As discussed in Chapter 13, calcium is an important regulator of the citric acid cycle. Calcium is transported across the mitochondrial inner membrane by a Ca²⁺ uniporter that is driven by the negative potential inside the matrix. 

(a) Assuming a membrane potential across the inner membrane of 180 mV (inside negative), calculate the ratio of the [Ca²⁺] in the matrix to that 

(b) Cytoplasmic [Ca^{2 +}] is on the order of 10^-7 M in a healthy cell. Based on your answer in (a), calculate the [Ca^{2 +}] that would exist in the matrix
at equilibrium. Is this a physiologically reasonable answer? If not, provide an explanation.

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in the cytoplasm (i.e., AG = 0). [Ca²+]m [Ca²+ ]c that would exist at equilibrium