Chapter 6 Questions (end of chapter) – Flashcards
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c
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How is the structure of saturated fats different from that of unsaturated fats?
a) All of the carbons in the hydrocarbon tails of saturated fats are bonded to one another with double bonds.
b) Saturated fats have three hydrocarbon tails bonded to the glycerol molecule instead of just two.
c) The hydrocarbon tails in a saturated fat have the maximum number of hydrogens possible.
d) Saturated fats have no oxygens present.
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a
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What distinguished amphipathic lipids from other lipids?
a) Amphipathic lipids have polar and nonpolar regions.
b) Amphipathic lipids have saturated and unsaturated regions.
c) Amphipathic lipids are steroids.
d) Amphipathic lipids dissolve in water.
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b
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If a solution surrounding a cell is hypertonic relative to the inside of the cell, how will water move?
a) It will move into the cell via osmosis.
b) It will move out of the cell via osmosis.
c) It will not move, because equilibrium exists.
d) It will evaporate from the cell surface more rapidly.
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d
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When does a concentration gradient exist?
a) when membranes rupture
b) when solute concentrations are high
c) when solute concentration are low
d) when solute concentrations differ on the two sides of a membrane
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For osmosis to occur, a concentration gradient and membrane that allows water to pass, but not the solute, must be present.
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What two conditions must be present for the effects of osmosis to occur?
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Channel proteins form pores in the membrane and carrier proteins undergo conformational changes to shuttle molecules or ions across the membrane.
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In terms of structure, how do channel proteins differ from carrier proteins?
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b
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If a cell were placed in a solution with a high potassium concentration and no sodium, what would happen to the sodium-potassium pump's activity?
a) It would stop moving ions across the membrane.
b) It would continue using ATP to pump sodium out of the cell and potassium into the cell.
c) It would move sodium and potassium ions across the membrane, but no ATP would be used.
d) It would reverse the direction of sodium and potassium ions to move them against their gradients.
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No, because they have no polar end to interact with water. Instead, these lipids would float on the surface of water, or collect in droplets suspended in water, reducing their interaction with water to a minimum.
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Cooking oil lipids consist of long, unsaturated hydrocarbon chains. Would you expect these molecules to form membranes spontaneously? Why or why not? Describe, on a molecular level, how you would expect these lipids to interact with water.
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Hydrophilic, phosphate-containing head groups interact with water; hydrophobic hydrocarbon tails associate with each other. A bilayer is more stable than are independent phospholipids in solution.
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Explain why phospholipids form a bilayer in solution, and why the process is spontaneous.
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Ethanol's polar hydroxyl group reduces the speed at which it can cross a membrane, but its small size and lack of charge would allow it to slowly cross membranes - between the rates of water and glucose transport.
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Ethanol (C2H5OH) is the active ingredient in alcoholic beverages. Would you predict that this molecule crosses lipid bilayers quickly, slowly, or not at all? Explain your reasoning.
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Only nonpolar, hydrophobic amino acid residues would be found in the portion of the protein that crosses the membrane. In the interior of the bilayer, these residues would be hidden from the water solvent and interact with the nonpolar lipid tails.
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Integral membrane proteins are anchored in lipid bilayers. Of the following four groups of amino acids - nonpolar, polar, charged/acidic, charged/basic - which would likely be found in the portion that crosses the lipid bilayer? Explain your reasoning.
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Chloride ions from sodium chloride will move from the left side to the right through the CFTR. Water will initially move from the right side to the left by osmosis, but as chloride ions move to the right, water will follow. Na+ and K+ ions will not move across the membrane.
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Examine the experimental chamber in Fig 6.7a. If the lipid bilayer were to contain the CFTR molecule, what would pass through the membrane if you added a 1-molar solution of sodium chloride on the left side and a 1-molar solution of potassium ions on the right? Assume that there is an equal amount of water on each side at the start of the experiment.
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c
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In an experiment, you create two groups of liposomes - one made from red blood cell membranes and the other from frog egg cell membranes. When placed in water, those made with red blood cell membranes burst more rapidly than those made from frog membranes. What is the best explanation for these results?
a) The red blood cell liposomes are more hypertonic relative to water than the frog egg liposomes.
b) The red blood cell liposomes are more hypotonic relative to water than the frog egg liposomes.
c) The red blood cell liposomes contain aquaporins, which are not abundant in the frog egg liposomes.
d) The frog egg liposomes contain ion channels, which are not present in the red blood cell liposomes.
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Flip-flops should be rare because they require a polar head group to pass through the hydrophobic portion of the lipid bilayer. To test this prediction, you could monitor the number of dyed phospholipids that transfer from one side of the membrane to the other in a given period of time.
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When phospholipids are arranged in a bilayer, it is theoretically possible for individual molecules in the bilayer to flip-flop. That is, a phospholipid could turn 180° and become part of the membrane's other surface. From what you know about the behavior of polar heads and nonpolar tails, predict whether flip-flops are frequent or rare. Then design an experiment, using a planar bilayer with one side made up of phospholipids that contain a dye molecule on their hydrophilic head, to test your prediction.
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Organisms that live in very cold environments are likely to have highly unsaturated phospholipids. The kinks in unsaturated hydrocarbon tails keep membranes fluid and permeable, even at low temperatures. Organisms that live in very hot environments would likely have phospholipids with saturated tails to prevent membranes from becoming too fluid and permeable.
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Unicellular organisms live in a wide range of habitats, from the hot springs in Yellowstone National Park to the freezing temperatures of the Antarctic. Make a prediction about about the saturation status of membrane phospholipids in organisms that live in extremely cold environments. Explain your reasoning.
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Adding a methyl group makes a drug more hydrophobic and thus more likely to pass through a lipid bilayer. Adding a charged group makes it hydrophilic and reduces its ability to pass through the lipid bilayer. These modifications would help target the drug to either the inside or outside of cells, respectively.
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When biomedical researcher design drugs, they sometimes add methyl (CH3) groups or charged groups to the molecules. If these groups are not directly involved in the activity of the drug, predict the purpose of these modifications and explain why these strategies are necessary.
