Plasma Membrane (PDF)

The Plasma Membrane The plasma membrane serves many functions: interior The boundary between the _________ extracellular of the cell and the ________________ environment Controls what enters and exits the cell Houses enzymes...

The Plasma Membrane The plasma membrane serves many functions: interior The boundary between the _________ extracellular of the cell and the ________________ environment Controls what enters and exits the cell Houses enzymes involved in many chemical reactions _____________________ of the cell  & carbohydrates The Plasma Membrane The plasma membrane is a fluid mosaic of lipids and proteins flexible layer Lipid molecules form a _______________ Proteins are embedded in the plasma membrane carbohydrates on the surface of the _______________ plasma membrane act as cell identification tags The Lipid Bilayer Phospholipids are amphipathic hydrophilic Amphipathic = molecules that have _______________ and hydrophobic properties __________________ In water, phospholipids form a stable bilayer heads Hydrophilic __________ face outward (towards the water) tails face inward (away from water) Hydrophobic _________  Membrane Fluidity Membranes must be fluid to function properly, but not TOO fluid Lipids have rapid lateral movement, but they rarely flip-flop Why would you expect flip-flops to be rare events? Lipid composition affects membrane fluidity Saturated fatty acids have no double ce bond resulting in ________________, straight chains that allow for maximum interaction between the fatty acid tails This makes membranes more viscous (thicker) Solid at room temperature, e.g., animal fats some double c bond resulting Unsaturated fatty acids have _________________, in bent chains that space tails apart This makes membranes more fluid Liquid at room temperature, e.g., vegetable fats Lipid composition affects membrane fluidity Cholesterol act as a fluidity buffer diff temperatures Has different effects on membrane fluidity at ___________________ At warm temperatures (e.g., 37°C), cholesterol restrains the movement __________________ of phospholipids preventing At cool temperatures, it maintains fluidity by ________________ tight packing of phospholipids Let’s practice! Which part of a phospholipid can interact with water? 1. The saturated fatty acid 2. The unsaturated fatty acid 3. The phosphate 4. None. Phospholipids do not interact with water  Membrane Proteins Peripheral membrane proteins Touch the membrane or another protein superficially ionic-hydrogen-bond interactions with hydrophilic lipid and _________________________ protein groups Integral membrane proteins transmembrane proteins  Membrane proteins do cellular work! different proteins embedded in The plasma membrane is a mosaic of ___________ the lipid bilayer of types proteinsdetermine most of the membrane’s specific functions The _______________ Membrane Carbohydrates Carbohydrates are found on the exterior surface of the cell membrane _____________ cell-cell They provide specificity for _________ or _____________ cell-protein interactions Glycolipids: carbohydrate attached to a lipid (e.g., blood antigens that determine blood type) Glycoproteins: carbohydrate attached to a protein (e.g., receptors) ABO blood group antigens are glycolipids Let’s review! In which of the following locations could you find an integral membrane protein? 1. Completely on the outside surface of the cell membrane 2. Completely on the inside surface of the cell membrane 3. Floating freely in the cytoplasm 4. Spanning the cell membrane, with some parts visible to the outside and inside of the cell Membranes are selectively permeable The cell membrane controls traffic into and out of the cell by being selectively permeable → It allows some substances to cross but not others  What makes the membrane selectively permeable? 1. Permeability of the lipid bilayer ______________________ hydrophobic molec pass through the membrane rapidly (e.g., CO2, O2, steroid hormones) polar molecules and __________ ______________________ ions do not cross the membrane easily 2. Transport proteins (transmembrane) Each transport protein is _______________ specific to the solutes it can transport Molecules pass through the membrane via passive transport or active transport  Passive Transport diffuse Substances ___________ through membranes without work by the cell No energy (ATP) is required Diffusion = tendency for particles to spread out spontaneously from where they are ____________ more concentrated to where they are less concentrated __________________ Dynamic equilibrium is present when molecules move in opposite equal rates directions at __________________ Passive Transport Each solute in solution follows their own independent concentration gradient  Passive Transport: Facilitated Diffusion Molecules that cannot cross the lipid bilayer can still be passively transported across the plasma membrane via facilitated diffusion → Does not require energy Facilitated diffusion = substances moving ______ down a concentration gradient through transport proteins E.g., _______________ hydrophilic substances: water, ions Let’s practice! Which way is the net flow of salt in each beaker? outel in a content Let’s practice! The cell membrane is permeable to water and glucose, but not sucrose. Water is the 5% glucose solvent in the beaker and in the cell. 20% sucrose In which direction will glucose move? 20% glucose 1. Into the cell 5% sucrose 2. Out of the cell 3. Stays where it is  Osmosis Solutions are solute(s) dissolved in a solvent Water is the solvent for most of life’s solutions Osmosis is the diffusion of ________ water across selectively permeable a _________________________ membrane Water diffuses across a membrane from the region of lower solute concentration (i.e., high water concentration) to the region of higher solute concentration (i.e., low water concentration)  Let’s consider… Recall that water is a polar molecule. Can water cross the plasma membrane easily?  Water and Facilitated Transport Water is a polar molecule that CAN diffuse across the lipid bilayer because it Aquaporin is small, but, it can only do so _________ slowly Some cell types (e.g., kidney cells) faster transport require __________________ of water either in or out of the cell transmembrane protein Aquaporins are_____________________ ___________ channels that facilitate the transport of water across the cell membrane  Tonicity Tonicity = the ability of a solution to cause a cell to gain or lose water Hypertonic = environment has ________ higher [solute] than inside of the cell Hypotonic = environment has _________ lower [solute] than inside of the cell Isotonic = equal [solutes] inside and outside the cell Osmoregulation = the control of water balance Many marine organisms have cells that are isotonic to seawater, but organisms that live in ______________ or _____________ environments need a mechanism to prevent excessive uptake or loss of water Osmosis in Organisms Without Cell Walls Shrink in a hypertonic Osmosis causes cells to ______ solution, and ______ swell in a hypotonic solution Osmosis in Organisms with Cell Walls hypotonic solutions: rigid cell Plant cells do best in ___________ wall prevents membranes from rupturing, making them turgid In _________ isotonic environments, plant cells become flaccid Cells of the aquatic plant Elodea in a hypotonic solution In _________ hypertenic environments they shrivel Cells of the aquatic plant Elodea in a hypertonic solution Active Transport: Transport Proteins Some transport proteins can move solutes across the membrane against a concentration gradient ___________________________ Active transport requires energy in the form of ATP E.g., Na+/K+ pump  + Na /K +pump actively transports ions against their concentration gradient Always more Na+ outside of the cell ATP ATP Always more K+ inside of the cell Let’s practice! Cells actively transport calcium out of the cell. Is calcium more concentrated inside or outside the cell? Explain!  Active Transport: Bulk Transport Large molecules/large quantities of smaller molecules exocytosis can be transported across the membrane by __________ endocytosis or _____________ inside Exocytosis: membrane-bound vesicle from ___________ the cell fuses with the cell membrane and expels its Exocytosis to the outside contents ____________________ Endocytosis: membrane folds inward, trapping material outside from _______________ inside for use ______________ the cell Alp-energy In exo- and endocytosis, ________ is required for vesicle fusion/creation and transport Endocytosis