SCIENCES

Back of the Envelope Calculations
QUESTION
ANSWER

Of the food calories we ingest, how
many of them are used to generate ATP?
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FOOD TO ATP CALCULATIONS


ESTIMATES / ASSUMPTIONS

3 x 10^13 cells/average human

500 mitochondria/cell (note: 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 10^23 molecules of that substance



CALCULATIONS

STEP 1: (-7.3kcal/mole ATP) x (1mole/6.022 x 10^23 molecules) = ~1.2 -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 10^13 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: roughly 1500 kcal of an average 2000-2200 kcal diet (~3/4 of calorie intake) is used to generate ATP molecules, which are then utilized to drive other processes within cells. The remaining calories ingested (roughly 500 kcals) generate body heat, maintain body structures, etc., etc., etc.


Updated: December 22, 2016 12:26 PM