Date: 13.03.2016

Author: Raphaël Duérinck Chauchard

The Krebs’ cycle is an eloquent and essential system designed to generate large amounts of cellular energy required for life. Disruption of the Krebs’ cycle, whether caused by deficiencies in energy substrates, stress, age etc. leads to an inhibition of normal energy production and contributes to a wide range of metabolic disturbances, skin damages and ageing.

All cells must produce energy to survive. Hans A. Krebs first elucidated the process of cells converting food into energy, the Citric Acid Cycle, in 1937. Krebs proposed a specific metabolic pathway within the cells to account for the oxidation of the basic components of food – carbohydrates, protein and fats – w for energy. The Krebs’ cycle takes place inside the mitochondria or ‘power plant’ of cells and provides energy required for the organism to function.

Mitochondria are found in all cells in the human body, with the exception of mature red blood cells. The primary function of these tiny organelles (each cell contains between 500 and 2,000 mitochondria) is to convert energy found in nutrient molecules and store it in the form of adenosine triphosphate (ATP). ATP is the universal energy-yielding molecule used by enzymes to perform a wide range of cellular functions. Humans cannot survive, even for a second, without a constant supply of ATP.

In order to carry out energy conversion, mitochondria require oxygen. The purpose of our respiratory and circulatory systems is to deliver oxygen to the tissues for use by mitochondria, and to eliminate carbon dioxide. The consumption of oxygen by mitochondria is called cellular respiration.

In simple terms, the Krebs’ cycle metabolizes acetyl coenzyme A into citric acid and then runs through a complex series of biological oxidations, producing free hydrogen ions. A net of two molecules of ATP is created at this stage in the Krebs’ cycle. The hydrogen ions then enter a biochemical chain, known as oxidative phosphorylation, which is a highly efficient aerobic energy generator. Oxidative phosphorylation generates 36 molecules of ATP during a sequence of steps that combine hydrogen electrons to molecular oxygen to form water. Therefore, each molecule of citric acid that rotates through the Krebs’ cycle, generates 38 molecules of ATP for tissue fuel.

There are different points where metabolites enter the Krebs’ cycle. Most of the products of protein, carbohydrates and fat metabolism are reduced to the molecule acetyl coenzyme A that enters the Krebs’ cycle. Glucose, the primary fuel in the body, is first metabolized into pyruvic acid and then into acetyl coenzyme A. The breakdown of the glucose molecule forms two molecules of ATP for energy in the Embden Meyerhof pathway process of glycolysis. On the other hand, amino acids (energy booster) and some chained fatty acids can be metabolized into Krebs intermediates and enter the cycle at several points.

When oxygen is unavailable or the Krebs’ cycle is inhibited, the body shifts its energy production from the Krebs’ cycle to the Embden Meyerhof pathway of glycolysis, a very inefficient way of making energy.

As well as producing far less energy, glycolysis also produces lactic acid as a by-product. Increased lactic acid is a common acidotic condition that can be caused by a variety of metabolic problems. Accumulation of lactic acid in muscle tissue produces the pain and inflammation we experience after exercising. While untrained individuals have a low lactate threshold, highly trained, elite athletes are extremely efficient at converting lactate to glucose and therefore have lower lactate levels.


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