Plasma/Cell Membrane

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

1. 1 ABOUT AUTHOR

2. PLASMA MEMBRANE By GUL MUNEER 2

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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. H ow could you define plasma membrane? A n 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

7. STRUCTURE OF PLASMA MEMBRANE 7

8. Summary Section 2 – pages 175-178 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. Phospholipids Fatty acid tails hydrophobic Phosphate group head hydrophilic Arranged as a bilayer Fatty acid Phosphate Phospholipids, glycolipids , cholesterol are amphipathic lipids containing hydrophobic and hydrophillic ends 9

10. Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads 10

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. Fluid mosaic model In 1972, S.J. Singer & G. Nicolson proposed Fluid mosaic model. 12

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. 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. Membrane proteins Membrane proteins are categorized into two groups: 1- Extrinsic (peripheral) membrane proteins 2- Intrinsic (integral) membrane proteins 15

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. 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. Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Extracellular fluid Cholesterol Cytoplasm Glycolipid Transmembrane proteins Filaments of cytoskeleton Peripheral protein Glycoprotein Phospholipids 18

19. Proteins domains anchor molecule Within membrane nonpolar amino acids hydrophobic anchors protein into membrane On outer surfaces of membrane polar amino acids hydrophilic extend into extracellular fluid & into cytosol Polar areas of protein Nonpolar areas of protein 19

20. NH 2 H + COOH Cytoplasm Retinal chromophore Nonpolar (hydrophobic) a -helices in the cell membrane H + Porin monomer b -pleated sheets Bacterial outer membrane proton pump channel in photosynthetic bacteria water channel in bacteria function through conformational change = shape change Examples 20

21. Classes of amino acids What do these amino acids have in common ? nonpolar & hydrophobic 21

22. Classes of amino acids What do these amino acids have in common? polar & hydrophilic 22

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. 4.α- helix ( hydrophobic face) embedded in lipid bilayerthe . 24

25. Cytoplasmic side  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 25

26. Plasma Membrane : Membrane Proteins Functional classification Transmembrane Proteins 26

27. Plasma Membrane : Membrane Proteins Functional classification Transmembrane Proteins 27

28. Plasma Membrane : Membrane Proteins Functional classification Peripheral Proteins (only one side of the membrane) 28

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. 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. 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. Four major phospholipids found in mammalian plasma membrane There are many ‘minor’ phospholipids exists, too. 32

33. Cholesterol Unique to plasma membrane Stabilize membrane 33

34. Cholesterol Unique to plasma membrane Stabilize membrane Cholesterol 34

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37. Movement across the Cell Membrane 37

38. Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion 38

39. Summary Section 2 – pages 175-178 Transport proteins allow needed substances or waste materials to move through the plasma membrane. 39

40. Aquaporins Water moves rapidly into & out of cells evidence that there were water channels 1991 | 2003 Peter Agre John Hopkins Roderick MacKinnon Rockefeller 40

41. Diffusion 2nd Law of Thermodynamics governs biological systems universe tends towards disorder (entropy) Diffusion movement from high  low concentration 41

42. Diffusion Move from HIGH to LOW concentration “passive transport” no energy needed diffusion osmosis movement of water 42

43. Diffusion through phospholipid bilayer What molecules can get through directly? fats & other lipids inside cell outside cell lipid salt aa H 2 O sugar NH 3 What molecules can NOT get through directly? polar molecules H 2 O ions salts, ammonia large molecules starches, proteins 43

44. Channels through cell membrane Membrane becomes semi-permeable with protein channels specific channels allow specific material across cell membrane inside cell outside cell sugar aa H 2 O salt NH 3 44

45. Section 8.1 Summary – pages 195 - 200 The diffusion of water across a selectively permeable membrane is called osmosis . Osmosis: Diffusion of Water Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within a cell. 45

46. freshwater balanced saltwater Managing water balance Cell survival depends on balancing water uptake & loss 46

47. Section 8.1 Summary – pages 195 - 200 Passive Transport When a cell uses no energy to move particles across a membrane passive transport occurs. Concentration gradient Plasma membrane 47

48. Section 8.1 Summary – pages 195 - 200 Passive Transport by proteins Passive transport of materials across the membrane using transport proteins is called facilitated diffusion . Plasma membrane Channel proteins Concentration gradient 48

49. Facilitated Diffusion Diffusion through protein channels channels move specific molecules across cell membrane no energy needed “The Bouncer” open channel = fast transport facilitated = with help high low 49

50. Section 8.1 Summary – pages 195 - 200 Passive transport by proteins The movement is with the concentration gradient, and requires no energy input from the cell. Concentration gradient Plasma membrane Step 1 Step 2 Carrier proteins 50

51. Section 8.1 Summary – pages 195 - 200 Active Transport Movement of materials through a membrane against a concentration gradient is called active transport and requires energy from the cell. Plasma membrane Concentration gradient Carrier proteins Cellular energy Step 1 Step 2 51

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” “costs” energy = ATP “The Doorman” conformational change ATP low high 52

53. symport antiport Active transport Many models & mechanisms ATP ATP 53

54. Getting through cell membrane Passive Transport Simple diffusion diffusion of nonpolar , hydrophobic molecules lipids high  low concentration gradient Facilitated transport diffusion of polar, hydrophilic molecules through a protein channel high  low concentration gradient Active transport diffusion against concentration gradient low  high uses a protein pump requires ATP ATP 54

55. Transport summary simple diffusion facilitated diffusion active transport ATP 55

56. How about large molecules? Moving large molecules into & out of cell through vesicles & vacuoles Endocytosis ( 2 Types) phagocytosis = “cellular eating” pinocytosis = “cellular drinking” exocytosis exocytosis 56

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. Section 8.1 Summary – pages 195 - 200 Transport of Large Particles Endocytosis is a process by which a cell surrounds and takes in material from its environment. Endocytosis Exocytosis Digestion Nucleus Wastes 58

59. Section 8.1 Summary – pages 195 - 200 Transport of Large Particles Exocytosis is the expulsion or secretion of materials from a cell. Endocytosis Exocytosis Digestion Nucleus Wastes 59

60. THE END 60

61. THANK YOU 61