In a typical mammalian cell, the net transport by the sodiumpotassium exchange pump that maintains the 70 mV membrane potential is 500 singly charged ions per second. How much work does the pump do each second?

In a typical mammalian cell, the net transport by the sodiumpotassium exchange pump that maintains the 70 mV membrane potential is 500 singly charged ions per second. How much work does the pump do each second?

Physics for Scientists and Engineers: Foundations and Connections

1st Edition

ISBN:9781133939146

Author:Katz, Debora M.

Publisher:Katz, Debora M.

Chapter26: Electric Potential

Section: Chapter Questions

Problem 33PQ: A source consists of three charged particles located at the vertices of a square (Fig. P26.32),...

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Assume a length of axon membrane of about 0.10 m is excited by an action potential (length excited = nerve speed pulse duration = 50.0 m/s 2.0 103 s = 0.10 m). In the resting state, the outer surface of the axon wall is charged positively with K+ ions and the inner wall has an equal and opposite charge of negative organic ions, as shown in Figure P18.43. Model the axon as a parallel-plate capacitor and take C = 0A/d and Q = C V to investigate the charge as follows. Use typical values for a cylindrical axon of cell wall thickness d = 1.0 108 m, axon radius r = 1.0 101 m, and cell-wall dielectric constant = 3.0. (a) Calculate the positive charge on the outside of a 0.10-m piece of axon when it is not conducting an electric pulse. How many K+ ions are on the outside of the axon assuming an initial potential difference of 7.0 102 V? Is this a large charge per unit area? Hint: Calculate the charge per unit area in terms of electronic charge e per squared (2). An atom has a cross section of about 1 2 (1 = 1010 m). (b) How much positive charge must flow through the cell membrane to reach the excited state of + 3.0 102 V from the resting state of 7.0 102 V? How many sodium ions (Na+) is this? (c) If it takes 2.0 ms for the Na+ ions to enter the axon, what is the average current in the axon wall in this process? (d) How much energy does it take to raise the potential of the inner axon wall to + 3.0 102 V, starting from the resting potential of 7.0 102 V? Figure P18.43 Problem 43 and 44.
Assume a length of axon membrane of about 0.10 m is excited by an action potential (length excited = nerve speed pulse duration = 50.0 m/s 2.0 103 s = 0.10 m). In the resting state, the outer surface of the axon wall is charged positively with K+ ions and the inner wall has an equal and opposite charge of negative organic ions, as shown in Figure P18.43. Model the axon as a parallel-plate capacitor and take C = 0A/d and Q = C V to investigate the charge as follows. Use typical values for a cylindrical axon of cell wall thickness d = 1.0 108 m, axon radius r = 1.0 101 m, and cell-wall dielectric constant = 3.0. (a) Calculate the positive charge on the outside of a 0.10-m piece of axon when it is not conducting an electric pulse. How many K+ ions are on the outside of the axon assuming an initial potential difference of 7.0 102 V? Is this a large charge per unit area? Hint: Calculate the charge per unit area in terms of electronic charge e per squared (2). An atom has a cross section of about 1 2 (1 = 1010 m). (b) How much positive charge must flow through the cell membrane to reach the excited state of + 3.0 102 V from the resting state of 7.0 102 V? How many sodium ions (Na+) is this? (c) If it takes 2.0 ms for the Na+ ions to enter the axon, what is the average current in the axon wall in this process? (d) How much energy does it take to raise the potential of the inner axon wall to + 3.0 102 V, starting from the resting potential of 7.0 102 V? Figure P18.43 Problem 43 and 44.
Rank the potential energies of the four systems of particles shown in Figure CQ16.4 from largest to smallest. Include equalities if appropriate. Figure CQ16.4
A source consists of three charged particles located at the vertices of a square (Fig. P26.32), where the square has sides of length 0.243 m. The charges are q1 = 35.0 nC, q2 = 65.0 nC, and q3 = 56.5 nC. Find the electric potential at point A located at the fourth vertex. FIGURE P26.32 Problems 32 and 33.
Every cell in the body has organelles called mitochondria that can generate a voltage difference between their interior and exterior. If the capacitance of a mitochondrion is 4.0×10−11F and the potential difference between the interior and exterior is 0.18 V, how much electrical energy does it store? If a mitochondrion were to use all of its stored electrical energy to produce ATP molecules, and each ATP molecule requires 9.5×10−20J, how many molecules could it produce? (In reality, ATP molecules are produced by the flow of protons caused by the proton motive force, and not by the direct conversion of electrical energy stored by the capacitance of mitochondria.)
Potential in a different kind of cell. A typical mammalian cell at 37 ∘C, with only potassium channels open, will have the following equilibrium: K+ (intracellular) ⇌ K+ (extracellular), with an intracellular concentration of 150 mM K+, and 4.0 mM K+ in the extracellular fluid. What is the potential, in volts, across this cell membrane? Note: in this case, n = the charge on the ion, and Eo for a concentration cell = 0.00 V.
A potential difference of 102 mV exists between the inner and outer surfaces of the membrane of a cell. The inner surface is negative relative to the outer surface. How much work is required to eject a positive sodium ion (Na+) from the interior of the cell?
The nuclear fusion of two protons in stars releases 1.442 MeV, or about 2.3 × 10-13 J. In order to fuse, the two protons must get within 10-15 m of each other (about the radius of a proton). What is the change in electric potential when moving one proton from infinitely far away to within 10-15 m of another proton? How much energy is necessary to push the protons this close together? Your answer should show you why it is difficult to develop a self-sustaining fusion reactor.
In Example 23.14 we estimated the capacitance of the cell membrane to be 89 pF, and in Example 23.15 we found that approximately 10,000 Na+ ions flow through an ion channel when it opens. Based on this information and what you learned about the action potential, estimate the total number of sodium channels in the membrane of a nerve cell.
A potential difference exists between the inner and outer surfaces of the membrane of a cell. The inner surface is negative relative to the outer surface. If 1.25 x 10^-20 J of work is required to eject a positive sodium ion (Na+) from the interior of the cell, what is the magnitude of the potential difference between the inner and outer surfaces of the cell?
A potential difference AV exists between the inner and outer surfaces of the membrane of a cell. The inner surface is negative relative to the outer surface. If 1.50 × 10-20 J of work is required to eject a positive potassium ion (K*) from the interior of the cell, what is the magnitude of the potential difference (in millivolts) between the inner and outer surfaces of the cell? |AV| = mV
Why are birds not electrocuted by sitting upon a high potential power line?