The term “glycolysis” is composed of the Greek “glycos” which means “sugar”, and “lysis” which means “breakdown”. In this sense, glycolysis is the process by which the composition of glucose is modified to extract sufficient energy for the benefit of cells. In fact, it not only acts as a source of energy, but also affects cellular activity in different ways without necessarily generating additional energy.
For example, it produces a high yield of molecules that allow both aerobic and anaerobic metabolism and cellular respiration. Broadly speaking, aerobic is a type of metabolism that consists of extracting energy from organic molecules from the oxidation of carbon using oxygen. In anaerobic the element used to achieve oxidation is not oxygen but sulfate or nitrate.
At the same time, Glucose is an organic molecule composed of a 6-ring membrane which is found in the blood, and which is generally the result of the transformation of carbohydrates into sugars. In order to enter the cells, glucose travels through the proteins responsible for transporting it from the outside of the cell to the cytosol (intracellular fluid, that is, the liquid found in the center of the cells).
Through glycolysis, glucose is converted into an acid called “pivuric” or “pyruvate” which has a very important role in biochemical activity. This process occurs in the cytoplasm (the part of the cell that is between the nucleus and the membrane). But for glucose to become pyruvate, a very complex chemical mechanism must occur composed of different phases.
Its 10 phases
Glycolysis is a process that has been studied since the second decade of the 19th century, when chemists Louis Pasteur, Eduard Buchner, Arthur Harden and William Young began to detail the mechanism of fermentation. These studies allowed us to know the development and different forms of reaction in the composition of the molecules.
It is one of the oldest cellular mechanisms, and it is also the fastest way to obtain energy and metabolize carbohydrates For this, 10 different chemical reactions must occur, divided into two large phases. The first of them consists of spending energy by transforming the glucose molecule into two different molecules; while the second phase is the obtaining of energy through the transformation of the two molecules generated in the previous stage.
That said, we will see below the 10 phases of glycolysis.
1. Hexokinase
The first step in glycolysis is to convert the D-glucose molecule into a glucose-6-phosphate molecule (glucose molecule phosphorylated at carbon 6). To generate this reaction, an enzyme known as Hexokinase must participate, and it has the function of activating glucose. so that it can be used in subsequent processes
2. Phosphoglucose isomerase (Glucose-6 P isomerase)
The second reaction of glycolysis is the transformation of glucose-6-phosphate into fructose-6-phosphate. For it An enzyme called phosphoglucose isomerase must act This is the phase of defining the molecular composition that will allow glycolysis to be consolidated in the two stages that follow.
In this phase, fructose-6-phosphate is converted to fructose 1,6-bisphosphate, through the action of phosphofructokinase and magnesium This is an irreversible phase, which causes glycolysis to begin to stabilize.
4. Aldolase
Now fructose 1,6-bisphosphate is divided into two isomeric sugars, that is, two molecules with the same formula, but whose atoms are arranged differently, which means they also have different properties. The two sugars are dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP), and the cleavage occurs due to the activity of the enzyme aldolase
5. Triphosphate isomerase
Phase number 5 consists of reserving the glyceraldehyde phosphate for the next stage of glycolysis. For this, it is necessary for an enzyme called triphosphate isomerase to act within the two sugars obtained in the previous stage (dihydroxyacetone phosphate and glyceraldehyde 3-phosphate). This is where the first of the great stages that we described at the beginning of this numbering ends, whose function is to generate energy expenditure
6. Glyceraldehyde-3-phosphate Dehydrogenase
In this phase the obtaining of energy begins (during the previous 5 it had only been spent). We continue with the two sugars generated previously and their activity is the following: produce 1,3-bisophosphoglycerate by adding an inorganic phosphate to glyceraldehyde 3-phosphate.
In order to add this phosphate, the other molecule (glyceraldehyde-3-phosphate dehydrogenase) must be dehydrogenated. This means that the energy of the compound begins to increase.
7. Phosphoglycerate kinase
In this phase there is another transfer of a phosphate, to form adenosine triphosphate and 3-phosphoglycerate. It is the 1,3-bisphosphoglycerate molecule that receives a phosphate group from phosphoglycerate kinase.
From the previous reaction, 3-phosphoglycerate was obtained. Now it is necessary to generate 2-phosphoglycerate, through the action of an enzyme called phosphoglycerate mutase The latter relocates the position of the phosphate from the third carbon (C3) to the second carbon (C2), thus obtaining the expected molecule.
9. Enolase
An enzyme called enolase is responsible for removing the water molecule from 2-phosphoglycerate. In this way the precursor of pyruvic acid is obtained and we are approaching the end of the glycolysis process. This precursor is phosphoenolpyruvate.
10. Pyruvate Kinase
Finally, a transfer of phosphorus from phosphoenolpyruvate to adenosine diphosphate occurs. This reaction occurs due to the action of the enzyme pyruvate kinase, and allows glucose to finish transforming into pyruvic acid.
