Plasma/Cell Membrane
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Plasma/Cell Membrane



General overview of 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



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Plasma/Cell Membrane Plasma/Cell Membrane Presentation Transcript

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  • 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
  • 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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  • 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
  • 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
  • Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads 10
  • 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
  • Fluid mosaic model In 1972, S.J. Singer & G. Nicolson proposed Fluid mosaic model. 12
  • 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
  • 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
  • Membrane proteins Membrane proteins are categorized into two groups: 1- Extrinsic (peripheral) membrane proteins 2- Intrinsic (integral) membrane proteins 15
  • 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
  • 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
  • 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
  • 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
  • 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
  • Classes of amino acids What do these amino acids have in common? nonpolar & hydrophobic 21
  • Classes of amino acids What do these amino acids have in common? polar & hydrophilic 22
  • 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
  • 4.α- helix (hydrophobic face) embedded in lipid bilayerthe. 24
  • 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
  • Plasma Membrane : Membrane Proteins Functional classification Transmembrane Proteins 26
  • Plasma Membrane : Membrane Proteins Functional classification Transmembrane Proteins 27
  • Plasma Membrane : Membrane Proteins Functional classification Peripheral Proteins (only one side of the membrane) 28
  • 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
  • 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
  • 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
  • Four major phospholipids found in mammalian plasma membrane There are many „minor‟ phospholipids exists, too. 32
  • Cholesterol Unique to plasma membrane Stabilize membrane 33
  • Cholesterol Cholesterol Unique to plasma membrane Stabilize membrane 34
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  • Movement across the Cell Membrane 37
  • 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
  • Transport proteins allow needed substances or waste materials to move through the plasma membrane. 39
  • Aquaporins  Water 1991 | 2003 moves rapidly into & out of cells  evidence that there were water channels Peter Agre John Hopkins Roderick MacKinnon Rockefeller 40
  • Diffusion  2nd Law of Thermodynamics governs biological systems  universe tends towards disorder (entropy)  Diffusion  movement fromhighlowconcentration 41
  • Diffusion  Move from HIGH to LOW concentration  “passive transport”  no energy needed diffusion movement of water osmosis 42
  • 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
  • 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
  • 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
  • Managing water balance  Cell survival depends on balancing water uptake & loss freshwater balanced saltwater 46
  • Passive Transport When a cell uses no energy to move particles across a membrane passive transport occurs. Plasma membrane Concentration gradient 47
  • 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
  • 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
  • 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
  • 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
  • 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”
  • Active transport Many models & mechanisms ATP ATP antiport symport 53
  • 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
  • Transport summary simple diffusion facilitated diffusion ATP active transport 55
  • 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
  • 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
  • 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
  • Transport of Large Particles Exocytosis is the expulsion or secretion of materials from a cell. Nucleus Wastes Digestion Endocytosis Exocytosis 59
  • THE END 60
  • THANK YOU 61