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Back of the Envelope ATP Calculations
QUESTION
ANSWER

Of all the food calories we ingest, how
many of them are used to spin our mitochondrial ATP synthase motors, generating the ATP we use every day?
_____________________________

FOOD TO ATP CALCULATIONS


ESTIMATES / ASSUMPTIONS

  • 3 x 1013 cells per average human being

  • 500 mitochondria / cell (noting that liver, brain, & muscle contain up to 1000-2000/cell)

  • 2000 ATP synthase complexes / mitochondria

  • 50 ATPs synthesized/ATP synthase / second -7.3 kcals of energy needed to synthesize 1 mole of ATP

  • 1 mole of any substance = 6.022 x 1023 molecules of that substance


CALCULATIONS

STEP 1: (7.3kcal/mole ATP) x (1.0 mole / 6.022 x 1023 molecules) = 1.2 x 10-23 kcal/ATP molecule formed

STEP 2: (1.2 x 10-23 kcal/ATP) x (50 ATP/synthase*sec) = 6 x 10-22 kcal/synthase*sec

STEP 3: (6 x 10-22 kcal / synthase*sec) x (2000 synthase/mito. = 1.2 x -10-18 kcal/mito.*sec

STEP 4: (1.2 x 10-18 kcal/mito.*sec) x (500 mito/cell) = 6 x 10-16 kcal/cell*sec

STEP 5: (6 x 10-16 kcal/cell*sec) x (3 x 1013 cells/body) = 1.8 x -10-2 kcal/body*sec

STEP 6:(1.8 x 10-2/ kcal/body*sec) x (86,400 sec/day) = 1555 kcal/day

Summary: if energy conversion inefficiencies are disregarded and all ATP synthase rotors were to operate at peak speeds at all times, then ~1500 kcal of an average 2000 kcal diet would be used to generate ATP molecules. The efficiency of food energy utilization is only about 20-25%, so these numbers are approximations only. The point is: most of the food and oxygen we utilize is dedicated to driving ATP-synthase rotors!!


Updated: April 6, 2019 10:21 AM