The Oxidation of Glucose

With glucose being one of the most common sugars in the biosphere (and certainly the most common in labs), the oxidation of glucose is a major source of chemical energy for many organisms. This process - the conservation of energy through complete oxidation of glucose using oxygen - is called “respiration.” Much of the energy produced during glucose oxidation is stored as ATP. If we take a look at the full oxidation of glucose to carbon dioxide and water

Glucose + 6 O2 ⇌ 6 CO2 + 6 H2O

we find that ΔrG’m ≈ -2910 kJ / mol. According to our calculation from above, that’s enough energy to make ~65 ATP (in theory). But most organisms generate 30 ATP or less through the oxidization of glucose (Nelson et al., 2008; Flamholz et al., 2014). 1

Biochemistry textbooks often write this pathway as generating 36 ATP

Glucose + 6 O2 + 36 ADP + 36 Pi ⇌ 6 CO2 + 42 H2O + 36 ATP

giving a ΔrG’m of around -1350 kJ / mol. 2 In other words, there’s more free energy! Cells could, in principle, make a lot more ATP than they do in practice. Which begs the question: why not make more ATP? If you’re interested in learning more, consider looking up “chemical motive force” for reversible reactions.


See BioNumbers ID 111475, which discusses ATP yield from glucose in yeast, for example.


Remember ΔrG’m assumes all concentrations are 1 mM.