CELL MEMBRANE & CELL TRANSPORT

1. CELL MEMBRANE &CELL TRANSPORT

2. Homeostasis:Maintaining a Balance Organisms must adjust to changes in their environment. If not…DEATH! A formal definition is—maintaining a stable internal state despite what is going on externally.

3. What Maintains Homeostasis? The PLASMA or CELL MEMBRANE maintains the proper concentrations of materials by controlling the passage of molecules in and out of the cell. Therefore, the cell membrane’s function is to maintain HOMEOSTASIS through passive transport, active transport and cell communication!

4. This electron micrograph of the cell membrane shows the appearance of the phospholipid bilayer using several staining processes. The magnification on this structure is 53,260 X Cell Membrane X 53, 260

5. Characteristics of the Cell Membrane

6. The cell membrane is Selectively Permeableaka Semi-permeable Allows some things in/out and not others… • Oxygen, nitrogen,carbon dioxide, and other small, nonpolar molecules can diffuse directly • Water was once thought to move directly through, but it is now understood to travel through aquaporins (a type of transport protein). • Ions, sugars, and larger molecules move through transport proteins or in vesicles.

7. Plasma/Cell Membrane-Structure Phospholipid Bilayer with proteins embedded/floating in it Phospholipid Structure: • Polar Head (hydrophilic—”water loving”) • Nonpolar Tails—(hydrophobic—”water fearing”)

8. Phospholipid Polar Head Nonpolar Tails Bilayer Arrangement Outside of cell Inside cell

9. Proteins are embedded/floating in the lipid bilayer.

10. Protein in membrane

11. Cell Membrane Structure-Proteins These proteins are needed for the membrane to function properly. 3 Types of Membrane Proteins 1. Transport—regulate what enters or leaves cell 2. Marker—identify the cell 3. Receptor—allow cells to communicate

12. Transport Proteins—Channel Proteins Transport Protein Channel Protein • Function as “gates/passageways” • Allow polar sugars, amino acids, and ions to cross the membrane. • Special channel proteins: • Gated ion channels—gates that open/close • Carrier proteins—change shape to allow specific molecule to pass • Aquaporins—allow water to diffuse through (called osmosis) Carrier Protein http://personal.tmlp.com/Jimr57/textbook/chapter3/cms2.htm

13. Marker Proteins • Cell’s “Name Tag” • Protein sticks out of phospholipid layer • Often has carbohydrates attached to outside end • Functions in cell identification to identify the cell to other cells and molecules • Important in • immunity—so various white blood cells in your body do not mistake your cells for foreign cells - blood typing – so you can’t receive just any ol’type of blood http://personal.tmlp.com/Jimr57/textbook/chapter3/cms2.htm Marker Protein

14. Receptor Proteins • Function as “messenger/receiver” • Receive information from the environment (extracellular fluid, blood, interstitial fluid) and transmit that info to the inside of the cell • Protein has specific shape/charge to only allow certain molecules (like hormones) to bond • Triggers a response in cell • Ex) epinephrine can bind to a receptor protein and send a message inside that says “break down glycogen” http://personal.tmlp.com/Jimr57/textbook/chapter3/cms2.htm Receptor Protein

15. CELL TRANSPORT • Concentration gradient - the difference the concentration of a particular substance across a space. . • Equilibrium is reached when the molecules become even throughout a space.

16. Cell Transport Types • Passive Transport—no energy required, molecules move from high to low concentration (down or with concentration gradient) • Diffusion • Osmosis • Facilitated Diffusion • Active Transport—energy (ATP) required, molecules move from low to high concentration (up or against the concentration gradient) • Pumps • Vesicles

17. Passive Transport Diffusion, Osmosis, Facilitated Diffusion

18. Diffusion • Diffusion - the process by which molecules spread from areas of high concentration, to areas of low concentration • Molecules are said to go “Down” or “with” the concentration gradient. • Passive Transport-requires no energy

19. Osmosis • Osmosis - the diffusion of water molecules through a semi-permeable membrane requires no energy Ex. Water will move in the direction where there is a higher concentration of solute (and hence a lower concentration of water).

20. About this diagram: this represents a cell in a solution. The cell will not let the red particles pass through the membrane. The green molecules can pass through, as can water molecules. The arrows show the direction of particle movement. The green particles are moving in to the cell where their concentration is lower, and water is moving out of the cell because its concentration is higher inside diffusion osmosis

22. Isotonic Solution • Concentration of solute and solvent outside the cell is equal to/the same as the solution you are comparing it to (often the cytoplasm in cell) • Water is moving in and out at equal rates, no net movement into or out of cell since • Cell size would stay the same

23. Red blood cells in isotonic solution X 1000 Note that all the cells appear normal.

24. Hypertonic Solution • There are more solute (ex. salt) molecules in solution outside the cell when compared to the inside of cell • Water will move out of the cell • Cell would shrink • Plants cells shrink (plasmolysis) because cell membrane pulls away from cell wall, so plant wilts because water has left the central vacuole. Animal cell shrink (crenate). In both cases, the cell may die.

25. Crenated red blood cells in hypertonic salt solution X 1000 Notice that the cells have shrunk.

26. Hypotonic Solution • There are less solute (ex. salt) molecules in the solution outside the cell than inside the cell. • Water will move into the cell. • Cell will swell • Cell could burst (lyse) • Plant cells have vacuoles to collect extra water

27. Red blood cells in hypotonic solution X 1000 Note that the pinkish cells have swollen (the little dip in the middle of a normal rbc is not visible and one side bows out).

28. Osmosis Links Osmosis Examples http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm Hypotonic, Hypertonic, Isotonic Interactive Quiz http://www2.nl.edu/jste/osmosis.htm#Osmosis

29. Facilitated Diffusion (uses Transport Proteins, passive) • Moves substances (from high to low concentration) down the concentration gradient without using cell’s energy using channel/carrier proteins located in membrane

30. Active Transport in Cells

31. Why do cells need active transport? • Cells must transport certain amino acids, sugars, etc. into their cytoplasm from the surrounding fluid. • Some of these substances, however, are already in higher concentrations inside versus outside.

32. How does active transport work? • Some types involve carrier proteins that function as “pumps”. • Other types use vesicles. • Energy is provided by ATP.

33. Active Transport Using Pumps Sodium-Potassium Pump Proton Pumps

34. Example of active transport types using pumps • Sodium/Potassium Pump • Na+ pumped out of a cell • K+ pumped into a cell • Important because it prevents cells from bursting by lowering the sodium inside causing less water to enter through osmosis. • Used by many cells, including nerve cells, to send a chemo-electric message.

35. Sodium-Potassium Pump Sodium/Potassium pump: 3 Na+ out of cell (yellow diamonds) 2 K + into cell (red/purple squares) Here the energy of a phosphate from ATP (shown in pink) is used to exchange sodium atoms for potassium atoms.

37. Proton Pump Proton (H+) pump – forces protons out of a membrane enclosed space (organelle or cell), often to create a proton gradient down which the protons can flow back in Why would the cell “waste” energy on a proton pump? *Because the cell needs isolated areas of the cell with different pH for particular functions; ex) lysosomes – have proton pumps to maintain a pH=5 *Because the cell only uses one ATP to pump a proton out, and that proton can be used in co-transport Co-transport – process cells use to bring large molecules, such as sugars, into a cell with a minimum amount of energy used; usually a proton and a sugar enter a double tunneled protein at the same time; the tunnel only “works” when both molecules are present

38. Active Transport Using Vesicles Endocytosis & Exocytosis

39. Endocytosis Substances are moved into a cell by a vesicle that pinches off from the cell membrane Requires energy (ATP)

40. Types of Endocytosis • Pinocytosis—when the nutrient particles are dissolved in a liquid; “cellular drinking” • Phagocytosis—when the nutrient particles are solids; “cellular eating”

41. Exocytosis Exocytosis- substances inside a vesicle are released from a cell as the vesicle fuses with the cell membrane Involves the cell getting rid of waste or the cell secreting cell products (ex. Hormones, insulin) • Requires Energy (ATP)

43. Animations—Exocytosis, Endocytosis Exocytosis using ER and Golgi: http://www.wisc-online.com/objects/index_tj.asp?objid=AP11203 McGraw-Hill: Cotransport, Na-K pump, Endo/Exocytosis, & Proton Pump http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter6/animations.html#

44. Cell Membrane Physiology--Interactive http://www.getbodysmart.com/ap/nervoussystem/neurophysiology/membranephys/menu/menu.html