Early estimates suggested that the oxidation of glucose via aerobic respiration would produce 38 ATP. Why do biologists now think this amount of ATP per molecule of glucose is not achieved in cells?
a. The proton-motive force is used in other transport steps, and there is loss of energy due to inefficiency in the system reducing the ATP yield.
b. Some ATP diffuses away from the mitochondria and becomes unusable, reducing the effective yield of ATP.
c. The conversion of NADH to NAD is the rate-limiting step and therefore reduces the overall production of ATP.
d. The proton motor has a limit to how fast it can rotate, which reduces the total yield of ATP.
