Question

A metabolic reaction A to B is endergonic, with a standard free energy change of +0.5 kcal/mol. Describe two specific ways in which this reaction could be made favorable.

Answer 1

Two types of reactions : a) Exergonic reactions : An exergonic reaction is a reaction where the change in the free energy is negative indicating a spontaneous reaction.

b) Endergonic reaction : An  is a reaction in which the standard change in free energy is positive, and energy is absorbed. These kind of reactions are non spontaneous or unfavorable.

Two ways in which Endergonic reactions can be made favourable

1 )Endergonic reaction can occur by coupling them to another reaction which is exergonic more than them as in this case more than 0.5 kcal/ mol

For example biological reactions proceed via this method. Let assume this reaction below is

X. + Y ----------->. XY

too endergonic to occur. However it is made possible in the body by coupling it to a strongly exergonic reaction – such as the conversion of ATP into ADP and inorganic phosphate ions, ATP → ADP + P_i, so that

X. +. ATP. ----------->. ADP. +. XP_{​​​​​i}

XP. +. Y. -------------->. XY. + P_{​​​​i}

2)  If the following step of a Endergonic reaction is rapid and extremely Exergonic than that reaction can be pulled upto transition state because after that Exergonic reaction will take place.