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Chapter 4(5 Transport)


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Transport across membrane

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Chapter 4(5 Transport)

  1. 1. CELL STRUCTURE AND FUNCTION Dr Meera Narasimha, ICFAI University, Hyderabad CHAPTER- 4
  2. 2. II. Out Line: <ul><li>Getting through Membranes </li></ul><ul><li>Cell Size </li></ul><ul><li>Goals and Objectives: </li></ul><ul><li>Know the Molecular Structure of a Cell Membrane related to its Function . </li></ul>
  3. 3. GETTING THROUGH MEMBRANES <ul><li>Cell : Nutrients and Wastes. </li></ul><ul><li>PASSIVE TRANSPORT </li></ul><ul><li>DIFFUSION </li></ul><ul><li>DIALYSIS </li></ul><ul><li>OSMOSIS </li></ul><ul><li>FACILITATED DIFFUSION </li></ul><ul><li>ACTIVE TRANSPORT </li></ul>
  4. 4. Fluidity <ul><li>Bilayer </li></ul><ul><ul><li>Hydrophobic tails of each layer associate with each other. </li></ul></ul><ul><ul><li>Hydrophilic heads on the surface of the bilayer </li></ul></ul><ul><ul><li>Membranes are in motion with fast drifting lipids and slower drifting proteins </li></ul></ul>
  5. 5. <ul><li>Membrane fluidity may be influenced by: Presence/absence of Unsaturated Fatty Acid chains and Cholesterol </li></ul><ul><li>Fluidity of membranes is important for proper function </li></ul>
  6. 6. Fluidity Influences Permeability: <ul><li>Permeability : Movement of materials across a membrane </li></ul><ul><li>The hydrophobic portion of the bilayer: Selectively permeable </li></ul>
  7. 7. Cell Membrane is semi permeable <ul><li>Movement of Molecules across the membrane depends </li></ul><ul><li>on : i. Size </li></ul><ul><li>ii. Electric Charge </li></ul><ul><li>iii. Solubility </li></ul><ul><li>Membrane does not influence the direction of </li></ul><ul><li>movement . </li></ul><ul><li>Direction of Movement Molecules depends on </li></ul><ul><li>relative concentration of specific molecules on </li></ul><ul><li>the two sides of the membrane. </li></ul>
  8. 8. Cell recognize signal and respond to Signal <ul><li>Molecules are in constant , random motion . </li></ul><ul><li>NET Movement = Movement in one direction </li></ul><ul><li>– Movement of molecules in opposite direction. </li></ul><ul><li>Relative Concentration : Direction of </li></ul><ul><li>of Molecules determines Molecular movement. </li></ul>
  9. 9. Concentration Gradient <ul><ul><li>Involves a concentration gradient (diffusion </li></ul></ul><ul><ul><li>gradient) </li></ul></ul><ul><li>Difference in concentration of molecules over a distance . </li></ul>
  10. 10. DIFFUSION <ul><li>Molecules move from where they are most concentrated to where they are less concentrated. This is called diffusion. </li></ul><ul><li>DIFFUSION: Net Movement of a kind of </li></ul><ul><ul><li>Molecules from a place where that molecule is </li></ul></ul><ul><ul><li>in concentration to a place the molecule is </li></ul></ul><ul><ul><li>scarce . </li></ul></ul><ul><li>Uneven distribution of Molecules  Diffusion </li></ul>
  11. 11. Direction of Diffusion: <ul><li>Determined solely by the concentration gradient . </li></ul><ul><li>Diffusion is passive that does not require energy input. </li></ul><ul><li>Example: </li></ul><ul><ul><li>Oxygen diffusion </li></ul></ul>
  12. 12. DIFFUSION :
  13. 13. Passive Transport Mechanism : <ul><li>Simple Diffusion : The movement of a substance from higher concentration to lesser concentration </li></ul><ul><li>Occurs across the lipid bilayer </li></ul><ul><li>The bilayer is selectively permeable </li></ul>
  14. 14. No Conc. Gradient=Dynamic Equilibrium ( Movement of molecules is equal in all directions). <ul><li>Rate of Diffusion: Kinetic Energy & Size. </li></ul><ul><li>Free movement of Molecules. </li></ul><ul><li>Movement is random, cell has little control and is </li></ul><ul><li>passive. Example: Oxygen in cell. </li></ul><ul><li>Oxygen concentration in cell is low and CO 2 is </li></ul><ul><li>high and reverse in outside of the cell. </li></ul><ul><li>Circulatory System: Oxygen  Lungs  Into blood  </li></ul><ul><li>Oxygen rich Blood  Transports to body  Oxygen </li></ul><ul><li>diffuses into cells. </li></ul>
  15. 15. Selectively permeability of Membrane: <ul><li>Selectively permeability : Membrane will allow </li></ul><ul><li>certain molecules to pass across it and </li></ul><ul><li>prevent others from passing across it. </li></ul><ul><li>Selective Permeability depends : </li></ul><ul><li>Solubility: Vitamin A & D </li></ul><ul><li>Molecular Size: Water </li></ul><ul><li>Ions: </li></ul>
  16. 16. DIALYSIS : <ul><li>Dialysis: Net movement (Diffusion) of a </li></ul><ul><li>solute through a selectively permeable </li></ul><ul><li>membrane . </li></ul><ul><li>Kidney malfunction : Blood of patient is </li></ul><ul><li>diverted to a series of tubes composed of </li></ul><ul><li>selectively permeable membranes, toxins of </li></ul><ul><li>blood diffuse into surrounding fluids and </li></ul><ul><li>blood returns to patient. </li></ul>
  17. 17. Osmosis : <ul><li>Osmosis : the diffusion of water (solvent) across a membrane </li></ul><ul><ul><li>influenced by total solute concentration </li></ul></ul><ul><li>Water always moves toward the side with a greater concentration of solute </li></ul>
  18. 18. Osmosis
  19. 19. <ul><li>Diffusion of water through a selectively-permeable membrane. </li></ul><ul><li>Occurs when there is a difference in water concentration on opposite sides of the membrane. </li></ul><ul><li>Water will move to the side where there is less water </li></ul><ul><ul><li>Or more solute </li></ul></ul>
  20. 20. Osmotic Pressure: Pressure exerted on a membrane due to an imbalance of solute between the inside and outside of the membrane
  21. 21. Osmosis: Net movement (Diffusion) of Water through a selectively permeable membrane. <ul><li>Example: A solution of 10% Sucrose (90% water and </li></ul><ul><li>10% sugar) separated by a selectively permeable </li></ul><ul><li>membrane from a solution of 20% Sucrose (80% </li></ul><ul><li>water and 20% sugar). </li></ul><ul><li>The membrane allows water molecules to pass </li></ul><ul><li>freely but prevents sucrose from crossing. </li></ul><ul><li>Water from 10% sucrose solution diffuse to solution </li></ul><ul><li>with 20% sucrose. </li></ul><ul><li>In Osmosis, Water is diffusing substance </li></ul><ul><li>The semi permeable membrane is permits water to pass through than sucrose . </li></ul>
  22. 22. Water: <ul><li>Water is a medium required by all living cells to </li></ul><ul><li>function efficiently. </li></ul><ul><li>Cell has to balance with an environment: </li></ul><ul><li>Too little water in cell buildup of poisonous </li></ul><ul><li>substances and too much water in cell may </li></ul><ul><li>dilute cell contents. </li></ul>
  23. 23. Hypertonic vs. Hypotonic <ul><li>If a cell has less water (more solute) than its environment </li></ul><ul><ul><li>It is hypertonic to its surroundings. </li></ul></ul><ul><li>If a cell has more water (less solute) than its environment </li></ul><ul><ul><li>It is hypotonic to its surroundings. </li></ul></ul><ul><li>If a cell has equal amounts of water (and solute) as its environment </li></ul><ul><ul><li>It is isotonic to its surroundings. </li></ul></ul>
  24. 24. Physiological relevance of Osmosis
  25. 25. Isotonic Hypertonic Hypotonic
  26. 26. Tonicity : The ability of a solution to move water <ul><ul><li>Hypertonic: Greater ability to move H 2 O; gains water </li></ul></ul><ul><ul><li>Hypotonic: Lesser ability to move H 2 O; loses water </li></ul></ul><ul><ul><li>Isotonic: equal ability to move H 2 O; no net water movement </li></ul></ul>
  27. 27. DRINKING WATER <ul><li>When we drink small amounts of water, brain cells swell a little and send signals to kidneys to remove water. </li></ul><ul><li>Drinking large amounts of water in a very short time causes the brain to swell , and because the water cannot be removed quickly enough, the person may lose consciousness or even die because the brain cells swell too much. </li></ul>
  28. 28. Osmosis in Animal and Plant Cells
  29. 29. Transport of Molecules: Controlled Methods <ul><li>Molecules required by cell: </li></ul><ul><li>1. If Cannot pass through the membrane </li></ul><ul><li>2. If Occur in low concentration </li></ul><ul><li>A. Facilitated Diffusion </li></ul><ul><li>B. Active Transport </li></ul>
  30. 30. A. Facilitated Diffusion <ul><li>Facilitated Diffusion: Transport of materials </li></ul><ul><li>across membranes is helped (facilitated) by a </li></ul><ul><li>particular membrane protein. </li></ul><ul><li>Example: Movement of Glucose across the </li></ul><ul><li>membranes of certain cells. </li></ul>
  31. 31. Facilitated diffusion <ul><li>Some molecules have to be carried across the membrane. </li></ul><ul><ul><li>Accomplished by carrier proteins </li></ul></ul><ul><li>Still involves diffusion </li></ul><ul><ul><li>Follows a concentration gradient </li></ul></ul><ul><ul><li>Is passive transport </li></ul></ul><ul><ul><li>Example (glucose) </li></ul></ul>
  32. 32. B. Active Transport <ul><li>Molecules move across the membrane from low to high concentration , cell spends energy. </li></ul><ul><li>Active process is very specific . </li></ul><ul><li>Only certain molecules move. </li></ul><ul><li>They must be carried by Specific Carrier Proteins . </li></ul><ul><li>Example: Na & K ions. </li></ul>
  33. 33. Active transport <ul><li>Opposite of diffusion </li></ul><ul><li>Moves molecules across a membrane up their concentration gradient </li></ul><ul><li>Uses transport proteins in the membrane </li></ul><ul><ul><li>Specific proteins pump specific molecules </li></ul></ul><ul><li>Requires the input of energy </li></ul><ul><li>Example (Na and K ion,) </li></ul>
  34. 34. Kinds of Pumps <ul><li>Na + /K + </li></ul><ul><li>H + </li></ul><ul><li>Ca 2+ </li></ul>Some pumps create electrical differences across a membrane ( electrogenic pumps )
  35. 35. Exocytosis and Endocytosis <ul><li>Exocytosis : Transport of materials out of cell . </li></ul><ul><li>Exocytosis involve the movement of macromolecule out of the cell by the fusion of membrane bound vesicles to the plasma membrane </li></ul><ul><li>Endocytosis : Transport of materials into cell . </li></ul><ul><li>Endocytosis involves the movement of macromolecule into the cell by the pinching of the plasma membrane into membrane bound vesicles </li></ul><ul><ul><li>Phagocytosis - Pinocytosis </li></ul></ul>
  36. 36. Endocytosis & Exocytosis:
  37. 37. Endocytosis : <ul><li>Phagocytosis : ingestion of large particle </li></ul><ul><li>Pinocytosis : ingestion of small mixed solutes </li></ul><ul><li>Receptor-mediated pinocytosis : ingestion of specific solutes (ligands) with the aid of binding proteins areas called coated pits </li></ul>
  38. 38. Phagocytosis : A kind of endocytosis is a process cells use to wrap membrane around a particle and engulf it. <ul><li>Example: Leukocyte-Virus, Bacteria, Food & Foreign Material </li></ul><ul><li>In phagocytosis, material to be engulfed touches the surface of the Phagocyte and causes a portion of the outer cell membrane indented. </li></ul><ul><li>The indented cell membrane is pinched off inside the cell </li></ul><ul><li>to form a sac containing the engulfed material. </li></ul><ul><li>The phagosome ( phago = to eat; some =body) is composed of </li></ul><ul><li>single membrane, may brake down or combine with another </li></ul><ul><li>vacuole containing destructive enzymes. </li></ul>
  39. 39. Endocytosis and Exocytosis
  40. 40. Traffic Across Membranes
  41. 41. Signal Transduction: <ul><li>Cells detect specific signals and they transmit </li></ul><ul><li>these signals to the cell interior. </li></ul><ul><li>Signals can be: Physical or Chemical </li></ul><ul><li>Certain chemicals can pass through cell. </li></ul><ul><li>Estrogen , make direct contact with target </li></ul><ul><li>cells. </li></ul>
  42. 42. Signal Transduction : <ul><li>Most signal molecules cannot enter into cell. </li></ul><ul><li>These primary messengers remain outside their target cells. </li></ul><ul><li>Signal / Ligand molecules attach to a receptor </li></ul><ul><li>molecule on membrane and </li></ul><ul><li>this receptor/ligand initiates a sequence of events </li></ul><ul><li>within membrane that </li></ul><ul><li>transmits information through the membrane to the </li></ul><ul><li>interior, generating second messengers. </li></ul><ul><li>. </li></ul>
  43. 43. Signal Transduction: <ul><li>A cascade of chemical reactions that enables </li></ul><ul><li>the target cell to respond to the stimulus by </li></ul><ul><li>making a change in how the cell functions </li></ul><ul><li>Example: Epidermal Growth Factor attaches to </li></ul><ul><li>tyrosine Kinase Receptor </li></ul><ul><li>and triggers a chain of events inside membrane. </li></ul><ul><li>They stimulate a chemical reaction that ultimately </li></ul><ul><li>leads to gene action, </li></ul><ul><li>which in turn causes cell growth and division. </li></ul>
  44. 44. Cell Size : <ul><li>Cells vary greatly in size. </li></ul><ul><li>Size related to level of activity and rate of molecules move </li></ul><ul><li>across its membranes. </li></ul><ul><li>Cell have a constant supply of nutrients, oxygen and other </li></ul><ul><li>molecules. </li></ul><ul><li>Cell has to give out carbon di oxide and other waste products that harmful to it. </li></ul><ul><li>Most cells are small with few exceptions and easy to satisfy the cell needs . </li></ul><ul><li>Example: Egg cell –Yolk of egg is large cell and central portion is inactive stored food is yolk while white surrounds actual cell. </li></ul>
  45. 45. Cell Size <ul><li>Prokaryotic </li></ul><ul><li>cells </li></ul><ul><li>1-2 µm in </li></ul><ul><li>diameter </li></ul><ul><li>Eukaryotic </li></ul><ul><li>Cells </li></ul><ul><li>10-200 µm </li></ul><ul><li>in diameter </li></ul>
  46. 46. Surface Area to Volume Ratio: <ul><li>Cell grows amount of Surface Area increases </li></ul><ul><li>by the Square (X 2 ) but Volume increases by </li></ul><ul><li>the Cube (X 3 ). </li></ul><ul><li>Surface Area increases at a slower rate than </li></ul><ul><li>Volume. </li></ul><ul><li>The Surface Area to Volume Ratio changes </li></ul><ul><li>as cell grows. </li></ul>
  47. 47. Surface area to Volume Ratio <ul><li>Cell size is limited. </li></ul><ul><ul><li>Cells must get all of their nutrients from their environment through their cell membranes . </li></ul></ul><ul><ul><li>Volume increases more quickly than surface area. </li></ul></ul><ul><ul><li>Surface area-to-volume ratio must remain small (because metabolic and nutrition requirements). </li></ul></ul>
  48. 48. Cell Size <ul><li>Limits on cell size determined by ability to perform metabolic processes </li></ul><ul><ul><li>Lower: can all necessary components fit </li></ul></ul><ul><ul><li>Upper: can we regulate supplies adequately (surface to volume ratio) </li></ul></ul>
  49. 49. Acknowledgements <ul><li>I duly acknowledge book “Concepts in Biology by Enger, Ross and Baily, TataMcgrawhill publishers. </li></ul>