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. • Phospholipids form a double layer surrounding a cell • Made of a charged phosphate group, glycerol, and two fatty acid chains • Head is polar and forms hydrogen bonds with water (water-loving… “hydrophilic”) • Tail is non-polar (water-fearing… “hydrophobic”)

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. 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.

7. Other molecules • Cholesterol strengthens membranes, • Proteins aid cell identification and movement of molecules across membranes and cell signaling • Carbohydrates aid cell identification

8. Cell membranes are composed of two phospholipid layers.

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

10. 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.

11. cell membrane • Cell membranes are composed of two phospholipid layers. • The fluid mosaic model describes the membrane. • The membrane is flexible like a fluid and has a variety of molecules like the variety of tiles in a mosaic (picture)

12. Cell membranes are composed of two phospholipid layers. • The cell membrane is selectively permeable. • Allows some molecules to cross • Can also use terms such as semipermeable and selectively permeable • Enables a cell to maintain homeostasis

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

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. • Detect a signal molecule and perform an action in response • There are two types of receptors.

16. Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • There are two types of receptors. • intracellular receptor: Located inside the cell; binds to molecules that cross the membrane

17. Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • There are two types of receptors. • membrane receptor: Located in the membrane; Binds to molecules that Cannot cross the membrane