The Krebs cycle takes its name from its founder, Hans Krebs. The Krebs cycle is composed of a series of nine reactions
in total. First, an enzyme removes the acetyl group from acetyl Co-A. This two carbon molecule combines with a four carbon
molecule called oxaloacetate to form a six carbon molecule called citrate. The next series of reactions is classified
as oxidation/reduction reactions. These start with the formation of two molecule of CO2 and one molecule of ATP. During the
cycle electrons reduce NAD and FAD that joins with H+ ions to form NADH and FADH2. Note, an extra NADH was formed during the
four molecules of NADH and one molecule of FADH2 are produced for each molecule of pyruvate that enters into the mitochondrion.
Since two molecules of pyruvate enter into the matrix for each molecule of oxidized glucose, eight molecules of NADH+ and
two molecules of FADH2 are produced. The krebs cycle in itself synthesizes six molecules of NADH+, two molecules of FADH2
and two molecules of ATP. At this stage no oxygen was used in the described reactions. Oxygen only plays a role in oxidative
phosphorylation during chimiosmosis. As well, the electrons stored on NADH and FADH2 are used during the electron transport
to produce ATP. At the end of the Krebs cycle, the molecule of glucose has been completely catabolized forming four molecules
of ATP and 12 electron transporters.