The Cell Membrane

1. The Cell Membrane Ms. Napolitano Honors Biology

2. 12/10 – Do Now • Please get your clickers! • Turn in your webquest if you did not hand it in last class. • Think about the following question: Why are cells small?

3. The Cell Membrane • Selectively permeable – allows some substances to cross more easily than others • 8 nm thick • Fluid mosaic model • Fluid structure of phospholipids with a mosaic of various proteins embedded in it • Cholesterol maintains fluidity – acts as a temperature buffer • less fluid as temp increases (restricts movement) • More fluid as temp decreases (maintains space)

4. The Structure of the Cell Membrane

5. Membrane Proteins • Different types of cells contain different types of membrane proteins • Integral proteins – embedded into the hydrophobic core of the lipid bilayer • Can go all the way through the membrane • Peripheral proteins – on the surface of the membrane

6. Types of Membrane Proteins • Transport • Channel/carrier proteins allow polar molecules & ions to pass through hydrophobic layer • Channel & carrier proteins are substance specific • Enzymatic • Signal Transduction (chemical messages) • Receptor proteins transmit information from outside of the cell to inside of the cell • Cell Recognition • ID tags – glycolipids or glycoproteins • Intercellular Joining • Join together adjacent cells • Cell Support • Attach to cytoskeleton or extracellular matrix for stability

7. What type of membrane protein is this? • Integral • Peripheral

8. A cell that has been frozen will have a more fluid membrane than a cell at room temperature. • True • False

9. What would happen to a cell that lacks cholesterol in the membrane? • It would not be able to transport materials into/out of the cell • The membrane would change drastically with temperature • It would not be able to use enzymes effectively • Chemical messages would not be able to get into the cell

10. What is the function of membrane carbohydrates? • Transport • Signal transduction • Cell recognition • Intercellular joining

11. Passive Transport • Passive Transport – movement across the cell membrane that does not require energy • Diffusion – movement of particles from an area of high concentration to an area of low concentration until an equilibrium is reached • Said to go with/down its concentration gradient • Concentration gradient – the difference in the concentration of a substance across a space • Equilibrium – concentration of a substance is equal throughout a space • Doesn’t stop moving

12. Osmosis • Osmosis – the diffusion of free water across a selectively permeable membrane • Water diffuses across the cell membrane from a region of low solute concentration to that of a higher solute concentration until it reaches equilibrium

13. Really cool video! http://www.youtube.com/watch?v=EsJ73x4ycp0

14. Osmoregulation in Cells without Cell Walls • Osmoregulation – control of water balance • Tonicity – ability of a solution to cause a cell to gain/lose water • Isotonic solution – no net movement of water across the cell membrane • Hypertonic solution – more free water inside the cell • Cell loses water to environment and shrivels • Hypotonic solution – less free water inside the cell • Water will enter the cell and swell (and maybe lyse) • Some cells have a contractile vacuole to pump water out of the cell

15. Animal Cells

16. Osmoregulation of Cells with Cell Walls • Plant cells are healthiest in a hypotonic solution, osmotic pressure keeps cell walls turgid (very firm) • Plant cells are flaccid (limp) in an isotonic solution • In a hypertonic solution, the cell membrane will shrink and pull away from the cell wall • Called plasmolysis(wilting)

17. Plant Cell

18. U – Tube (not YouTube!)

19. Which of the following can readily diffuse across a lipid bilayer? • Glucose • Oxygen • Carbon dioxide • Both 2 & 3

20. If you immerse a living cell in a hypotonic solution, water will… • Diffuse into the cell • Diffuse out of the cell • Show no net movement

21. Plant 1 is in better shape than plant 2 because the cells of plant 1 are… • Turgid • Flaccid • Undergoing plasmolysis • The same as plant 2 Plant 1 Plant 2

22. The image below is a U-Tube with a semi-permeable membrane. How will water flow? • It won’t • Left to right  • Right to left 

23. 12/ 16 Do Now: • Get Your Clicker! • Compare/Contrast Active & Passive Transport • Compare/Contrast Diffusion & Osmosis

24. Facilitated Diffusion • Facilitated diffusion: passive transport aided by proteins • Channel proteins – hydrophilic passageways • Some always open for diffusion • Rate of movement is determined by concentration gradient • (+) charged ions more likely to diffuse into the cell • (-) charged ions more likely to diffuse out of the cell • Some ion channels have gates and can be opened by: • Stretching of the cell membrane • Change in electrical charge • Binding of specific molecules

25. Voltage Gated Channels • Nerve cells transmit electrical signals by opening a series of Na+ gated channels • Channel is closed • Area changes voltage • Channel opens briefly • Na+ flood into cell – voltage changes • Channel closes and electrical signal passes on to the next voltage channel

26. Chemically (Ligand) Gated Channels • Nerve cells send out a neurotransmitter called acetylcholine (ACh) to nearby muscle cells to signal muscles to contract • ACh binds to ACh receptor proteins • Receptor gate opens for a microsecond to allow Na+ in • Na+ sets off muscle contraction

27. Facilitated Diffusion • Carrier Proteins • Specific substance binds to carrier protein • Protein changes shape and transports substances across cell membrane • Molecule is released into the cell, and carrier protein returns to its original shape

28. Which image best represents facilitated diffusion? • 1 • 2 • 3 • 4 3 1 2 4

29. ____are transported by a particular carrier or pass through a particular channel. • All water soluble ions or molecules • Certain water soluble molecules or ions • All insoluble molecules or ions • Certain insoluble ions or molecules • Only the smallest molecules or ions

30. Active Transport • Active Transport – uses energy to move solutes against the concentration gradient • Carrier proteins act as “pumps” powered by ATP • Examples: • Sodium Potassium Pump • Proton Pump • Cotransport

31. Sodium Potassium Pump • Pumps 3 Na+ out of the cell and 2 K+ into the cell • Actively transports both ions against their concentration gradient, powered by ATP • Prevents Na+ from accumulating in the cell • Steps: • 3 Na+ and a P (from ATP) bind to inside protein pump • Pump changes shape transporting 3 Na+ across membrane and out • 2 K+ bind to pump and are transported across membrane • 2 K+ and P are released inside of cell

32. Sodium Potassium Pump

33. The sodium-potassium pump passes • More Na+ out than K+ in • K+ out and Na+ in on a one-for-one basis • Na+ out and K+ in on a one-for-one basis • K+ and Na+ in the same direction

34. Proton Pump • Actively transports protons (H+) through the internal membranes of mitochondria and chloroplasts

35. Cotransport (Coupled Transport) • Cotransport – an ATP-powered pump that transports a specific solute • Can indirectly drive the active transport of several other solutes • Ex: as proton pumps pump H+ out, H+ diffuse back into the cell pulling sucrose molecules into the cell with it

36. By a mechanism called cotransport • sugar moves down (with) its concentration gradient while sodium moves up (against) its concentration gradient • sodium moves outward against is concentration gradient while sugar moves inward down its concentration gradient • sugar and sodium move inward down their concentration gradient • sodium moves inward down its concentration gradient while sugar moves inward up its concentration gradient • sodium and sugar move outward against their concentration gradient

37. Bulk Transport • Substances that are too large to be transported by carrier proteins • Exocytosis (export) • Secretion of macromolecules by fusion of vesicles with membranes, releasing the contents outside of the cell • Endocytosis (import) • Cell membrane engulfs particles and pinches off to form vesicles inside the cell. Vesicle may fuse with lysosomes or other organelles • 3 Types: • Phagocytosis – engulf another organism • Pinocytosis – engulf fluid • Receptor-mediated - specific

38. Exocytosis (top)/Endocytosis (bottom)

39. A cell engaged in phagocytosis must be • engulfing a live organism • acquiring a liquid • engulfing a dead organism • transporting bulk dissolved nutrients • transporting bulk solid material

40. Substances transported by facilitated diffusion • move passively through specific channels from an area of greater concentration to one of lower concentration • are limited to solvents • must have movements coupled to those of other substances • may flow to a region of higher concentration by the expenditure of energy • are restricted to only one direction through the membrane

41. A contractile vacuole is an organelle that pumps excess water out of many freshwater protozoan cells. A freshwater protozoan was placed in solution A and observed to form contractile vacuoles at a rate of 11 per minute. The same protozoan was then placed in solution B and observed to form contractile vacuoles at a rate of 4 per minute. Based on this information, which of the following statements is correct? • Solution A is hyperosmotic to solution B. • Solutions A and B are isosmotic. • Solution B is hyperosmotic to solution A. • Solutions A and B are isosmotic to the protozoan cell. • Both a and b

42. The methods of membrane transport that don't require protein channels or carriers are • osmosis • Diffusion • Phagocytosis • Exocytosis • all of the above