In a chemical reaction, 1,3-bisphosphoglycerate + ADP yields 3-phosphoglycerate plus ATP. What is the delta G for this reaction?

Question

A.  Greater than zero.
B.  Less than zero.
C.  Equal to zero.
D.  Cannot be determined

Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?

  Gather Content
  What do you already know about free energy in enzymatic reactions? What other information is related to the question?

  Choose Answer
Do you have all the information needed to answer the question?

  Reflect on Process
  Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

B.  Less than zero.

Clarify Question
What is the key concept addressed by the question?
        · The question asks for you to determine the free energy characteristics for a chemical reaction.    
What type of thinking is required?
        · You are being asked to take what you already know about enzymes and free energy and apply your understanding to determine the energy characteristics of the enzyme-based reaction.

  Gather Content
  What do you already know about free energy in enzymatic reactions? What other information is related to the question?
        · To solve this problem you’ll need to apply what you know about free energy and how it is associated with different types of enzyme reactions. What free energy characteristics determine whether a reaction will occur or not?
        · What clues does the question give you about delta G? Does the reaction require the breakdown of ATP or produce ATP? What types of reaction require ATP hydrolysis in order to run?

  Choose Answer
Do you have all the information needed to answer the question?
        · Recall that the change in free energy in an enzyme-based reaction is classified as exergonic or endergonic. Exergonic reactions have a negative delta G and are spontaneous, whereas endergonic reactions have a positive delta G and are nonspontaneous. Remember also that nonspontaneous reactions can be made to work if there is sufficient investment of energy (e.g. coupled reactions).
        · Since the question says nothing about the need to invest energy such as ATP, that is one clue that the reaction is exergonic and has a negative delta G. Another clue is the reaction shows that ADP is converted to ATP rather than the other way around. The lack of ATP hydrolysis and coupling to an endergonic reaction indicates that the reaction must not have a positive delta G, which would indicate an endergonic reaction. Clearly, an energy conversion of some kind has occurred, so delta G definitely does change. The only suitable option left would be a negative delta G, which is corroborated by both the clues and the process of elimination.

  Reflect on Process
  Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        · Answering this question correctly depended on your ability to use your understanding of enzymes and free energy to determine what the free energy change would be for the reaction.
        · If you got an incorrect answer, did you remember that enzyme reactions can be classified as exergonic and endergonic based on whether or not their change in free energy is positive or negative? Did you remember that exergonic reactions have a negative delta G and endergonic reactions have a positive delta G? Were you able to see that ADP eventually formed ATP and infer that the reaction would have to be exergonic and therefore have a negative delta G?