The Krebs cycle refers to a complex series of chemical reactions that produce carbon dioxide and Adenosine triphosphate (ATP), a compound rich in energy. The cycle occurs by essentially linking two carbon coenzyme with carbon compounds; the created compound then goes through a series of changes that produce energy. This cycle occurs in all cells that utilize oxygen as part of their respiration process; this includes those cells of creatures from the higher animal kingdom such as humans. Carbon dioxide is important for various reasons, the main one being that it stimulates breathing, while ATP provides cells with the energy required for the synthesis of proteins from amino acids and the replication of deoxyribonucleic acid (DNA); both are vital for energy supply and for life to continue. In short, the Krebs cycle constitutes the discovery of the major source of energy in all living organisms.
The Krebs cycle, also known as the tricarboxylic acid cycle (TCA), was first recognized in 1937 by the man for whom it is named, German biochemist Hans Adolph Krebs. His highly detailed and extensive research in the field of cellular metabolism and other scientific endeavors gleaned him the Nobel Prize for Physiology or Medicine in 1953. Krebs's contributions to the fields of science and medicine are substantial; in addition to the citric acid cycle, Krebs also identified the urea cycle in 1932.
Within the Krebs cycle, energy in the form of ATP is usually derived from the breakdown of glucose, although fats and proteins can also be utilized as energy sources. Since glucose can pass through cell membranes, it transports energy from one part of the body to another. The Krebs cycle affects all types of life and is, as such, the metabolic pathway within the cells. This pathway chemically converts carbohydrates, fats, and proteins into carbon dioxide, and converts water into serviceable energy.
The Krebs cycle is the second stage of aerobic respiration, the first being glycolysis and last being the electron transport chain; the cycle is a series of stages that every living cell must undergo in order to produce energy. The enzymes that cause each step of the process to occur are all located in the cell's "power plant"; in animals, this power plant is the mitochondria; in plants, it is the chloroplasts; and in microorganisms, it can be found in the cell membrane. The Krebs cycle is also known as the citric acid cycle, because citric acid is the very first product generated by this sequence of chemical conversions, and it is also regenerated at the end of the cycle.