Explain why the ATP yield from processes such as cellular respiration is generally given as a theoretical number

Question

What will be an ideal response?

Answer 1

The maximum yield of ATP from a single molecule of glucose is 38 ATP molecules. However, any given glucose molecule may produce fewer than this number of ATP molecules for a variety of reasons. A eukaryotic cell spends 2 ATP molecules in transporting NADH produced during glycolysis into the mitochondrion; this reduces the theoretical yield to 36 ATP. The yield might be even lower, because in chemiosmosis there is no direct relationship between the number of electrons used to create a proton gradient and the number of ATP molecules produced from that proton gradient. Proton gradients are used to drive other processes and activities in the cell besides ATP production, so some of the energy that is represented by the proton gradient can be "siphoned off" before it is used to make ATP. Some of the intermediates of glycolysis and the Krebs cycle can be used as substrates for other metabolic processes, and when the intermediates are diverted, the theoretical ATP yield is not realized.