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The cell-membrane
- 1. AP Biology 2007-2008 The Cell Membrane
- 2. AP Biology Overview ī§ Cell membrane separates living cell from nonliving surroundings īĩ thin barrier = 8nm thick ī§ Controls traffic in & out of the cell īĩ selectively permeable īĩ allows some substances to cross more easily than others ī§ hydrophobic vs hydrophilic ī§ Made of phospholipids, proteins & other macromolecules
- 3. AP Biology Phospholipids Fatty acid Phosphate ī§ Fatty acid tails īĩ hydrophobic ī§ Phosphate group head īĩ hydrophilic ī§ Arranged as a bilayer Aaaah, one of those structureâfunction examples
- 5. AP Biology More than lipidsâĻ ī§ In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer Itâs like a fluidâĻ Itâs like a mosaicâĻ Itâs the Fluid Mosaic Model!
- 6. AP Biology 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
- 7. AP Biology Membrane fat composition varies ī§ Fat composition affects flexibility īĩ membrane must be fluid & flexible ī§ about as fluid as thick salad oil īĩ % unsaturated fatty acids in phospholipids ī§ keep membrane less viscous ī§ cold-adapted organisms, like winter wheat īˇ increase % in autumn īĩ cholesterol in membrane
- 8. AP Biology Membrane Proteins ī§ Proteins determine membraneâs specific functions īĩ cell membrane & organelle membranes each have unique collections of proteins ī§ Membrane proteins: īĩ peripheral proteins ī§ loosely bound to surface of membrane ī§ cell surface identity marker (antigens) īĩ integral proteins ī§ penetrate lipid bilayer, usually across whole membrane ī§ transmembrane protein ī§ transport proteins īˇ channels, permeases (pumps)
- 9. AP Biology 2007-2008 Why are proteins the perfect molecule to build structures in the cell membrane?
- 10. AP Biology Classes of amino acids What do these amino acids have in common? nonpolar & hydrophobic
- 11. AP Biology Classes of amino acids What do these amino acids have in common? polar & hydrophilic I like the polar ones the best!
- 12. AP Biology Proteins domains anchor molecule ī§ Within membrane īĩ nonpolar amino acids ī§ hydrophobic ī§ anchors protein into membrane ī§ On outer surfaces of membrane īĩ polar amino acids ī§ hydrophilic ī§ extend into extracellular fluid & into cytosol Polar areas of protein Nonpolar areas of protein
- 13. AP Biology NH2 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
- 14. AP Biology 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
- 15. AP Biology Membrane carbohydrates ī§ Play a key role in cell-cell recognition īĩ ability of a cell to distinguish one cell from another ī§ antigens īĩ important in organ & tissue development īĩ basis for rejection of foreign cells by immune system
- 17. AP Biology 2007-2008 Movement across the Cell Membrane
- 18. AP Biology Diffusion ī§ 2nd Law of Thermodynamics governs biological systems īĩ universe tends towards disorder (entropy) ī§ Diffusion īĩ movement from high īŽ low concentration
- 19. AP Biology Diffusion ī§ Move from HIGH to LOW concentration īĩ âpassive transportâ īĩ no energy needed diffusion osmosis movement of water
- 20. AP Biology Diffusion across cell membrane ī§ Cell membrane is the boundary between inside & outsideâĻ īĩ separates cell from its environment IN food carbohydrates sugars, proteins amino acids lipids salts, O2, H2O OUT waste ammonia salts CO2 H2O products cell needs materials in & products or waste out IN OUT Can it be an impenetrable boundary? NO!
- 21. AP Biology Diffusion through phospholipid bilayer ī§ What molecules can get through directly? īĩ fats & other lipids inside cell outside cell lipid salt aa H2Osugar NH3 ī§ What molecules can NOT get through directly? īĩ polar molecules ī§ H2O īĩ ions ī§ salts, ammonia īĩ large molecules ī§ starches, proteins
- 22. AP Biology Channels through cell membrane ī§ Membrane becomes semi-permeable with protein channels īĩ specific channels allow specific material across cell membrane inside cell outside cell sugaraaH2O saltNH3
- 23. AP Biology Facilitated Diffusion ī§ Diffusion through protein channels īĩ channels move specific molecules across cell membrane īĩ no energy needed âThe Bouncerâ open channel = fast transport facilitated = with help high low
- 24. AP Biology Active Transport âThe Doormanâ conformational change ī§ Cells may need to move molecules against concentration gradient īĩ shape change transports solute from one side of membrane to other īĩ protein âpumpâ īĩ âcostsâ energy = ATP ATP low high
- 25. AP Biology symportantiport Active transport ī§ Many models & mechanisms ATP ATP
- 26. AP Biology Getting through cell membrane ī§ Passive Transport īĩ Simple diffusion ī§ diffusion of nonpolar, hydrophobic molecules īˇ lipids īˇ high īŽ low concentration gradient īĩ Facilitated transport ī§ diffusion of polar, hydrophilic molecules ī§ through a protein channel īˇ high īŽ low concentration gradient ī§ Active transport īĩ diffusion against concentration gradient ī§ low īŽ high īĩ uses a protein pump īĩ requires ATP ATP
- 28. AP Biology How about large molecules? ī§ Moving large molecules into & out of cell īĩ through vesicles & vacuoles īĩ endocytosis ī§ phagocytosis = âcellular eatingâ ī§ pinocytosis = âcellular drinkingâ īĩ exocytosis exocytosis
- 29. AP Biology Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by molecular signal
- 30. AP Biology 2007-2008 The Special Case of Water Movement of water across the cell membrane
- 31. AP Biology Osmosis is diffusion of water ī§ Water is very important to life, so we talk about water separately ī§ Diffusion of water from high concentration of water to low concentration of water īĩ across a semi-permeable membrane
- 32. AP Biology Concentration of water ī§ Direction of osmosis is determined by comparing total solute concentrations īĩ Hypertonic - more solute, less water īĩ Hypotonic - less solute, more water īĩ Isotonic - equal solute, equal water hypotonic hypertonic water net movement of water
- 33. AP Biology freshwater balanced saltwater Managing water balance ī§ Cell survival depends on balancing water uptake & loss
- 34. AP Biology Managing water balance ī§ Isotonic īĩ animal cell immersed in mild salt solution ī§ example: blood cells in blood plasma ī§ problem: none īˇno net movement of water īŽ flows across membrane equally, in both directions īˇvolume of cell is stable balanced
- 35. AP Biology Managing water balance ī§ Hypotonic īĩ a cell in fresh water ī§ example: Paramecium ī§ problem: gains water, swells & can burst īˇ water continually enters Paramecium cell ī§ solution: contractile vacuole īˇ pumps water out of cell īˇ ATP īĩ plant cells ī§ turgid freshwater ATP
- 36. AP Biology Water regulation ī§ Contractile vacuole in Paramecium ATP
- 37. AP Biology Managing water balance ī§ Hypertonic īĩ a cell in salt water ī§ example: shellfish ī§ problem: lose water & die ī§ solution: take up water or pump out salt īĩ plant cells ī§ plasmolysis = wilt saltwater
- 38. AP Biology Aquaporins ī§ Water moves rapidly into & out of cells īĩ evidence that there were water channels 1991 | 2003 Peter Agre John Hopkins Roderick MacKinnon Rockefeller
- 39. AP Biology Cell (compared to beaker) īŽ hypertonic or hypotonic Beaker (compared to cell) īŽ hypertonic or hypotonic Which way does the water flow? īŽ in or out of cell .05 M .03 M OsmosisâĻ