Glycolysis is a chemical process that allows breathing and cell metabolism, specifically through the breakdown 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.

What is glycolysis?

The term “glycolysis” is composed of the Greek “glycos” meaning “sugar”, and “lysis” meaning “breakage”. In this sense, glycolysis is the process by which the composition of glucose is modified to extract sufficient energy for the benefit of the cells. In fact, not only does it act as a source of energy, but it also has an impact on cell activity in different ways , without necessarily generating additional energy.

For example, it produces a high yield of the molecules that enable both aerobic and anaerobic cell metabolism and respiration. Broadly speaking, aerobics is a type of metabolism that consists of extracting energy from organic molecules by oxidizing carbon with oxygen. In anaerobic, the element used to achieve oxidation is not oxygen but rather sulphate or nitrate.

In turn, glucose is an organic molecule composed of a 6-ringed membrane found in the blood, and which is usually 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 (the intracellular fluid, i.e. the fluid in the centre of the cells).

Through glycolysis, glucose is converted into an acid called “pivuric” or “pyruvate” that plays a very important role in biochemical activity. This process occurs in the cytoplasm (the part of the cell between the nucleus and the membrane). But for glucose to become pyruvate, a very complex chemical mechanism composed of different phases must occur.

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 to know the development and different forms of reaction in the composition of the molecules.

This is one of the oldest cellular mechanisms, and is also the fastest way to obtain energy and metabolize carbohydrates . This requires 10 different chemical reactions to occur, divided into two major phases. The first of these 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 look at 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 (molecule of glycosaphosphorylated at carbon 6). To generate this reaction it is necessary to involve an enzyme known as Hexokinase, and it has the function of activating glucose so that it can be used in subsequent processes .

2. Phosphoglucose isomerase (Glucose-6 P isomerase) (thixag__7)

The second reaction of glycolysis is the transformation of glucose-6-phosphate into fructose-6-phosphate. To do this an enzyme called phosphoglucose isomerase must act. This is the phase of definition of the molecular composition that will allow the consolidation of glycolysis in the two following stages.

3. Phosphofructokinase

In this phase, fructose-6-phosphate is converted into fructose 1.6-biphosphate, through the action of phosphofructokinase and magnesium . This is an irreversible phase, which causes glycolysis to begin to stabilize.

4. Aldolasa

Now fructose 1.6-biphosphate is divided into two isomer-type sugars, i.e. two molecules with the same formula, but whose atoms are arranged differently, so that they also have different properties. The two sugars are dihydroxyacetone phosphate (DHAP) and glycerol 3-phosphate (GAP), and the division occurs by the activity of the enzyme aldolase .

5. Isomerase triphosphate

Phase number 5 consists of reserving glyceraldehyde phosphate for the next stage of glycolysis. This requires the action of an enzyme called triphosphate isomerase within the two sugars obtained in the previous stage (dihydroxyacetone phosphate and 3-phosphate glyceraldehyde). This is where the first of the great stages 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 production begins (during the previous 5 phases it had only been spent). We continue with the two previously generated sugars and their activity is as follows: to produce 1.3-bisophosphoglycerate , by adding an inorganic phosphate to the 3-phosphate glycerol.

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, in order to form adenosine triphosphate and 3-phosphoglycerate. It is the molecule 1,3-bisphosphoglycerate that receives a phosphate group from the phosphoglycerate kinase.

8. Phosphoglycerate mutase

3-Phosphoglycerate was obtained from the above reaction. 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), and the expected molecule is obtained.

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 approach 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 through the action of the enzyme pyruvate kinase, and allows glucose to finish transforming into pyruvic acid.

Bibliographic references:

  • Glycolysis-10 steps explained steps by steps with diagram (2018). MicrobiologyInfo.com. Retrieved September 26, 2018. Available at https://microbiologyinfo.com/glycolysis-10-steps-explained-steps-by-steps-with-diagram/.