What initiates the Krebs cycle?

The initiation of the Krebs cycle, also known as the citric acid cycle or TCA cycle, begins with the conversion of Acetyl-CoA to citric acid. Acetyl-CoA, which is derived from the breakdown of carbohydrates, fats, and proteins, enters the cycle and reacts with oxaloacetate to form citric acid (or citrate). This first step is crucial as it sets the entire cycle in motion, allowing for a series of chemical reactions that generate energy-storing molecules such as NADH and FADH2, as well as ATP.

These energy carriers produced later in the cycle are vital for the electron transport chain, where the majority of ATP is generated. Understanding this initiation step is essential to grasp how cellular respiration efficiently converts biochemical energy from nutrients into usable energy for cellular functions. Other options related to NADH conversion, oxygen consumption, or ATP production occur later in the process and are dependent on the successful initiation of the Krebs cycle.