Question

1. In normal mitochondria the rate of electron transfer is tightly coupled to the demand for ATP. When the rate of use of ATP is relatively low, the rate of electron transfer is low; when demand for ATP increases, electron-transfer rate increases. Under these conditions of tight coupling, the number of ATP molecules (P) produced per atom of oxygen (O) consumed when NADH is the electron donor -- the so-called "P/O ratio" -- is about 2.5. (Lehninger EOC #6) a. Predict the effect of a relatively low concentration of uncoupling agent on the rate of electron transfer and the P/O ratio. b. Ingestion of uncouplers causes profuse sweating and an increase in body temperature. Explain this phenomenon in molecular terms. What happens to the P/O ratio in the presence of uncouplers? c. The uncoupler 2,4-dinitrophenol (DNP) was once prescribed as a weight-reducing drug. How could this agent, in principle, serve as a weight-reducing aid? d. Uncoupling agents are no longer prescribed, because some deaths occurred following their use. Why might the ingestion of uncouplers lead to death?

          1. In normal mitochondria the rate of electron transfer is tightly coupled to the demand for ATP.
When the rate of use of ATP is relatively low, the rate of electron transfer is low; when demand for
ATP increases, electron-transfer rate increases. Under these conditions of tight coupling, the
number of ATP molecules (P) produced per atom of oxygen (O) consumed when NADH is the
electron donor -- the so-called "P/O ratio" -- is about 2.5. (Lehninger EOC #6)
a. Predict the effect of a relatively low concentration of uncoupling agent on the rate of electron
transfer and the P/O ratio.
b. Ingestion of uncouplers causes profuse sweating and an increase in body temperature. Explain
this phenomenon in molecular terms. What happens to the P/O ratio in the presence of
uncouplers?
c. The uncoupler 2,4-dinitrophenol (DNP) was once prescribed as a weight-reducing drug. How
could this agent, in principle, serve as a weight-reducing aid?
d. Uncoupling agents are no longer prescribed, because some deaths occurred following their
use. Why might the ingestion of uncouplers lead to death?

1. In normal mitochondria the rate of electron transfer is tightly coupled to the demand for ATP.
When the rate of use of ATP is relatively low, the rate of electron transfer is low; when demand for
ATP increases, electron-transfer rate increases. Under these conditions of tight coupling, the
number of ATP molecules (P) produced per atom of oxygen (O) consumed when NADH is the
electron donor – the so-called "P/O ratio" – is about 2.5. (Lehninger EOC #6)
a. Predict the effect of a relatively low concentration of uncoupling agent on the rate of electron
transfer and the P/O ratio.
b. Ingestion of uncouplers causes profuse sweating and an increase in body temperature. Explain
this phenomenon in molecular terms. What happens to the P/O ratio in the presence of
uncouplers?
c. The uncoupler 2,4-dinitrophenol (DNP) was once prescribed as a weight-reducing drug. How
could this agent, in principle, serve as a weight-reducing aid?
d. Uncoupling agents are no longer prescribed, because some deaths occurred following their
use. Why might the ingestion of uncouplers lead to death?

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