Which of the following is true about the major molecules involved in the Krebs Cycle?

The Krebs Cycle, also known as the citric acid cycle, plays a vital role in cellular respiration by processing acetyl CoA derived from carbohydrates, fats, and proteins to produce energy. The true statement asserts that the major molecules involved in the cycle include acetyl CoA, citric acid, and oxaloacetic acid.

Acetyl CoA is the starting substrate that enters the cycle and is converted into citric acid (or citrate) upon its reaction with oxaloacetic acid. The cycle is highly dynamic, with oxaloacetic acid being regenerated to allow the process to continue. Citric acid is an intermediary compound that undergoes several transformations, ultimately leading back to oxaloacetic acid for the cycle to repeat.

In contrast, other options misalign with the fundamentals of the Krebs cycle: the cycle is not limited to just sugars and fats (option B); it produces not just ATP but also NADH and FADH2, which are crucial for the production of more energy through the electron transport chain (option C); and while oxygen is necessary for the ultimate energy extraction via oxidative phosphorylation, it does not directly participate as a substrate in the Krebs cycle itself (option D). The correct choice emphasizes the essential