1. Cell Membrane & CELLULAR TRANSPORT

2. THE CELL MEMBRANE
REMEMBER…The cell membrane controls the movement of substances into and out of the cell.

3. Types of Transport Mechanisms
Active Processes
Primary Active Transport
Na+/K+ pump
Secondary Active Transport
Coupled transport
Endocytosis
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
Exocytosis
Membrane vesicle
Passive Processes
Diffusion
Direct
Facilitated Diffusion
Protein carrier
Protein channel*
Osmosis
Aquaporins

4. “COME ON AND TAKE A FREE RIDE” – PASSIVE TRANSPORT
No ATP (energy) needed
There are three types:
DIFFUSION
-Small molecules (CO2, H2O, O2, salts) can move between the phospholipid molecules of the bilayer.
-Molecules move from a HIGH concentration ([]) to a LOW [] along a CONCENTRATION GRADIENT until a balance is achieved.

5. Diffusion

6. Diffusion

7. Direct Diffusion
Non-polar molecules easily cross non-polar interior of cell membrane
movement from [high] to [low]
Example:
Movement of O2 into cells from blood

8. Diffusion

9. Passive Transport 2. OSMOSIS
-The movement of water (from High to Low [ ]) through a selectively permeable membrane.

10. Comparing Osmosis and Diffusion
Osmosis is the movement of water across a cell membrane from an area of higher concentration to an area of lower concentration.
Diffusion is the movement of molecules other than water across a membrane from an area of higher concentration to and area of lower concentration.

11. How Osmosis Works

12. Osmosis and Random Motion

13. Osmotic Conditions Surrounding Cells
Isotonic solution – Solute [ ] outside of cell is equal to [ ] inside the cell. Cell remains normal.
Hypertonic solution – Fluid surrounding the cell has a higher solute [ ] than inside. Water diffuses out and the cell shrinks!
Hypotonic solution – [ ] of solute is higher inside the cell than outside. Water will diffuse into the cell. The cell expands!

14. Passive Transport
Osmosis is a VITAL fluid control process (blood and urine balance)

15. Learning Check: Wake up!
Pg 74 # 25 – 30
25) What is a concentration gradient?
26) Describe diffusion. Why does it occur?
27) What are three factors that affect diffusion. How do they work?

16. 28) What are the similarities and Differences between diffusion and osmosis?
29) If membranes were not semi-permeable, could diffusion/osmosis occur?
30)Why are diffusion/osmosis examples of passive transport?

17. Passive Transport 3. FACILITATED DIFFUSION
-Some proteins in the cell membrane provide a “tunnel” for larger molecules (glucose) to diffuse through.
-They go with the concentration gradient!

18. Protein Channel Diffusion
Polar molecules cannot easily cross non-polar interior of cell membrane
Pass through a hydrophilic protein channel
movement from [high] to [low]
Example:
Movement of ions in or out of the cell

19. Protein Channel Diffusion

20. Facilitated Diffusion – Protein Carrier
Entry of certain polar molecules into the cell must be tightly regulated
Molecules bind to specific carrier proteins to be transported across
movement from [high] to [low]
3 key characteristics
Specific
Passive
Saturation
Example:
Movement of glucose into the cells

21. Facilitated Diffusion

22. Extension…Sports Drinks!
Can you drink yourself to death??
Should the tonicity of a fluid replacement drink be isotonic, hypertonic or hypotonic???

23. Hypernatremia
Certain conditions may result in a decrease in the sodium concentration in interstitial fluid. For instance, during sweating the skin excretes sodium as well as water.
If we replace the lost fluid with plain water then we may produce a sodium deficit. The decrease in sodium concentration in the interstitial fluid lowers the osmotic pressure. Water moves from the interstitial fluid into the cells, producing two results that can be quite serious:

24. Hypernatremia
The first result, an increase in intracellular water concentration (water in the cell), called over hydration which disrupts nerve cell function. In severe over-hydration we may see disoriented behaviour, convulsions, coma, and even death
The second result is a loss of interstitial fluid volume that leads to a decrease in the interstitial fluid pressure. As the pressure drops, water moves out of the plasma, resulting in a loss of blood volume that may lead to circulatory shock.

25. Sports Drinks!

26. Isotonic - quickly replaces fluids lost by sweating and supplies a boost of carbohydrate. This drink is the choice for most athletes - middle and long distance running or team sports. Glucose is the body's preferred source of energy therefore it may be appropriate to consume Isotonic drinks where the carbohydrate source is glucose in a concentration of 6% to 8%
Hypotonic - quickly replaces fluids lost by sweating. Suitable for athletes who need fluid without the boost of carbohydrate e.g. jockeys and gymnasts.
Hypertonic - used to supplement daily carbohydrate intake normally after exercise to top up muscle glycogen stores. In ultra distance events, high levels of energy are required and Hypertonic drinks can be taken during exercise to meet the energy demands. need to be used in conjunction with Isotonic drinks to replace fluids.

27. ACTIVE TRANSPORT
ATP is the energy used to “pump” nutrients across cell membranes.
Using ATP, carrier proteins “pump” substances through a membrane from an area of LOW [ ] to an area of HIGH [ ] against the concentration gradient.
Eg. Page 76…the Na+/K+ pump in nerve cells

28. ACTIVE TRANSPORT

29. Active Transport Primary Active Transport
Uses ATP to move molecules from one side of the membrane to another, UP the concentration gradient
Example: Na + /K + pump or H+ pump

30. Na/K Pump

31. Active Transport Secondary Active Transport
With 3 Na+ moving OUTside the cell for every 2 K+ moving in, what would happen to the difference in charge across the cell?
This combination of a charge buildup with a concentration gradient is called an electrochemical gradient
This electrochemical gradient can serve as the energy source (not ATP), and can be ‘coupled’ with transport of other molecules  “coupled transport”

32. Coupled Transport

33. Learning Check
Page 77 #

34. A QUESTION!
HOW DO THE REALLY LARGE MOLECULES (Hormones, polysaccharides etc.) move in and out of cells??

35. An Answer!! By two processes called ENDOCYTOSIS AND EXOCYTOSIS.
Both methods require the use of vesicles and ATP!

36. ENDOCYTOSIS –Moving materials into the cell
Three Types…
Phagocytosis
(Cell Eating):
-Used by white blood cells and amoeba.
-The cell moves out and surrounds the solid particle.

37. ENDOCYTOSIS –Moving materials into the cell
2. Pinocytosis (Cell drinking)
-Same process as phagocytosis except the cell
is moving liquids.

38. Phagocytosis

39. ENDOCYTOSIS –Moving materials into the cell
3. RME – Receptor Mediated Endocytosis
-Special receptor molecules on the membrane bind with the large molecule to be moved.
-When enough receptor molecules have gathered in one place, pinocytosis occurs.
-E.g. Moving cholesterol into the cell.

40. EXOCYTOSIS – Moving materials out of the cell
The reverse of endocytosis
The vesicle (from the Golgi) fuses with the membrane and releases it’s contents out of the cell.
E.g. Hormones