Metabolism is the chemical process that involves the extraction of chemical ener
ID: 66404 • Letter: M
Question
Metabolism is the chemical process that involves the extraction of chemical energy from sugars and fats. One such reaction is: C6H12O6 + 6O2 6CO2 + 6H2O, Gº = -2870 kJ Some of this energy may be used to synthesize energy transport molecules, the most important of which is adenosine triphosphate (ATP). ADP + H3PO4 ATP + H2O, Gº = +30.6 kJ
a) How many ATP could be synthesized from the combustion of 1.0 mol of glucose?
b) Under normal physiological conditions, only 36 ATP molecules are produced. What percent of the energy is used and what percent is wasted? Where does the waste go?
Another biochemical reaction that produces ATP involves the conversion of acetylphosphate (CH3CO2PO3H2) to acetic acid and phosphoric acid. CH3CO2PO3H2 + H2O HC2H3O2 + H3PO4, Gº = -46.9 kJ c) Write the balanced chemical equation that shows the coupling of the acetylphosphate hydrolysis reaction and the ATP synthesis reaction. Determine the free energy change.
Explanation / Answer
a. For 100% energy efficiency, total number of ATP produced per 1.0 mol of glucose = 2870 kJ/mol glucose/ 30.6 kJ/ mol ATP = 94 ATP (This number is actually 32 because the energy efficiency is around 40% only)
b. Under normal physiological conditions, only 36 ATP molecules are produced. Thus, the energy efficiency is
= x kJ/ mol glucose/ 30.6 kJ/ mol ATP = 36 ===> x = 1101. 6.
Thus, the energy efficiency = 1101.6/ 2870* 100 = 38.3%