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. 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
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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. 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. 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 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. 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 Glycoprotein Extracellular fluid Glycolipid Phospholipids Cholesterol Peripheral protein Cytoplasm Transmembrane proteins Filaments of cytoskeleton 18
- 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. 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. 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. 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. 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 Cholesterol Unique to plasma membrane Stabilize membrane 34
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- 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. Transport proteins allow needed substances or waste materials to move through the plasma membrane. 39
- 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. Diffusion 2nd Law of Thermodynamics governs biological systems universe tends towards disorder (entropy) Diffusion movement fromhighlowconcentration 41
- 42. Diffusion Move from HIGH to LOW concentration “passive transport” no energy needed diffusion movement of water osmosis 42
- 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. 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. 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. Managing water balance Cell survival depends on balancing water uptake & loss freshwater balanced saltwater 46
- 47. Passive Transport When a cell uses no energy to move particles across a membrane passive transport occurs. Plasma membrane Concentration gradient 47
- 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. 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. 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. 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. 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. Active transport Many models & mechanisms ATP ATP antiport symport 53
- 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
- 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. 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. 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. Transport of Large Particles Exocytosis is the expulsion or secretion of materials from a cell. Nucleus Wastes Digestion Endocytosis Exocytosis 59
- 60. THE END 60
- 61. THANK YOU 61