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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