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Glucolysis: what is it and what are its 10 phases?

Glucolysis: what is it and what are its 10 phases?

March 30, 2024

Glycolysis is a chemical process that allows respiration and cellular metabolism, specifically by means of the decomposition of glucose.

In this article we will see in more detail what glycolysis is and what it is for, as well as its 10 phases of action.

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What is glycolysis?

The term "glycolysis" is composed of the Greek "glycos" which means "sugar", and "lysis" which means "rupture". In this sense, glycolysis is the process by which the composition of glucose is modified to extract enough energy to benefit the cells. In fact, it not only acts as an energy source, but also impacts on cellular activity in different ways , without necessarily generating additional energy.

For example, it produces a high yield of molecules that allow metabolism and cellular respiration both aerobic and anaerobic. Broadly speaking, aerobic is a type of metabolism that consists of extracting energy from organic molecules from the oxidation of carbon by oxygen. In the anaerobic the element used to achieve oxidation is not oxygen but sulphate 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 "pyluric acid" or "pyruvate" which has a very important role in biochemical activity. This process occurs in the cytoplasm (the part of the cell that lies between the nucleus and the membrane). But for glucose to become pyruvate, a very complex chemical mechanism composed of different phases must occur.

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Its 10 phases

Glycolysis is a process that has been studied since the second decade of the nineteenth century, when chemists Louis Pasteur, Eduard Buchner, Arthur Harden and William Young began to detail the mechanism of fermentation. These studies allowed to know the development and different forms of reaction in the composition of the molecules.

It is one of the oldest cellular mechanisms, and is likewise the fastest way to obtain energy and metabolize carbohydrates . For this it is necessary that 10 different chemical reactions 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 obtaining energy by transforming the two molecules generated in the previous stage.

Having said that, we will now see 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-phosphorylated molecule on carbon 6). To generate this reaction it is necessary to participate in an enzyme known as Hexoquinasa, and has the function of activating glucose so that it can be used in later 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 must act an enzyme called phosphoglucose isomerase . This is the phase of defining the molecular composition that will consolidate glycolysis in the two stages that follow.

3. Phosphofructokinase

In this phase, fructose-6-phosphate is converted to fructose 1,6-bisphosphate, through the action of phosphofructokinase and magnesium . It is an irreversible phase, which means that glycolysis begins to stabilize.

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4. Aldolasa

Now the fructose 1,6-bisphosphate is divided into two isomer-type sugars, that is, two molecules with the same formula, but whose atoms are arranged in different ways, which also have different properties. The two sugars are dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP), and the division occurs due to the activity of the enzyme aldolase .

5. Trifosphate isomerase

Phase number 5 consists of reserving the glyceraldehyde phosphate for the next stage of glycolysis.For this it is necessary that an enzyme called triphosphate isomerase act inside 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 the energy expenditure .

6. Glyceraldehyde-3-phosphate Dehydrogenase

In this phase, the energy generation starts (during the previous 5 it was only spent). We continue with the two sugars generated previously and its activity is as follows: produce 1,3-bisphosphoglycerate , 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 begins to increase the energy of the compound.

7. Phosphoglycerate kinase

In this phase there is another transfer of a phosphate, to be able to form adenosine triphosphate and 3-phosphoglycerate. It is the 1,3-bisphosphoglycerate molecule that receives a phosphate group from the phosphoglycerate kinase.

8. Phosphoglycerate mutase

From the above reaction, 3-phosphoglycerate was obtained. Now it is necessary to generate 2-phosphoglycerate, by means of the action of an enzyme called phosphoglycerate mutase . The latter relocates the position of the third carbon phosphate (C3) to the second carbon (C2), and thus the expected molecule is obtained.

9. Enolase

An enzyme called enolase is responsible for removing the water molecule of 2-phosphoglycerate. In this way, the precursor of pyruvic acid is obtained and we are nearing the end of the glycolysis process. This precursor is phosphoenolpyruvate.

10. Pyruvate kinase

Finally, a phosphorus transfer of phosphoenolpyruvate to adenosine diphosphate occurs. This reaction occurs by the action of the enzyme pyruvate kinase, and allows the glucose to finish transforming into pyruvic acid.

Bibliographic references:

  • Glycolysis-10 steps explained steps by steps with diagram (2018). Retrieved September 26, 2018. Available at //

Steps of glycolysis | Cellular respiration | Biology | Khan Academy (March 2024).

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