Why is the Krebs cycle also called the citric acid cycle?

The Krebs cycle is also known as the citric acid cycle primarily because citric acid is indeed the first compound formed during the cycle. When the cycle begins, acetyl-CoA, derived from carbohydrates, fats, and proteins, combines with oxaloacetate to form citric acid (or citrate). This initial formation of citric acid is a crucial step, as it sets the stage for the series of chemical reactions that follow, which are aimed at further breaking down citric acid to produce energy in the form of ATP and other high-energy carriers, such as NADH and FADH2.

Each round of the Krebs cycle leads to the regeneration of oxaloacetate, allowing the cycle to continue processing more acetyl-CoA. The name "citric acid cycle" effectively reflects the importance of citric acid as the starting compound in this energy-producing pathway. This connection to the cycle's function is a significant aspect of cellular respiration, highlighting how nutrients are converted into usable energy.