Here are five hypothetical reactions numbered 15 1 A B G 5

Here are five hypothetical reactions (numbered 1-5).

1. A B                              G°\' = -5 kJ/mol

2. B C + D                       G°\' = +8 kJ/mol

3. B E                              G°\' = -10 kJ/mol

4. E F                               G°\' = +5 kJ/mol

5. D F                               G°\' = +1 kJ/mol

From these five reactions it is possible to write TWO metabolic paths that could generate the metabolite F starting with metabolite A. Which of these two pathways will proceed spontaneously based on the overall G°\' value?

Question options:

1, 5

1, 3, 4

1, 3, 5

1, 2, 5

The answer is NOT C.

Solution

The option 1 and 2 are correct.

For option 1: the production of F can be achieved if it is produced by substrates E or D. It is because these two only are making product F. in the option D---F is mentioned so the process require 1 kJ/mol energy which can be gain from A---B ( because it generates 5 kJ/mol energy; which is sufficient). It is possible because the final product F is required whether it come from any way. It is not necessary to have a reaction which makes B---D. Also cells always tend to spend less energy.

For option 2: it is achieved because overall reaction energy is -10KJ/mol. It is spontaneous.

The other options:

3: it is an unnecessary reaction because not considering sequential products. The B---E is unnecessary when there is no conversion of E—F. the question require product F starting with metabolite A. The fourth option is not favorable because of overall +4KJ energy.