I recreate the TCA in vitro, and have 150 molecules of Fumarate in the beginning. I then add 100 molecules of Acetyl CoA to the reaction. Assuming that 200 molecules of CO2 are produced in the end, MOST LIKELY, how many molecules of Fumarate will be left at the end? Explain your answer.

The Krebs cycle is also called the citric acid cycle or the TCA (tricarboxylic acid) cycle is an array of chemical reactions utilized by all the aerobic species to discharge the stored energy via the acetyl-CoA oxidation, which is obtained from fats, carbohydrates, and proteins into ATP and CO2.

In the TCA or the Kreb's cycle, the end product is oxaloacetate, that is, a four-carbon compound. If one adds Acetyl-CoA, that is, a two-carbon compound in the cycle, it gets converted to citrate, that is, a six-carbon compound, and the process of TCA cycle begins. Then after losing two molecules of carbon dioxide the formation of fumarate takes place, which then gets converted to malate, and then finally into the final component of the cycle, that is, the oxaloacetate.

As it is mentioned that at the start there were 150 molecules of fumarate, and as the reaction gets started with the addition of acetyl-CoA, so the molecules of fumarate had no role to play and it remained as such right from the start.