Plasma/Cell Membrane

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General overview of Plasma/ Cell membrane.
Definition of Plasma/ Cell membrane
Structure of Plasma membrane
1. Sandwitch model OR Danielli- Davson Model
2. Fluid mosaic model
Plasma Membrane Proteins
Chemical Composition of Plasma/ Cell Membrane
Movement across the Cell Membrane
Channels through cell membrane

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Plasma/Cell Membrane

  1. 1. GUL MUNEER S/O ABDUL RAZZAQUE BIOCHEMIST RY BS PART II UNIVERSITY OF SINDH 2K10/BCH/2 3 PROUD TO BE BIOCHEMIST WE EXPLORE THE SECRETS OF LIFE 1
  2. 2. PLASMA MEMBRANE By GUL MUNEER 2
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  5. 5. What is plasma membrane? Outermost layer (animal)  Thickness is 5-8 nm  Selectively permeable  Serve as outer boundary  Allows some substances to cross more easily than others  Made of Phospholipids, proteins & conjugated molecules  Separate and protect cell from external environment  Provide connecting system b/w cell & its environment  Also called cell membrane  5
  6. 6. How could you define plasma membrane? An outermost envelope surrounding the cell that separates and protects the cell from the external environment and provides a connecting system B/w the cell and its environment is called plasma membrane. 6
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  8. 8. Structure of the Plasma Membrane The plasma membrane is composed of two layers of phospholipids back-to-back. Phospholipids are lipids with a phosphate attached to them. 8
  9. 9. Phospholipids  Phosphate Fatty acid tails  hydrophobic  Phosphate group head  hydrophilic  Fatty acid Arranged as a bilayer Phospholipids, glycolipids, cholesterol are amphipathic lipids containing hydrophobic and 9 hydrophillic ends
  10. 10. Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads 10
  11. 11. Sandwitch model OR Danielli- Davson Model Proposed by Davson and Danielle in 1935 “Cell membrane is lipid bilayer sandwitched B/w two monomolecular protein layers” 11
  12. 12. Fluid mosaic model In 1972, S.J. Singer & G. Nicolson proposed Fluid mosaic model. 12
  13. 13. What is Fluid mosaic model? “Cell membrane is lipid bilayer in which proteins are partially embeded like Floating iceburgs in sea” The fluid mosaic model describes the plasma membrane as a flexible boundary of a cell. The phospholipids move within the membrane. 13
  14. 14. OVERVIEW Lipid molecules are present in a fluid state capable of rotating and moving. The proteins occur as a „mosaic‟ of discontinuous particles that penetrate deeply into and even through the lipid sheet. Globular proteins are irregularly embedded in the lipid bilayer. 14
  15. 15. Membrane proteins Membrane proteins are categorized into two groups: 1- Extrinsic (peripheral) membrane proteins 2- Intrinsic (integral) membrane proteins 15
  16. 16. Extrinsic membrane protein Proteins loosely associated with membrane surface  Located entirely outside of the lipid bilayer  Either on the extracellular or cytoplasmic surface  Also called Peripheral membrane proteins:  Example:  Cytochrome C of Mitochondria  Cell surface identity marker (antigens)  16
  17. 17. Intrinsic membrane proteins Directly incorporated within the lipid bilayer  Tightly bound to lipid bilayer  Provides channel for the water-soluble substances  Also called Integral membrane proteins  Example:  Transmembrane protein  Transport proteins  Channels, permeases (pumps)  17
  18. 18. Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Glycoprotein Extracellular fluid Glycolipid Phospholipids Cholesterol Peripheral protein Cytoplasm Transmembrane proteins Filaments of cytoskeleton 18
  19. 19. Proteins domains anchor molecule  Within membrane  nonpolar amino acids Polar areas of protein  hydrophobic  anchors protein into membrane  On outer surfaces of membrane  polar amino acids  hydrophilic  extend into extracellular fluid & into cytosol Nonpolar areas of protein 19
  20. 20. Examples Retinal chromophore H+ NH2 water channel in bacteria Porin monomer b-pleated sheets Bacterial outer membrane Nonpolar (hydrophobic) a-helices in the cell membrane COOH H+ Cytoplasm proton pump channel in photosynthetic bacteria function through conformational change = 20 shape change
  21. 21. Classes of amino acids What do these amino acids have in common? nonpolar & hydrophobic 21
  22. 22. Classes of amino acids What do these amino acids have in common? polar & hydrophilic 22
  23. 23. Association of membrane proteins with the lipid bilayer Transmembrane Proteins 1. A single α-helix 2. Multiple α-helices 3. Rolled up β-sheet 23
  24. 24. 4.α- helix (hydrophobic face) embedded in lipid bilayerthe. 24
  25. 25. 5. Protein covalently attaches lipid chain – fatty acid chain or prenyl group (cytoplasmic side) 6. Protein attaches phosphatidylinositol via an oligosaccharide linker 7, 8. Noncovalent interaction between proteins Cytoplasmic side  25
  26. 26. Plasma Membrane : Membrane Proteins Functional classification Transmembrane Proteins 26
  27. 27. Plasma Membrane : Membrane Proteins Functional classification Transmembrane Proteins 27
  28. 28. Plasma Membrane : Membrane Proteins Functional classification Peripheral Proteins (only one side of the membrane) 28
  29. 29. Chemical composition Composed of Lipids, Proteins and Carbohydrates.  Actual components differs from tissue to tissue.  Lipids of cell membrane are  Phospholipids  Glycolipids  Sterol  Cholesterol  29
  30. 30. Why carbohydrates are not inserted into the biological membrane? The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins. 30
  31. 31. Membrane carbohydrates  Play a key role in cell-cell recognition  ability of a cell to distinguish one cell from another  Antigens (MHC) important in organ & tissue development  basis for rejection of foreign cells by immune system  31
  32. 32. Four major phospholipids found in mammalian plasma membrane There are many „minor‟ phospholipids exists, too. 32
  33. 33. Cholesterol Unique to plasma membrane Stabilize membrane 33
  34. 34. Cholesterol Cholesterol Unique to plasma membrane Stabilize membrane 34
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  37. 37. Movement across the Cell Membrane 37
  38. 38. Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Enzyme activity Cell surface receptor Cell surface identity marker Cell adhesion Attachment to the cytoskeleton 38
  39. 39. Transport proteins allow needed substances or waste materials to move through the plasma membrane. 39
  40. 40. Aquaporins  Water 1991 | 2003 moves rapidly into & out of cells  evidence that there were water channels Peter Agre John Hopkins Roderick MacKinnon Rockefeller 40
  41. 41. Diffusion  2nd Law of Thermodynamics governs biological systems  universe tends towards disorder (entropy)  Diffusion  movement fromhighlowconcentration 41
  42. 42. Diffusion  Move from HIGH to LOW concentration  “passive transport”  no energy needed diffusion movement of water osmosis 42
  43. 43. Diffusion through phospholipid bilayer  What molecules can get through directly?  fats & other lipids  What molecules can lipid inside cell salt NH3 NOT get through directly?  polar molecules  H2O  ions  salts, ammonia outside cell sugar aa H2O  large molecules  starches, proteins 43
  44. 44. Channels through cell membrane  Membrane becomes semi-permeable with protein channels  specific channels allow specific material across cell membrane inside cell NH3 H2O salt aa sugar outside cell 44
  45. 45. Osmosis: Diffusion of Water The diffusion of water across a selectively permeable membrane is called osmosis. Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within a cell. 45
  46. 46. Managing water balance  Cell survival depends on balancing water uptake & loss freshwater balanced saltwater 46
  47. 47. Passive Transport When a cell uses no energy to move particles across a membrane passive transport occurs. Plasma membrane Concentration gradient 47
  48. 48. Passive Transport by proteins Passive transport of materials across the membrane using transport proteins is called facilitated diffusion. Channel proteins Plasma membrane Concentration gradient 48
  49. 49. Facilitated Diffusion  Diffusion through protein channels channels move specific molecules across cell membrane facilitated = with help  no energy needed  open channel = fast transport high low “The Bouncer”49
  50. 50. Passive transport by proteins The movement is with the concentration gradient, and requires no energy input from the cell. Carrier proteins Concentratio n gradient Plasma membrane Step 1 Step 2 50
  51. 51. Active Transport Movement of materials through a membrane against a concentration gradient is called active transport and requires energy from the cell. Carrier proteins Plasma membrane Concentration gradient Cellular energy Step 1 Step 2 51
  52. 52. Active Transport  Cells may need to move molecules against concentration gradient    shape change transports solute from one side of membrane to other protein “pump” conformational change “costs” energy = ATP low ATP high 52 “The Doorman”
  53. 53. Active transport Many models & mechanisms ATP ATP antiport symport 53
  54. 54. Getting through cell membrane  Passive Transport  Simple diffusion  diffusion of nonpolar, hydrophobic molecules    Facilitated transport   diffusion of polar, hydrophilic molecules through a protein channel   lipids high  low concentration gradient high  low concentration gradient Active transport  diffusion against concentration gradient  low  high uses a protein pump  requires ATP  ATP 54
  55. 55. Transport summary simple diffusion facilitated diffusion ATP active transport 55
  56. 56. How about large molecules?  Moving large molecules into & out of cell  through vesicles & vacuoles  Endocytosis ( 2 Types) 1. 2. phagocytosis = “cellular eating” pinocytosis = “cellular drinking”  exocytosis exocytosis 56
  57. 57. ENDOCYTOSIS - Cell membrane surrounds the substances by infolding in the form of vacuole or forms a vesicle. Two Types of Endocytosis Phagocytosis – engulf solid particles Pinocytosis – engulf liquid material 57
  58. 58. Transport of Large Particles Endocytosis is a process by which a cell surrounds and takes in material from its environment. Nucleus Wastes Digestion Endocytosis Exocytosis 58
  59. 59. Transport of Large Particles Exocytosis is the expulsion or secretion of materials from a cell. Nucleus Wastes Digestion Endocytosis Exocytosis 59
  60. 60. THE END 60
  61. 61. THANK YOU 61

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