Citric acid cycle (Krebs cycle): the main process of aerobic oxidation of carbohydrates, fats or amino acids in the body. It starts with the condensation of acetyl-CoA and oxaloacetic acid to generate citric acid (tricarboxylic acid), then generates CO2, NADH and FADH2 through a series of oxidation steps, and finally generates oxaloacetic acid for recycling, thus providing a basis for cells to degrade acetyl to generate energy. It was put forward by krebs.

The circulation of 1 and tricarboxylic acid is the main way for the body to obtain energy. Anaerobic glycolysis of 1 molecule of glucose produces only two ATP molecules, while aerobic oxidation produces 38 ATP molecules, of which 24 ATP molecules are produced by tricarboxylic acid cycle. Under normal physiological conditions, many tissues and cells get energy from aerobic oxidation of sugar. Aerobic oxidation of sugar not only has high energy release efficiency, but also gradually releases energy and stores it in ATP molecules.

2. Tricarboxylic acid cycle is a * * * co-metabolic pathway, through which sugar, fat and protein are completely oxidized in the body. Acetyl-CoA, the initiator of the tricarboxylic acid cycle, is not only the oxidative decomposition product of sugar, but also comes from the metabolism of glycerol, fatty acids and some amino acids in protein. Therefore, the tricarboxylic acid cycle is actually a * * co-pathway, through which three main organic substances are oxidized in the body and supplied with energy. It is estimated that two-thirds of organic matter in human body is oxidized by tricarboxylic acid cycle.

3. Tricarboxylic acid cycle is the contact mechanism of the transformation of three main organic substances in the body. Because sugar and glycerol are metabolized in the body, the intermediate products of the tricarboxylic acid cycle, such as α-ketoglutaric acid and oxaloacetic acid, can be converted into certain amino acids. However, some amino acids can be converted into α -ketoglutaric acid and oxaloacetic acid by different ways, and then into sugar or glycerol by gluconeogenesis. Therefore, the tricarboxylic acid cycle is not only the ultimate * * * same pathway for the catabolism of three main organic compounds, but also the contact mechanism of their mutual transformation.