Question

In order to conserve energy, regulatory mechanisms evolved in cells to control

a)the fastest reactions because their ΔGs are the most negative

b)reactions that are far from equilibrium because they produce molecules a cell may not need

c)reactions that readily proceed forwards and backwards because they produce no net change

d)the slowest reactions because their ΔGs are the most positive

Answer 1

in order to conserve energy, regulatory mechanisms evolved in cells to control

reactions that are far from equilibrium because they produce molecules that a cell may not need.

The same can be understood by the taking an example of glycolytic pathway which is regulated essentially at the phosphofructokinase step that converts fructose-6-phosphate to fructose -1,6 - bisphosphate. Phosphofructokinase is regulated by energy charge of the cell. The end product ATP of glycolysis inhibits the reaaction by raising the Km, whereas the AMP activates the reaction Thus, when energy is needed, glycolysis proceeds as usual, and stops when energy is plentiful.

There is no use in controlling a reaction that has reached equilibrium, since it neither moves forward nor backward, such a state is harmful for a cell. A cell always needs to have some charge, which it attains by not letting the reactions reach quilibrium.