ATP is produced in glycolysis and ETS by oxidative phosphorylation during respiration.
The correct answer and explanation is:
ATP is produced in glycolysis and the electron transport system (ETS) by different mechanisms. In glycolysis, ATP is generated through substrate-level phosphorylation. In contrast, in the electron transport system, ATP is produced by oxidative phosphorylation, a process dependent on the electron transfer chain and chemiosmosis.
Glycolysis occurs in the cytoplasm and involves the breakdown of one molecule of glucose (a six-carbon sugar) into two molecules of pyruvate. This process involves several enzyme-catalyzed steps, one of which includes the transfer of a phosphate group to ADP to form ATP. Although glycolysis consumes two ATP molecules in the initial steps, it generates four ATP molecules later, resulting in a net production of two ATP molecules. This is an example of substrate-level phosphorylation, where a phosphate group is directly transferred from a high-energy substrate molecule to ADP.
Electron Transport System (ETS), which takes place in the inner mitochondrial membrane, involves a series of protein complexes that transfer electrons from molecules of NADH and FADH2 to oxygen, the final electron acceptor. As electrons move through the complexes, protons (H+) are pumped across the inner mitochondrial membrane, creating a proton gradient. This gradient is used by ATP synthase, a membrane protein, to produce ATP from ADP and inorganic phosphate. The production of ATP via the electron transport chain is referred to as oxidative phosphorylation because it relies on the oxidation of NADH and FADH2 to drive the synthesis of ATP.
In summary, glycolysis produces ATP through substrate-level phosphorylation by directly transferring a phosphate to ADP, whereas the electron transport system produces ATP by oxidative phosphorylation, harnessing the energy from electron transfers to generate a proton gradient used to drive ATP synthesis. Both processes are essential in cellular respiration, contributing to the cell’s energy production.