1. Topic: Cell Membrane
Objective: Describe and draw the phospholipid bilayer

2. Cell membranes are composed of two phospholipid layers.
The cell membrane has 2 major functions.
1. forms a boundary between inside and outside of the cell
2. controls passage of materials
cell membrane
outside cell
inside cell

3. The cell membrane is known as the fluid mosaic model because:
The parts of the cell membrane are not locked in place, are able to float, are able to move from one region of the cell to another
cell membrane
protein
cholesterol
carbohydrate
chain
protein channel

4. Basic building block of the cell membrane – phospholipid
A kind of fat (lipid) molecule
Has a polar head
The polar head is attracted to water
Has two long nonpolar tails
The nonpolar tails are repelled by water
Polar head
Nonpolar tails

5. Water can interact with the polar heads (on outside and inside of cell) and the nonpolar tails (on inside of bilayer) can stick together if the phospholipids line up in two layers – the lipid bilayer

6. The lipid bilayer stops polar molecules
The polar molecules cannot pass by the nonpolar tails of the lipid bilayer
Most food molecules are polar though
They need to get through the cell membrane
There are passageways through the cell membrane
The passageways are made of proteins
These protein gates open and close to allow polar food molecules through

7. 3 Proteins that stick out from the cell membrane may act as:
1. Channels—where molecules and ions pass through the membrane (look like big donuts with holes)
2. Receptors—specific shape on outside of receptor like lock and key
3. Markers—identifies the type of cell and help direct cells to their proper location 1. 3. 2.

8. Cell membranes are composed of two phospholipid layers.
The cell membrane is selectively permeable
Means membrane is picky
Lets in oxygen, sugars, proteins
Expels wastes like carbon dioxide.
-Some molecules can cross the membrane while others cannot.