Coupled Systems: The Electron Transport Chain and Oxidative Phosphorylation

In the mitochondria of almost all kinds of life above bacteria, the two closely coupled systems of the electron transport chain and the atp synthase act continuously to provide essential energy for life processes. The visualization of the two systems above follows elements from Ahern and Karp.

The Electron Transport Chain

The electron transport chain or ETC is tightly coupled to the process of oxidative phosphorylation via the atp synthase system for the production of useful energy for metabolism in the form of ATP. These coupled processes are present in all mitochondria, which are present in all plant and animal life above the level of microbes. Even in the microbes, there are ETCs embedded in the cell membranes, even though they don't possess mitochondria.

A normal animal cell will have on the order of a thousand mitochondria, and each mitochondrion has on the order of a thousand ETCs, so a cell has something on the order of a million of these coupled energy tools! (Ahern)

Electrons are transported through the ETC by means of four large protein complexes called complex I through IV. Complex I makes use of the electron carrier NADH which has been given energy in the TCA cycle. Complex I pumps protons into the inter-membrane space and hands off the energetic electrons to the small electron courier Co Q which aids in transporting to Complex III. Complex II makes use of the electron carrier FADH₂ and provides electrons to Co Q. Complex III pumps protons to the inter-membrane space and continues the electron transport, delivering the electrons to cytochrome-C. Complex IV continues the process of pumping protons to add to the proton excess in the inter-membrane space and makes the final delivery of the electrons to oxygen in the mitochondrial matrix.

Oxidative Phosphorylation to Produce ATP