The main process in mitochondria is known as cellular respiration. Most of the chemical reactions involved in cellular respiration happen in the mitochondria. Cellular respiration is the process by which the chemical energy of food molecules is released and captured in the form of ATP. Carbohydrates, fats, and proteins can all be used as fuels in cellular respiration, but glucose is most commonly used as an example to examine the reactions and pathways involved. ATP is used to provide energy for most of the immediate work that the cell does. There are two phases of cellular respiration in mitochondria: glycolysis and the complete oxidation of pyruvic acid to carbon dioxide and water.
In anaerobic respiration, pyruvate is not metabolized by cellular respiration but undergoes a process of fermentation. The pyruvate is not transported into the mitochondrion, but remains in the cytoplasm, where it is converted to waste products that may be removed from the cell. This serves the purpose of oxidizing the hydrogen carriers so that they can perform glycolysis again and removing the excess pyruvate. This waste product varies depending on the organism. In skeletal muscles, the waste product is lactic acid. This type of fermentation is called lactic acid fermentation. In yeast, the waste products are ethanol and carbon dioxide. This type of fermentation is known as alcoholic or ethanol fermentation. The ATP generated in this process is made by substrate phosphorylation, which is phosphorylation that does not involve oxygen.
Anaerobic respiration is less efficient at using the energy from glucose since 2 ATP are produced during anaerobic respiration per glucose, compared to the 38 ATP per glucose produced by aerobic respiration. This is because the waste products of anaerobic respiration still contain plenty of energy.
The Endosymbiotic Theory was first proposed by former Boston University Biologist Lynn Margulisin the 1960's and...