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Fluid Mosaic Model
The document describes the fluid mosaic model of the cell membrane. It discusses key aspects of the model, including: - The membrane is made up of a lipid bilayer with proteins embedded within it, giving it a mosaic-like structure. - The lipid bilayer is fluid and allows for lateral movement of proteins and lipids. Integral proteins span the membrane while peripheral proteins are loosely attached. - Experimental evidence from electron microscopy provides support for the model, showing a mosaic-like structure of particles within a smooth lipid matrix. - The fluid mosaic model accounts for membrane properties and suggests new ways of thinking about membrane functions based on its structure and dynamics.
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Fluid Mosaic Model
- 1. Fluid Mosaic Model ofThe Structure of Cell Membrane Wenny Pintalitna Tarigan Pend.Biologi 2013
- 2. Background Biological membranes playa crucial role in almost all cellular phenomena Organization of proteins and lipids of membranes can be discerned Generalizations about protein structure – understanding the properties and functions of protein molecules Detailed structure
- 3. Objectives Thermodynamics andMembrane Structure Properties of proteins and lipids of functional membrane The fluid mosaic model in detail Experimental evidence in terms of the model The fluid mosaic model suggests new ways of thinking about membrane functions and membrane phenomena
- 4. Thermodynamics and Membrane Structure Two kinds of non covalent interactions are hydrophobic and hydrophilic Hydrophybic – non polar groups, away from water, requires energy Hydrophylic – polar groups for aqueous environment
- 5. Thermodynamics and Membrane Structure Ratio of proteins to lipids = 1.5 – 4 Cell membrane recognition sites activate enzyme in membrane which begins "cascade" of events which activate other enzymes. This is called signal transduction (pg 155 Campbell)
- 6. Properties of Proteins Peripheral Proteins - mild treatment: increase the ionic strength - dissociate them intact from the membrane - weak non covalent – not strongly associated with membrane lipid (free of lipid) - spread out as monolayer Integral/Transmembrane Proteins - drastric treatment (using many reagents) - remain associated with lipid - globular in shape, no on the surface – prevent membrane thickness larger than 75-90 A
- 7. Classes of aminoacids What do these amino acids have in common? nonpolar & hydrophobic
- 8. Classes of aminoacids What do these amino acids have in common? polar & hydrophilic
- 9. Proteins domains anchormolecule 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 Properties of Proteins
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- 11. Membrane Proteins peripheral proteins looselybound to surface of membrane cell surface identity marker (antigens) integral proteins penetrate lipid bilayer, usually across whole membrane transmembrane protein transport proteins channels, permeases (pumps)
- 12. NH2 H+ COOH Cytoplasm Retinal chromophore Nonpolar (hydrophobic) -helices in the cellmembrane 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
- 13. Many Functions ofMembrane Proteins Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion
- 14. Stronger electron microscopeswould show that the cell membrane was not covered in protein, but rather had protein embedded in it. Proteins Embedded on Cell Membrane
- 15. Knife Plasma membrane Cytoplasmiclayer Proteins Extracellular layer Inside of extracellular layer Inside of cytoplasmic layer TECHNIQUE RESULTS Properties of Lipid
- 16. Membrane phospholipids form abilayer Phospholipids Have a hydrophilic head and two hydrophobic tails Are the main structural components of membranes CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH CH CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 CH2 CH2 CH3 CH3 CH3 N + O O O–P O CH2 C H CH2 C O C O O O Phosphate group Symbol Hydrophilic head Hydrophobic tails Properties of Lipid
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- 18. Figure 7.6 Lateral movementoccurs 107 times per second. Flip-flopping across the membrane is rare ( once per month). Properties of Lipid
- 19. Figure 7.8 Fluid Unsaturated hydrocarbon tails Viscous Saturatedhydrocarbon tails (a) Unsaturated versus saturated hydrocarbon tails (b) Cholesterol within the animal cell membrane Cholesterol Properties of Lipid
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- 21. FUNCTIONS: Cellprotection and/or insulation Receptor sites for binding of other molecules - signaling Attachment of cells to one another = tissues Carbohydrate Chains – Cell ID – autoimmunity Carbohydrate
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- 23. Hydrophilic region of protein Hydrophobicregion of protein Phospholipid bilayer Mosaic: Proteins dispersed among phospholipids in membrane
- 24. Membrane is acollage 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
- 25. Membrane fat compositionvaries Fat composition affects flexibility membrane must be fluid & flexible about as fluid as thick salad oil % unsaturated fatty acids in phospholipids keep membrane less viscous cold-adapted organisms, like winter wheat increase % in autumn cholesterol in membrane Fluid Mosaic Model
- 26. Permeability to polar molecules? Membrane becomes semi-permeable via protein channels specific channels allow specific material across cell membrane outside cell inside cell sugaraaH2O saltNH3
- 27. Experimental Evidence Integralprotein - a globular molecule - embedded in the membrane. In this technique, a frozen specimen is fractured with a microtome knife; some of the frozen water is sub-limed (etched) from the fractured surface if desired; The surface is then shadow cast with metal, and the surface replica is examined in the electron microscope. By this method the topography of the cleaved surface is revealed. A characteristic feature of the exposed surface of most functional membranes examined by this technique, including plasma lemma, vacuolar, nuclear, chloroplast, mitochondrial, and bacterial membranes, is a mosaic-like structure consisting of a smooth matrix interrupted by a large number of particles.
- 28. New Ways ofThinking Model restrictions imposed by thermodynamics. In this model, the proteins that are integral to the membrane are a heterogeneous set of globular molecules (amphipathic structure) The bulk of the phospholipid is organized as a fluid bilayer, although a small fraction of the lipid may interact specifically with the membrane proteins. The fluid mosaic structure is therefore formally analogous to a two-dimensional oriented solution of integral proteins (or lipoproteins) in the viscous phospholipid bilayer solvent. Evidence stated that all of which are consistent with, and add much detail to, the fluid mosaic model.
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