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4.3: The Plasma Membrane
Functions of the Plasma MembraneAllows only certain molecules
to enter or leave
Separates inside from outside
Allows waste to be expelled
Interacts with its environment QuickTime™ and a
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Two Parts of Membrane1. Membrane Lipids -
Phospholipids form a bilayer
Heads are in the water, tails are out
Sterols - other lipids between the tails that make the membrane more firm, prevent freezing
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Two Parts of Membrane2. Membrane Proteins -
“Integral proteins”
Embedded in the lipid bilayer
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Uses:
To identify the cell type
Channels, allow certain substances to enter
Docking sites for chemical messengers
Fluid Mosaic ModelThe idea that the membrane behaves like a fluid
more than a solid.
The proteins can move laterally within the bilayer.
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