Fundamentals of Human Nutrition/Citric Acid cycle
12.4 Citric Acid Cycle
The citric acid cycle, also called the Krebs cycle, is the final stage of the oxidation of glucose. The carbon atoms enter the cycle as acetyl-CoA formed in the previous step (decarboxylation of pyruvate) and are oxidized in mitochondrial eight reactions to form various compounds such as CO2 and various hydrogens which are then captured by the NAD and FAD, produzind to three molecules of NADH and FADH2, and ATP release. These molecules formed during the Krebs cycle (NADH and FADH2) are acceptors H (receptors) intermediates of hydrogen which bind to protons (H +), released during the stages of metabolism of glucose, giving them for oxygen, which is acceptor (receiver) end of hydrogens.
After the Krebs cycle, molecules of NADH and FADH2 produced during all stages of metabolism of glucose, are transferred to the mitochondrial cristae, so that the electrons present in these molecules are transferred to oxygen, are the final electron receptor. This process is called oxidative phosphorylation. The electrons are passed from molecule to molecule in cytochromes present in mitochondrial cristae. When the electron "jumps" from one cytochrome to another until you reach the end acceptor (oxygen), is the release of energy, which is converted into ATP.
The general formula of complete metabolization of glucose consists:
Glucose + 6O2 → 6CO2 + 6H2O + 38ATP
After all the glucose metabolism (glycolysis by oxidative phosphorylation) for the formation of carbon dioxide, water and 38 ATP molecules. This process is called cellular respiration, therefore the cell receives oxygen and sugar (in this case glucose) and releases energy in the form of ATP, carbon dioxide and water.