What Are The Four Metabolic Pathways?

By Antonia Čirjak on May 5 2020 in Answer

Tau-protein kinase, an enzyme which participates in 14 metabolic pathways.
Tau-protein kinase, an enzyme which participates in 14 metabolic pathways.
  • Metabolic pathways are generally divided into two categories: catabolism and anabolism.
  • Thousands of metabolic pathways exist, and they are all complex biological processes that play an integral role in the preservation of an organism's life.
  • The full discovery of the Glycolysis pathway lasted for 100 years, and it is one of the earliest discovered pathways.

Unless you are a biology aficionado, there is a chance you have not heard about the main metabolic pathways. Maybe you do not know what a metabolic pathway is. Just in case, we will take this chance to explain the basic terminology. In simple terms, a metabolic pathway is a series of chemical reactions that take place inside of a basic biological unit of all living organisms, also known as a cell.

Those same chemical reactions are necessary to keep the cell living and growing. Generally, metabolic pathways are classified as that which acquire energy from nutrients (catabolism) and that which produce new cell components (anabolism). Catabolism and anabolism are "sets" of metabolic pathways.

Very Short Introduction To Metabolism

There is a chance you already know that metabolism is closely tied to nutrition. It is a biological fact that metabolism is dependant upon nutrients to produce the energy required by our bodies, which in turn synthesizes new biomolecules like protein and nucleic acids. Food gives us various materials that our body cannot produce by itself and which are essential for its performance. Simply put, all of these chemical reactions are then sorted into metabolic pathways that take the chemicals from nutrition and transform it into another chemical.

Most Important Metabolic Pathways In Humans

There are thousands of metabolic pathways, with many of them incorporating various long steps and complex processes that serve the goal of maintaining an organism's life. Even though there are more than four metabolic pathways in humans, some of them are considered to be more important than others. 

  • Glycolysis is such a pathway, one that converts the simple sugar glucose into pyruvate (an alpha-keto acid), and a hydrogen ion. This metabolic pathway is known to be independent of oxygen, and also the oldest of the metabolic pathways discovered (it took close to 100 years for its discovery). This pathway is generally described in two phases. The first phase, which is also known as the preparatory phase, is a phase where ATP is consumed. In case you are not familiar, ATP is short for adenosine triphosphate. It is a chemical compound where energy comes from (the same energy that enables much of the processes in our cells). Think about clenching your fists or flexing your biceps for a more visual demonstration. The second phase is the production of ATP, gaining of tasty, energetic molecules.
  • Citric acid cycle or the Krebs cycle got its name because of the citric acid (found in citrus fruits) that is consumed and regenerated in this particular cycle. It is the foundation in the process of energy production and biosynthesis, adding to the processes that were initiated by glycolysis. It connects carbs, fat, and protein metabolism. The enzymes of the Krebs cycle can be found in pretty much every cell that uses oxygen. The discovery of this cycle is heavily credited towards Albert Szent-Gyorgyi, who made important discoveries about its key components, namely the fumaric acid.
  • The next important metabolic pathway is called oxidative phosphorylation, where cells use enzymes (proteins that are also catalysts) for nutrient oxidation and release of oxygen. Almost every organism that uses oxygen for its survival performs this metabolic pathway.
  • Pentose phosphate pathway happens in the same place as glycolysis in the cytosol of a cell (except for in plants where it takes place in plastids). This pathway is catabolic, and it is considered as an alternative way of oxidizing glucose. The two main phases of this pathway are the oxidative phase and the non-oxidative phase of the synthesis of carbon sugars.

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