A total of 30.5 kJ/mol of free energy is needed to synthesize ATP from ADP and P

Question

A total of 30.5 kJ/mol of free energy is needed to synthesize ATP from ADP and Pi? when the reactants and products are at 1M concentrations and the temperature is 25*C. Because the actual physiological concentrations of ATP, ADP, and Pi? are not 1M, and the temperature is 37*C, the free energy required to synthesize ATP under physiological conditions is different from delta G'^0.

A) Calculate the free energy required to synthesize ATP in a human liver cell when the physiological concentrations of ATP, ADP, and Pi? are 3.5, 1.50, and 5.0 mM, respectively.

B) A 68kg (150 lb) adult requires a calorie intake of 2,000 kcal (8,360 kJ) of food per day. The food is metabolized and the free energy is used to synthesize ATP, which then provides energy for the body's daily chemical and mechanical work. Assuming that the efficiency of converting food energy into ATP is 50%, calculate the weight (kg) of ATP used by an adult (68 kg) in a day. What percentage of the body weight does this represent?

C) Although adults synthesize large amounts of ATP daily, their body weight, structure, and composition do not change significantly during this period. Explain this apparent contradiction.

Explanation / Answer

Given here ?Go' = 30.5kJ/mol; T = 37+273 = 310K; [ATP] = 3.5mM; [ADP] = 1.5 mM; [Pi] = 5.0 mM

Now, the free energy required to synthesize ATP is given by , ?G=?G°'+ RT ln[ATP] /[ADP][Pi]

(a) Therefore, ?G = 30500J/mol + 8.315J*mol-1*K-1 (298K) ln 103*(3.5)/(1.5)*5 = 46352 J/mol or 46.35kJ/mol

(b) We have calculated that 46.35 kJ or energy is required to synthesize one mol of ATP. Now if mol wt of ATP is 507.18 g/mol, then we can say that 46.35 kJ of energy is required to synthesize 507.18 g of ATP or 0.507kg of ATP.

So, if 50% of 8360kJ of energy is consumed in synthesizing ATP then, total kgs of ATP synthesized per day will be given by 46.35*(0.5*8360)/0.507 = 382136 kg of ATP.

(c) Since all of the ATP produced daily is used up by the human body in doing different biological (metabolic processes), chemical, and mechanical work hence no observable change happensin weight, structure, and composition of the body, although human body does change on a microscopic level everday.

Thanks!

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