The ATP in glycolysis is produced in the cell cytoplasm but that from the Krebs Cycle is produced in the mitochondria. The mitochondrial membrane contains an ATP-synthase protein complex that harnesses a proton flow into the production of ATP from ADP and Pi.

Is the ATP made in the cytoplasm during glycolysis made in a similar or different way?



The ATP in glycolysis is produced directly in certain reactions of the type:

X-PO32– + ADP → Y + ATP

in a process is called substrate-level phosphorylation.

A key preceding reaction in the pathway is the one catalysed by glyceraldehyde 3-phosphate dehydrogenase, in which free orthophosphate is incorporated into a sugar phosphate in a reaction of the type:

Z + PO43– → X-PO32–

(I have used X, Y and Z because other changes occur in the structures.)

This is totally different from the oxidative phosphorylation that occurs in the mitochondrion. In both cases the (free) energy driving the generation of ATP comes from oxidation of sugars involving cofactors such as NAD+ to NADH. In oxidative phosphorylation the reoxidation of NADH in the membrane (ultimately by molecular oxygen) is used to set up a proton gradient, which can then be used to drive the ATP-synthase. In substrate-level phosphorylation the chemistry of the intermediates is manipulated so that particular reactions involve sufficient free energy change to drive the conversion of ADP to ATP directly. (The anaerobic reoxidation of the NADH does not produce ATP in this latter case.)

You should read a text-book of biochemistry for the details, which are too extensive to present here. Berg et al. Section 16.1 covers this well, and is available on-line.

  • $\begingroup$ I have edited my original answer that had the unintended implication that ATP was generated in the G3PDH reaction. I have also tried to illustrate the principle of substrate-level phosphorylation, but have used general reactions to avoid the distraction of the actual chemistry, which can be found elsewhere. $\endgroup$ – David Sep 21 '16 at 4:57

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