Bioenergetics and ATP Questions and Answers

Answer: B

The actual free energy change is equal to standard free energy change for the reaction.

The actual free energy change is related to the standard value by

\[ \Delta G = \Delta G^{\circ} + RT\ln Q \]

where Q is the ratio of product to reactant concentrations. With every reactant and product at 1 M, Q = 1 and \(\ln 1 = 0\), so \(\Delta G = \Delta G^{\circ}\) at the start of the reaction.

\(\Delta G\) is zero only at equilibrium, when Q equals the equilibrium constant, which these conditions do not describe. It would be less or greater than \(\Delta G^{\circ}\) only if Q were below or above 1.

Answer: B

The swimmer should increase Fats.

A non-stop Channel swim lasts many hours in cold water. The body's carbohydrate store (liver and muscle glycogen) holds only about 2000 kcal and is largely used up within the first couple of hours of hard exercise, after which prolonged, moderate-intensity work runs increasingly on fat oxidation. Fat yields about 9 kcal per gram against about 4 for carbohydrate and protein, so it is the most compact fuel reserve, and a layer of body fat also insulates the swimmer against the cold.

Protein is used for building and repair rather than as a main fuel, so the options with protein are not the answer. Carbohydrates help in the early part of the swim, but the paper's point is the long-endurance demand, which fat meets.

Answer: C

The cell type is B.

\[ \begin{aligned} \Delta G &= \Delta G^{\circ\prime} \\ &+ RT \ln\frac{[ADP][P_{i}]}{[ATP]} \end{aligned} \]

Since \(\Delta G^{\circ\prime}\) is the same for all four, \(\Delta G\) is most negative where the mass-action ratio is smallest. In mM:

• L: \(1.8 \times 5.0 / 3.0 = 3.0\)
• K: \(1.3 \times 3.0 / 3.9 = 1.0\)
• B: \(0.7 \times 2.7 / 2.7 = 0.7\)
• M: \(0.9 \times 8.0 / 7.2 = 1.0\)

B has the smallest ratio, so the logarithm term is most negative there. M has the most ATP, but its high phosphate level brings its ratio up to that of K; L has the largest ratio and the least negative \(\Delta G\).

Answer: B

The strongest electron donor is the NAD⁺/NADH couple.

The tendency to donate electrons is measured by the standard reduction potential: the more negative it is, the more readily the reduced form gives up electrons. Approximate values at pH 7:

• NAD⁺/NADH: -0.32 V
• FAD/FADH₂ (free): about -0.22 V
• Pyruvate/lactate: -0.19 V
• Fumarate/succinate: +0.03 V

NADH has the most negative potential and so the highest tendency to donate electrons, which is why it feeds the respiratory chain at its start. Succinate is the weakest donor of the four.

Answer: C

The molecule without a phosphoanhydride bond is fructose-1,6-bisphosphate.

A phosphoanhydride bond links two phosphate groups through an oxygen (P-O-P). In fructose-1,6-bisphosphate the two phosphates are attached separately to C1 and C6 of the sugar through phosphoester bonds (C-O-P); they are never joined to each other.

The others all contain the anhydride. ADP has one (between its α and β phosphates), ATP has two (α-β and β-γ), and pyrophosphate is itself two phosphates joined by a single anhydride bond.