Cell membrane
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Cell membrane
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Cell membrane
- 1. 2007-2008AP Biology 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 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
- 10. 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
- 12. 2007-2008AP Biology Movement across the Cell Membrane
- 13. AP Biology Diffusion ī§ 2nd Law of Thermodynamics governs biological systems īĩ universe tends towards disorder (entropy) ī§ Diffusion īĩ movement from high â low concentration ī§ Diffusion īĩ movement from high â low concentration
- 14. AP Biology Diffusion ī§ Move from HIGH to LOW concentration īĩ âpassive transportâ īĩ no energy needed diffusion osmosis movement of water
- 15. 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!
- 16. 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
- 17. 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
- 18. AP Biology Facilitated Diffusion ī§ Diffusion through protein channels īĩ channels move specific molecules across cell membrane īĩ no energy needed âThe BouncerââThe Bouncerâ open channel = fast transport facilitated = with help high low
- 19. AP Biology Active Transport âThe DoormanââThe 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
- 20. AP Biology symportantiport Active transport ī§ Many models & mechanisms ATP ATP
- 21. AP Biology Getting through cell membrane ī§ Passive Transport īĩ Simple diffusion ī§ diffusion of nonpolar, hydrophobic molecules īˇ lipids īˇ high â low concentration gradient īĩ Facilitated transport ī§ diffusion of polar, hydrophilic molecules ī§ through a protein channel īˇ high â low concentration gradient ī§ Active transport īĩ diffusion against concentration gradient ī§ low â high īĩ uses a protein pump īĩ requires ATP ATP
- 23. 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
- 24. AP Biology Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by molecular signal
- 25. 2007-2008AP Biology The Special Case of Water Movement of water across the cell membrane
- 26. 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
- 27. 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
- 28. AP Biology freshwater balanced saltwater Managing water balance ī§ Cell survival depends on balancing water uptake & loss
Editor's Notes
- The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins.
- Signal transduction - transmitting a signal from outside the cell to the cell nucleus, like receiving a hormone which triggers a receptor on the inside of the cell that then signals to the nucleus that a protein must be made.
- The four human blood groups (A, B, AB, and O) differ in the external carbohydrates on red blood cells.
- Movement from high concentration of that substance to low concentration of that substance.
- Donuts! Each transport protein is specific as to the substances that it will translocate (move). For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, its structural isomer. Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane -- simply provide corridors allowing a specific molecule or ion to cross the membrane. These channel proteins allow fast transport. For example, water channel proteins, aquaporins, facilitate massive amounts of diffusion.
- Some transport proteins do not provide channels but appear to actually translocate the solute-binding site and solute across the membrane as the protein changes shape. These shape changes could be triggered by the binding and release of the transported molecule. This is model for active transport.
- Plants: nitrate & phosphate pumps in roots. Why? Nitrate for amino acids Phosphate for DNA & membranes Not coincidentally these are the main constituents of fertilizer Supplying these nutrients to plants Replenishing the soil since plants are depleting it