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1 The Plasma Membrane The Plasma Membrane - Gateway to the Cell.

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Presentation on theme: "1 The Plasma Membrane The Plasma Membrane - Gateway to the Cell."— Presentation transcript:

1 1 The Plasma Membrane The Plasma Membrane - Gateway to the Cell

2 2 Photograph of a Cell Membrane

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

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

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

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

7 7 Structure of the Cell Membrane

8 8 Phospholipids Make up the cell membrane Contains 2 fatty acid chains that are nonpolar Head is polar & contains a –PO 4 group

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

10 10

11 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.


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