Cell Membranes and Transport

1. Cell Membranes and Transport B9 - Analyze the structure and function of the cell membrane

2. Cell Walls • NB** Cell walls are different from cell membranes • Stiff, non-living • Made of complex carbohydrates • Cellulose for plants • Chitin for fungi • Chitin-like frame for bacteria • Used for support and protection • Very porous; entry only controlled by size

3. Cell Membranes “gate keepers” • 1. Isolate form outside • 2. Control entry and exit • 3. Communicate with others • 4. Bare identification (I’m one of you!)

4. Which of these statements are true comparing cell walls with membranes?

5. Fluid Mosaic Model • A phospholipid bilayer with proteins scattered through it • “fluid” because the proteins seem to “float” around the bilayer • Hydrophilic heads on the outside • Hydrophobic tails on the inside

7. Hydrophobic layer is a barrier to H2O soluble molecules (but makes it less fluid)

8. Cholesterol in the bilayer is even less permeable to H2O soluble molecules (but makes it less fluid)

9. “Protein Mosaic” • Membrane proteins will interact with the hydrophobic and hydrophilic layers of the bilayer • Some proteins will protrude into the cytoplasm, some into the extracellular space, others into both

10. Glycoproteins • Membrane proteins that have a carbohydrate chain attached • Often seen in proteins that protrude outside the cell

11. Glycolipids • Membrane lipids that have a carbohydrate chain attached • Both glycoproteins and glycolipids OFTEN function in cell-to-cell communication and/or recognition

12. What does the “fluid” in “fluid mosaic model” refer to? • A. The structure of the cell membrane • B. The structure of the cell wall • C. The fact that the membrane is made up mostly of water • D. The fact that the membrane is always changing, so it seems to be “fluid” • E. The fact that the membrane is made up of lipids, and they tend to “flow”

13. What does “mosaic” mean? • A. a picture • B. a lipid • C. a bunch of different things clumped together on a background • D. a type of protein that lets things into the cell • E. No idea!

14. Which of the following is true regarding this diagram? • A. 1a and 1b are fatty acids • B. 3 is a phosphate group • C. 5 is the hydrophobic end of the molecule • D. 6 is the hydrophobic end of the molecule • E. this is a type of lipid

15. Which one is a: • 1. Phospholipid • 2. Glycoprotein • 3. Cholesterol

16. 3 major membrane Protein Categories: • 1. Transport proteins • Regulated, fast method for specific molecules to enter and exit • Channel proteins • Carrier proteins

17. 2. Receptor Proteins • When activated, set off enzymatic sequences inside the cell

18. 3. Recognition Proteins • “identification tags”

19. Membrane Transport - RATE • Depends on: • Gradient (concentration, electrical or pressure) • Size of molecule • Lipid solubility • # of transporters

20. Diffusion • The random net movement of molecules from an area of high concentration to an area of low concentration. • (this is following the “concentration gradient”)

21. Osmosis • The diffusion of WATER across a selectively permeable membrane • (this is also following the “concentration gradient” and does not require energy)

22. Osmotic Effects • Isotonic solution • Same solute concentration • Cell is happy (no net loss or gain of water)

23. HYPERtonic solutions • [Solute] is greater outside the cell than inside the cell • Cell is not happy • It will crenate (shrink)

24. HYPOtonic solutions • Solute concentation is less outside the cell than inside • Cell is not happy • Cell will lyse

26. Active transport • Often against the concentration gradient • Therefore, REQUIRES ENERGY • (ATP --> ADP + P) • Uses transporter proteins

27. Endocytosis - 3 types

28. PhagocytosisLarge particles

29. 2. Pinocytosis • Liquid and • smaller particles only

30. Receptor-mediated Endocytosis • Uses receptors to bind first to the desired molecules, then gathers them together before enclosing them in a membrane