Initiation of Electron Transport Chain:
Once the NADH has been made from a metabolite in the citric
acid cycle inside of the mitochondria, it interacts with the
first complex 1 enzyme, known as NADH reductase. This complex
1 contains a coenzyme flavin mononucleotide (FMN) which is similar
The sequence of events is that the NADH, plus another hydrogen
ion enter the enzyme complex and pass along the 2 hydrogen ions,
ultimately to an interspace in the mitochondria. These hydrogen
ions, acting as a pump, are utilized by ATP synthetase to produce
an ATP for every two hydrogen ions produced. Three complexes
(1, 3, 4) act in this manner to produce 2 hydrogen ions each,
and thus will produce 3 ATP for every use of the complete electron
In addition, NADH passes along 2 electrons to first FMN, then
to an iron-sulfur protein (FeS), and finally to coenzyme Q. The
net effect of these reactions are to regenerate coenzyme NAD+.
This regeneration of reactants occurs in many of the reactions
so that a cycling effect occurs. The NAD+ is ready
to react further with metabolites in the citric acid cycle.
Coenzyme Q, which also picks up an additional 2 hydrogen ions
to make CoQH2, is soluble in the lipid membrane and
can move through the membrane to come into contact with enzyme
In summary, the very first enzyme complex in the electron
transport chain is coupled with the formation of ATP. The coupled
reaction may be written as:
a) MH2 + NAD+ ---> NADH + H+
+ M + energy
b) ADP + P + energy ---> ATP + H2O
|Quiz: What is the definition
of a coupled reaction?
|When NADH converts back to NAD+,
is this oxidation or reduction?
|When CoQ converts to CoQH2, is this
oxidation or reduction?
of Electron Transport - Thomas M. Terry, The University of
Link to Chime: Electron
Transfer Flavin - Department of Biochemistry,The University