Krebs Cycle Enzyme Overview
The Krebs cycle is a series of chemical reactions that occur within living cells to convert carbon dioxide (CO 2 ) into organic compounds such as glucose and fatty acids. These processes are essential for life. Without these reactions, life would not exist.
In order for the Krebs cycle to take place, there must be two things: energy and a catalyst. The energy is in the form of a molecule called adenosine triphosphate, or ATP. The catalyst for the reaction is a molecule called citrate.
The first two reactions of the cycle involve ATP and citrate. The first reaction results in the formation of an enzyme called citrate lyase. The second reaction uses up the remaining phosphate in ATP and results in the formation of an unstable compound called oxaloacetate (OAA).
These first two reactions are irreversible; they cannot be reversed, or undone. This means that new ATP and citrate must be provided in order for the cycle to continue. The next three reactions involve OAA.
In these reactions, OAA loses a carbon dioxide molecule and becomes the compound isocitrate.
The last two reactions of the krebs cycle involve isocitrate. In these reactions, a hydrogen ion is removed and another carbon dioxide molecule is added. These reactions result in the formation of another enzyme called alpha-ketoglutarate.
These last two reactions are also irreversible, meaning that new isocitrate must be provided in order for these reactions to continue. The last reaction of the krebs cycle involves alpha-ketoglutarate. In this reaction, a carbon dioxide molecule is added and an extra hydrogen ion is removed.
This results in the production of the compound succinyl-CoA. Succinyl-CoA is an important compound, as it can enter another process called the electron transport chain, which is how cells produce ATP.
As you can see, the reactions of the krebs cycle are very important. They provide a link to the electron transport chain, which is how cells produce the energy molecule ATP. Without the krebs cycle, life could not exist.
It is important to note that the reactions that take place in the krebs cycle are not the only reactions that produce ATP and organic compounds. Other reactions also take place in the process of cellular respiration. These other reactions occur outside of the mitochondria and involve different enzymes.
It is also important to note that the reverse of each reaction is not the reverse of any other reaction in the krebs cycle. The reverse of one reaction is the same as another reaction. The reason for this has to do with the fact that the krebs cycle is a cycle, and in order to maintain a cycle, the reverse of one reaction must be the same as the forward reaction of another reaction.
Krebs Cycle Summary
Below is a quick summary of the krebs cycle. Remember, this is only a summary. If you want more detail, read the entire main article.
Quick Krebs Cycle Summary ATP + Acetyl-coA + NAD+ + CoA = Citrate ل Citrate Lyase (irreversible) Citrate = Αcitric Acid + Carbon Dioxide (irreversible) Isocitrate + H+ + ATP = α-Ketoglutarate + ADP + Pi (irreversible) α-Ketoglutarate + H2O = Succinyl-CoA + CO2 (irreversible) Dehydrogenation of FAD (Flavin Adenine Dinucleotide) by Succinyl-CoA Synthase Produces Succinyl-CoA which Leads to the Formation of GTP (Guanosine Triphosphate)
Reviewed by Denise W. Chen, August 2018
Sources & references used in this article:
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