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

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

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

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

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

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

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.

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.