Cell Membranes and Transport

1. Cell Membranes and Transport

2. What is going on in this picture?

3. Phospholipids

4. Phospholipids • Fatty acid chains • A phosphate group • Glycerol backbone. • Polar heads • Nonpolar fatty acids

5. The Fluid Mosaic Model

6. Fluid Mosaic Model • Transports: • Small molecules • Between the phospholipids • Large molecules?!

7. Composition of the Plasma Membrane • Lipid bilayer • Peripheral proteins • Integral proteins • Cholesterol • Glycoproteins • Alpha helix protein

8. Homeostasis • Maintaining a Balance • Nutrients • Water • Wastes • Selectively permeable

9. Diffusion Cell membrane Outside cell Inside cell

10. Diffusion Cell membrane diffusion Outside cell Inside cell

11. Diffusion Cell membrane Outside cell Inside cell EQUILIBRIUM

12. Facilitated Diffusion Cell membrane diffusion Protein channel Outside cell Inside cell

13. Facilitated Diffusion Cell membrane diffusion Protein channel Outside cell Inside cell EQUILIBRIUM

14. Osmosis CONCENTRATED SOLUTION DILUTE SOLUTION Cell membrane partially permeable. Sugar molecule VERY Low conc. of water molecules. High water potential. VERY High conc. of water molecules. High water potential. Outside cell Inside cell

15. Osmosis Cell membrane partially permeable. Low conc. of water molecules. High water potential. OSMOSIS High conc. of water molecules. High water potential. Outside cell Inside cell

16. Osmosis Cell membrane partially permeable. OSMOSIS Outside cell Inside cell EQUILIBRIUM. Equal water concentration on each side. Equal water potential has been reached. There is no net movement of water

17. Cellular Transport - Passive • No energy is needed to move particles • Types of passive transport: • Diffusion • Facilitated diffusion • Osmosis

18. What determines the rate of diffusion? • Steepness of the concentration gradient • Temperature • Surface area • Type of molecule or ion diffusing

19. What’s the Point?

20. Cell Concentrations • Hypertonic solutions • More dissolved solute, less water • Hypotonic solutions • Less dissolved solute, more water • Isotonic solutions • Equal amounts of dissolved solute and water

21. Cell Concentrations – Isotonic • If the outside solution is isotonic to the inside of the cell… • The inside of the cell has the same amount of dissolved solute as outside the cell • So the water moves… • IN and OUT at equal rates!

22. Cell Concentrations – Hypotonic • If the outside solution is hypotonic to the inside of the cell… • The outside of the cell has less solute and more water than the inside of the cell • So the water moves… • INTO the cell until equilibrium is reached.

23. Cell Concentrations – Hypertonic • If the outside solution is hypertonic to the inside of the cell… • The outside of the cell has more solute and less water than the inside of the cell • So the water moves… • OUT of the cell until equilibrium is reached.

24. Overcoming Osmosis • Contractile vacuoles • Turgor pressure

25. Cellular Transport - Active • Active transport • Energy is needed to move particles UP the concentration gradient

28. Cellular Transport - Active • Carrier proteins • Endocytosis • Pinocytosis • Phagocytosis • Exocytosis

29. Active/Passive Molecules That Move Across the Membrane Direction Energey Needed? Protein Needed? Diffusion Osmosis Facilitated Diffusion Active Transport How Molecules Cross the Membrane