Question

Which of the following is an end product of citric acid cycle?
A. Citric acid
B. Lactic acid
C. Pyruvic acid
D. Carbon dioxide

Answer 1

The last step of this cycle creates two carbon dioxide molecules, one GTP or ATP, and reduces NADH and$FADH_2$ forms.

Complete answer:
The citric acid cycle (CAC) is also known as the TCA or Krebs cycle. This mechanism is a sequence of chemical reactions used by almost each aerobic creature to unlock accumulated energy by the oxidation of acetyl-CoA from proteins, fats, and carbohydrates.
In the citric acid cycle, the acetyl unit of acetyl CoA is bound to an oxaloacetate molecule to produce a citrate molecule. Citrate is oxidized by a series of steps, liberating two carbon dioxide molecules with each acetyl group fed into the cycle. In this process, 3 NAD+ molecules are decreased to NADH, 1 FAD molecule is decreased to $FADH_2$ and 1 GTP or ATP is produced. Since the last product of the citric acid cycle is also the initial reagent, the cycle begins in the presence of enough reactants.
The citric acid cycle occurs in the matrix of mitochondria like the transformation of pyruvate to acetyl CoA. In this cycle, about all enzymes are soluble except for the succinate dehydrogenase enzyme which is found in the internal membrane of the mitochondria. The citric acid cycle is a closed loop. In this cycle, the last element of the system recreates the element used in the initial step. The last steps of the cycle are a sequence of redox, dehydration, hydration and decarboxylation reactions that produce two carbon dioxide molecules, one GTP or ATP, and reduced NADH and $FADH_2$ forms.

Thus, the correct answer is option D. i.e., Carbon dioxide.

Note: Citric acid cycle is a process of chemical reactions used by almost each aerobic creature to obtain energy by oxidation of acetate obtained from proteins, fats, and carbohydrates into carbon
dioxide.