Reaction A: glucose + fructose ⇔ sucrose ΔG°’ = +27.0 kJ/mol Reaction B: ATP ⇔ ADP + Pi ΔG°’ = –30.5 kJ/mol Which of the following statements are true regarding reaction A and reaction B at standard conditions?
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A negative ΔG°’ indicates a spontaneous (exergonic) reaction at standard conditions, while a positive ΔG°’ indicates a non-spontaneous (endergonic) reaction. The magnitude relates to how far from equilibrium the reaction is favored. Show more…
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In plant cells, the enzyme sucrose synthase combines glucose and fructose to generate sucrose. This reaction could be considered a coupled reaction with ATP hydrolysis as follows: ATP + H2O → ADP + Pi ΔG = -7.6 kcal/mol glucose + fructose → sucrose + H2O ΔG = X kcal/mol glucose + fructose + ATP → sucrose + ADP + Pi ΔG = -1.2 kcal/mol a) What is the ΔG for directly combining glucose and fructose to form sucrose (Solve for "X" in the above reactions)? In other words, what is ΔG for sucrose synthesis if the reaction were not coupled to ATP hydrolysis? You must explain your work to get full credit (2 pts). b) Would you ever expect the uncoupled synthesis of sucrose to take place in a cell? Use the ΔG you calculated in part (a) to explain why or why not in terms of energy requirements and thermodynamic spontaneity (3 pts).
Adi S.
1.9 Reactions are classified based on whether they give off, absorb heat or whether the free energy of the system decreases or increases during the reaction. Consider the following reaction under standard condition of 25°C, pH 7.5, to answer the following questions: The overall reaction: ATP + Glucose ⇔ ADP + Glucose-6-P (a) What do you understand by an induced-fit model of hexokinase? (b) Why is water excluded for the reaction catalysed by hexokinase? (c) Determine the equilibrium constant of the overall reaction if the free energy change is zero. (d) Predict the direction of the reaction.
Dominador T.
A3. The synthesis of sucrose from glucose and fructose is facilitated through the use of ATP as an energy source. The reaction equations for the process, with their Gibbs energy signs, are shown below: glucose + fructose ⇌ sucrose ΔG = Positive ATP + H2O ⇌ ADP + Pi ΔG = Negative glucose + fructose + ATP ⇌ sucrose + ADP + Pi ΔG = Overall Negative Answer A, B, and C. A. The two reactions shown above the line are coupled to generate the overall reaction under the line. Draw energy pathway diagrams that represent the top two reactions and the overall reaction. Correctly label ΔG and the axes in each case. B. The first reaction and the overall reaction have ΔGs as shown below. glucose + fructose ⇌ sucrose ΔG = +27 k glucose + fructose + ATP ⇌ sucrose + ADP + Pi ΔG = -3k Using these data, calculate the ΔG of the hydrolysis of ATP. Show your calculation. C. As part of the overall reaction, glucose is phosphorylated. Draw out a plausible general mechanism for how the reactions are coupled. You may show each molecule in cartoon form. There is no need to write out the structures in full.
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