1. The Plasma Membrane -
Gateway to the Cell

2. Photograph of a Cell Membrane

3. Cell Membrane
The cell membrane is flexible and allows a unicellular organism to move

4. Homeostasis Balanced internal condition of cells
Also called equilibrium
Maintained by plasma membrane controlling what enters & leaves the cell

5. Functions of Plasma Membrane
1. Protective barrier
2. Regulate transport in & out of cell (selectively permeable)
3. Allow cell recognition
4. Provide anchoring sites for filaments of cytoskeleton

6. Functions of Plasma Membrane
5. Provide a binding site for enzymes
6. Interlocking surfaces bind cells together (junctions)
7. Contains the cytoplasm (fluid in cell)

7. Structure of the Cell Membrane

8. Phospholipids Make up the cell membrane
Contains 2 fatty acid chains that are nonpolar
Head is polar & contains a –PO4 group

9. Cell Membrane Polar heads are hydrophilic “water loving”
Nonpolar tails are hydrophobic “water fearing”
Makes membrane “Selective” in what crosses

11. Solubility
Materials that are soluble in lipids can pass through the cell membrane easily

12. Crossing the membrane. Molecules cross the membrane in several ways.
Some methods require the cell to expend energy, some do not.
How a particular molecule crosses the membrane depends on the molecules size, polarity, and concentration inside versus outside the cell.
Small non-polar molecules easily pass through the membrane.
Small polar molecules are transported via proteins.
Large molecules are moved in vesicles.

13. Chemical signals are transmitted across the cell membrane
A receptor is a protein that detects a signal molecule and performs an action in response.
It recognizes and binds to only certain molecules, which ensures that the right cell gets the right signal at the right time.
When receptors are activated (they combine with a hormone or neurotransmitter), they change shape.
This relays information to the cell.