Topic 2.4: Cell Membranes

1. Topic 2.4: Cell Membranes

2. Functions of a plasma membrane: Hold the cell together Control what go in and comes out (diffusion, osmosis, active transport) Protect the cell Allow the cell to recognize and be recognized (cell signaling and immunity) Bind to other cells and molecules A site for biochemical reactions (enzymes, areas for reactions).

3. http://www.youtube.com/watch?v=00PPPt7EJqo

4. Phospholipids form closed spheres called liposomes when mixed with water. Click to start animation

5. Move bubble model ideas from: http://www.accessexcellence.org/AE/AEC/AEF/1995/wardell_membranes.php

6. The Fluid Mosaic Model What is a fluid? What is a Mosaic? What is a model? The fluid mosaic model tells us: The structure of the membrane is flexible Adaptable In motion It is not solid, or fragile like the skin of a bubble. The phospholipids have freedom of movement in the horizontal plane: they can move around reach other, and can flow with pressure, yet they do not break.

7. The Fluid Mosaic Model What is a fluid? What is a Mosaic? What is a model? The individual phospholipids are attached to each other by: Weak attractions, the cumulative effect of which is a very strong membrane. The phospholipids have freedom of movement in the horizontal plane: they can move around reach other, and can flow with pressure, yet they do not break.

8. http://www.youtube.com/watch?v=hepoJgGJtNc Why doesn’t this egg cell rupture when the pipette drills in through the membrane?

9. What are the name and functions of these parts of the plasma membrane? Glycoproteins combine with carbohydrates to make chemical receptors. Integral proteins Enzymes - sites for chemical reactions Pumps – for active transport of molecules. Channel proteins carry molecules through the plasma membrane Peripheral proteins Act as receptors & recognize other cells Cholesterol - affects membrane fluidity at different temperatures

10. Click to start cell signaling animation http://www.youtube.com/watch?v=U6uHotlXvPo

11. Click to start animation http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP1101

12. The phospholipid bilayer is selectively permeable controlled Entry/exit of molecules • Molecular movement: • Pass through membrane easily (diffusion) • Go through a ‘tunnel’ (facilitated diffusion) • Need energy to get them though (active transport) • Large molecules use their own membrane to get them through (endo-/exco-cytosis) Polar heads - attracted to other polar (charged) molecules Non-polar tails: Repel any charged molecule. Preventing passage of ions through the membrane.

13. Solutions consist of solutes dissolved in a solvent Concentration is a measure of the amount of solute in the solution

14. Diffusion is: • The passive net movement of molecules • From regions of high concentration to low concentration. • Passive – requires no energy • Net – overall movement ( in both directions) • High to low – Down a concentration gradient • Diffusion can occur through a partially or selectively permeable membrane.

15. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/

16. Try the lab bench for Diffusion and Osmosis http://www.phschool.com/science/biology_place/labbench/index.html

17. Diffusion is… • the passive net movement of molecules from regions of high concentration to low concentration A higher concentration gradient leads to an increased rate of diffusion as molecules have more energy and move more quickly

18. Explain three factors, other than temperature that affect the rate of diffusion of a solute across a membrane Surface area Concentration gradient Length of diffusion path

19. Adaptations in biology: Maintaining a large gradient Source Keep adding molecules to the ‘high’ side of the gradient …and removing them from the ‘low’ side. Sink e.g. carrying oxygenated blood away from the lungs, carrying glucose-rich blood away from the small intestine, carrying starch-rich sap from the leaf.

20. Adaptations in biology: Maximizing surface area for absorption Alveoli in lungs Membrane folds in mitochondria and in cristae in the chloroplasts. Root hairs for water and mineral ion uptake Villi for absorption of digested food molecules.

21. Adaptations in biology: Reducing the length of diffusion path: Membrane are incredibly thin (7-10 nm) Folded membranes increase she SA:Vol ration More membrane in a smaller volume means shorter distances across which molecules must diffuse. http://www.masterfile.com/stock-photography/image/861-03336305/A-typical-mitochondrion-from-the-pancreas-showing-the-cristae-matrix-and-matrix-granules.--TEM-X45000

22. Facilitated diffusion is the passive net movement of particles from regions of high concentration to low concentration, through a selectively permeable membrane, facilitated by carrier proteins. Selectively permeable membranes, such as the plasma membrane, do not allow all molecules to pass through. It depends on the properties of the molecules. Carrier proteins (channel proteins) are integral globular proteins in the plasma membrane that allow some molecules to pass through Channel proteins are specific to the molecules. Facilitated diffusion is down a concentration gradient, therefore is passive (does not require energy).

23. Facilitated diffusion is the passive net movement of particles from regions of high concentration to low concentration, through a selectively permeable membrane, facilitated by carrier proteins. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/

24. Osmosis is the passive net movement of water molecules from regions of low solute concentration to high solute concentration through a partially selectively permeable membrane. Passive = requires no energy Net = overall movement (both back and forth) • The solute molecules cannot pass through the membrane, due to their properties. • Osmosis: • Movement down a concentration gradient • But the movement of water molecules, not the solute molecules.

25. Osmosis is the passive net movement of water molecules from regions of low solute concentration to high solute concentration through a partially selectively permeable membrane. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/

26. Can you explain why the water levels changed? More water Less water http://2six.edu.glogster.com/transport-in-living-things-iii/

27. Does this explanation help? http://www.youtube.com/watch?v=sdiJtDRJQEc

28. Explanation: Water moves by osmosis from an area of low solute concentration (more water) to high solute concentration (less water). The solute particles cannot move to balance the concentration because they are too large to fit through the pores of the selectively permeable membrane. http://2six.edu.glogster.com/transport-in-living-things-iii/

29. Compare diffusion and osmosis Similar: Both are passive Both are down a concentration gradient Osmosis – only water molecules Different: Diffusion is of solutes Partially-permeable membrane essential. Membrane not needed

30. Try out this fun tutorial on Diffusion and Osmosis!! http://education.uoit.ca/lordec/ID_LORDEC/diffusion_osmosis/garib_diffusion_osmosis.swf

31. Analyze the information in this graph Explain the significance of the point labeled in red Explain the blue line Deduce the experimental method used to generate this graph. Discuss how the dependent variable was recorded and calculated. How would the researcher ensure that data were sufficient, relevant, and reliable. Discuss the variables that needed to be controlled in the investigation. What could be the impact of each of them? How could they be controlled?

32. Osmosis: finding the concentration of salt in potato cells

33. Active transport uses energy, in the form of ATP, to move molecules against a concentration gradient, using membrane protein pumps. • The molecules cannot pass though the membrane, due to their properties. • Active transport is key in homeostasis in organisms: • Re-setting nerves after impulses have passed though • Absorbing glucoses in the gut.

34. Try out this fun tutorial on Membrane Transport!! http://programs.northlandcollege.edu/biology/Biology1111/animations/active1.swf

35. Active transport continued… • Protein pumps: • Specific to their molecules. • The molecules binds to the active site of the pump. • The release of energy from ATP results in a conformational change in the shape of the protein pump http://plantcellbiology.masters.grkraj.org/html/Plant_Cellular_Physiology4-Absorption_Of_Mineral_Nutrients.htm

36. http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio03.swf::Sodium-Potassium%20Exchange%20Pumphttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio03.swf::Sodium-Potassium%20Exchange%20Pump

37. ATP – Adenosine Tri-Phosphate Hydrolysis – of the bond releases one phosphate and a lot of energy. water To break

38. Exocytosis Vs. Endocytosis Exo – Exit Cytosis – cell Sis - Process Endo – Enter Cytosis – cell Sis - process • Exocytosis : • The export of macromolecules from the cell. • Endocytosis: • The import of macromolecules. • Phagocytosis: • The ingestion of solid molecules. • Pinocytosis: • The ingestion of liquids and solutes. http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio02.swf::Endocytosis%20and%20Exocytosis

39. Vesicle transport: Exocytosis of protein molecules using Golgi apparatus http://www.uic.edu/classes/bios/bios100/lectures/cells.htm

40. http://www.youtube.com/watch?v=bD4z27ASN1M

41. Vesicle transport resources: http://learn.genetics.utah.edu/content/begin/cells/vesicles/ • Vesicles transport macromolecules (those which are too large for diffusion or protein channels) and newly formed molecules such as proteins. • Vesicle formed from phospholipid bilayer • Protects the contents as they travel through the cytoplasm. • When the vesicle reaches the cell membrane it fuses with the membrane and release its contents. Try the link to see some videos on how vesicles move in a cell. budding vesicle fusing Contents released