Chapter 5 Exam Review PDF

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Chapter 5 – Structure & Function of Plasma Membranes Exam Review 1. Components and Structure of Plasma Membranes What is/are the function(s) of the plasma membrane? Separate living cells from its surroundings, exhibits selective permeability What is meant by selective permeability? Allowing some substances to cross it more easily than others What are the 4 major membrane components? Phospholipid bilayer, proteins (integral and peripheral), carbs, cholesterol What are phospholipids? Why are they amphipathic? Which end is hydrophobic/hydrophilic? Phospholipids are the most abundant lipid in most membranes, they are amphipathic because they have a hydrophilic, polar phosphate head and two hydrophobic fatty acids tails. What is the function of the phospholipid bilayer? They create a selectively permeable barrier to the movement of ions molecules important for cellular function What membrane component determines most of the membrane’s specific functions? proteins What is the difference between integral and peripheral proteins? What are some of the functions each serves? Integral proteins integrate completely into the membrane structure and peripheral proteins are on the membrane’s exterior and interior surfaces. They serve as enzymes, structural attachments for the cytoskeleton’s fibers, or as part of the cell’s recognition sites What are the 6 major functions of membrane proteins? Transport, enzymatic activity, attachment to the cytoskeleton and extracellular matrix, cell-cell recognition, intercellular joining, signal transduction Where are carbohydrates found on the plasma membrane? On the cell’s exterior surface What is a glycoprotein? A glycolipid? The glycocalyx? What is the function of the glycocalyx? Glycoprotein is a combination of carbohydrates and proteins, glycolipid is combination of carbohydrates and lipids, glycocalyx is a highly charged layer of membrane-bound biological macromolecules attached to a cell membrane. This layer functions as a barrier between a cell and its surrounding. Explain the Fluid Mosaic Model. The idea that the components of plasma membranes are not fixed, but rather float around, kept in proper orientation by hydrophobic and hydrophilic forces When moving laterally do proteins or lipids move faster? Phospholipids move fast where proteins move slow As membranes cool, they switch from a fluid state to a solid state. How fluid are membranes usually? Usually the same fluid as salad oil

What makes membranes remain fluid at lower temperatures? If they are rich in phospholipids with unsaturated hydrocarbon tails What impacts does cholesterol have on membrane fluidity at different temperatures? At warm temp., cholesterols restrain movement of phospholipids and at cool temp., it maintains fluidity by preventing tight packing What cell components build the membrane? What is meant by “sidedness” of the membrane? Asymmetrical distribution of proteins, lipids, and associated carbs in the plasma membrane. 2. Transport across the plasma membrane What types of molecules can cross the phospholipid bilayer easily? (hydrophobic vs. hydrophilic; non-polar vs. polar)? What are transport proteins? How are carrier proteins different from channel proteins? Transport proteins allow passage of hydrophilic substances across the membrane, carrier proteins bind to the molecule and change shape to shuttle them across the membrane, while channel proteins have a hydrophobic channel that only allow certain molecules or ions to pass through Passive Transport What is passive transport? Does it require energy? Passive transport is diffusion of a substance across a membrane with no energy invested What is diffusion? What is osmosis? How are the two different? Diffusion is a tendency for molecules to spread out evenly into the available space; osmosis is the diffusion of free water across the selective permeable membrane What is a solvent? A solute? A solvent is the liquid in which a solute is dissolved to form a solution. A solute is substance dissolved in a liquid to form a solution What is dynamic equilibrium? When the rates of the forward and reverse reactions are equal What factors impact diffusion? How? extent of concentration gradient (increase), mass of molecules (decrease), Temperature (increase), solvent density (decrease), solubility (decrease), plasma membrane surface area (increase), plasma membrane thickness (decrease), distance traveled (decrease) In what direction does water travel in osmosis (from low to high or high to low concentrations of solute)? Water diffuses across a membrane from the region of low solute concentration to the region of higher solute concentration until the solute concentration is equal on both sides Define: tonicity, isotonic solution, hypertonic solution, hypotonic solution. Tonicity- ability of a surrounding solution to cause a cell to gain or lose water. Isotonic solution- solute concentration is the same as inside the cell; no net water movement across the plasma membrane Hypertonic solution- solute concentration is greater than that inside the cell; cell loses water Hypotonic solution- solute concentration is less than that inside the cell; cell gains water

What happens to a plant and animal cell in isotonic, hypertonic, and hypotonic solutions? In hypotonic solutions, animal cells become lysed and in plant cells they become turgid (normal); they bloat in short. In isotonic solutions, the animal cell is normal sized (like blood cell) and plant cell is rectangle shaped; flaccid. In hypertonic solution, the animal cell is shriveled and the plant cell is plasmolyzed (also shriveled). What is osmoregulation? How does the Paramecium osmoregulate in a hypotonic solution? Osmoregulation is the control of solute concentrations and water balance , is a necessary adaptation for life in such environments. Paramecium has a contractile vacuole that can pump access water out of the cell Define plasmolysis, turgid, and flaccid in the context of plant cells. When might you get each of these (i.e. would the solution by hyper-, hypo-, or iso- tonic?) Which is preferable to the plant? A plant in hypotonic solutions swells until the wall opposes uptake; the cell is now turgid (very firm). If a plant cell and its surroundings are isotonic, there is no net movements of water into the cell; the cell becomes flaccid (limp), and the plants may wilt, in hypertonic environment, plants cells lose water; eventually the membrane pulls away from the wall, a usually lethal effect called plasmolysis What is facilitated diffusion? Can it involve channel proteins, carrier proteins, or both? Passive movement of molecules across the plasma membrane that is sped up by transport proteins; it involves channel proteins which includes aquaporins and ion channels What are aquaporins? Ion channels? Gated channels? Aquaporins are channel protein that allows water through the membrane at a very high rate, ion channels/gated channels are pore-forming membrane proteins that allow ions to pass through the channel pore How do channel proteins facilitate diffusion? Carrier proteins? Channel proteins include aquaporins that allow water to pass through he membrane at a very high rate and have ion channels that open or close in response to a stimulus (gated channels), Carrier proteins undergo a subtle change in shape that translocate the solute-binding site across the membrane. Does facilitated diffusion/passive transport alter the direction of travel? Does it require energy input? direction is not changed an no net energy input is required Active Transport What is active transport? Does it require energy? Can it move molecules against a concentration gradient? method of transporting material that requires energy, yes What is the sodium-potassium pump? How does it work? What is moved into/out of the cell? At what ratio? An important pump in animal cells which maintain the electrochemical gradient (and the correct concentration of Na+ and K+) in living cells The sodium-potassium pump moves K+ into the cell while moving Na+ out at the same time, at a ratio of three Na+ for every two K+ ions moved in. The Na+-K+ ATPase exists in two forms, depending on its orientation to the cell's interior or exterior and its affinity for either sodium or potassium ions. The process consists of the following six steps.

1. With the enzyme oriented towards the cell's interior, the carrier has a high affinity for sodium ions. Three ions bind to the protein. 2. The protein carrier hydrolyzes ATP and a low-energy phosphate group attaches to it. 3. As a result, the carrier changes shape and reorients itself towards the membrane's exterior. The protein’s affinity for sodium decreases and the three sodium ions leave the carrier. 4. The shape change increases the carrier’s affinity for potassium ions, and two such ions attach to the protein. Subsequently, the low-energy phosphate group detaches from the carrier. 5. With the phosphate group removed and potassium ions attached, the carrier protein repositions itself towards the cell's interior. 6. The carrier protein, in its new configuration, has a decreased affinity for potassium, and the two ions moves into the cytoplasm. The protein now has a higher affinity for sodium ions, and the process starts again. What is an electrical gradient? a combined electrical and chemical force that produces a gradient Is a cell usually electrically negative or electrically positive with respect to the extracellular fluid? Why is this important? Inside of cell normally electrically negative with respect to the extracellular fluid What two forces drive the electrochemical gradient? A chemical force an electrical force What is membrane potential? The voltage across a membrane What is an electrogenic pump? What are the two major examples of electrogenic pumps we discussed? Electrogenic pump is a transport protein that generates voltage across a membrane (ex. ). What is the difference between primary and secondary active transport? primary moves ions across a membrane and creates a difference in charge across that membrane it is directly dependent on ATP. secondary is the movement of material due to the electrochemical gradient established by primary active transport. What is co-transport? Cotransport occurs when active transport of a solute indirectly drives transport of other solutes What are the three types of carrier proteins for active transport? Uniporter, symporter, antiporter Bulk Transport What is bulk transport? Does it require energy? Does require energy What kinds of molecules are transported by bulk transport? Large molecules like polysaccharides and proteins What is the difference between endocytosis and exocytosis? In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents to the cells exterior; in endocytosis, the cell takes in molecules and particulate matter by forming new vesicles from the plasma membrane

What are the three types of endocytosis? Under what conditions are each used? Phagocytosis- cell takes in large particles or other cells, pinocytosis-cell take in molecules, including water, which the cell needs from extracellular fluid, receptor-mediated endocytosisclathrin attaches to the plasma membrane’s cytoplasmic side. Define phagocytosis, pinocytosis, potocytosis, receptor-mediated endocytosis. Phagocytosis- cell takes in large particles or other cells, pinocytosis-cell take in molecules, including water, which the cell needs from extracellular fluid, potocytosis- variation of pinocytosis’ uses a coating protein, caveolin, on the plasma membrane’s cytoplasmic side which performs a similar function to clathrin, receptor-mediated endocytosis- clathrin attaches to the plasma membrane’s cytoplasmic side. How is receptor-mediated endocytosis related to hypercholesterolemia? The flu? Failure of RME can cause hypercholesterolemia. While RME is designed for specific substances (“bad” cholesterol/ low-density lipoprotein), other substances can gain entry at the same time (flu, diphtheria, cholera toxin)...