The Respiratory Balance Sheet

It is possible to make calculations of the net gain of ATP for every glucose molecule oxidised; but in reality this can remain only a theoretical exercise.

These calculations can be made only on certain assumptions that:

There is a sequential, orderly pathway functioning, with one substrate forming the next and with glycolysis, TCA cycle and ETS pathway following one after another.

The NADH synthesised in glycolysis is transferred into the mitochondria and undergoes oxidative phosphorylation.

None of the intermediates in the pathway are utilised to synthesise any other compound.

Only glucose is being respired -no other alternative substrates are entering in the pathway at any of the intermediary stages.

ATP molecules produced during respiration

Net Gain of ATP

There is a net gain of 38 ATP molecules during aerobic respiration of one molecule of glucose.

The details of ATP produced have been given in the above table.

In most eukaryotic cells the net gain of ATP is 36 molecules.

Efficiency of Aerobic Respiration

(i) One ATP yields about 34 kJ energy.

(ii) Total energy obtained from 38 ATP moelcule is 1292 kJ. The glucose molecules stores energy of about 2870 kJ.

(iii) Efficiency = = 45%