AP Bio --> Membrane Structure and Function
Midterm Review Chapter 7
Terms in this set (16)
Explain why phospholipids are amphipathic molecules.
Phospholipids are amphipathic because they have hydrophilic heads and hydrophobic tails.
Describe the fluidity of the components of a cell membrane and explain how membrane fluidity is influenced by temperature and membrane composition.
Membrane composition -> Membranes must be fluid to work properly. Saturated fats make it "stiff" because they are solid at room temperature. Unsaturated fats helps it "bend" which helps the cell work better - liquid at room temperature
Temperature -> Remains fluid as temperature decreases, membrane remains fluid to a lower temperature if it is rich in phospholipid with unsaturated hydrocarbon tails (cholesterol is a "temperature buffer")
Explain how cholesterol resists changes in membrane fluidity with temperature change.
Cholesterol at moderate temperature reduces membrane fluidity by reducing phospholipid movement, but at low temperatures, it hinders solidification by disrupting the regular packing of phospholipids.
Distinguish between peripheral and integral proteins.
Integral -> Penetrate the hydrophobic core of the lipid bilayer -permanently attached (many are transmembrane proteins; which span the membrane - others extend only partway) The hydrophobic regions of these proteins consist of one or more stretches of nonpolar amino acids
Peripheral -> Not embedded in the lipid bilayer at all. Appendages loosely bound to the surface of the membrane - often to exposed parts of integral proteins.
Functions -> Cell adhesion, enzymatic activity, transport
List six major functions of membrane proteins.
Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to the cytoskeleton and extracellular matrix (ECM)
Explain the role of of membrane carbohydrates in cell-cell recognition.
Membrane carbohydrates bond to lipids or proteins. The membrane carbohydrates found on the outside varies from species to species; diversity enables membrane carbohydrates to function as markers that distinguish one cell from another.
Explain how hydrophobic molecules cross cell cell membranes.
Can dissolveHydrophobic (nonpolar) molecules, such as hydrocarbons, carbon dioxide, and oxygen, candissolve in the lipid bilayer of the membrane and cross it with ease, without the aid of membrane proteins.
Define diffusion. Explain why diffusion is a spontaneous process.
Diffusion; the movement of molecules of any substance so that they spread out evenly into the available space. It goes from a region where it is more concentrated to a region that is less concentrated. (Net diffusion -> Equilibrium) It is spontaneous because there is no energy involved.
Explain why a concentration gradient of a substance across a membrane represents potential energy.
Potential energy is stored energy -> "it drives diffusion" -> in general requires no energy
Distinguish among hypertonic, hypotonic, and isotonic solutions.
Hypertonic solution -> The cell has more solute than its surroundings. (Cell shrivels)
Isotonic solution -> The cell has the same amount of solute as its surroundings. (Nothing happens)
Hypotonic solution -> The cell has less solute than its surroundings. (Cell explodes)
Define osmosis and predict the direction of water movement based on differences in solute concentrations.
Osmosis -> The diffusion of water across a selectively permeable membrane
Involves tonicity -> Ability of a solution to cause a cell to gain or lose water
Nonpenetrating solutes -> cannot cross the membrane -> if this concentration is higher, water will tend to leave the cell and vice versa
Penetrating solutes -> can cross the membrane
Describe how living cells with and without cell walls regulate water balance.
With walls -> The cell wall will expand only so much before it exerts a back pressure on the cell that opposes further water uptake.
Without walls -> It can tolerate neither excessive uptake nor excessive loss of water.
Explain how transport proteins facilitate diffusion.
Many polar molecules and ions impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane. Many polar molecules and ions impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane.
Distinguish among osmosis, facilitated diffusion, and active transport.
Osmosis -> Diffusion of water across a selectively permeable membrane
Facilitated diffusion -> No energy -> uses integral channel proteins to transport hydrophilic substances (molecules/ions)
Active transport -> Movement of a substance across a cell membrane using energy
Explain how large molecules are transported across a cell membrane.
In some instances, (receptor-mediated) Endocytosis ("pockets") and proteins help by recognizing the molecules to be passed through
Distinguish between pinocytosis and receptor-mediated endocytosis.
Pinocytosis -> Type of endocytosis in which the cell ingests extracellular fluid and its dissolve solutes.
Receptor-mediated endocytosis -> Movement of specific molecules into a cell by the inward budding - enables cell to acquire bulk quantities of specific substances even if not concentrated in fluid (proteins are involved)
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