Question

The phosphate translocase is an inner mitochondrial membrane symporter that transports H2PO4- and H+ into the mitochondrial matrix. Phosphate is a substrate for Complex V (the ATP Synthase), the enzyme that couples the synthesis of ATP to the H+ gradient formed by the electron transport chain. (a) Bongotoxin is a hypothetical compound that inhibits the phosphate translocase of the inner mitochondrial membrane. Explain why electron transport from NADH to O2 stops when bongotoxin is added to mitochondria (ie., why do electrons stop flowing through the electron transport chain even with an abundance of NADH and O2 present). What effect will the addition of the weak acid dinitrophenol (DNP) to the cytosol have on electron transport in bongotoxin-inhibited mitochondria? Be sure to explain your answers. (b) How much free energy is released (in KJ) when one mole of protons flows from the mitochondrial inner membrane space (IMS) to the mitochondrial matrix when the [H+] in the IMS is 7.9 x 10-8, the [H+] in the matrix is 7.9 x 10-10, and the membrane potential (∆) is 100 mV (negative inside)?

          The phosphate translocase is an inner mitochondrial membrane symporter that transports H2PO4- and H+
into the mitochondrial matrix. Phosphate is a substrate for Complex V (the ATP Synthase), the enzyme
that couples the synthesis of ATP to the H+ gradient formed by the electron transport chain.
(a) Bongotoxin is a hypothetical compound that inhibits the phosphate translocase of the inner
mitochondrial membrane. Explain why electron transport from NADH to O2 stops when bongotoxin is
added to mitochondria (ie., why do electrons stop flowing through the electron transport chain even
with an abundance of NADH and O2 present). What effect will the addition of the weak acid
dinitrophenol (DNP) to the cytosol have on electron transport in bongotoxin-inhibited mitochondria?
Be sure to explain your answers.
(b) How much free energy is released (in KJ) when one mole of protons flows from the mitochondrial
inner membrane space (IMS) to the mitochondrial matrix when the [H+] in the IMS is 7.9 x 10-8, the
[H+] in the matrix is 7.9 x 10-10, and the membrane potential (∆) is 100 mV (negative inside)?

Added by Dakota M.

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