10 Principles Of Bioenergetics

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| By Catherine Halcomb

Catherine Halcomb

Community Contributor

Quizzes Created: 1428 | Total Attempts: 5,932,599

Questions: 12 | Attempts: 2,701 | Updated: Mar 21, 2023

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Questions and Answers

1.

Describe why anabolism and catabolism need to be precisely regulated. Include in your answer what is meant by reciprocal regulation of anabolic and catabolic pathways.
2.

Describe using an equation, how a reaction in a biochemical pathway may occur spontaneously despite the standard free energy for that reaction being positive. Outline the difference between free energy and standard free energy in your answer.
3.

Which is INCORRECT? Energy is required by cells for:
- A.
  
  Transport of molecules or ions against a concentration gradient
- B.
  
  Synthesis of new chemical bonds
- C.
  
  Maintenance of body temperature
- D.
  
  Mechanical movement
- E.
  
  Hydrolysis of a molecule during an exothermic reaction
Correct Answer
E. Hydrolysis of a molecule during an exothermic reaction

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.

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4.

Which statement about catabolic reactions is true?
- A.
  
  Catabolic reactions are degradative and are generally exergonic
- B.
  
  Catabolic reactions are part of pathways responsible for synthesis for new chemical bonds
- C.
  
  Catabolic reactions generally have free enthalpy values close to zero and standard free energy values less than zero
- D.
  
  Catabolic reactions occur primarily in catabolic organisms
- E.
  
  Catabolic reactions oppose the second law of thermodynamics
Correct Answer
A. Catabolic reactions are degradative and are generally exergonic

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.

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5.

Which is NOT a mechanism for regulating metabolic pathways?
- A.
  
  Control of intracellular substrate concentration
- B.
  
  Control of allosteric enzymes by inhibitors and activators
- C.
  
  Control of cell temperature
- D.
  
  Control of amount of enzymes
- E.
  
  Control of enzymes through signalling substances (e.g. hormones)
Correct Answer
C. Control of cell temperature

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.

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6.

Reciprocal regulation refers to:
- A.
  
  The division of energy from the catalytic pathway by the anabolic pathway
- B.
  
  The opposite reaction type that is being referred to
- C.
  
  The ability of cells to simultaneously activate anabolic and catabolic reactions
- D.
  
  The ability of cells to simultaneously inactive anabolic and catabolic reactions
- E.
  
  Activation of one pathway, while suppressing the opposite pathway
Correct Answer
E. Activation of one pathway, while suppressing the opposite pathway

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.

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7.

If the ΔG'° of the reactions A → B is +20kJ/mol, under standard conditions the reaction:
- A.
  
  Will proceed spontaneously from right to left
- B.
  
  Will proceed spontaneously from left to right
- C.
  
  Will never reach equilbrium
- D.
  
  Will proceed to equilibrium at a rapid rate
- E.
  
  Is currently at equilibrium
Correct Answer
A. Will proceed spontaneously from right to left

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.

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8.

If the ΔG'° of the reaction A → B is -100 kJ/mol, under standard conditions the reaction:
- A.
  
  Is at equilbirum
- B.
  
  Will never reach equilibrium
- C.
  
  Will not occur spontaneously
- D.
  
  Will proceed at a rapid rate
- E.
  
  Will proceed spontaneously from left to right
Correct Answer
E. Will proceed spontaneously from left to right

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.

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9.

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
- A.
  
  Reaction 1 will proceed from right to left
- B.
  
  Reaction 2 will proceed from left to right
- C.
  
  Reaction 3, the sum of reaction 1 and 2, will occur spontaneously with overall free energy of –10 kJ/mol
- D.
  
  Reaction 1 will not proceed from left to right unless an enzyme is present
- E.
  
  Reaction 2 will proceed spontaneously
Correct Answer
D. Reaction 1 will not proceed from left to right unless an enzyme is present

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.

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10.

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?
- A.
  
  -9.1 kJ/mol
- B.
  
  -15.8 kJ/mol
- C.
  
  -200.2 kJ/mol
- D.
  
  +22.5 kJ/mol
- E.
  
  0 kJ/mol
Correct Answer
A. -9.1 kJ/mol

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)

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11.

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
- A.
  
  ΔG'° is +1.7 kJ/mol
- B.
  
  ΔG'° is –1.7 kJ/mol
- C.
  
  ΔG'° is incalculably large and negative
- D.
  
  ΔG'° is incalculably large and positive
- E.
  
  ΔG'° is zero
Correct Answer
A. ΔG'° is +1.7 kJ/mol

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)

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12.

What is the standard-state free energy (ΔG°) for the hydrolysis of ATP to ADP?
- A.
  
  +45.6 kJ/mol
- B.
  
  -45.6 kJ/mol
- C.
  
  -30.5 kJ/mol
- D.
  
  15.6 kJ/mol
- E.
  
  12.2 kJ/mol
Correct Answer
C. -30.5 kJ/mol

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

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Current Version
Mar 21, 2023

Quiz Edited by
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Apr 22, 2016

Quiz Created by
Catherine Halcomb

10 Principles Of Bioenergetics

Describe why anabolism and catabolism need to be precisely regulated. Include in your answer what is meant by reciprocal regulation of anabolic and catabolic pathways.

Describe using an equation, how a reaction in a biochemical pathway may occur spontaneously despite the standard free energy for that reaction being positive. Outline the difference between free energy and standard free energy in your answer.

Which is INCORRECT? Energy is required by cells for:

Which statement about catabolic reactions is true?

Which is NOT a mechanism for regulating metabolic pathways?

Reciprocal regulation refers to:

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

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

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

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

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

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?