
What is the cytoplasm?
◦ Cyto = “cell”
◦ Plasma= “liquid substance of the cell”

Cytoplasm?
◦
Clear, gelatinous fluid inside the cell

What contains it?
◦ Plasma Membrane

Do all cells have this?
◦ YES!

Cells need an inside & an outside…
◦ separate cell from its environment
◦ cell membrane is the boundary
IN
OUT
food
- sugars
- proteins
- fats
salts
O2
H2O
waste
- ammonia
- salts
- CO2
- H2O
products
- proteins
cell needs materials in & products or waste out
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
Why have a plasma membrane?
◦ Allow nutrients to move in and out of the cell

How does it control how much goes in and
out?
◦ Selective permeability
 Per= “through”
 Meare= “ to glide”

Therefore, what does it mean?

What’s the point for allowing materials in and
out of the cell?
HOMEOSTASIS!!!!!

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?
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

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
“repelled by water”
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

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 aa
O2
H 2O
salt
waste
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
What molecules can get through the cell
membrane directly?
◦ fats and oils can pass directly through
inside cell
waste
outside cell
lipid
sugar aa
salt
H2O
but…
what about
other stuff?
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
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
H 2O
aa
sugar
outside cell
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
Channels are made of proteins
◦ proteins both “like” water & “like” lipids
bi-lipid
membrane
protein channels
in bi-lipid membrane
12

Proteins act as doors in the membrane
◦ channels to move specific molecules through cell
membrane
HIGH
LOW
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

Embedded all the way
through the bilayer
Allow ions to pass
through the membrane



Integral Proteins
Bond to only one side
of the membrane
Attach to or near
integral proteins
Help with ion
identification
Peripheral Proteins



Cell signaling
Maintains membrane
fluidity
Secures Proteins
Cholesterol



Lipid or Protein with a
carbohydrate attached
Provide energy
Cellular recognition
Glycolipid and
Glycoprotein

Why do molecules move through membrane if
you give them a channel?
HIGH
?
LOW
?
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
Diffusion
◦ move from HIGH to LOW concentration
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