Part ABacteria have a membrane potential, although themechanisms of how it is maintained diffor fromthose of mammalian cells. The transport of protonsacross the cell membrane is an important part ofthe machanism, so a bacterium's membranepotential varies with the protonconcentration-the pH-of the surrounding fluid.One strain of bacteria was found to have amembrane potential of -120 mV at a pH of 7.5. Abacterium can be modeled as a 1.5-um-diametersphere.How many positive ions are needed on the exxterior surtace to establish this membrane potential? (There are an equalnumber of negative ions on the interior surface.) Assume that the mombrane propertios are the same an those ofmammalian cells,lonsSubmitRequest Answer

Membrane Potential: It represents a balance between the equilibrium potentials of the ions that can…

Answered: Bacteria have a membrane potential,…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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Quantitative – diffusion time: Consider a spherical, single-celled organism which needs oxygen tosurvive. a. Assume oxygen needs to diffuse from the outside of the cell to its center. Write an equation thatgives the diffusion time in terms of the cell radius. b. The cell has a 4 micron (m) diameter, and diffusion coefficient of oxygen is 1.8 x 10-5 cm2/s inwater (assume diffusion is the same through the cell membrane). How long does it take for oxygento diffuse to the center of the cell? c. Cells typically need key molecules such as oxygen to survive. Diffusion times of oxygen can limithow big cells can become. If the cell gets too large for oxygen to reach its center, the cell coulddie. Calculate the size of a cell at which oxygen diffusion time becomes too slow and so limits theability of the cell to get that big. Explain your assumptions. How does this compare to typical cellsizes?
Electronegativity is the ability for an atom or molecule to attract electrons (see chapter 2). Considering the components of theelectron-transport chain, with protein I being the beginning of the chain and protein IV the end of the chain, which end has thehigher electronegativity? Explain your answe
which surface to volume ratio woud be the most efficient for transmembrane transport of substance in cells
During an investigation on membrane transport, a researcher exposed bacterial cells to different concentrations of two different solutes: A and B. The rate of transport of each solute into cells isrepresented in the graphSolute ASolute BSolute ConcentrationWhich of the following best explains the greater rate of transport for solute A than for solute B at higher solute concentrations?A Solute A is being transported by simple diffusion, which does not rely on membrane proteins to control the rate of transportSolute A is being transported by active transport, which uses ATP and has higher rates of transport than passive transportSolute A is being transported by facilitated diffusion, which uses membrane proteins to increase the rate of transportRate of Transport
Depicted is a rod-shaped bacterium that can be approximated as a cylinder with two spherical caps, r = 0.5 micron. If the difference between the osmolarities inside and outside is 10 mosM, what would be the tension in the bacterial envelope? Is it uniform? (concentrations are expressed in mol/L)
Hoechst 33342 is a membrane-permeant dye thatfluoresces when it binds to DNA. When a population ofcells is incubated briefly with Hoechst dye and then sortedin a flow cytometer, which measures the fluorescence ofeach cell, the cells display various levels of fluorescence asshown in Figure Q17–1.
(a)Aquaporins and membrane channel protein in plant and animal,they permit the movement of water across the membrane.Explain why this is necessary.(b) Explain the importance of cell surface membrane to cell
The cell membranes of mammalian red blood cells are permeableto urea. If red blood cells are dropped into a solution of urea thatis identical in osmotic pressure (isosmotic) to the cytoplasm ofthe cells, although the cells do not swell and burst as quickly aswhen they are dropped simply into pure water, they eventuallyswell and burst. Explain. Also discuss how you would designa solution into which red cells could be placed without everswelling. (Hint: Think about whether urea will stay on theoutside of the cells and the implications for osmotic pressures.)
Ion transporters are “linked” together—not physi-cally, but as a consequence of their actions. For example,cells can raise their intracellular pH, when it becomes tooacidic, by exchanging external Na+ for internal H+, usinga Na+–H+ antiporter. The change in internal Na+ is thenredressed using the Na+-K+ pump.A. Can these two transporters, operating together,normalize both the H+ and the Na+ concentrations insidethe cell?B. Does the linked action of these two pumps causeimbalances in either the K+ concentration or the mem-brane potential? Why or why not?
For fusion of a vesicle with its target membrane tooccur, the membranes have to be brought to within 1.5 nmso that the two bilayers can join (Figure Q13–1). Assum-ing that the relevant portions of the two membranes at thefusion site are circular regions 1.5 nm in diameter, calcu-late the number of water molecules that would remainbetween the membranes. (Water is 55.5 M and the volumeof a cylinder is πr2h.) Given that an average phospholipid occupies a membrane surface area of 0.2 nm2, how manyphospholipids would be present in each of the opposingmonolayers at the fusion site? Are there sufficient watermolecules to bind to the hydrophilic head groups of thisnumber of phospholipids? (It is estimated that 10–12 watermolecules are normally associated with each phospho-lipid head group at the exposed surface of a membrane.)
Some antibiotics act as carriers that bind an ion on one side of a membrane, diffuse through the membrane, and release the ion on the other side. The conductance of a lipid-bilayer membrane containing a carrier antibiotic decreased abruptly when the temperature was lowered from 40°C to 36° C. In contrast, there was little change in conductance of the same bilayer membrane when it contained a channel-forming antibiotic. Why?
20. Active transport of a substanceacross a membrane requires A A gradientB the expenditure of ATPCwaterD diffusion

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