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Membrane Transport and the Membrane Potential www.freelivedoctor.com
Extracellular Environment <ul><li>Includes all parts of the body outside of cells </li></ul><ul><ul><li>Cells receive nour...
Body Fluids <ul><li>Two compartments </li></ul><ul><ul><li>Intracellular (~67% of body’s H 2 0) </li></ul></ul><ul><ul><li...
Extracellular matrix <ul><li>Connective tissue </li></ul><ul><ul><li>Fibers </li></ul></ul><ul><ul><ul><li>Collegen </li><...
Extracellular matrix <ul><li>Ground substance </li></ul><ul><ul><ul><li>Interstitial fluid is in the hydrated gel </li></u...
Transport across cell membrane <ul><li>Plasma (cell) membrane </li></ul><ul><ul><li>Is selectively permeable </li></ul></u...
Transport across cell membrane <ul><li>Plasma (cell) membrane </li></ul><ul><ul><li>Site of chemical reactions </li></ul><...
Transport across cell membrane <ul><li>Transport categories </li></ul><ul><ul><li>Based on structure </li></ul></ul><ul><u...
Transport across cell membrane <ul><ul><li>Based on energy requirements </li></ul></ul><ul><ul><ul><li>Passive transport <...
Diffusion and Osmosis <ul><li>Cell membrane separates ICF from ECF. </li></ul><ul><li>Cell membrane is selectively permeab...
Diffusion and Osmosis <ul><li>Energy requirements for transport through the cell membrane: </li></ul><ul><ul><li>Passive t...
Diffusion <ul><li>Physical process that occurs: </li></ul><ul><ul><li>Concentration difference  across the membrane </li><...
Diffusion Slide number: 1 www.freelivedoctor.com Solute Solvent
Diffusion Slide number: 2 www.freelivedoctor.com Solute Solvent
Diffusion Slide number: 3 www.freelivedoctor.com
Diffusion Slide number: 4 www.freelivedoctor.com
Diffusion Through Cell Membrane <ul><li>Cell membrane permeable to: </li></ul><ul><ul><li>Non-polar molecules (0 2 )  </li...
Rate of Diffusion <ul><li>Dependent upon: </li></ul><ul><ul><li>The magnitude of concentration gradient. </li></ul></ul><u...
Osmosis <ul><li>Net diffusion of H 2 0 across a selectively permeable membrane. </li></ul><ul><li>2 requirements for osmos...
Effects of Osmosis <ul><li>Movement of H 2 0 form high concentration of H 2 0 to lower concentration of H 2 0. </li></ul>w...
H 2 0 moves by osmosis into the lower H 2 0 concentration until equilibrium is reached (270 g/l glucose). www.freelivedoct...
<ul><li>The force that would have to be exerted to prevent osmosis. </li></ul><ul><li>Indicates how strongly the solution ...
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Molality and Osmolality <ul><li>Ratio of solute to H 2 0 critical to osmosis. </li></ul><ul><li>Use molality (1.0 m): </li...
<ul><li>NaCl ionized when dissolved in H 2 0 forms 1 mole of Na +  and 1 mole of Cl - , thus has a concentration of 2 Osm....
Tonicity <ul><li>The effect of a solution on the osmotic movement of H 2 0. </li></ul><ul><li>Isotonic: </li></ul><ul><ul>...
Tonicity <ul><li>Hypotonic:  </li></ul><ul><ul><li>Osmotically active solutes in a lower osmolality and osmotic pressure t...
Regulation of Plasma Osmolality <ul><li>Maintained in narrow range. </li></ul><ul><li>Reguatory Mechanisms: </li></ul><ul>...
Carrier-Mediated Transport <ul><li>Transport across cell membrane by protein carriers. </li></ul><ul><li>Characteristics o...
<ul><li>Transport maximum (Tm): </li></ul><ul><ul><li>Carriers have become saturated. </li></ul></ul><ul><li>Competition: ...
Facilitated Diffusion <ul><li>Facilitated diffusion: </li></ul><ul><li>Passive: </li></ul><ul><ul><li>ATP not needed.  Pow...
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Facilitated diffusion Slide number: 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or ...
Facilitated diffusion Slide number: 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or ...
Facilitated diffusion Slide number: 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or ...
Active Transport <ul><li>Movement of molecules and ions against their concentration gradients. </li></ul><ul><ul><li>From ...
Primary Active Transport <ul><li>ATP directly required for the function of the carriers. </li></ul><ul><li>Molecule or ion...
Na +  - K +  ATP-ase Pump <ul><li>Primary active transport. </li></ul><ul><li>Carrier protein is also an ATP enzyme that c...
P Extracellular   fluid 1. Three sodium ions (Na + ) and adenosine   triphosphate (ATP) bind to the carrier protein. 2. Th...
Extracellular   fluid Three sodium ions (Na + ) and adenosine triphosphate (ATP) bind to the carrier protein. Cytoplasm Na...
P K + ADP Na + The ATP breaks down to adenosine diphosphate (ADP) and a phosphate (P) and releases energy. www.freelivedoc...
K + Na + The carrier protein changes shape, and the Na +  are transported across the membrane. www.freelivedoctor.com Carr...
The Na +  diffuse away from the carrier protein. Na + www.freelivedoctor.com
Two potassium ions (K + ) bind to the carrier protein. K + www.freelivedoctor.com
The phosphate is released. P www.freelivedoctor.com
The carrier protein changes shape, transporting K +  across the membrane, and the K +  diffuse away from the carrier prote...
Secondary Active Transport <ul><li>Coupled transport. </li></ul><ul><li>Energy needed for uphill movement obtained from do...
Secondary  Active Transport <ul><li>Cotransport (symport): </li></ul><ul><ul><li>Molecule or ion moving in the same direct...
Membrane Transport of Glucose <ul><li>Glucose transport is an example of: </li></ul><ul><ul><li>Cotransport </li></ul></ul...
Bulk Transport <ul><li>Many large molecules are moved at the same time. </li></ul><ul><ul><li>Exocytosis </li></ul></ul><u...
<ul><li>Proteins and phosphates are negatively charged at normal cellular pH. </li></ul><ul><li>These anions attract posit...
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<ul><li>Theoretical voltage produced across the membrane if only 1 ion could diffuse through the membrane. </li></ul><ul><...
<ul><li>Potential difference of – 90 mV, if K +  were the only diffusible ion. </li></ul>www.freelivedoctor.com
Nernst Equation <ul><li>Membrane potential that would exactly balance the diffusion gradient and prevent the net movement ...
Resting Membrane Potential <ul><li>Resting membrane potential is less than E k  because some Na +  can also enter the cell...
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Membranes And Transport

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Transcript of "Membranes And Transport"

  1. 1. Membrane Transport and the Membrane Potential www.freelivedoctor.com
  2. 2. Extracellular Environment <ul><li>Includes all parts of the body outside of cells </li></ul><ul><ul><li>Cells receive nourishment </li></ul></ul><ul><ul><li>Cells release waste </li></ul></ul><ul><ul><li>Cells interact (through chemical mediators) </li></ul></ul>www.freelivedoctor.com
  3. 3. Body Fluids <ul><li>Two compartments </li></ul><ul><ul><li>Intracellular (~67% of body’s H 2 0) </li></ul></ul><ul><ul><li>Extracellular (~33% of body’s H 2 0) </li></ul></ul><ul><ul><ul><li>Blood plasma: about 20% of this </li></ul></ul></ul><ul><ul><ul><li>Tissue fluid (or interstitial fluid) </li></ul></ul></ul><ul><ul><ul><ul><li>Includes extracellular matrix </li></ul></ul></ul></ul><ul><ul><ul><li>Lymph </li></ul></ul></ul>www.freelivedoctor.com
  4. 4. Extracellular matrix <ul><li>Connective tissue </li></ul><ul><ul><li>Fibers </li></ul></ul><ul><ul><ul><li>Collegen </li></ul></ul></ul><ul><ul><ul><ul><li>about 15 kinds </li></ul></ul></ul></ul><ul><ul><ul><ul><li>In the basal lamina bind to carbo on plasma membrane </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Then binds to matrix of CT </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Proteoglycans and glycoproteins </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Binds ET to CT </li></ul></ul></ul></ul></ul><ul><ul><ul><li>Elastin </li></ul></ul></ul>www.freelivedoctor.com
  5. 5. Extracellular matrix <ul><li>Ground substance </li></ul><ul><ul><ul><li>Interstitial fluid is in the hydrated gel </li></ul></ul></ul><ul><ul><ul><li>Chemically complex </li></ul></ul></ul><ul><ul><ul><ul><li>Molecules linked to the fibers </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Carbohydrates on plasma membrane </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Glycoproteins </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Proteoglycans </li></ul></ul></ul></ul><ul><ul><ul><li>Integrins </li></ul></ul></ul><ul><ul><ul><ul><li>Kind of glycoprotein </li></ul></ul></ul></ul><ul><ul><ul><ul><li>From cytoskeleton to extracellular matrix </li></ul></ul></ul></ul><ul><ul><ul><ul><li>“ glue” cells to matrix </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Relay signals between these compartments </li></ul></ul></ul></ul>www.freelivedoctor.com
  6. 6. Transport across cell membrane <ul><li>Plasma (cell) membrane </li></ul><ul><ul><li>Is selectively permeable </li></ul></ul><ul><ul><ul><li>Generally not permeable to </li></ul></ul></ul><ul><ul><ul><ul><li>Proteins </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Nucleic acids </li></ul></ul></ul></ul><ul><ul><ul><li>Selectively permeable to </li></ul></ul></ul><ul><ul><ul><ul><li>Ions </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Nutrients </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Waste </li></ul></ul></ul></ul><ul><ul><li>It is a biological interface between the two compartments </li></ul></ul>www.freelivedoctor.com
  7. 7. Transport across cell membrane <ul><li>Plasma (cell) membrane </li></ul><ul><ul><li>Site of chemical reactions </li></ul></ul><ul><ul><ul><li>Enzymes located in it </li></ul></ul></ul><ul><ul><ul><li>Receptors: can bond to molecular signals </li></ul></ul></ul><ul><ul><ul><li>Transporter molecules </li></ul></ul></ul><ul><ul><li>Recognition factors: allow for cellular adhesion </li></ul></ul>www.freelivedoctor.com
  8. 8. Transport across cell membrane <ul><li>Transport categories </li></ul><ul><ul><li>Based on structure </li></ul></ul><ul><ul><ul><li>Carrier-mediated </li></ul></ul></ul><ul><ul><ul><ul><li>Facilitated diffusion </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Active transport </li></ul></ul></ul></ul><ul><ul><ul><li>Non-carrier mediated </li></ul></ul></ul><ul><ul><ul><ul><li>Diffusion </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Osmosis </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Bulk flow (pressure gradients) </li></ul></ul></ul></ul><ul><ul><ul><li>Vesicle mediated </li></ul></ul></ul><ul><ul><ul><ul><li>Exocytosis </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Endocytosis </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Pinocytosis </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>phagocytosis </li></ul></ul></ul></ul></ul>www.freelivedoctor.com
  9. 9. Transport across cell membrane <ul><ul><li>Based on energy requirements </li></ul></ul><ul><ul><ul><li>Passive transport </li></ul></ul></ul><ul><ul><ul><ul><li>Based on concentration gradient </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Does not use metabolic energy </li></ul></ul></ul></ul><ul><ul><ul><li>Active transport </li></ul></ul></ul><ul><ul><ul><ul><li>Against a gragient </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Uses metabolic energy </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Involves specific carriers </li></ul></ul></ul></ul>www.freelivedoctor.com
  10. 10. Diffusion and Osmosis <ul><li>Cell membrane separates ICF from ECF. </li></ul><ul><li>Cell membrane is selectively permeable. </li></ul><ul><li>Mechanisms to transport molecules and ions through the cell membrane: </li></ul><ul><ul><li>Carrier mediated transport </li></ul></ul><ul><ul><li>Non-carrier mediated transport </li></ul></ul>www.freelivedoctor.com
  11. 11. Diffusion and Osmosis <ul><li>Energy requirements for transport through the cell membrane: </li></ul><ul><ul><li>Passive transport: </li></ul></ul><ul><ul><ul><li>Net movement down a concentration gradient. </li></ul></ul></ul><ul><ul><li>Active transport: </li></ul></ul><ul><ul><ul><li>Net movement against a concentration gradient. </li></ul></ul></ul><ul><ul><ul><li>Requires energy. </li></ul></ul></ul>www.freelivedoctor.com
  12. 12. Diffusion <ul><li>Physical process that occurs: </li></ul><ul><ul><li>Concentration difference across the membrane </li></ul></ul><ul><ul><li>Membrane is permeable to the diffusing substance. </li></ul></ul><ul><li>Molecules/ions are in constant state of random motion due to their thermal energy. </li></ul><ul><ul><li>Eliminates a concentration gradient and distributes the molecules uniformly. </li></ul></ul>www.freelivedoctor.com
  13. 13. Diffusion Slide number: 1 www.freelivedoctor.com Solute Solvent
  14. 14. Diffusion Slide number: 2 www.freelivedoctor.com Solute Solvent
  15. 15. Diffusion Slide number: 3 www.freelivedoctor.com
  16. 16. Diffusion Slide number: 4 www.freelivedoctor.com
  17. 17. Diffusion Through Cell Membrane <ul><li>Cell membrane permeable to: </li></ul><ul><ul><li>Non-polar molecules (0 2 ) </li></ul></ul><ul><ul><li>Lipid soluble molecules (steroids) </li></ul></ul><ul><ul><li>Small polar covalent bonds (C0 2 ) </li></ul></ul><ul><ul><li>H 2 0 (small size, lack charge) </li></ul></ul><ul><li>Cell membrane impermeable to: </li></ul><ul><ul><li>Large polar molecules (glucose) </li></ul></ul><ul><ul><li>Charged inorganic ions (Na + ) </li></ul></ul>www.freelivedoctor.com
  18. 18. Rate of Diffusion <ul><li>Dependent upon: </li></ul><ul><ul><li>The magnitude of concentration gradient. </li></ul></ul><ul><ul><ul><li>Driving force of diffusion. </li></ul></ul></ul><ul><ul><li>Permeability of the membrane. </li></ul></ul><ul><ul><ul><li>Neuronal cell membrane 20 x more permeable to K + than Na + . </li></ul></ul></ul><ul><ul><li>Temperature. </li></ul></ul><ul><ul><ul><li>Higher temperature, faster diffusion rate. </li></ul></ul></ul><ul><ul><li>Surface area of the membrane. </li></ul></ul><ul><ul><ul><li>Microvilli increase surface area. </li></ul></ul></ul>www.freelivedoctor.com
  19. 19. Osmosis <ul><li>Net diffusion of H 2 0 across a selectively permeable membrane. </li></ul><ul><li>2 requirements for osmosis: </li></ul><ul><ul><li>Must be difference in solute concentration on the 2 sides of the membrane. </li></ul></ul><ul><ul><li>Membrane must be impermeable to the </li></ul></ul><ul><ul><li>solute. </li></ul></ul><ul><ul><li>Osmotically active solutes : solutes that cannot pass freely through the membrane. </li></ul></ul>www.freelivedoctor.com
  20. 20. Effects of Osmosis <ul><li>Movement of H 2 0 form high concentration of H 2 0 to lower concentration of H 2 0. </li></ul>www.freelivedoctor.com
  21. 21. H 2 0 moves by osmosis into the lower H 2 0 concentration until equilibrium is reached (270 g/l glucose). www.freelivedoctor.com
  22. 22. <ul><li>The force that would have to be exerted to prevent osmosis. </li></ul><ul><li>Indicates how strongly the solution “draws” H 2 0 into it by osmosis. </li></ul>www.freelivedoctor.com
  23. 23. www.freelivedoctor.com
  24. 24. Molality and Osmolality <ul><li>Ratio of solute to H 2 0 critical to osmosis. </li></ul><ul><li>Use molality (1.0 m): </li></ul><ul><ul><li>1 mole of solute is dissolved in 1 kg H 2 0. </li></ul></ul><ul><li>Osmolality (Osm): </li></ul><ul><ul><li>Total molality of a solution. </li></ul></ul><ul><li>Plasma osmolality = 300 mOsm/l. </li></ul>www.freelivedoctor.com
  25. 25. <ul><li>NaCl ionized when dissolved in H 2 0 forms 1 mole of Na + and 1 mole of Cl - , thus has a concentration of 2 Osm. </li></ul><ul><li>Glucose when dissolved in H 2 0 forms 1 mole, thus has a concentration of 1 Osm. </li></ul>www.freelivedoctor.com
  26. 26. Tonicity <ul><li>The effect of a solution on the osmotic movement of H 2 0. </li></ul><ul><li>Isotonic: </li></ul><ul><ul><li>Equal tension to plasma. </li></ul></ul><ul><ul><li>RBCs will not gain or lose H 2 0. </li></ul></ul>www.freelivedoctor.com
  27. 27. Tonicity <ul><li>Hypotonic: </li></ul><ul><ul><li>Osmotically active solutes in a lower osmolality and osmotic pressure than plasma. </li></ul></ul><ul><ul><li>RBC will hemolyse. </li></ul></ul><ul><li>Hypertonic: </li></ul><ul><ul><li>Osmotically active solutes in a higher osmolality and osmotic pressure than plasma. </li></ul></ul><ul><ul><li>RBC will crenate. </li></ul></ul>www.freelivedoctor.com
  28. 28. Regulation of Plasma Osmolality <ul><li>Maintained in narrow range. </li></ul><ul><li>Reguatory Mechanisms: </li></ul><ul><li>Osmoreceptors stimulate hypothalamus: </li></ul><ul><ul><li>ADH released. </li></ul></ul><ul><ul><li>Thirst increased. </li></ul></ul>www.freelivedoctor.com
  29. 29. Carrier-Mediated Transport <ul><li>Transport across cell membrane by protein carriers. </li></ul><ul><li>Characteristics of protein carriers: </li></ul><ul><ul><li>Specificity: </li></ul></ul><ul><ul><ul><li>Interact with specific molecule only. </li></ul></ul></ul><ul><ul><li>Competition: </li></ul></ul><ul><ul><ul><li>Molecules with similar chemical structures compete for carrier site. </li></ul></ul></ul><ul><ul><li>Saturation: </li></ul></ul><ul><ul><ul><li>Carrier sites filled. </li></ul></ul></ul>www.freelivedoctor.com
  30. 30. <ul><li>Transport maximum (Tm): </li></ul><ul><ul><li>Carriers have become saturated. </li></ul></ul><ul><li>Competition: </li></ul><ul><ul><li>Molecules X and Y compete for same carrier. </li></ul></ul>www.freelivedoctor.com
  31. 31. Facilitated Diffusion <ul><li>Facilitated diffusion: </li></ul><ul><li>Passive: </li></ul><ul><ul><li>ATP not needed. Powered by thermal energy. </li></ul></ul><ul><ul><li>Involves transport of substance through cell membrane from higher to lower concentration. </li></ul></ul>www.freelivedoctor.com
  32. 32. www.freelivedoctor.com
  33. 33. Facilitated diffusion Slide number: 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Region of lower concentration Region of higher concentration www.freelivedoctor.com Cell membrane Protein carrier molecule Transported substance
  34. 34. Facilitated diffusion Slide number: 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Region of lower concentration Region of higher concentration www.freelivedoctor.com Cell membrane Protein carrier molecule
  35. 35. Facilitated diffusion Slide number: 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Region of lower concentration Region of higher concentration www.freelivedoctor.com Protein carrier molecule Transported substance
  36. 36. Active Transport <ul><li>Movement of molecules and ions against their concentration gradients. </li></ul><ul><ul><li>From lower to higher concentrations. </li></ul></ul><ul><li>Requires ATP. </li></ul><ul><li>2 Types of Active Transport: </li></ul><ul><ul><li>Primary </li></ul></ul><ul><ul><li>Secondary </li></ul></ul>www.freelivedoctor.com
  37. 37. Primary Active Transport <ul><li>ATP directly required for the function of the carriers. </li></ul><ul><li>Molecule or ion binds to carrier site. </li></ul><ul><li>Binding stimulates phosphorylation (breakdown of ATP). </li></ul><ul><li>Conformational change moves molecule to other side of membrane. </li></ul>www.freelivedoctor.com
  38. 38. Na + - K + ATP-ase Pump <ul><li>Primary active transport. </li></ul><ul><li>Carrier protein is also an ATP enzyme that converts ATP to ADP and P i . </li></ul>www.freelivedoctor.com
  39. 39. P Extracellular fluid 1. Three sodium ions (Na + ) and adenosine triphosphate (ATP) bind to the carrier protein. 2. The ATP breaks down to adenosine diphosphate (ADP) and a phosphate (P) and releases energy. 3 . The carrier protein changes shape, and the Na + are transported across the membrane. 4 . The Na + diffuse away from the carrier protein. 5 . Two potassium ions (K + ) bind to the carrier protein. 6 . The phosphate is released. 7 . The carrier protein changes shape, transporting K + across the membrane, and the K + diffuse away from the carrier protein. The carrier protein can again bind to Na + and ATP. Cytoplasm Na + ATP K + ADP 1 3 Na + Na + K + P K + 4 5 6 7 www.freelivedoctor.com Breakdown of ATP (releases energy) Carrier protein changes shape (requires energy) 2 Carrier protein resumes original shape ATP binding site Carrier protein
  40. 40. Extracellular fluid Three sodium ions (Na + ) and adenosine triphosphate (ATP) bind to the carrier protein. Cytoplasm Na + ATP www.freelivedoctor.com ATP binding site Carrier protein
  41. 41. P K + ADP Na + The ATP breaks down to adenosine diphosphate (ADP) and a phosphate (P) and releases energy. www.freelivedoctor.com Breakdown of ATP (releases energy)
  42. 42. K + Na + The carrier protein changes shape, and the Na + are transported across the membrane. www.freelivedoctor.com Carrier protein changes shape (requires energy)
  43. 43. The Na + diffuse away from the carrier protein. Na + www.freelivedoctor.com
  44. 44. Two potassium ions (K + ) bind to the carrier protein. K + www.freelivedoctor.com
  45. 45. The phosphate is released. P www.freelivedoctor.com
  46. 46. The carrier protein changes shape, transporting K + across the membrane, and the K + diffuse away from the carrier protein. The carrier protein can again bind to Na + and ATP. K + www.freelivedoctor.com Carrier protein resumes original shape
  47. 47. Secondary Active Transport <ul><li>Coupled transport. </li></ul><ul><li>Energy needed for uphill movement obtained from downhill transport of Na + . </li></ul>www.freelivedoctor.com
  48. 48. Secondary Active Transport <ul><li>Cotransport (symport): </li></ul><ul><ul><li>Molecule or ion moving in the same direction. </li></ul></ul><ul><li>Countertransport (antiport): </li></ul><ul><ul><li>Molecule or ion is moved in the opposite direction. </li></ul></ul>www.freelivedoctor.com
  49. 49. Membrane Transport of Glucose <ul><li>Glucose transport is an example of: </li></ul><ul><ul><li>Cotransport </li></ul></ul><ul><ul><li>Primary active transport </li></ul></ul><ul><ul><li>Facilitated diffusion </li></ul></ul>www.freelivedoctor.com
  50. 50. Bulk Transport <ul><li>Many large molecules are moved at the same time. </li></ul><ul><ul><li>Exocytosis </li></ul></ul><ul><ul><li>Endocytosis </li></ul></ul>www.freelivedoctor.com
  51. 51. <ul><li>Proteins and phosphates are negatively charged at normal cellular pH. </li></ul><ul><li>These anions attract positively charged cations that can diffuse through the membrane pores. </li></ul><ul><li>Membrane more permeable to K + than Na + . </li></ul><ul><ul><li>Concentration gradients for Na + and K + . </li></ul></ul><ul><li>Na + / K + ATP pump 3 Na + out for 2 K + in. </li></ul><ul><li>All contribute to unequal charge across the membrane. </li></ul>Membrane Potential www.freelivedoctor.com
  52. 52. www.freelivedoctor.com
  53. 53. www.freelivedoctor.com
  54. 54. <ul><li>Theoretical voltage produced across the membrane if only 1 ion could diffuse through the membrane. </li></ul><ul><li>Potential difference: </li></ul><ul><li>Magnitude of difference in charge on the 2 sides of the membrane. </li></ul>Equilibrium Potentials www.freelivedoctor.com
  55. 55. <ul><li>Potential difference of – 90 mV, if K + were the only diffusible ion. </li></ul>www.freelivedoctor.com
  56. 56. Nernst Equation <ul><li>Membrane potential that would exactly balance the diffusion gradient and prevent the net movement of a particular ion. </li></ul><ul><li>Equilibrium potential for K + = - 90 mV. </li></ul><ul><li>Equilibrium potential for Na + = + 65 mV. </li></ul>www.freelivedoctor.com
  57. 57. Resting Membrane Potential <ul><li>Resting membrane potential is less than E k because some Na + can also enter the cell. </li></ul><ul><li>The slow rate of Na + efflux is accompanied by slow rate of K + influx. </li></ul><ul><li>- 65 mV </li></ul>www.freelivedoctor.com
  58. 58. www.freelivedoctor.com
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