The plasma membrane

1. The plasma membrane Maintaining control of the internal environment

2. You will learn • The structure of the plasma membrane • How the plasma membrane functions as a semi-permeable membrane

3. Vocabulary • Homeostasis • Selectively Permeable • Fatty acid tail • Hydrophilic • Hydrophobic • Phospholipid bilayer • Fluid mosaic model

4. What does a cell membrane need to do? • Bring nutrients in • Let waste out • Allow ions to move back and forth • Maintain homeostasis

5. Function of plasma membrane • Cell membrane acts as a gatekeeper. • It has selective permeability Water freely enters and leaves the cell Other particles, such as ions, are controlled: • certain times • certain amounts • certain places

6. Structure of plasma membrane • Made of lipids (fats) with a phosphate head • Lipid portion is 2 fatty acid tails. The tail is hydrophobic: does NOT like water • Phosphate head is hydrophilic: it DOES like water. phospholipid

7. Polar means an unequal sharing of electrons- polar molecules are water soluble- they are hydrophylic • Non-polar means equal sharing. These molecules are hydrophobic

8. Three views of the same molecule

9. In water, phospholipids spontaneously form a stable two layer sheet called a phospholipid bi-layer

10. Here is what a phospholipid bi-layer looks like as a sphere

11. Cholesterol embedded in membrane keeps it fluid • The bi-layer is known as the Fluid MosaicModel, because proteins embedded in the membrane can move

12. Some proteins span membrane and determine which molecules can enter or leave. These are transport proteins. • Other proteins on the surface act as receptors