The metabolic pathway known as the Krebs cycle is essential for cellular respiration in aerobic organisms.
Krebs cycle is one of the names given to a series of chemical reactions that occur in aerobic organisms as part of the process of cellular respiration . In eukaryotic cells , the cycle also known as tricarboxylic acid cycle or citric acid cycle takes place in the mitochondrial matrix (an area or compartment located within the mitochondria ). In prokaryotic cells , however, this event takes place in the cytoplasm .
These metabolic pathways enable the release of stored energy through the oxidation of the molecule acetylcoenzyme A (commonly referred to as Acetyl-CoA ). In this context, an oxidative phenomenon of proteins , carbohydrates and lipids occurs that involves three stages: after the production of Acetyl-CoA , glycolysis , beta oxidation involving fatty acids and the chemical reaction defined as oxidative deamination, the Krebs cycle takes place . Next comes the metabolic process classified as oxidative phosphorylation , which generates adenosine triphosphate (ATP) by taking advantage of the energy that arises when nutrients are oxidized.
It is worth mentioning the existence of a reaction that opposes the aforementioned Krebs cycle , which is why it is classified as the reverse Krebs cycle . It is a resource that certain bacteria use to produce organic compounds based on water (H2O) and carbon dioxide (CO2) .
Function of the Krebs cycle
The Krebs cycle , which is powered by acetyl-CoA , involves chemical reactions essential for cellular respiration to take place.
The process is set in motion when an acetyl group consisting of a pair of acetyl-CoA carbons is transferred to an acceptor compound consisting of four carbons (a metabolite called oxaloacetic acid , oxaloacetate in its ionized form) and a citrate is formed thanks to a condensation reaction. This citrate undergoes chemical transformations and therefore loses carboxyl groups . Complex events occur during this stage that allow the four-carbon oxaloacetate to be regenerated at the end of each cycle.
The Krebs cycle is followed by oxidative phosphorylation . During this period, an electron transport chain is observed that uses the potential energy of the electrons to launch protons into the area between the membranes of the mitochondria .
It is essential for science to know in detail the characteristics, scope and applications of the Krebs cycle, since pathologies and anomalies or defects related to it have been detected. For example, genes linked to the Krebs cycle have been identified that predispose certain individuals to develop neuroendocrine tumors such as paragangliomas and pheochromocytomas .
It is also constructive to know that sequences of reactions involved in the Krebs cycle are required for the maintenance of life, since each stage individually is not enough for this purpose. By deepening the research and knowledge surrounding this process, we can come to understand how, approximately four billion years ago, life manifestations were activated on planet Earth . A few years ago, to detail a specific case, a group of scientists, appealing to representative elements of ancient terrestrial sediments, demonstrated in a laboratory in the United Kingdom that the Krebs cycle can be reflected in a metabolic pathway that is characterized by being free of enzymes and is activated by a class of particles known as sulfate radicals .
The Krebs cycle takes place, for example, in the mitochondrial matrix of eukaryotic cells.
History
According to experts' speculations, the Krebs cycle has been undergoing changes over time. It is even said that numerous alternatives to this process have emerged, but this one seems to have been consolidated by combining the other options in a single metabolic pathway .
Regarding the most widely used name, it should be noted that it bears the surname of the biochemist who discovered it: Hans Adolf Krebs . In 1953, he and Fritz Lipmann were awarded a Nobel Prize for the discovery of coenzyme A and the citric acid cycle .
Equally important was the work of Albert Szent-Györgyi , a physiologist of Hungarian origin who also received a Nobel Prize , in this case in 1937 for his contributions to cellular respiration .
The cytoplasm is the area of prokaryotic cells where the Krebs cycle takes place.
Importance of the Krebs cycle
The Krebs cycle is of great importance for cellular metabolism . It is essential, for example, for aerobic organisms , through cellular respiration , to be able to use oxygen to achieve the decomposition of glucose molecules, among other substances of organic origin, in order to obtain energy .
This cycle is also key to the process of synthesizing metabolic precursors . Within this framework, there is the possibility of diverting various intermediate molecules involved in the Krebs cycle towards different metabolic pathways and thus synthesizing compounds that are essential for optimal cell functioning.