2. Cell (plasma) membrane
ī§ Cells need an inside & an outsideâĻ
īĩ
separate cell from its environment
īĩ
cell membrane is the boundary
IN
food
- sugars
- proteins
- fats
salts
O2
H2O
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OUT
waste
- ammonia
- salts
- CO2
- H2O
products
- proteins
cell needs materials in & products or waste out
3. Building a membrane
ī§ How do you build a barrier that keeps
the watery contents of the cell separate
from the watery environment?
â FATS â
â LIPIDS â
Remember:
oil & water
donât mix!!
What substance
do you know
that doesnât mix
with water?
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4. Lipids of cell membrane
ī§ Membrane is made of special kind of lipid
īĩ
īĩ
phospholipids
âsplit personalityâ
âattracted to waterâ
ī§ Membrane is a double layer
īĩ
phospholipid bilayer
phosphate
inside cell
lipid
outside cell
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ârepelled by waterâ
5. Semi-permeable membrane
ī§ Cell membrane controls what gets in or out
ī§ Need to allow some materials â but not all
â to pass through the membrane
īĩ
semi-permeable
ī§ only some material can get in or out
So what needs to get across the membrane?
sugar lipids
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aa
O2
H2O
salt
waste
6. Crossing the cell membrane
ī§ What molecules can get through the cell
membrane directly?
īĩ
fats and oils can pass directly through
inside cell
waste
outside cell
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lipid
salt
sugar aa
H2O
butâĻ
what about
other stuff?
7. Cell membrane channels
ī§ Need to make âdoorsâ through membrane
īĩ
protein channels allow substances in & out
ī§ specific channels allow specific material in & out
ī§ H2O channel, salt channel, sugar channel, etc.
inside cell
waste salt
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H2O
aa
sugar
outside cell
8. How do you build a semi-permeable
cell membrane?
ī§ Channels are made of proteins
īĩ
proteins both âlikeâ water & âlikeâ lipids
bi-lipid
membrane
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protein channels
in bi-lipid membrane
9. Protein channels
ī§ Proteins act as doors in the membrane
īĩ
channels to move specific molecules
through cell membrane
HIGH
LOW
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10. Movement through the channel
ī§ Why do molecules move through
membrane if you give them a channel?
HIGH
?
LOW
?
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11. Molecules move from high to low
ī§ Diffusion
īĩ
move from HIGH to LOW concentration
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12. Diffusion
ī§ Move from HIGH to LOW concentration
passive transport
īĩ no energy needed
īĩ
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diffusion
diffusion of water
osmosis
13. Simple Diffusion
ī§ Move from HIGH to LOW
fat
inside cell
LOW
fat
fat
fat
fat
fat
Which way
will fat move?
HIGH
outside cell
fat
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fat
fat
fat
fat
fat
fat
fat
14. Facilitated Diffusion
ī§ 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. Diffusion
ī§ Move from HIGH to LOW concentration
īĩ
directly through membrane
ī§ simple diffusion
ī§ no energy needed
īĩ
help through a protein channel
ī§ facilitated diffusion (with help)
ī§ no energy needed HIGH
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LOW
17. Active transport
ī§ Cells may need molecules to move
against concentration âhillâ
īĩ
need to pump âuphillâ
ī§ from LOW to HIGH using energy
protein pump
īĩ requires energy
ī§ ATP
īĩ
ATP
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20. Osmosis
ī§ Water is very important, so we talk about
ī§
water separately
Osmosis
īĩ
diffusion of water from HIGH concentration
of water to LOW concentration of water
ī§ across a semi-permeable membrane
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21. Keeping water balance
ī§ Cell survival depends on balancing
water uptake & water loss
freshwater
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balanced
saltwater
22. 1
Keeping right amount of water in cell
ī§ Freshwater
KABOOM!
freshwater
a cell in fresh water
īĩ high concentration of water
around cell
īĩ
ī§ cell gains water
ī§ example: Paramecium
ī§ problem: cells gain water,
swell & can burst
īˇ water continually enters
No problem,
here
Paramecium cell
ī§ solution: contractile vacuole
īˇ pumps water out of cell
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24. 2
Keeping right amount of water in cell
ī§ Saltwater
Iâm shrinking,
Iâm shrinking!
a cell in salt water
īĩ low concentration of water
around cell
īĩ
ī§ cell loses water
example: shellfish
īĩ problem: cell loses water
īĩ
ī§ in plants: plasmolysis
ī§ in animals: shrinking cell
īĩ
solution: take up water
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I will
survive!
saltwater
25. 3
Keeping right amount of water in cell
ī§ Balanced conditions
īĩ
Thatâs
better!
no difference in
concentration of water
between cell & environment
ī§ cell in equilibrium
ī§ example: blood
ī§ problem: none
īˇ water flows across
membrane equally,
in both directions
īˇ volume of cell doesnât
change
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I could
be betterâĻ
balanced
26. Ice Fishing in Barrow
QuickTimeâĸ and a
YUV420 codec decompressor
are needed to see this picture.
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Editor's Notes
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.