KEY CONCEPT The cell membrane is a barrier that separates a cell from the external environment.

1. KEY CONCEPT The cell membrane is a barrier that separates a cell from the external environment.

2. Cell membranes are composed of two phospholipid layers.

3. cell membrane • Cell membranes are composed of two phospholipid layers. • The cell membrane has two major functions.

4. cell membrane • Cell membranes are composed of two phospholipid layers. • The cell membrane has two major functions. • forms a boundary between inside and outside of the cell outside cell inside cell

5. cell membrane • Cell membranes are composed of two phospholipid layers. • The cell membrane has two major functions. • forms a boundary between inside and outside of the cell • controls passage of materials outside cell inside cell

6. Cell membranes are composed of two phospholipid layers.

7. cell membrane • Cell membranes are composed of two phospholipid layers. • The cell membrane is made of a phospholipid bilayer.

8. carbohydrate chain protein cell membrane cholesterol protein protein channel • Cell membranes are composed of two phospholipid layers. • The cell membrane is made of a phospholipid bilayer. • There are other molecules embedded in the membrane.

9. carbohydrate chain protein cell membrane cholesterol protein protein channel • Cell membranes are composed of two phospholipid layers. • The cell membrane is made of a phospholipid bilayer. • There are other molecules embedded in the membrane. • The fluid mosaic model describes the membrane.

10. Cell membranes are composed of two phospholipid layers. • Form a double layer surrounding a cell. • Composed of a charged phosphate group, glycerol and 2 fatty acid chains • Outside (head) is polar; inside (tails) is nonpolar • Other molecules: • Cholesterol: strengthens • Proteins: cell identification and movement of molecules • Carbohydrates: “antennae” for cell identification

11. Fluid Mosaic Model • Describes the arrangement of molecules making up the cell membrane • The membrane is flexible like a fluid and has a variety of molecules like a mosaic. • Think of “Jello” gelatin with fruit

12. Cell membranes are composed of two phospholipid layers. • The cell membrane is selectively permeable. Some molecules can cross the membrane while others cannot.

13. Selective Permeability • Allows some materials to cross • Enables a cell to maintain homeostasis • Molecules can cross in a variety of ways • Another term: semipermeable

14. Cell membranes are composed of two phospholipid layers. • The cell membrane is selectively permeable. Some molecules can cross the membrane while others cannot.

15. Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • There are two types of receptors. • Intracellular: located inside a cell; bind to molecules that can cross a membrane • Membrane: located in the membrane; bind to molecules that cannot cross the membrane; a change in shape transmits the message to the cell interior

16. Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • There are two types of receptors. • intracellular receptor

17. Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • There are two types of receptors. • intracellular receptor • membrane receptor