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Transcript
The Cell Membrane The Fluid Mosaic Model AP Biology Cell membrane must be more than lipids… 1972 - S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer It’s like a fluid… It’s like a mosaic… It’s the Fluid Mosaic Model! AP Biology Phosphate 1. Phospholipids Phosphate head + Choline hydrophilic Fatty acid tails “attracted to water” hydrophobic Arranged as a bilayer Fatty acid “repelled by water” Aaaah, one of those structure–function examples AP Biology Membrane fat composition varies 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 1b. cholesterol in membrane Maintains the fluidity of the cell especially in cold conditions AP Biology Arranged as a Phospholipid bilayer Serves as a cellular barrier / border sugar H 2O salt polar hydrophilic heads nonpolar hydrophobic tails impermeable to polar molecules polar hydrophilic heads waste AP Biology lipids 2. Proteins Determines what goes in and out specific channels allow specific material across cell membrane W/O water would never diffuse through inside cell NH AP Biology 3 salt H 2O aa sugar outside cell Proteins domains anchor molecule Polar areas (EXTRA) Within membrane of protein nonpolar amino acids hydrophobic anchors protein into membrane On outer surfaces of membrane in fluid polar amino acids hydrophilic extend into AP Biology extracellular fluid & into cytosol Nonpolar areas of protein + H H+ Examples Retinal chromophore NH2 aquaporin = water channel in bacteria Porin monomer H 2O b-pleated sheets Bacterial outer membrane Nonpolar (hydrophobic) a-helices in the cell membrane COOH H++ H Cytoplasm proton pump channel in photosynthetic bacteria H O AP Biology 2 function through conformational change = protein changes shape Membrane Proteins A. integral proteins penetrate lipid bilayer, usually across whole membrane transmembrane protein 1. ex: transport proteins Channel – have a tube that allows materials to go from one side of the membrane to the other Aquaporin – no energy required 2. Carrier channel is specific, changes its shape for the substance, no E required Glucose transport protein AP Biology Membrane Proteins B. peripheral proteins Embedded either on the ECM (outside) or cytoplasmic (inside) side ECM side – links to ECM Cytoplasmic – links to microfilaments or tethers organelles AP Biology Fig. 6-30a Collagen Proteoglycan complex EXTRACELLULAR FLUID Fibronectin Integrins Plasma membrane Microfilaments AP Biology CYTOPLASM Many Functions of Membrane Proteins “Channel” Outside Plasma membrane Inside Transporter Enzyme activity Signal Transduction Cell adhesion Attachment to the cytoskeleton “Antigen” AP Biology Cell surface identity marker Functions of Proteins in Cell Membrane 1. Transfer 1. Sodium-potassium pump (low high con) Requires Energy, ATP is constant 2. Enzymatic Activity 1. 2. Perform as enzymes Carbohydrate metabolism 3. Signal Transduction 1. 2. AP Biology Receiving signals effect Stimulus response! 4. Intercellular Joining 4. 5. Plasmodesmata Gap/tight junctions 5. Cell-cell recognition 6. Attachment 4. AP Biology To ECM or filament 3. Oligarsaccharides (carb chains) Glycolipids A,B,O, Rh+, Rh Play a key role in cell-cell recognition Glycoporteins Ligans (anything that fits into carbon chains) The carb chains vary from person to person AP Biology Traffic Across the Membrane Cross easily (no assitance) Lipid soluble molecules (ex: sex hormones) Gases (oxygen or CO2) Cross w/ assistance Water (and water soluble materials Large molecules Ions (sodium, potassium) Proteins, glucose AP Biology 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 AP Biology Transmembrane proteins Cytoplasm Filaments of cytoskeleton 1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model Any Questions?? AP Biology PASSIVE TRANSPORT AP Biology 2007- Diffusion The tendency of a substance to spread out evenly inro space to reach dynamic equilibrium Diffusion AP Biology movement from HIGH LOW concentration Down concentration gradient DOES NOT REQUIRE ENERGY Due to the kinetic energy in the molecules AP Biology Passive Transport Diffusion across a membrane movement of water AP Biology diffusion osmosis 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 AP Biology “The Bouncer” The Special Case of Water Movement of water across the cell membrane AP Biology 2007- Osmosis is just diffusion of water Diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane Tonicity - comparing the solute concentrations on opposite sides of a membrane, and the direction water moves AP Biology Concentration of water Direction of osmosis is determined by comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water water AP Biology hypotonic hypertonic net movement of water Hyperosmotic – area w/more water (hypotonic solution) Hypoosmatic – area w/ less water AP Biology Managing water balance Cell survival depends on balancing water uptake & loss AP Biology freshwater balanced saltwater 1991 | 2003 Aquaporins Water moves rapidly into & out of cells evidence that there were water channels protein channels allowing flow of water across cell membrane AP Biology Peter Agre Roderick MacKinnon John Hopkins Rockefeller Do you understand Osmosis… .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 SEE WATER POTENTIAL POWERPOINT AP Biology Active Transport Cells may need to move molecules against concentration gradient – requires ATP Hydrolysis conformational shape change transports solute from one side of membrane to other (caused by ATP) Low High concentration conformational change Use carrier proteins High ATP Low AP Biology Active transport Many models & mechanisms ATP AP Biology ATP antiport symport 1. Ion pumps 1. Sodium – Potassium pump (Na+/K-) 2. Endocytosis AP Biology Endocytosis phagocytosis fuse with lysosome for digestion pinocytosis non-specific process receptor-mediated endocytosis triggered by molecular signal AP Biology Moving large molecules into & out of cell through vesicles & vacuoles endocytosis phagocytosis = “cellular eating” Engulfing Intake of solid particles Nonspecific Creates a phagosome to be digested w/ a lysosome pinocytosis = “cellular drinking” Intake of large fluid nonspecific Receptor mediated endocytosis Intake of specific molecules (due to receptors) Creation of clathrin-enclosed coated pit (vesicle) with specific molecules inside AP Biology 3. Exocytosis the release of substances from the cell AP Biology Transport summary simple diffusion facilitated diffusion active transport AP Biology ATP Any Questions?? AP Biology Ghosts of Lectures Past (storage) AP Biology 2007- Diffusion through phospholipid bilayer What molecules can get through directly? fats & other lipids inside cell NH3 What molecules can lipid salt NOT get through directly? polar molecules H 2O outside cell sugar aa H 2O ions (charged) salts, ammonia large molecules starches, proteins AP Biology Membrane fat composition varies 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 AP Biology cholesterol in membrane Diffusion across cell membrane Cell membrane is the boundary between inside & outside… separates cell from its environment Can it be an impenetrable boundary? NO! OUT IN food carbohydrates sugars, proteins amino acids lipids salts, O2, H2O AP Biology OUT IN waste ammonia salts CO2 H2O products cell needs materials in & products or waste out