Biology Chapter 12 Principles of Membrane Transport - 5500 Words

Biology Chapter 12: Principles of Membrane Transport (Multiple Choice Questions Sample) Content: CHAPTER 12MEMBRANE TRANSPORT2009 Garland Science PublishingPrinciples of Membrane Transport12-1Indicate whether the following statements are true or false. If a statement is false, explain why it is false.A.CO2 and O2 are water-soluble molecules that diffuse freely across cell membranes.B.The differences in permeability between artificial lipid bilayers and cell membranes arise from variations in phospholipid content.C.Transporters are similar to channels, except that they are larger, allowing folded proteins as well as smaller organic molecules to pass through them.D.Cells expend energy in the form of ATP hydrolysis so as to maintain ion concentrations that differ from those found outside the cell.ANSWERA. False. Lipid-linked proteins are classified as integral membrane proteins because although they are not transmembrane proteins, they are covalently bound to membrane lipids and cannot be dissociated without disrupting the membrane's integrity.B. False. An embedded protein employs an amphipathic helix. The hydrophobic side interacts with the fatty acid tails of the membrane lipids and the hydrophilic portion interacts with the aqueous components of the cytosol.C. True.D. False. Membrane proteins that pump ions in either direction across the membrane are in the functional class of transporters.12-2Although the extracellular environment has a high sodium ion concentration and the intracellular environment has a high potassium ion concentration, both must be neutralized by negatively charged molecules. In the extracellular case, what is the principal anion?(a)HCO3à ¢Ã¢â€š ¬(b)Clà ¢Ã¢â€š ¬(c)PO43à ¢Ã¢â€š ¬(d)OHà ¢Ã¢â€š ¬12-3Circle the molecule in each pair that is more likely to diffuse through the lipid bilayer.A.amino acidsorbenzeneB.Clà ¢Ã¢â€š ¬orethanolC.glycerolorRNAD.H2OorO2E.adenosineorATP12-4We can test the relative permeability of a phospholipid bilayer by using a synthetic membrane that does not contain any protein components. Some uncharged, polar molecules are found to diffuse freely across these membranes, to varying degrees. Which of the following has the lowest rate of diffusion across an artificial membrane? Why?(a)glucose(b)water(c)glycerol(d)ethanolANSWERBenzene, ethanol, glycerol, O212-5For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once.A molecule moves down its concentration gradient by __________________ transport, but requires __________________ transport to move up its concentration gradient. Transporter proteins and ion channels function in membrane transport by providing a __________________ pathway through the membrane for specific polar solutes or inorganic ions. __________________ are highly selective in the solutes they transport, binding the solute at a specific site and changing its conformation so as to transport the solute across the membrane . On the other hand, __________________ discriminate between solutes mainly on the basis of size and electrical charge.activetransporter proteinsion channelsamino acidhydrophilicnoncovalentamphipathichydrophobicpassiveANSWERA molecule moves down its concentration gradient by passive transport, but requires active transport to move up its concentration gradient. Transporter proteins and ion channels function in membrane transport by providing a hydrophilicpathway through the membrane for specific polar solutes or inorganic ions. Transporter proteins are highly selective in the solutes they transport, binding the solute at a specific site andchanging its conformation so as to transport the solute across the membrane. On the other hand, ion channels discriminate between solutes mainly on the basis of size and electrical charge.Transporters and their Functions12-6A hungry yeast cell lands in a vat of grape juice and begins to feast on the sugars there, producing carbon dioxide and ethan ol in the process:C6H12O6 + 2ADP + 2Pi + H+ à ¯ 2CO2 + 2CH3CH2OH + 2ATP + 2H2OUnfortunately, the grape juice is contaminated with proteases that attack some of the transport proteins in the yeast cell membrane, and the yeast cell dies. Which of the following could account for the yeast cellà ¢Ã¢â€š ¬s demise?(a)toxic buildup of carbon dioxide inside the cell(b)toxic buildup of ethanol inside the cell(c)diffusion of ATP out of the cell(d)inability to import sugar into the cell12-7Ion channels are classified as membrane transport proteins. Channels discriminate by size and charge. In addition to Na+, which one of the following ions would you expect to be able to freely diffuse through a Na+ channel? Explain your answer.(a)Mg2+(b)H+(c)K+(d)Clà ¢Ã¢â€š ¬12-8Transporters, in contrast to channels, work by ________________.(a)specific binding to solutes(b)a gating mechanism(c)filtering solutes by charge(d)filtering solutes by size12-9Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called _____________.(a)active transport(b)free diffusion(c)facilitated diffusion(d)passive transport12-10Indicate whether the statements below are true or false. If a statement is false, explain why it is false.A.Facilitated diffusion can be described as the favorable movement of one solute down its concentration gradient being coupled with the unfavorable movement of a second solute up its concentration gradient.B.Transporters undergo transitions between different conformations, depending on whether the substrate-binding pocket is empty or occupied.C.The electrochemical gradient for K+ across the plasma membrane is small. Therefore, any movement of K+ from the inside to the outside of the cell is driven solely by its concentration gradient.D.The net negative charge on the cytosolic side of the membrane enhances the rate of gl ucose import into the cell by a uniporter.ANSWERA. False. This describes coupled transport, which is one type of active transport. Facilitated diffusion can also be called passive transport, in which a solute always moves down its concentration gradient.B. True.C True.D. False. Glucose is an uncharged molecule, and its import is not directly affected by the voltage difference across the membrane if glucose is being transported alone.If the example given were the Na/glucose symporter, we would have to consider the charge difference across the membrane.12-11It is thought that the glucose transporter switches between two conformational states in a completely random fashion. How is it possible for such a system to move glucose across the membrane efficiently in a single direction?Although the opening of the glucose transporter on one side of the membrane or the other is random, the binding of glucose into the binding site of the transporter is not a random event. The affinity between th e glucose molecule and the transporter governs the binding event: transporter + glucose ÃÆ' transporter-glucose At high glucose concentrations the complex formation is favored; at low glucose concentrations dissociation of glucose from the transporter is favored. So, as long as there is a large concentration gradient, efficient transport can occur by the simple rules of binding equilibria.12-12Active transport requires the input of energy into a system so as to move solutes against their electrochemical and concentration gradients. Which of the following is not one of the common ways to perform active transport?(a)Na+-coupled(b)K+-coupled(c)ATP-driven(d)light-driven12-13The Na+-K+ ATPase is also known as the Na+-K+ pump. It is responsible for maintaining the high extracellular sodium ion concentration and the high intracellular potassium ion concentration. What happens immediately after the pump hydrolyzes ATP?(a)Na+ is bound.(b)ADP is bound.(c)The pump is phosphorylated.(d)The pum p changes conformation.12-14If ATP production is blocked in an animal cell, the cell will swell up. Explain this observation.ATP is required to power the Na+-K+ pump, which is necessary for maintaining osmotic balance. The pump requires ATP hydrolysis to drive its pumping cycle. So, in theabsence of ATP production, the Na+ concentration inside the cell will increase. This is followed by passive diffusion of water across the membrane, causing the cell to swell.12-15Fill in Table Q12-15. In the "type of transport" column, designate whether the transporter works by uniport, symport, or antiport mechanisms.28003527686000Table Q12-15Na+-K+ pump is antiport that requires ATP the main function is to maintain the gradients of Na n K ion across plasma membrane.Na-glucose symport energy source Na gradient the import of glucose across plama membrane.Ca pump uniport requires ATP function is to export CA ion from the cytosol bacteriarhopdosin is a uniport energy source light exporting H ion s from the cell12-16You have prepared lipid vesicles (spherical lipid bilayers) that contain Na+-K+ pumps as the sole membrane protein. All of the Na+-K+ pumps are oriented in such a way that the portion of the molecule that normally faces the cytosol is on the inside of the vesicle and the portion of the molecule that normally faces the extracellular space is on the outside of the vesicle. Assume that each pump transports one Na+ ion in one direction and one K+ ion in the other direction during each pumping cycle (see Figure Q12-16 for how the Na+-K+ pump normally functions in the plasma membrane).5086357493000Figure 12-16Predict what would ha...