Biochemistry: The Chemical Reactions of Living Cells, Volume 2 - D. Metzler 1980

How electrons meet oxygen, how ATP is generated in the process, and other related phenomena

In this chapter, we will examine The oxidation of the reduced hydrogen carriers NADH and FADH₂. Aerobic Respiration is more familiar to us because it also occurs in our own bodies. Hydrogen atoms from NADH, FADH₂, and other reduced carriers pass along a chain of auxiliary carriers with progressively increasing positive reduction potentials, ultimately interacting with O₂ to form H₂О. In effect, it is not hydrogen atoms that are transferred, but electrons. The nuclei of the hydrogen atoms likely move freely through the solvent as protons. For this reason, the carrier chain is frequently referred to as the Electron Transport Chain or the Respiratory Chain. The oxidation of NADH and FADH₂ yields significantly more energy for The Cell than Fermentation; consequently, the chemistry of The electron transport chain and its associated ATP synthesis reactions is of paramount importance.

Some organisms, particularly Bacteria, derive energy by oxidizing H₂, H₂S, or Fe²⁺ rather than organic substrates. Furthermore, certain specialized bacteria perform Anaerobic respiration in which NO^-₃, SO^2-₄, or СО₂ act as oxidants for either reduced carriers or Reduced Inorganic Compounds. In this chapter, we will explore these energy-yielding processes, as well as the chemistry of reactions whereby oxygen atoms from O₂ molecules are incorporated into Organic compounds. Investigating cellular oxidation processes is quite challenging, largely because the relevant Enzymes are located on or within cellular membranes. In bacteria, these enzymes reside on the inner surface of The Plasma Membrane or on mesosome membranes. In eukaryotes, they are found in The inner mitochondrial membrane and, to a lesser extent, in the membranes of The Endoplasmic reticulum. The Study of Oxidative Phosphorylation (p. 391) has been particularly fraught with setbacks. Isolating the components involved proved extremely difficult, and reassembling those components back into an actively functioning system proved even harder.