all — to pass through the membrane  semi-permeable  only some material can get in or out So what needs to get across the membrane? sugar lipids Regents Biology aa O2 H2O salt waste
    6. 6. Crossing the cell membrane  What molecules can get through the cell membrane directly?  fats and oils can pass directly through inside cell waste outside cell Regents Biology lipid salt sugar aa H2O but… what about other stuff?
    7. 7. Cell membrane channels  Need to make “doors” through membrane  protein channels allow substances in & out  specific channels allow specific material in & out  H2O channel, salt channel, sugar channel, etc. inside cell waste salt Regents Biology H2O aa sugar outside cell
    8. 8. How do you build a semi-permeable cell membrane?  Channels are made of proteins  proteins both “like” water & “like” lipids bi-lipid membrane Regents Biology protein channels in bi-lipid membrane
    9. 9. Protein channels  Proteins act as doors in the membrane  channels to move specific molecules through cell membrane HIGH LOW Regents Biology
    10. 10. Movement through the channel  Why do molecules move through membrane if you give them a channel? HIGH ? LOW ? Regents Biology
    11. 11. Molecules move from high to low  Diffusion  move from HIGH to LOW concentration Regents Biology
    12. 12. Diffusion  Move from HIGH to LOW concentration passive transport  no energy needed  Regents Biology diffusion diffusion of water osmosis
    13. 13. Simple Diffusion  Move from HIGH to LOW fat inside cell LOW fat fat fat fat fat Which way will fat move? HIGH outside cell fat Regents Biology fat fat fat fat fat fat fat
    14. 14. Facilitated Diffusion  Move from HIGH to LOW through a channel sugar sugar sugar sugar inside cell sugar sugar LOW Which way will sugar move? HIGH outside cell sugar Regents Biologysugar sugar sugar sugar sugar sugar
    15. 15. Diffusion  Move from HIGH to LOW concentration  directly through membrane  simple diffusion  no energy needed  help through a protein channel  facilitated diffusion (with help)  no energy needed HIGH Regents Biology LOW
    16. 16. Simple vs. facilitated diffusion simple diffusion inside cell lipid facilitated diffusion inside cell H2O protein channel outside cell Regents Biology outside cell H2O
    17. 17. Active transport  Cells may need molecules to move against concentration “hill”  need to pump “uphill”  from LOW to HIGH using energy protein pump  requires energy  ATP  ATP Regents Biology
    18. 18. Transport summary simple diffusion facilitated diffusion active transport Regents Biology ATP
    19. 19. Osmosis Movement of Water Across Cell Membrane Regents Biology 2006-2007
    20. 20. Osmosis  Water is very important, so we talk about  water separately Osmosis  diffusion of water from HIGH concentration of water to LOW concentration of water  across a semi-permeable membrane Regents Biology
    21. 21. Keeping water balance  Cell survival depends on balancing water uptake & water loss freshwater Regents Biology balanced saltwater
    22. 22. 1 Keeping right amount of water in cell  Freshwater KABOOM! freshwater a cell in fresh water  high concentration of water around cell   cell gains water  example: Paramecium  problem: cells gain water, swell & can burst  water continually enters No problem, here Paramecium cell  solution: contractile vacuole  pumps water out of cell Regents Biology
    23. 23. Controlling water  Contractile vacuole in Paramecium Regents Biology
    24. 24. 2 Keeping right amount of water in cell  Saltwater I’m shrinking, I’m shrinking! a cell in salt water  low concentration of water around cell   cell loses water example: shellfish  problem: cell loses water   in plants: plasmolysis  in animals: shrinking cell  solution: take up water Regents Biology I will survive! saltwater
    25. 25. 3 Keeping right amount of water in cell  Balanced conditions  That’s better! no difference in concentration of water between cell & environment  cell in equilibrium  example: blood  problem: none  water flows across membrane equally, in both directions  volume of cell doesn’t change Regents Biology I could be better… balanced
    26. 26. Ice Fishing in Barrow QuickTime™ and a YUV420 codec decompressor are needed to see this picture. Regents Biology
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