LECTURE 8 - THE RESPIRATORY CHAIN

Abstract

This chapter discusses the respiratory chain in mitochondria without specific consideration of the phosphorylation process. The donors that feed hydrogen atoms into the respiratory chain are nutrients that are degraded by the cell to pyruvate, fatty acids, or amino acids. These compounds are converted to acetyl CoA, oxaloacetate, or α-ketoglutarate, and channeled into a pathway where they are subjected to the well-known intramolecular acrobatics of the Krebs cycle. The respiratory chain consists of proteins with firmly bound prosthetic groups such as the iron porphyrins and flavin nucleotides. In addition, mitochondria contain cofactors such as pyridine nucleotides and quinones that can be reversibly removed from the particles. The absorption spectra of the protein-bound prosthetic groups and cofactors change on reduction, and are sufficiently different from each other to permit individual measurements even in intact cells. The chapter provides an overview of cytochromes a, a3, c, c1 and b. In the chain of succinate oxidation, there is succinate dehydrogenase, and in the chain of DPNH oxidation there is DPNH dehydrogenase, both of which transfer electrons to cytochrome b. These two flavoproteins have been obtained from mitochondria in a highly purified state.