. In a biochemical reaction, A + B-->C with äG = 30 kJ/mol. Which of the following reactions might be effectively coupled to this reaction so that it becomes more spontaneous?

Question

. In a biochemical reaction, A + B-->C with äG = 30 kJ/mol. Which of the following reactions might be effectively coupled to this reaction so that it becomes more spontaneous?

I. C + D are the reactants, and B + E are the products

äG = -40 kJ/mol

II. C + D are the reactants, and B + E are the products

äG = +40 kJ/mol

a.I only
b.II only
c.I or II
d.Neither I nor II can increase spontaneity.
e.No coupling is required as the reaction is already spontaneous.

Answer 1

Aren't I and II the same?

Answer 2

The only difference is the + and - for the dGrxn

Answer 3

Thank you for pointing out the obvious. I missed it.

I see it this way.
I. A+B==> C +30 (not spontaneous)
...C+D==> B+E -40
------------------
B and C cancel and adding we get
A + D ==> E +30-40 = -10 (spontaneous)
Under the other one dGrxn = +70 kJ.
So I think I should help. II will not.

Answer 4

Thank you very much! That's what I got. I appreciate it.

Answer 5

To determine which of the given reactions might be effectively coupled to the given biochemical reaction to make it more spontaneous, we need to consider the change in Gibbs free energy (ΔG) for each reaction.

In an exergonic (spontaneous) reaction, the change in Gibbs free energy (ΔG) is negative (ΔG < 0). Conversely, in an endergonic (non-spontaneous) reaction, ΔG is positive (ΔG > 0).

Given the following reactions:

I. C + D → B + E, ΔG = -40 kJ/mol
II. C + D → B + E, ΔG = +40 kJ/mol

We can determine if these reactions are effectively coupled with the given biochemical reaction (A + B → C) by adding the ΔG values. For a reaction to become more spontaneous, the total ΔG should be negative.

For reaction I, where ΔG = -40 kJ/mol, we can add this to the ΔG of the biochemical reaction (30 kJ/mol):
ΔG_total = ΔG_biochemical + ΔG_reaction I
= 30 kJ/mol + (-40 kJ/mol)
= -10 kJ/mol

Since ΔG_total is negative (-10 kJ/mol), reaction I can be effectively coupled to the biochemical reaction to increase spontaneity.

For reaction II, where ΔG = +40 kJ/mol, we can add this to the ΔG of the biochemical reaction (30 kJ/mol):
ΔG_total = ΔG_biochemical + ΔG_reaction II
= 30 kJ/mol + 40 kJ/mol
= 70 kJ/mol

Since ΔG_total is positive (70 kJ/mol), reaction II is not effectively coupled to the biochemical reaction to increase spontaneity.

Therefore, only reaction I can effectively couple with the biochemical reaction to make it more spontaneous. Hence, the correct answer is a. I only.