Glycolysis – concept, phases, functions, and what is gluconeogenesis

We explain what glycolysis is, its phases, functions and importance in metabolism. We also talk about gluconeogenesis.

What is glycolysis?

Glycolysis or glycolysis is a metabolic pathway that serves as the initial step for carbohydrate catabolism in living beings. It consists fundamentally in the breakdown of glucose molecules through the oxidation of the glucose molecule, thus obtaining amounts of chemical energy that can be used by cells.

Glycolysis is not a simple process, but consists of a series of ten consecutive enzymatic chemical reactions, which transform a glucose molecule (C₆H₁₂OR₆) in two pyruvate (C₃H₄OR₃), useful for other metabolic processes that continue to provide energy to the body.

This series of processes can occur in the presence or in the absence of oxygen, and occurs in the cytosol of cells, as an initial part of cellular respiration. In the case of plants, it is part of the Calvin cycle.

The reaction rate of glycolysis is so high that it has always been difficult to study it. It was formally discovered in 1940 by Otto Meyerhoff and the same years later by Luis Leloir, although all this thanks to previous works from the late nineteenth century.

This metabolic route is usually named after the surnames of the greatest contributors to its discovery: the Embden-Meyerhoff-Parnas route. On the other hand, the word “glycolysis” comes from the Greek glycos, “Sugar”, and lysis, “breaking off”.

Phases of glycolysis

Glycolysis is studied in two different phases, which are:

• First phase: energy expenditure. In this first stage, the glucose molecule is transformed into two glyceraldehyde, a low-energy-yielding molecule. For this, two units of biochemical energy are consumed (ATP, Adenosine Triphosphate). However, in the next phase the energy obtained thanks to this initial investment will be doubled.
  Thus, phosphoric acids are obtained from ATP, which contribute phosphate groups to glucose, composing a new and unstable sugar. This sugar soon divides, resulting in two similar molecules, phosphated and with three carbons.
  Despite having the same structure, one of them is different, so it is additionally treated with enzymes to make it identical to the other, thus obtaining two identical compounds. All this happens in a chain of reactions of five steps.
• Second phase: obtaining energy. The glyceraldehyde in the first phase is converted into a high-energy biochemical compound in the second. To do this, it couples with new phosphate groups, after losing two protons and electrons.
  Thus, these intermediate sugars are subjected to a process of change that gradually releases their phosphates, thus obtaining four ATP molecules (twice the amount invested in the previous step) and two pyruvate molecules, which will continue their cycle. on your own, glycolysis finished. This second phase of reactions consists of five more steps.

Functions of glycolysis

Glycolysis obtains the necessary energy for simple and complex mechanisms.

The main functions of glycolysis are simple: obtaining biochemical energy necessary for the different cellular processes. Thanks to the ATP obtained from the breakdown of glucose, many forms of life get the energy to survive or to trigger much more complex chemical processes.

Therefore, glycolysis usually acts as a trigger or biochemical detonator of other major mechanisms, like the Calvin cycle or the Krebs cycle. Both eukaryotes and prokaryotes are practitioners of glycolysis.

Importance of glycolysis

Glycolysis is a very important process in the field of biochemistry. On the one hand it has a great evolutionary importance, since It is the basic reaction for the increasingly complex life and for the support of the cellular life. On the other hand, their study reveals details about the various existing metabolic pathways and about other aspects of the life of our cells.

For example, recent studies at universities in Spain and the University Hospital of Salamanca detected links between neuronal survival in the brain and the increase in glycolysis to which neurons may be subjected. This could be key in understanding diseases such as Parkinson’s disease or Alzheimer’s disease.

Glycolysis and gluconeogenesis

If glycolysis is the metabolic pathway that breaks down the glucose molecule for energy, gluconeogenesis is a metabolic pathway that goes the other way: the construction of a glucose molecule from non-carbohydrate precursors, that is, not linked at all with sugars.

This process it is almost exclusive to the liver (90%) and kidneys (10%), and takes advantage of resources such as amino acids, lactate, pyruvate, glycerol and any carboxylic acid as a carbon source. In the absence of glucose, such as fasting, they allow the organism to be stable and functioning for a reasonable period, while the glycogen stores in the liver last.