Chapter 12, Problem 12.120EP

Interpretation Introduction

Interpretation: To determine the reason why NADH and FADH₂ molecules do not yield the same number of ATP molecules.

Concept introduction: Electron transport chain is a sequence of biochemical reactions in which electrons and hydrogen atoms from the citric acid cycle are transferred to various intermediate carriers and finally reacts with molecular oxygen to form a water molecule. The reaction of the formation of the water is:

${\text{O}}_2+4{\text{e}}^{-}+4{\text{H}}^{+}\to 2{\text{H}}_{\text{2}}\text{O}$

There are four complexes associated with the electron transport chain that is present in the inner mitochondrial membrane. The four complexes that help in the electron transfer in the electron transport chain are:

Complex I: $\text{NADH-coenzyme}\text{Q reductase}$

Complex II: $\text{Succinate-coenzyme}\text{Q reductase}$

Complex III: $\text{Coenzyme}\text{Q-cytochrome c reductase}$

Complex IV: $\text{Cytochrome c oxidase}$

FADH₂ is the reduced form of flavin adenine dinucleotide. The main function of flavin adenine dinucleotide is to act as an oxidizing agent and used by the cell in oxidation reactions like oxidation of fatty acid.

NADH is the reduced form of nicotinamide adenine dinucleotide. It is employed as an oxidizing agent in various reactions like oxidation of secondary alcohol into a ketone. Its structure consists of three subunits: nicotinamide, ribose, and ADP.