cell membranes movement across...
TRANSCRIPT
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2006-2007
Cell Membranes
&
Movement Across Them
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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
OUT waste
- ammonia
- salts
- CO2
- H2O
products
- proteins
cell needs materials in & products or waste out
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Building a membrane
How do you build a barrier that keeps
the watery contents of the cell separate
from the watery environment?
What substance
do you know
that doesn’t mix
with water?
FATS
LIPIDS
Remember: oil & water don’t mix!!
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Lipids of cell membrane Membrane is made of special kind of lipid
phospholipids
“split personality”
Membrane is a double layer
phospholipid bilayer
inside cell
outside cell
lipid
“repelled by water”
“attracted to water”
phosphate
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Question 1
List two alternative names for the cell
membrane.
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Selectively permeable membrane
Cell membrane controls what gets in or out
Need to allow some materials — but not all — to pass through the membrane
Selectively permeable only some material can get in or out
aa H2O sugar lipids salt waste
So what needs to get across the membrane?
O2
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Question 2
Why is the cell membrane described as
selectively permeable?
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Crossing the cell membrane
What molecules can get through the cell
membrane directly?
fats and oils can pass directly through
inside cell
outside cell
lipid
salt
aa H2O sugar
waste
but…
what about
other stuff?
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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
outside cell
sugar aa H2O
salt waste
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Question 3
Identify three items that are transported
across the cell membrane.
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How do you build a semi-permeable
cell membrane?
Channels are made of proteins
proteins both “like” water & “like” lipids
bi-lipid membrane
protein channels in bi-lipid membrane
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Protein channels
Proteins act as doors in the membrane
channels to move specific molecules
through cell membrane
HIGH
LOW
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Movement through the channel
Why do molecules move through
membrane if you give them a channel?
?
?
HIGH
LOW
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Molecules move from high to low
Diffusion
Molecules move from HIGH to LOW
concentration
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Diffusion
Move from HIGH to LOW concentration
passive transport
no energy needed
diffusion osmosis
diffusion of water
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Question 4
Define diffusion and osmosis.
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Simple Diffusion
Move from HIGH to LOW
inside cell
outside cell
Which way
will fat move?
fat
fat
fat
fat
fat
fat fat
fat fat
fat
fat
fat
fat
fat
LOW
HIGH
8 fat
molecules
6 fat
molecules
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Facilitated Diffusion Molecules move from HIGH to LOW
through a channel
inside cell
outside cell
sugar
sugar
sugar
sugar
sugar sugar
sugar sugar
sugar sugar
sugar
Which way will
sugar move?
sugar
sugar
LOW
HIGH
7 sugar
molecules
6 sugar
molecules
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Question 5
Define facilitated diffusion.
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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
LOW
6
molecules
2
molecules
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Simple vs. facilitated diffusion
inside cell
outside cell
lipid inside cell
outside cell
H2O
simple diffusion facilitated diffusion
H2O
protein channel
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Question 6
What does facilitated diffusion use to
transport molecules that simple
diffusion does not use?
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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
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Question 7
Define active transport.
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Transport summary
simple
diffusion
facilitated
diffusion
active
transport
ATP
15 molecules 2 molecules
12 molecules 3 molecules
2 molecules 12 molecules
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Question 8
Sketch the previous slide.
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2006-2007
Osmosis Movement of Water Across
Cell Membrane
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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
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Question 9
Define osmosis.
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Keeping water balance
Cell survival depends on balancing
water uptake & water loss
freshwater balanced saltwater
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Keeping right amount of water in cell
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
Paramecium cell
solution: contractile vacuole
pumps water out of cell
freshwater
No problem, here
KABOOM!
1
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Controlling water
Contractile vacuole in Paramecium
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Keeping right amount of water in cell
Saltwater
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
saltwater
I will survive!
I’m shrinking, I’m shrinking!
2
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Keeping right amount of water in cell
Balanced conditions
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
balanced
I could be better…
That’s better!
3
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Just Observe This Slide
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Sketch the graphics (be sure to include the arrows and descriptions!!!)
Hypo = Less
Less Solute
Outside Cell
Sketch This Slide!
Osmotic Solutions
Iso = Equal
Same Solute
Concentration
Outside & Inside Cell
Hyper = More
More Solute
Outside Cell