10 Principles Of Bioenergetics

1. Which statement about catabolic reactions is true?

Catabolic reactions are degradative and are generally exergonic

Catabolic reactions are part of pathways responsible for synthesis for new chemical bonds

Catabolic reactions generally have free enthalpy values close to zero and standard free energy values less than zero

Catabolic reactions occur primarily in catabolic organisms

Catabolic reactions oppose the second law of thermodynamics

Catabolic reactions are degradative and generally exergonic because they involve the breakdown of larger molecules into smaller ones, releasing energy in the process. This energy release is due to the breaking of chemical bonds, which results in a decrease in the overall energy of the system. Therefore, catabolic reactions are characterized by the release of energy and the degradation of complex molecules.

Explanation

Catabolic reactions are degradative and generally exergonic because they involve the breakdown of larger molecules into smaller ones, releasing energy in the process. This energy release is due to the breaking of chemical bonds, which results in a decrease in the overall energy of the system. Therefore, catabolic reactions are characterized by the release of energy and the degradation of complex molecules.

2. If the ΔG'° of the reaction A → B is -100 kJ/mol, under standard conditions the reaction:

Is at equilbirum

Will never reach equilibrium

Will not occur spontaneously

Will proceed at a rapid rate

Will proceed spontaneously from left to right

The negative value of ΔG° indicates that the reaction is exergonic, meaning it releases energy. This suggests that the reaction will proceed spontaneously in the forward direction (from left to right) under standard conditions.

Explanation

The negative value of ΔG° indicates that the reaction is exergonic, meaning it releases energy. This suggests that the reaction will proceed spontaneously in the forward direction (from left to right) under standard conditions.

3. Which is INCORRECT? Energy is required by cells for:

Transport of molecules or ions against a concentration gradient

Synthesis of new chemical bonds

Maintenance of body temperature

Mechanical movement

Hydrolysis of a molecule during an exothermic reaction

Hydrolysis is a process that requires energy input, not the release of energy. In hydrolysis, a molecule is broken down into smaller components by the addition of water. This process requires energy to break the bonds holding the molecule together. In an exothermic reaction, energy is released, not consumed. Therefore, hydrolysis of a molecule during an exothermic reaction is incorrect.

Explanation

Hydrolysis is a process that requires energy input, not the release of energy. In hydrolysis, a molecule is broken down into smaller components by the addition of water. This process requires energy to break the bonds holding the molecule together. In an exothermic reaction, energy is released, not consumed. Therefore, hydrolysis of a molecule during an exothermic reaction is incorrect.

4. Which is NOT a mechanism for regulating metabolic pathways?

Control of intracellular substrate concentration

Control of allosteric enzymes by inhibitors and activators

Control of cell temperature

Control of amount of enzymes

Control of enzymes through signalling substances (e.g. hormones)

Control of cell temperature is not a mechanism for regulating metabolic pathways. While temperature can affect the rate of metabolic reactions, it is not a direct regulatory mechanism. The other options listed - control of intracellular substrate concentration, control of allosteric enzymes by inhibitors and activators, control of amount of enzymes, and control of enzymes through signaling substances - all play important roles in regulating metabolic pathways.

Explanation

Control of cell temperature is not a mechanism for regulating metabolic pathways. While temperature can affect the rate of metabolic reactions, it is not a direct regulatory mechanism. The other options listed - control of intracellular substrate concentration, control of allosteric enzymes by inhibitors and activators, control of amount of enzymes, and control of enzymes through signaling substances - all play important roles in regulating metabolic pathways.

5. If the ΔG'° of the reactions A → B is +20kJ/mol, under standard conditions the reaction:

Will proceed spontaneously from right to left

Will proceed spontaneously from left to right

Will never reach equilbrium

Will proceed to equilibrium at a rapid rate

Is currently at equilibrium

The positive value of ΔG° indicates that the reaction is non-spontaneous in the forward direction under standard conditions. Therefore, the reaction will proceed spontaneously in the reverse direction, from right to left, in order to reach equilibrium.

Explanation

The positive value of ΔG° indicates that the reaction is non-spontaneous in the forward direction under standard conditions. Therefore, the reaction will proceed spontaneously in the reverse direction, from right to left, in order to reach equilibrium.

6. What is the standard-state free energy (ΔG°) for the hydrolysis of ATP to ADP?

+45.6 kJ/mol

-45.6 kJ/mol

-30.5 kJ/mol

15.6 kJ/mol

12.2 kJ/mol

The standard-state free energy (∆G°) for the hydrolysis of ATP to ADP is -30.5 kJ/mol.

Explanation

The standard-state free energy (∆G°) for the hydrolysis of ATP to ADP is -30.5 kJ/mol.

7. Reciprocal regulation refers to:

The division of energy from the catalytic pathway by the anabolic pathway

The opposite reaction type that is being referred to

The ability of cells to simultaneously activate anabolic and catabolic reactions

The ability of cells to simultaneously inactive anabolic and catabolic reactions

Activation of one pathway, while suppressing the opposite pathway

Reciprocal regulation refers to the activation of one pathway while simultaneously suppressing the opposite pathway. This means that when one pathway is activated, the other pathway is inhibited or suppressed. This type of regulation allows cells to carefully control and balance the activation of anabolic (building up) and catabolic (breaking down) reactions. By activating one pathway and suppressing the opposite pathway, cells can ensure that the energy and resources are allocated appropriately and efficiently based on their current needs.

Explanation

Reciprocal regulation refers to the activation of one pathway while simultaneously suppressing the opposite pathway. This means that when one pathway is activated, the other pathway is inhibited or suppressed. This type of regulation allows cells to carefully control and balance the activation of anabolic (building up) and catabolic (breaking down) reactions. By activating one pathway and suppressing the opposite pathway, cells can ensure that the energy and resources are allocated appropriately and efficiently based on their current needs.

8. When a mixture containing an equal concentration of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme phosphohexose isomerase, the final mixture contains twice as much glucose 6-phosphate as fructose 6-phosphate. Which one of the following statements is correct, when applied to the reaction below (R = 8.315 J/mol•K and T = 298 K)? Glucose 6-phosphate ↔ fructose 6-phosphate

ΔG'° is +1.7 kJ/mol

ΔG'° is –1.7 kJ/mol

ΔG'° is incalculably large and negative

ΔG'° is incalculably large and positive

ΔG'° is zero

Keq = [B]/[A] = 1/2
ΔGo = -RT ln Keq
ΔGo = -8.315 x 298x ln (1/2)
ΔGo = +1718 J/mol = +1.7 kJ/mol (answer a)

Explanation

Keq = [B]/[A] = 1/2
ΔGo = -RT ln Keq
ΔGo = -8.315 x 298x ln (1/2)
ΔGo = +1718 J/mol = +1.7 kJ/mol (answer a)

9. Given the following information, calculate the actual free energy of the below reaction. A → B; K_eq = 10; concentration in the cell of A = 0.2 M; B = 0.05 M; R = 8.315 J/mol.K; T = 298 K?

-9.1 kJ/mol

-15.8 kJ/mol

-200.2 kJ/mol

+22.5 kJ/mol

0 kJ/mol

ΔGo = -RT ln Keq= -8.315 x 298 x ln10 = -5700 J/mol
ΔG = ΔGo + RT ln ([B]/[A])
ΔG = -5700 J/mol + 8.315 x 298 x ln (0.05/0.2)
ΔG = -5700 - 3400
ΔG = -9100 J/mol = -9.1 kJ/mol (answer a)

Explanation

ΔGo = -RT ln Keq= -8.315 x 298 x ln10 = -5700 J/mol
ΔG = ΔGo + RT ln ([B]/[A])
ΔG = -5700 J/mol + 8.315 x 298 x ln (0.05/0.2)
ΔG = -5700 - 3400
ΔG = -9100 J/mol = -9.1 kJ/mol (answer a)

10. Which is NOT true about the following reactions?A → B ΔG = +20 kJ/mol = reaction 1C → D ΔG = –30 kJ/mol = reaction 2 A + C → B + D = reaction 3

Reaction 1 will proceed from right to left

Reaction 2 will proceed from left to right

Reaction 3, the sum of reaction 1 and 2, will occur spontaneously with overall free energy of –10 kJ/mol

Reaction 1 will not proceed from left to right unless an enzyme is present

Reaction 2 will proceed spontaneously

The given statement is true because the positive value of ΔG for reaction 1 indicates that it is not spontaneous in the forward direction. In order for the reaction to proceed from left to right, an enzyme is required to lower the activation energy barrier.

Explanation

The given statement is true because the positive value of ΔG for reaction 1 indicates that it is not spontaneous in the forward direction. In order for the reaction to proceed from left to right, an enzyme is required to lower the activation energy barrier.