Oxidative metabolism is the catabolic first half of metabolism in which the cell breaks down molecules into energy, or adenosine triphosphate (ATP). The second half of metabolism involves the use of that cellular energy to build molecules such as tissues and organs, and it is referred to as anabolism. Aerobic cellular respiration, a process requiring the use of oxygen, is the most efficient form of ATP production. ATP can also be produced anaerobically, without the presence of oxygen.
Oxidative metabolism begins with the breakdown of organic nutrients such as carbohydrates, sugars, proteins, vitamins and fats. Glucose, a simple sugar, is the most common nutrient to be broken down in a process known as glycolysis, or glucose metabolism. Glucose metabolism produces two pyruvate molecules that enter the mitochondria of the cell and are initiated into the Krebs cycle. The mitochondrion is an organelle that supplies cellular energy to the rest of the cell.
The Krebs cycle, referred to as the citric acid cycle as well as the tricarboxylic acid (TCA) cycle, describes the oxidative part of oxidative metabolism. Oxidation is the reduction of electrons and the release of energy. This cycle begins with one pyruvate molecule that, after a series of chemical reactions, is input into the cycle as oxaloacetic acid. The cycle begins and ends with oxaloacetic acid, which undergoes a series of enzyme-initiated chemical reactions during the cycle to produce energy.
In the citric acid cycle, oxidation of the carbon atoms results in the production of carbon dioxide and energy. There are two pyruvate molecules input into the mitochondria from one glucose metabolism reaction, so the TCA cycle involves two cycle turns for completion. Each turn produces one ATP, and so at the completion, two ATP are produced. Oxidative metabolism is an efficient process in that it produces numerous byproducts, known as reaction intermediates, that are almost immediately used for anabolism after catabolism is complete.
Oxidative metabolism is affected by diseases such as type 1 diabetes. Type 1 diabetes prevents glucose from entering the cell, and if it is left untreated, there will be no glucose available for normal production of energy via glycolysis. The body will then resort to the breakdown of fatty acids to fuel itself. The breakdown of fatty acids results in an acidic byproduct known as ketone bodies. If left untreated, the quantity of ketone bodies acidifies the potenz hydrogen (pH) of the blood and leads to the life-threatening condition ketoacidosis.