Q: If the standard reduction potential for FAD is -0.22 V and for ubiquinone (Q) is 0.04 V, what is the value of $$E^{\circ}$$_{cell}$$ for the oxidation of FADH_2$ by Q?

$$E^{\circ}$$_{cell} = 0.04 - (-0.22) = 0.26\ \text{V}$$

Q: Using $$n = 2$$ electrons and $$F = 96,485\ \text{C/mol}$$, what is the standard free energy change ($$\Delta G$$^{\circ}$$) for the oxidation of FADH_2$ by Q, given E$$^{\circ}$$_{cell} = 0.26\ \text{V}$$?

$$\Delta G$$^{\circ}$$ = -2 \times 96,485 \times 0.26 = -50,972.2\ \text{J/mol}$$

Question 1

Given the standard reduction potentials $$E^{\circ}$$ for ubiquinone (Q) and FAD of 0.04 V and -0.22 V, respectively, what is the correct formula to calculate the standard free energy change ($$\Delta G$$^{\circ}$$) for the oxidation of FADH_2$ by Q?

Accepted Answer

$$\Delta G$$^{\circ}$$ = -$$nFE^{\circ}$$_{cell}$$

Question 2

If the standard reduction potential for FAD is -0.22 V and for ubiquinone (Q) is 0.04 V, what is the value of $$E^{\circ}$$_{cell}$$ for the oxidation of FADH_2$ by Q?

Accepted Answer

$$E^{\circ}$$_{cell} = 0.04 - (-0.22) = 0.26\ 	ext{V}$$

Question 3

Using $$n = 2$$ electrons and $$F = 96,485\ 	ext{C/mol}$$, what is the standard free energy change ($$\Delta G$$^{\circ}$$) for the oxidation of FADH_2$ by Q, given E$$^{\circ}$$_{cell} = 0.26\ 	ext{V}$$?

Accepted Answer

$$\Delta G$$^{\circ}$$ = -2 	imes 96,485 	imes 0.26 = -50,972.2\ 	ext{J/mol}$$

Question 4

The synthesis of ATP from ADP and $$P_i$$ under standard conditions requires approximately $$\Delta G$$^{\circ}$$ = +30.5\ 	ext{kJ/mol}. $$Based on your calculation for the oxidation of FADH$$_2 by Q$$, is this reaction able to drive ATP synthesis?

Accepted Answer

Yes, because $$\Delta G$$^{\circ}$$ for the oxidation is more negative than the requirement for ATP synthesis.

Question 5

Which of the following best describes the role of standard reduction potential ($$E^{\circ}) in $$determining the direction of electron flow in a redox reaction?

Accepted Answer

Electrons flow from the species with lower $$E^{\circ} to $$the species with higher $$E^{\circ}.$$

Question 6

If a redox reaction has a positive $$E^{\circ}$$_{cell}$$, what can be inferred about its spontaneity under standard conditions?

Accepted Answer

The reaction is spontaneous because $$\Delta G$$^{\circ}$$ is negative.

Question 7

Which equation correctly relates the standard free energy change ($$\Delta G$$^{\circ}$$) to the equilibrium constant (K$) for a reaction?

Accepted Answer

$$\Delta G$$^{\circ}$$ = -RT \ln K$$

Question 8

A patient has a mutation that decreases the reduction potential of FAD in their mitochondria. What effect would this have on the free energy change for the oxidation of FADH$$_2 by Q$$?

Accepted Answer

The free energy change would become more negative, increasing the driving force for ATP synthesis.

Question 9

Which of the following statements about the relationship between $$E^{\circ}$$_{cell}$$ and $$\Delta $$G^{\circ} is $$correct?

Accepted Answer

A higher $$E^{\circ}$$_{cell}$$ corresponds to a more negative $$\Delta $$G^{\circ}.$$

Question 10

In a biochemical pathway, if the reduction potential of the electron acceptor is increased, what is the effect on the overall free energy change of the pathway?

Accepted Answer

The overall free energy change becomes more negative, favoring the pathway.

Question 11

Which of the following best explains why the oxidation of FADH$$_2 by Q $$can drive ATP synthesis under standard conditions?

Accepted Answer

Because the free energy released ($$\Delta G$$^{\circ}$$) is greater than the energy required for ATP synthesis.

Question 12

If the number of electrons transferred ($$n) in a $$redox reaction is doubled, what happens to the standard free energy change ($$\Delta G$$^{\circ}$$)?

Accepted Answer

$$\Delta G$$^{\circ}$$ is doubled.

Question 13

Which of the following is a plausible consequence if the reduction potential of Q is decreased in the electron transport chain?

Accepted Answer

The driving force for ATP synthesis would decrease.

Question 14

A scientist wants to increase the yield of ATP in a cell by manipulating the electron transport chain. Which strategy would be most effective?

Accepted Answer

Increase the reduction potential of the terminal electron acceptor.

Question 15

Which of the following is NOT a correct interpretation of the relationship between reduction potential and free energy?

Accepted Answer

A positive $$E^{\circ}$$_{cell}$$ always results in a positive $$\Delta $$G^{\circ}.$$

Calculating Free Energy from Redox Potentials and ATP Synthesis Feasibility

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