Question 1

Which of the following statements best describes the difference between equilibrium and homeostasis in cellular systems?

Accepted Answer

Homeostasis is a steady state in which concentrations of reactants and products are maintained far from equilibrium values, requiring continuous energy input.

Question 2

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

Accepted Answer

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

Question 3

A reaction has $$\Delta H \u003e 0$$ and $$\Delta S \u003e 0. $$Under what temperature conditions will this reaction be spontaneous?

Accepted Answer

At high temperatures, because the entropy term ($$T\Delta S) $$can outweigh the positive enthalpy.

Question 4

Which of the following best explains why phosphoenolpyruvate (PEP) has a higher phosphoryl group transfer potential than ATP?

Accepted Answer

PEP hydrolysis results in products with greater resonance stabilization, charge repulsion relief, and tautomerization.

Question 5

Consider the hydrolysis of ATP under cellular conditions: $$[ATP] = 5\,mM$$, $$[ADP] = 0.1\,mM$$, $$[P_i] = 35\,mM$$, $$\Delta G$$^{\circ'}$$ = -30.5\,kJ/mol. $$Which equation would you use to calculate the actual free energy change ($$\Delta G) $$under these conditions?

Accepted Answer

$$\Delta G = \Delta G$$^{\circ'}$$ + RT \ln \left( \frac{[ADP][P_i]}{[ATP]} \right)$$

Question 6

Which of the following is true regarding the second law of thermodynamics as it applies to biological (open) systems?

Accepted Answer

The change in free energy ($$\Delta G) $$determines whether a process is spontaneous at constant temperature and pressure.

Question 7

A cell maintains a sodium ion gradient across its membrane, with $$[Na^+]_{outside} = 145\,mM$$ and $$[Na^+]_{inside} = 12\,mM. If $$the membrane potential is $$-70\,mV ($$inside negative), which equation would you use to calculate the free energy change ($$\Delta G) $$for sodium ion transport from outside to inside?

Accepted Answer

$$\Delta G = RT \ln \left( \frac{[Na^+]_{inside}}{[Na^+]_{outside}} \right) + zF\Delta \psi$$

Question 8

Which of the following processes is considered exergonic?

Accepted Answer

The hydrolysis of ATP to ADP and inorganic phosphate under cellular conditions.

Question 9

Which statement best describes the role of coupling in cellular metabolism?

Accepted Answer

Coupling allows endergonic reactions to proceed by linking them to exergonic reactions, such as ATP hydrolysis.

Question 10

Which of the following is the correct expression for the Gibbs free energy change ($$\Delta G) at $$constant temperature and pressure?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 11

Which of the following statements about the standard reduction potential ($$E^{\circ'}) is $$correct?

Accepted Answer

A species with a higher $$E^{\circ'}$$ has a greater tendency to be reduced.

Question 12

Given the following half-reactions and their standard reduction potentials: 
$$	ext{NAD}^+ + 2e^- + H^+ ightarrow 	ext{NADH}$$, $$E^{\circ'} = -0.32$$\,V$$ 
$$	ext{Acetaldehyde} + 2e^- + 2H^+ ightarrow 	ext{Ethanol}$$, E$$^{\circ'}$$ = -0.20\,V$$ 
What is the standard free energy change ($$\Delta G$$^{\circ'}$$) for the oxidation of ethanol by NAD$$^+$$? (Use n = 2$, F = 96.5$$\,kJ/mol\cdot V$$)

Accepted Answer

$$\Delta G$$^{\circ'}$$ = -2 	imes 96.5 	imes (-0.20 - (-0.32)) = -2 	imes 96.5 	imes (0.12) = -23.16\,kJ/mol$$

Question 13

Which of the following best explains why living systems operate far from equilibrium?

Accepted Answer

Because maintaining homeostasis requires constant energy input to keep concentrations of metabolites far from equilibrium.

Question 14

Which of the following is NOT a reason why ATP hydrolysis is highly exergonic?

Accepted Answer

Tautomerization of the ADP product.

Question 15

A biochemical reaction has $$\Delta G$$^{\circ'}$$ = +5\,kJ/mol$$ but is observed to proceed spontaneously in a cell. Which of the following best explains this observation?

Accepted Answer

The actual concentrations of reactants and products make $$\Delta G$$ negative, even though $$\Delta G$$^{\circ'}$$ is positive.

Question 16

Which of the following is the correct definition of enthalpy ($$H) in $$the context of biochemistry?

Accepted Answer

Enthalpy is the heat exchanged between the system and the surroundings at constant pressure.

Question 17

Which of the following statements about the biochemical standard state is correct?

Accepted Answer

The activity of water is set to 1 and the activity of protons is set to 1 at pH 7.

Question 18

Which of the following is a real-life example of coupling an unfavorable reaction to a favorable one in biological systems?

Accepted Answer

Synthesis of ATP from ADP and $$P_i$$ during glycolysis using the energy released from phosphoenolpyruvate hydrolysis.

Chapter 3: The Energetics of Life – Thermodynamics and Free Energy in Biochemistry

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