Though the net amount of ATP in the body is rather small (measured in a few gram

Question

Though the net amount of ATP in the body is rather small (measured in a few grams: example, mammalian skeletal muscle contains about 375 mg/100 g of tissue), its reuse and reprocessing over a 24 hour period is considerable. One biochemist calculated the effective amount of ATP synthesized by a person in a 24 hour period. It is estimated to be equivalent to a person's body weight. The molar mass of ATP is 507.21 g/mol. (A) How many moles of ATP would a 150 lb person produce in a 24 hour period? (B) The energy of hydrolysis of ATP is about 7.5 kcal/mol. The energy to biol 1.0 g of water at 100 degrees C (bp) is 539 cal/g. The energy required to heat liquid water from some temperature below the bp, to the bp is 1.0 cal/g degree C. If a quantity of water is initially at 37 degrees C and heated with the energy liberated by hydrolysis of ATP determined in part (A), how many moles of water can be brought to a boil? (1.0 lb = 453.6 g)

Explanation / Answer

a)

ATP produced in 24 hours = weight of person = 150 lb

= 150 lb * 453.6 g/lb = 68040 g

= 68040 g / 507.21 g/mol = 134.15 mol

b)

The energy of hydrolysis of ATP = 7.5 kcal/mol

Energy of hydrolysis of ATP produced (Q) = 7.5 * 134.15 = 1006.09 kcal

Let the mass water required be M grams

The energy required to heat liquid water from 37 C to 100 C (Q1):

= 1.0 cal/g C * M * (100 – 37) = 63 M cal

The energy to boil M g of water at 100 degrees C (Q2):

= 539 cal/g * M = 539 M cal

Total energy required to boil M grams of water = Q1 + Q2 = 539 M + 63 M = 602 M cal

= 0.602 M kcal

Q = Q1 + Q2

1006.09 = 0.602 M

M = 1671.25 g

Moles of water that can be brought to boil = M / 18 g/mol

= 1671.25 / 18 = 92.8 moles

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