Why does the Kreb Cycle stop in the absence of oxygen?

Question

I know why the Electron Transport Chain stops due to the lack of O2, but why does the Kreb Cycle stop as well?

I thought Kreb Cycle didn't require oxygen directly to function?

Answer 1

Oxidation

Yes, the Kreb Cycle needs oxygen to operate, but if it is present at the wrong time then it will join with the other molecules forming new substances that don't help in creating energy and so substaining the cycle. This is why the oxygen is tied up with carbon to produce the waste CO2, which is then carred away and exhaled by the creature.

Oxygen is a greedy molecule and highly reactive, when it gets a chance it rusts or oxidizes things like iron and that destroyes it. In the Kreb Cycle the oxygen will interfere and stop important molecules forming by forming their own molecules thus stopping the cycle.

"Two carbons are oxidized to CO2, and the energy from these reactions is stored in GTP." Withou the GTP (Guanosine-5'-triphosphate: http://en.wikipedia.org/wiki/Guanosine_triphosphate) the substrate for the RNA isn't made. Substrate is the foundation so without a foundation you don't get the proper molecule, this would then interfere with transcription. You also need the energy produced by this reaction to continue the Kreb Cycle.

According to Wikipedia: http://en.wikipedia.org/wiki/Kreb_Cycle
"The citric acid cycle, also known as the tricarboxylic acid (TCA) cycle, the Krebs cycle, or Szent-Györgyi-Krebs cycle (after Hans Adolf Krebs and Albert Szent-Györgyi who first determined the chemical intermediates and reaction sequence of the cycle), is a series of enzyme-catalysed chemical reactions of central importance in all living cells that use oxygen as part of cellular respiration. In aerobic organisms, the citric acid cycle is part of a metabolic pathway involved in the chemical conversion of carbohydrates, fats and proteins into carbon dioxide and water to generate a form of usable energy. It is the third of four metabolic pathways that are involved in carbohydrate catabolism and ATP production, the other three being glycolysis and pyruvate oxidation before it, and electron transport chain after it.

The citric acid cycle also provides precursors for many compounds such as certain amino acids, and some of its reactions are therefore important even in cells performing fermentation."

According to Wikipedia: http://en.wikipedia.org/wiki/Guanosine_triphosphate
"Guanosine-5'-triphosphate (GTP) is a purine nucleotide. Its main role is as substrate for the synthesis of RNA during transcription. Its structure is similar to that of the guanine nucleotide, the only difference being that there are two extra phosphate groups added on.

It also has the role of a source of energy or an activator of substrates in metabolic reactions, like that of ATP, but more specific. It is used as a source of energy for protein synthesis."