dioxide and a thioester bond is formed in its place between the former alphaketoglutarate
and coenzyme A to create a molecule of succinyl-coenzyme
A complex.
Step 5
A water molecule sheds its hydrogen atoms to coenzyme A. Then, a free-floating
phosphate group displaces coenzyme A and forms a bond with the succinyl
complex. The phosphate is then transferred to a molecule of GDP to produce
an energy molecule of GTP. It leaves behind a molecule of succinate.
Step 6
In this step, succinate is oxidized by a molecule of FAD (Flavin adenine
dinucleotide). The FAD removes two hydrogen atoms from the succinate and
forces a double bond to form between the two carbon atoms, thus
creating fumarate.
Step 7
An enzyme adds water to the fumarate molecule to form malate. The malate
is created by adding one hydrogen atom to a carbon atom and then adding a
hydroxyl group to a carbon next to a terminal carbonyl group.
Step 8
In this final step, the malate molecule is oxidized by a NAD molecule. The
carbon that carried the hydroxyl group is now converted into a carbonyl group.
The end product is oxaloacetate which can then combine with acetyl-coenzyme
A and begin the Krebs cycle all over again.
Summary of Krebs Cycle
In summary, three major events occur during the Krebs cycle. One GTP
(guanosine triphosphate) is produced which eventually donates a phosphate
group to ADP to form one ATP; three molecules of NAD are reduced; and one
molecule of FAD is reduced. Although one molecule of GTP leads to the
production of one ATP, the production of the reduced NAD and FAD are far more
significant in the cell’s energy-generating process. This is because NADH and
FADH2 donate their electrons to an electron transport system that generates large
amounts of energy by forming many molecules of ATP.
Yield of ATP
At this point the yield of ATP is 4 moles per mole of Glucose as it passes through
the Krebs cycle.