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.

3. 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

4. carbohydrate chain protein cell membrane cholesterol protein protein channel • There are other molecules embedded in the membrane. The fluid mosaic model describes the membrane

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

6. l • Cell Membrane analogies: Fluid Mosaic Model A sandwich of molecules Phospholipid bylayer Functions-protective boundary between the inside and outside environment of the cell Controls transport of materials in and out Maintain homeostasis Maintains selective permeability Communicates, signals, and identifies cells and molecules

7. : • Structure: • Hydrophilic polarhead-phosphate group • Hydrophobic fatty acid tails (2) • Transport protein channels • Carbohydrate chains • Protein receptors • Cholesterol-strength and stability

8. Three types of Membrane Proteins 1.Channel Proteins are transport proteins-provide passageways for sugars, ions, amino acids “Gates to the Cells Interior” 2. Marker Proteins-cell surface markers, cell identifiers,aids the immune system. “Name Tags 3. Receptor Proteins-changes shape-send signals (for ex. Binds with Hormones (a ligand) “Informers of the Cell” • Intracellular receptors • Membrane receptors

9. 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