The electron flow from the substrate(NADH2
or FADH2)to O2 (through ETS) is
the source of energy for the formation of ATP. This is called oxidative
Transfer of hydrogen and electrons through ETS
As stated earlier, the most common acceptor in
respiration reactions is NAD. Thus, stet is transferred to Co-Q
via-FMN (Flavin mononucleotide).
At one step in Kreb’s cycle, hydrogen is accepted
by FAD. From FAD, it is transferred to Co-Q.
At Co-Q, the hydrogen undergoes ionization, i.e.
it splits into electrons and protons.
2e- + 2H+
Therefore, from Co-Q onwards, only the electrons
are transferred through the ETS along the chain of the electron
carrying molecules. The protons (H+) are transferred across the
inner membrane into the intermembrane space.
The first electron acceptor in the chain is cytochrome.
b. It accepts the electrons from Co-Q and transfers them first to
cytochrome C1, and then to cytochrome C1. From cytochrom C1, electrons
are accepted by cytochrome oxidase. In the final step, cytochrome
oxidase donates electrons to the free molecular oxygen. In other
words, oxygen acts as the last electron acceptor in the respiratory
chain (aerobic respiration).
Oxygen receives 2 electrons through the ETS and
2 protons directly from the aqueous medium to form one molecule
1/2O2 + 2 e- + 2H+ ®H2O
Utilization of oxygen at the end of the ETS is
the final step in aerobic respiration and is called terminal