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Ch. 8 - Energy and Enzymes: An Introduction to Metabolism
All textbooksFreeman 8th EditionCh. 8 - Energy and Enzymes: An Introduction to MetabolismProblem 7
Chapter 8, Problem 7

In Figure 8.10, the energetic coupling of substrate phosphorylation and an endergonic reaction are shown. If the hydrolysis of ATP releases 7.3 kcal of free energy, use the graph in this figure to estimate what you would expect the ∆G values to be for the uncoupled reaction and the two steps in the coupled reaction.

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Identify the free energy change (ΔG) for the uncoupled reaction. The graph shows that the endergonic reaction requires an energy input, which is approximately +3.4 kcal/mol.
Determine the free energy change (ΔG) for the hydrolysis of ATP. The hydrolysis of ATP releases 7.3 kcal/mol of free energy.
Calculate the free energy change (ΔG) for the first step of the coupled reaction (formation of BP). The energy released from ATP hydrolysis (7.3 kcal/mol) is used to form BP, which is an exergonic reaction. The ΔG for this step is approximately -3.9 kcal/mol (7.3 kcal/mol - 3.4 kcal/mol).
Calculate the free energy change (ΔG) for the second step of the coupled reaction (formation of AB). The formation of AB from BP is an exergonic reaction, releasing energy. The ΔG for this step is approximately -3.4 kcal/mol.
Summarize the ΔG values: Uncoupled reaction: +3.4 kcal/mol, Coupled reaction (first step): -3.9 kcal/mol, Coupled reaction (second step): -3.4 kcal/mol.

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Related Practice
Textbook Question

Which of the following correctly describe an active site? Select True or False for each statement. T/F It is the location in an enzyme where substrates bind. T/F It is the place where a molecule or ion binds to an inactive enzyme to induce a shape change to make it active. T/F It is the portion of an enzyme where chaperones bind to help enzymes fold. T/F It is the site on an enzyme where catalysis occurs.

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Explain the lock-and-key model of enzyme activity. What is incorrect about this model?

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Textbook Question

If you were to expose glucose to oxygen on your lab bench, why would you not expect to see it burn as described by the reaction in Figure 8.6? a. The reaction is endergonic and requires an input of energy. b.The reaction is not spontaneous unless an enzyme is added. c. The sugar must first be phosphorylated to increase its potential energy. d. Activation energy is required for the sugar and oxygen to reach their transition state.

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Textbook Question

You have discovered an enzyme that appears to function only when a particular sugar accumulates. Which of the following scenarios would you predict to be responsible for activating this enzyme? a. The sugar cleaves the enzyme to form the active conformation. b. The sugar is an allosteric regulatory molecule for the enzyme. c. The sugar is a competitive inhibitor for the enzyme. d. The sugar phosphorylates the enzyme to form the active conformation

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