Chapter 4.2: Transport across the CSM

1. Chapter 4.2: Transport across the CSM INB Pg33

2. CSM transport • Phospholipid bilayer creates effective barrier against water soluble molecules and ions • Prevents aqueous contents from escaping • Some essential transport is achieved through diffusion, facilitated diffusion, osmosis, active transport and bulk transport

3. Diffusion • Diffusion: net movement, as a result of random motion of its molecules or ions, of a substance from a region of high concentration to a region of low concentration • Particles move down a concentration gradient

4. Rates of Diffusion • ‘steepness’ of concentration gradient: greater difference = higher rate • Temperature: higher temperature = higher rate • Surface area of diffusion: greater surface area – higher rate • Nature of molecules/ions: small molecules = greater rate

5. Diffusion • Respiratory gases cross membrane by diffusion (uncharged and nonpolar) • Water (even though it is polar) can cross because molecules are very small

6. Facilitated diffusion • Diffusion that takes place with the help of a certain protein molecule • Channel proteins • Carrier proteins

7. Channel proteins • Water-filled pores • Fixed shape • Allow charged substances (usually ions) to diffuse through membrane • Gated to allow for selectivity and control of movement

8. Carrier proteins • Flips between shapes to alternately open binding sites on interior/exterior of membrane • Direction of movement depends on concentration gradient inside and outside of cell

10. Osmosis • Type of diffusion involving water molecules only

11. Water potential • Water potential: tendency of water molecules to move from one place to another • Measured by Greek symbol psi Ψ

12. Water potential • Water potential for pure water is 0 • Solutes make water potential less than 0, the more solute, the more negative the water potential • The amount that solutes lower the water potential is called solute potential

13. Pressure potential • Increasing pressure increases water potential • The contribution made by pressure to water potential is called pressure potential and is given by symbol Ψp • Pressure potential makes water potential less negative (more positive)

14. Water potential in animal cells

15. Osmosis in plant cells

16. Do Now 1/14/14 • IDOLATRY(aiDOLL ah tree) n. • blind or excessive devotion to something • Ben’s parents worried about his IDOLATRY to the occult. • Elvis’ IDOLATROUS fans stormed Graceland. • Peter has an IDOLATROUS addiction for the game of golf. • Warm up: Draw a membrane and label what will keep out ions + increase membrane fluidity, what will control rigidity and help keep out polar molecules, what allows for cell recognition and what allows polar molecules to enter.

17. Active Transport • Active transport moves molecules/ions against concentration gradient • Achieved by carrier proteins (specific for structure of particular ion/molecule) • Requires ATP for energy, supplied by cellular respiration • Can occur into or out of the cell

18. Sodium-potassium pump • Found in CSM of all animal cells • Use ~30% avg cell energy and ~70% neuron cell energy • Pump 3 Na+ ions out of the cell and 2 K+ ions into the cell • Net result: inside of cell become more negative than the outside

19. Sodium-potassium pump • Difference in charges between inside membrane and outside creates a potential difference (p.d.) which allows nerve cells to propagate a signal

20. Active transport • Important in re-absorption in the kidneys, where certain useful molecules and ions have to be re-absorbed into the blood after filtration into the kidney tubules • Involved in absorption of products of digestion in the gut

21. Active transport • Used to load sugar from photosynthesizing cells of leaves into phloem tissue for transport around the plant

22. Active transport • http://www.youtube.com/watch?v=Kd3LorZcJew&feature=related

23. Bulk transport • Bulk transport involves the mechanism of moving large quantities of molecules into the cell (endocytosis) or out of the cell (exocytosis) • Large molecules such as proteins or polysaccharides, part of cells, or even whole cells may be transported across the membrane

24. Endocytosis • Involves the engulfing of material by the CSM to form a small sac, or endocytic vacuole • Two forms: phagocytosis and pinocytosis

25. phagocytosis • ‘cell eating’ • Bulk up take of solid material • Cells specializing in this are called phagocytes and the vacuoles are called phagocytic vacuoles • Ex: engulfing of bacteria by immune cells

26. endocytosis • http://www.youtube.com/watch?feature=fvwp&NR=1&v=a4aZE5FQ284 • http://www.youtube.com/watch?v=JnlULOjUhSQ

27. Pinocytosis • ‘cell drinking’ – bulk uptake of liquid into cell • Vacuoles ( vesicles) formed are often extremely small, in which the process is called micro-pinocytosis • Human egg cells take up nutrients from cells that surround it by pinocytosis • http://www.youtube.com/watch?v=InG6xF9D4EM

28. exocytosis • Process by which bulk material is removed from a cell • Ex: how plants transport materials out of CSM to make cell wall • Ex: secretion of digestive enzymes of the pancreas • Secretory vesicle from the Golgi carry the enzymes to the CSM and release their contents

29. Bulk transport • http://www.youtube.com/watch?v=aWItglvTiLc&feature=related • http://www.youtube.com/watch?v=pvOz4V699gk&feature=fvwrel

30. Homework • Pg 81 #5,6,7 (ING Pg 34)