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Transcript
AP Biology Phosphate Phospholipids Phosphate head The Cell Membrane “attracted to water” ___________ ___________ Arranged as a ________ Fatty acid “repelled by water” Aaaah, one of those structure–function examples AP Biology AP Biology Arranged as a Phospholipid bilayer Serves as a cellular barrier / border sugar H2O aqueous environment salt ______ hydrophilic heads ______ hydrophobic tails Cell membrane defines cell Cell membrane _________ living cell from thin barrier = 8nm thick Controls traffic in & out of the cell impermeable to polar molecules allows some substances to cross more easily than others hydrophobic (nonpolar) vs. hydrophilic (polar) ______ hydrophilic heads waste AP Biology ______ AP Biology 1 AP Biology Permeability to polar molecules? ___________________________________ ___________________________________ specific channels allow specific material across cell membrane inside cell NH AP Biology 3 salt H2O aa Cell membrane is more than lipids… Transmembrane proteins embedded in phospholipid bilayer create semi-permeabe channels lipid bilayer membrane protein channels in lipid bilyer membrane sugar outside cell AP Biology Classes of amino acids Why are proteins the perfect molecule to build structures in the cell membrane? What do these amino acids have in common? _________________________ AP Biology 2007-2008 AP Biology 2 AP Biology Proteins domains anchor molecule Classes of amino acids What do these amino acids have in common? Polar areas of protein Within membrane ________amino acids ______________ anchors protein into membrane I like the polar ones the best! On outer surfaces of membrane in fluid _______amino acids ____________ extend into AP Biology ______________________ AP Biology + H H extracellular fluid & into cytosol Nonpolar areas of protein + Examples Many Functions of Membrane Proteins Retinal chromophore “Channel” NH2 Outside aquaporin = water channel in bacteria Porin monomer Plasma membrane H2O β -pleated sheets Inside Bacterial outer membrane Transporter Nonpolar (hydrophobic) α-helices in the cell membrane COOH H+ H + Cytoplasm Enzyme activity Cell surface receptor Cell adhesion Attachment to the cytoskeleton “Antigen” proton pump channel in photosynthetic bacteria H O AP Biology 2 function through _______________ change = protein changes shape AP Biology Cell surface identity marker 3 AP Biology Cell membrane must be more than lipids… Membrane Proteins Proteins determine membrane’s specific functions cell membrane & organelle membranes each have unique collections of proteins In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer Classes of membrane proteins: _____________________ loosely bound to surface of membrane ex: cell surface identity marker (________) _____________________ It’s like a fluid… It’s like a mosaic… It’s the Fluid Mosaic Model! penetrate lipid bilayer, usually across whole membrane ___________________ protein ex: transport proteins channels, permeases (pumps) AP Biology AP Biology Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Glycoprotein __________________ Membrane carbohydrates Play a key role in __________________ Glycolipid ability of a cell to distinguish one cell from another _________ important in organ & tissue development basis for rejection of foreign cells by _______________ Phospholipids Cholesterol Peripheral protein AP Biology Transmembrane proteins Cytoplasm Filaments of cytoskeleton 1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model AP Biology 4 AP Biology Any Questions?? Movement across the Cell Membrane AP Biology AP Biology Diffusion ___________________________ governs biological systems universe tends towards disorder (entropy) Simple Diffusion Move from ______to ______concentration “passive transport” no energy needed movement of water Diffusion AP Biology movement from _____→ → _____concentration AP Biology diffusion osmosis 5 AP Biology Facilitated Diffusion Diffusion through protein channels channels move specific molecules across cell membrane facilitated = with help ________________ open channel = fast transport HIGH Active Transport Cells may need to move molecules ___________ concentration gradient conformational shape change transports solute from one side of membrane to other ________________ “costs” energy = _____ LOW conformational change ATP LOW HIGH “The Bouncer” AP Biology Active transport Getting through cell membrane Many models & mechanisms ________________ ATP “The Doorman” AP Biology _______________ diffusion of nonpolar, hydrophobic molecules lipids HIGH → LOW concentration gradient ATP __________________ diffusion of polar, hydrophilic molecules through a ________________ HIGH → LOW concentration gradient __________________ diffusion _________ concentration gradient uses a _____________ requires _____ LOW → HIGH AP Biology antiport symport ATP AP Biology 6 AP Biology Transport summary How about large molecules? Moving large molecules into & out of cell simple diffusion ___________ = “cellular eating” facilitated diffusion ____________= “cellular drinking” active transport through vesicles & vacuoles __________ ___________ ATP AP Biology AP Biology exocytosis Endocytosis ____________ fuse with lysosome for digestion The Special Case of Water __________ non-specific process ________________ _____________ triggered by molecular signal AP Biology Movement of water across the cell membrane AP Biology 2007-2008 7 AP Biology Osmosis is just diffusion of water Water is very important to life, Concentration of water Direction of osmosis is determined by so we talk about water separately comparing total solute concentrations Diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane ____________ - more solute, less water ____________ - less solute, more water _________ - equal solute, equal water water AP Biology AP Biology hypotonic hypertonic ____ movement of water 1 Managing water balance Cell survival depends on balancing Managing water balance Hypotonic water uptake & loss a cell in ____________ high concentration of water around cell problem: ____________, ___________________ KABOOM! example: ___________ ex: water continually enters Paramecium cell solution: _______________ pumps water out of cell ATP ATP plant cells No problem, here turgid = full cell wall protects from bursting AP Biology freshwater balanced saltwater AP Biology freshwater 8 AP Biology 2 Pumping water out Contractile vacuole in Paramecium Managing water balance Hypertonic I’m shrinking, a cell in __________ I’m shrinking! low concentration of water around cell problem: ________________ ________________ example: ________ ATP solution: take up water or pump out salt AP Biology AP Biology I will survive! plant cells _______________ = wilt can recover 3 1991 | 2003 Managing water balance Isotonic animal cell immersed in ___________ solution saltwater Aquaporins Water moves rapidly into & out of cells That’s perfect! evidence that there were water channels protein channels allowing flow of water no difference in concentration of water between cell & environment across cell membrane problem: none no ____ movement of water flows across membrane equally, in both directions I could _________________ be better… volume of cell is stable example: ________________________ slightly salty IV solution in hospital AP Biology balanced AP Biology Peter Agre Roderick MacKinnon John Hopkins Rockefeller 9 AP Biology Do you understand Osmosis… Any Questions?? .05 M .03 M Cell (compared to beaker) → hypertonic or hypotonic Beaker (compared to cell) → hypertonic or hypotonic Which way does the water flow? → in or out of cell AP Biology AP Biology 10
