The Krebs cycle, also known as the TCA cycle or citric acid cycle, is a metabolic pathway used by organisms that use oxygen to generate energy. It produces important compounds such as amino and fatty acids, and also releases carbon dioxide, NADH, FADH2, and either ATP or GTP. Courses on Khan Academy, where one can learn about various subjects for free, often cover the TCA cycle. This cycle breaks down carbohydrates, proteins, and fats and plays a crucial role in producing energy in the form of ATP or GTP. The main function of the Krebs cycle is to produce and store energy, but it also contributes to other biosynthetic reactions. The Krebs cycle works by converting acetyl CoA into citrate and then going through a series of reactions in a closed loop.