1. Membranes -Composed of a phospholipid bilayer with embedded proteins
-Likened to a “Fluid Mosaic” in structure

2. Different views of phospholipid structure

3. The Fluid Mosaic model of membrane structure

4. Cell membranes consist of four components
Phospholipid bilayer –
Transmembrane proteins –
Interior protein network –
Cell surface markers -

5. Proteins and protein complexes perform key functions
Transporters –
Enzymes –
Cell surface receptors –
Cell surface identity (antigens) –
Cell-to-cell adhesion proteins –
Attachments to cytoskeleton –

6. Functions of plasma membrane proteins

7. Diffusion processes Passive Transport – no energy required
Simple diffusion
Facilitated diffusion
Osmosis
Active Transport – requires ATP
Sodium-potassium pump
Coupled transport

8. Simple diffusion
-Occurs with CO2, O2, and some non-polar organic compounds

9. Facilitated Diffusion
Molecules bind to a specific carrier protein to gain access to the cytoplasm
Process is still passive as there is no energy (ATP) expended and substances move along a concentration gradient

10. Osmosis = movement of H2O across a selectively permeable membrane
Water moves along a concentration gradient; from area of higher concentration to area of lower concentration

11. Tonicity of solutions
A solution contains a solute(s) dissolved in a solvent
Hypertonic solutions contain MORE solute than a comparable solution
Hypotonic solutions contain LESS solute than a comparable solution
Hence, Hypertonic and Hypotonic relate to 2 solutions that are being compared to one another

12. Fig. 5.13

13. The Sodium-Potassium pump: example of active transport

14. Coupled transport – symport movement across the membrane

15. Examples of bulk transport