Rebecca Davenport BIOL 1406 BW1 10 3 16 Ch 7 blueprint 1 Cell membranes a i Phosolipid bilayer foundation of cell membrane ii Amphipathic molecules 1 Hydrophobic water fearing region faces in TAILS 2 Hydrophilic water loving region faces out HEAD iii Contain proteins other lipids and other molecules 1 Everything except Nucleic Acids 2 Carbohydrates on outside of membrane are how cells identify each other iv Fluid mosaic model 1 Membrane exhibits properties that resemble a fluid because lipids and proteins can move relative to each other within the membrane a They spin sway and rarely flip 2 It s considered a mosaic because of lipid protein and other molecules that make each membrane unique from one another v Factors affecting fluidity 1 Length of fatty acid tailsa Shorter tails are less likely to interact so the membrane is more fluid because they won t get tangled 2 Presence of double bonds in tailsa The double bonds create a kink in the fatty acid tail i Saturated less fluid ii Unsaturated more fluid 3 Presence of cholesterola Cholesterol tends to stabilize membranes less fluid b The cholesterol molecules stack up in the membrane and don t allow much movement c vi Proteins associated with membranes 1 Integral membrane proteinsa One or more regions that are physically embedded in the hydrophobic region of the phosolipid bilayer 1 Transmembrane protein goes through the entire membrane 2 Non transmembrane protein does not go all the way through the membrane 2 Peripheral membrane or extrinsic proteinsa Found on one side of the membrane or the other b Is not integrated in the membrane b Transportation across the membrane i Selectivity permeable plasma membrane 1 Essential molecules enter 2 Metabolic intermediates remain 3 Wastes products exit ii Gases and small nonpolar molecules move easily iii Barrier to most hydrophilic substances 1 Small polar molecules move slowly 2 Ions and large polar molecules can t penetrate the phosolipid bilayer directly iv Cells maintain gradients 1 Living cells maintain a relativity constant internal environment different form their external environment 2 Concentration gradienta Concentration of a solute is higher on one side of a membrane than the other Passive v Active No EXTRA energy required vi Regular extra energy typically ATP vii DOWN gradient High to low viii AGAINST gradient low to high ix Passive diffusion small x Primary Active transport low phobic nonpolar molecules wiggle to high concentration uses ATP across membrane barrier xi xiii Facilitated diffusion small philic polar molecules being transported by carrier proteins energy to help carrier change shape only use carrier proteins xii Secondary active transportlow to high concentration Preexisting concentration gradient will piggy back so you don t have to use ATP xiv Diffusion of water high concentration of free h2o to low concentration of free h2o aka like to go from low solute to high solute h2o likes to work aka dissolve solute xv xvi Passive transportation movement of molecules through a membrane 1 No energy is required because molecules are moving from high concentration to low concentration 2 Molecules move in response to a concentration gradient 3 Types of passive transportationa Diffusion movement of molecules from high concentration to low concentration i Osmosis a type of diffusion 1 Diffusion of water across a semipermeable membrane 2 Water diffuses through a membrane from an area with more free water to an area with less free water 3 Tonicity ability of a solution to cause a cell to gain or lose water a Compare solute concentration inside and outside the cell b Hypertonic more c Hypotonic less d Isotonic equal e ii b Facilitated diffusion movement of a molecule from high to low concentration with the help of a specific transport protein 1 Is specific 2 Is passive 3 Saturates when all carriers are occupied ii A protein is facilitating the transport of a molecule iii Transport proteins provide passageway for the movement of ions and hydrophilic molecules across membranes 1 Some move molecules passively and others actively 2 2 classes based on manner of movement a b Channels form passageway for direct diffusion of ions or molecules across the membrane Like a toilet paper roll c Carriers principal pathway for the uptake of organic molecules i Conformational changechanging shape ii lock and key fit bind and release iii Uniporter single molecule or ion iv Symporter cotransporter 2 or more ions or molecules transported in same direction v Antiporter 2 or more ions or molecules transported in opposite directions xvii Active transportation movement of a solute across a membrane against its gradient from a region of low concentration to higher concentration 1 Energetically unfavorable and requires the input of energy 2 Only uses carrier proteins cause they can change shape to move molecules over 3 Primary active transport moving low concentration to high concentration by ATP a Use ATP get protein pump to transport solute b Ion pump c 4 Secondary active transporta Use pre existing gradient to drive transport of solute b One molecule moving down its gradient while it pulls the second along 2nd is moving up its gradient xviii Bulk transport transport larger molecules such as proteins and polysaccharides and even very large particles 1 Exocytosis EXIT material inside the cell packaged into vesicles and excreted into the extracellular medium a 2 Endocytosis ENTER a Phagocytosis plasma membrane extended outward to engulf a particle i Particle will eventually be broken down by lysosome b Pinocytosis plasma membrane folds inward to gulp the extracellular fluid i Nonspecific all solutes from extracellular fluid are taken into the cell ii Regions of plasma membrane that form vesicle are lined with coat proteins c Receptor mediated endocytosis i Specialized form of pinocytosis ii Specific for certain molecules due to presence receptors on the plasma membrane d
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