Hey people I’m back again missed me? Lolz well today I’m going to talk a bit about the citric acid cycle aka the TCA cycle aka the Kerbs cycle. Okay so all of you must have done a little research on glycolysis so this won’t be that difficult to learn.
In aerobic conditions the end product of glycolysis is pyruvic acid. The next step is the formation of acetyl coenzyme A (acetyl CoA) and this is the initiator of the citric acid cycle. In carbohydrate metabolism, acetyl CoA links glycolysis and the citric acid cycle. The citric acid cycle contains the final oxidation reactions, linked to the electron transport chain, which produces the majority of ATP in the body. Formation of acetyl CoA comes from carbohydrates, as well as metabolism of fatty acids and amino acids. The reactions of the citric acid cycle and the electron transport chain both occur in the mitochondria.
Now here is a little help for those of you who are confused:
Step 1: The acetic acid subunit of acetyl CoA is combined with oxaloacetate to form a molecule of citrate. The acetyl coenzyme A acts only as a transporter of acetic acid from one enzyme to another. After Step 1, the coenzyme is released by hydrolysis so that it may combine with another acetic acid molecule to begin the Krebs cycle again.
Step 2: The citric acid molecule 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 added back. Only now, the hydroxyl group and hydrogen molecule are reversed with respect to the original structure of the citrate molecule. Thus, isocitrate is formed.
Step 3: In this step, the 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. This structure is very unstable, so a molecule of CO2 is released creating alpha-ketoglutarate.
Step 4: In this step, coenzyme A, returns to oxidize the alpha-ketoglutarate molecule. A molecule of NAD is reduced again to form NADH and leaves with another hydrogen. This instability causes a carbonyl group to be 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: 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 then combines with acetyl-coenzyme A and begin the Krebs cycle all over again.
Well I know that was alot as usual but don’t worry the semester is almost over keep the faith and study, study, study.