1. Unit 4: Cells 4.3 Cell Membrane

2. Cell membrane/Plasma Membrane
The cell membrane is made up of a phospholipid bilayer, proteins, and cholesterol

3. Phospholipid Bi-layer
Made up of 2 parts:
Phosphorus head
Polar: will form weak bonds with other polar substances

4. Phospholipid Bi-Layer
2. Lipid Tails
Non-polar: will form weak bonds with other non- polar substances.
Water inside and outside the cell will repel these tails causing them to be on the inside of the membrane.
Substances that will dissolve in
lipids, like cholesterol, will pass
freely through the membrane.

5. Draw the Phospholipid Bilayer

6. Other Molecules- Proteins
There are two main types of proteins within the phospholipid bilayer:
Channel/Integral: they go all the way through the membrane
Surface/Peripheral: on only one side of the membrane

7. Functions of Proteins:
Marker Proteins/Cell Signaling: tell us what type of cell it is.
Ex: liver cell, lung cell, skin cell, etc.
Receptor Proteins: bind to specific substances and act like signals molecules on the outside of the cell.
Carrier/Transport Proteins: aid in the movement of substances in and out of the cell.
Enzymes: aid in the chemical reactions of the cell.

8. Other Molecules- Cholesterol
Cholesterol is an additional type of lipid found in the cell membrane
Cholesterol helps to strengthen the bilayer and regulate proteins

9. The Fluid Mosaic Model
Together, the bi-layer and proteins make up the fluid mosaic model.
The cell membrane is not rigid like an egg shell, it is fluid, like the surface of a soap bubble.
The proteins are not stationary, they move around the membrane freely.
The bi-layer is NOT bonded together, there are only weak attractions.
This means that the membrane can be flexible and change shape.

10. Function of the Cell Membrane

11. Four Functions of the Cell Membrane:
Separation of internal and external environment
Cell Signaling
Selective transport
Excretion of Waste