1. Chapter 5 Membranes and Transport

2. Cell Membrane Function: To control passage of substances Selectively permeable: Some substances and chemicals can pass through, some can’t – Based on size and charge of molecule

3. Fluid mosaic model Membrane includes three parts – Phospholipid bilayer (fluid) – Proteins (mosaic) – Cholesterol

4. Phospholipid bilayer Made of phospholipids Phospholipid – Glycerol with phosphate heads – Fatty acid tails

5. Proteins Functions of membrane proteins – Enzyme activity – Cell to cell signaling (glycoprotein) – Cell recognition (glycoprotein) – Transport of materials Channel proteins Pump proteins

6. Glycoproteins A Protein with a carbohydrate chain attached Used for cell recognition and cell signaling Used to recognize tissue types in transplant patients

7. Membrane Proteins Transport Proteins

8. Cholesterol Helps maintain fluidity level of membrane – Too much=stiff – Too little=flimsy

9. Selectively permeable Can freely pass through lipid bilayer – Small non-polar molecules (not charged) Oxygen gas Carbon dioxide

10. Selectively permeable Cannot pass through freely – Charged molecules (polar) Water Ions Na+, K+, H+ – Large molecules Amino acids Proteins Glucose

11. Concentration Gradient The gradual difference in the concentration of solutes in a solution between two regions The membrane separates the two regions

12. Concentration Gradient Since membrane is selectively permeable a concentration gradient can build up – Solute will collect on one side and then move through membrane to reach equilibrium Equilibrium: The state in which the concentrations of the diffusing substance in the two compartments become equal.

14. Passive transport Moving materials across a membrane, down the concentration gradient without cellular energy Molecules are bouncing off of each other: referred to as kinetic energy

15. Types of Passive Transport Diffusion: Movement of materials through the lipid bilayer down a concentration gradient Examples: – Diffusion of Oxygen into blood from lungs – Diffusion of Carbon dioxide out of blood to lungs

16. Types of Passive Transport Osmosis: Movement of water through aquaporins down the concentration gradient – Movement of water from high water concentrations to low water concentrations

17. Hypertonic Solution is higher in solute or lower in water concentration relative to cell Water will move from high water to low water

18. Hypotonic Solution is lower in solute or higher in water concentration relative to cell Water will move from high water to low water

19. Isotonic Solution outside and inside the cell are at equilibrium Water will move back and forth equally

20. What happens if… The cell is placed in a hypertonic environment? The cell is placed in a hypotonic environment? The cell is placed in an isotonic environment?

22. Types of Passive Transport Facilitated Diffusion: Movement of materials down a concentration gradient through channel proteins – For large or charged molecules – Example: Glucose or amino acids

23. Passive Transport Comments All types of passive transport: – Movement from high to low concentrations – Trying to reach equilibrium

24. Active Transport Movement of materials independent of concentration gradient using cellular energy – Usually movement from low to high concentrations – Requires the cell to use ATP (energy) to move materials

25. Active Transport Uses Transport proteins called pumps – Proton pumps – Sodium-Potassium pumps (required for nerve impulses)

26. Active Transport Example We need Sodium and Potassium on certain sides of the membrane – Cannot rely on diffusion so cell must pump them to the right side Independent of concentration gradient

27. Active Transport

28. Exocytosis Type of active transport when the cell exports materials where a vesicle fuses with the cell membrane Used for very large molecules Example: proteins

29. Endocytosis Type of active transport where the membrane fuses with the cell membrane to import materials from the outside Cell brings in food or other proteins