In which part of the cell does the electron transport chain (ETC) occur?

The electron transport chain (ETC) occurs in the mitochondrial matrix and on the inner mitochondrial membrane. It is a crucial step in cellular respiration, where high-energy electrons from NADH and FADH2, generated from earlier metabolic processes (such as glycolysis and the citric acid cycle), are used to create a proton gradient across the inner mitochondrial membrane. This gradient ultimately drives the synthesis of ATP through oxidative phosphorylation.

The mitochondrial matrix is home to the various enzymes and other components that participate in the electron transport process. Here, electrons are passed through a series of protein complexes, each of which utilizes the energy from electron transfers to pump protons into the intermembrane space, creating a high concentration of protons outside the inner membrane. When protons flow back into the mitochondrial matrix through ATP synthase, ATP is produced.

In contrast, the nucleus is responsible for housing genetic material and overseeing cellular activities, the cytoplasm is where a multitude of metabolic processes occur but does not host the ETC, and the endoplasmic reticulum serves as a site for protein and lipid synthesis and does not play a direct role in the electron transport chain. Thus, the mitochondrial matrix is uniquely suited for the operation of the ETC due to its specific enzyme composition and