Guess! What type of acid these fruits contain? It is citric acid. Citric acid is the first product formed in the Krebs cycle, and therefore this acid occurs in the metabolism of virtually all living things. Glycolysis releases less than a quarter of the chemical energy stored in glucose; most of the energy remains stockpiled in the two molecules of pyruvate. There are many high-energy electrons left in pyruvate.
Next, cells complete cellular respiration by oxidizing pyruvate to form carbon dioxide. Glycolysis results in a net gain of 2 ATP and 2 NADH molecules from one molecule of glucose. Keep in mind, this gain represents an effective transfer of 20 kcal of energy to ATP (about 10 kcal each) and about 80 kcal of energy to NADH (about 40 kcal each), for a total of about 100 kcal. The complete oxidation of glucose results in the release of 684 kcal of energy, therefore, there is a good amount of energy still remaining in pyruvate. The oxidation of pyruvic acid into CO2 and water is called Krebs cycle.
This cycle is also called citric acid cycle because the cycle begins with the formation of citric acid. Citric acid is a carboxylic acid containing 3 COOH groups. Hence this cycle is also called as tri carboxylic acid cycle or TCA cycle. This cycle occurs only in the presence of oxygen. Hence it is an aerobic process. It takes place in the mitochondria.
Krebs cycle/Citric acid cycle/Tricarboxylic acid The tricarboxylic acid cycle (TCA cycle) is a series of enzyme-catalyzed chemical reactions that form a key part of aerobic respiration in cells. This cycle is also called the Krebs cycle and the citric acid cycle. In eukaryotes, pyruvate is transported across the mitochondrial membrane and then converted to acetyl CoA (with the production of NADH and carbon dioxide). Acetyl CoA is then oxidized by a series of enzymes that make up a cyclical series of reactions known as the Krebs cycle. During the Krebs cycle, electrons are removed from acetyl CoA and these electrons reduce more NAD+, along with another electron carrier, FAD. The ATP that is produced is generated via substrate–level phosphorylation, just as it was in glycolysis. Each NADH and FADH2 molecule that is formed is an important source of energy that will be used to generate ATP.
The main reactants of citric acid cycle are : acetyl CoA, NAD+, FAD, ADP, and inorganic phosphate and products (carbon dioxide, NADH, FADH2, and ATP) from what is actually a multistep process.
Glucose catabolism ends during the Krebs cycle. This does not mean that all of the energy previously contained in glucose was used in the production of ATP. In fact, only one additional ATP molecule (per molecule of pyruvate) is produced by substrate–level phosphorylation in the Krebs cycle. The balance of extracted energy is tied up in NADH and FADH2. In the next phase of cellular respiration, the high-energy electrons within NADH and FADH2 will be passed to a set of membrane–bound enzymes in the mitochondrion, collectively referred as the electron transport chain.