Krebs is very fun

Steps of the Krebs cycle

Step 1

Acetyl CoA is combined with oxaloacetate to form a six carbon molecule of citrate.  The acetyl coenzyme A acts only as a transporter of acetic acid from one enzyme to another. Once combined, CoA is released that it may combine with another acetic acid molecule to begin the Krebs cycle again.

Step 2

Citrate undergoes an isomerization.  A hydroxyl group and a hydrogen molecule are removed from the citrate structure in the form of water.  The two carbons form a double bond until the water molecule is hadded back.  The Hydroxyl group and hydrogen molecule are in different positions so isocitrate is formed.

Step 3

Isocitrate molecule is oxidized by a NAD molecule.  The NAD molecule is reduced by the hydrogen atom and the hydroxyl group.   The NAD binds with a hydrogen atom and carries off the other hydrogen atom leaving a carbonyl group.  A molecule of CO2 is released creating alpha-ketoglutarate.

Step 4

Coenzyme A, returns to oxidize the alpha-ketoglutarate molecule.  A molecule of NAD is reduced again to form NADH and leaves with another hydrogen.  A carbon group is released as carbon dioxide and a thioester bond is formed in its place between the former alpha-ketoglutarate 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

Succinate is oxidized by a molecule of FAD. 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 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

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.