1 Foundations of Biology/Spring 2018 Practice questions for Exam 3 . A cell biol

Question

1 Foundations of Biology/Spring 2018 Practice questions for Exam 3 . A cell biologist interested in Ca2 transport across the plasma membrane of yeast made the following Page 9 of measurements on cells at 25°C: Vm -150 mV [Ca2] 20 mM [Ca2+]s = 0.4 mM For a charged solute: AGinward RT In zFVm F 23,062 cal/mol-V ISl. a) What is the free energy change for the inward movement of Ca2 into the yeast celr? b) Ass suming no change in either [Ca?) or [Ca2lo at what membrane potential would there be no net movement of Ca2 across the membrane? The advantage to the cell of the gradual oxidation of glucose during cellular respiration compared with it combustion to CO2 and H2O in a single step is: a) more free energy is released for a given amount of glucose oxidized b) c) d) no energy is lost as heat. energy can be extracted in usable amounts. more CO2 is produced for a given amount of glucose oxidized. The final metabolite produced by glycolysis is: a) acetyl CoA. b) pyruvate c) 3-phosphoglycerate. d) glyceraldehyde 3-phosphate. -oxidation of fatty acids is: The final metabolite produced by a) acetyl CoA. b) pyruvate. c) 3-phosphoglycerate. alvceraldehyde 3-phosphate. inle to regenerate citric acid by reacting with malate is:

Explanation / Answer

Solution :

Question 1:

Vm = -150 mV = - 0.15V

T = 25°C = 298.15

z = 2

[Ca2+] inside = 20mM = 0.02 M

[Ca2+] outside = 0.4mM = 0.0004 M

?G[in] = + RT ln (S[in] / S[out]) + zFV

a) Calculation of free energy change for the inward movement of Ca+2 into the yeast cell :

?G[in] = + RT ln (S[in] / S[out]) + zFV, substitutng values we get :

?G[in] = 8.314*298.15 * ln(0.02/0.0004) + (2*96491.4*-0.15) = -19255.23 J/mol

b)Membrane potential at which there be no net movement of calcium across the membrane :

When there is no net movement of calcium across the membrane RT ln (S[in] / S[out]) + zFV = 0

V = + RT ln (S[in] / S[out])/zF

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