Metabolic way

The metabolic way (in English: metabolic pathway ) is a concept recovering a unit of biochemical reactions bound by a produced or a Substrat. It is an ordered whole of Enzyme S (Protéine S) and substrates. It includes/understands a substrate basic and led to a finished product, with one or more intermediate stages between the two molecules.

A metabolic way is also, in the biological vocabulary, a whole of metabolic reactions (anabolic or catabolic) catalyzed by enzymes.

Analytical approach

If one breaks up a metabolic way into simpler elements, one can obtain a list of N reactions biochemical IH, I pertaining to {1; N} on the basis of a substrate S to arrive at a product P. These reactions can be dependant between them within a metabolic way, because each reaction IH (I pertaining to {2; n-1}, i.e. all the reactions except the first and the last) uses at least a product P of another reaction of the list of the IH like substrate and as a product a substrate of another reaction has. In a more intuitive way, one can chain the reactions on the basis of an initial substrate to arrive at a finished product.

Biological approach

The metabolic way is a concept making it possible to apprehend a biological function. Within a cell, multiple molecules interact perpetually. All these molecules take part in biochemical reactions, transforming molecules into other molecules or building vaster molecular buildings. If it is possible to consider these reactions individually, the emergence of the Biologie of the systems leaves the place to a more general design of the biochemical reactions within a cell. That makes it possible to apprehend the various biochemical reactions by group. Within one of these groups, the reactions which have place contribute to the same objective. There exists for example a metabolic way of synthesis for each amino-acid (Homo sapiens does not have them all, this is why there exist essential amino-acids). These particular metabolic ways are also called " ways of biosynthèse".

Since a metabolic way is an ordered succession of biochemical reactions, it is sensitive to the presence of each actor taking part in his good progress. If it misses a particular enzyme during the process, then the whole of the way is in general made ineffective. In the same way, if it misses a particular substrate, the finished product could not be reached.

In order to control the activity of these metabolic ways, of the loops of feedback exist too. For example, one of the product P is an inhibiter of an enzyme E intervening upstream in the way. In this case, the enzyme E takes part (in fine) in the synthesis of the product P, which controls to him even the activity of E in return. This can end at a metabolic way when this one " travaille" too much quickly.

Current examples

Among the whole of the metabolic ways referred to date, some are particularly known and were particularly well studied. One can quote:

the anaerobic Glycolysis. It is the metabolic way most widespread within the alive world, since all the being alive use it.
the Cycle of Krebs. It is about a metabolic way which with the characteristic to be cyclic. Thus, one of the basic substrates is also the product of end of reaction.
the Cycle of the urea, there too a cyclic metabolic way
all ways of synthesis of the amino-acids and fatty-acids

Modularity

The approaches of systemic biology bring to think that the living organisms are doubtless modular. In light, that means that it is possible to form " groupes" molecules interacting to lead to a particular result. One can also see that as a possible whole division of the reactions within a cell in independently functional sub-units provided all their members are present. These sub-units are modules within a vaster architecture. The interconnection of these modules leads to the complexity of the cell.

The metabolic ways, which are an example of these modules, are thus also, for the researcher, an abstraction making it possible to apprehend the operation of a cell to a higher degree of complexity. Each module becomes a " box noire" (that one will be able to always study separately), which one must “simply” know the entries and the exits. One can thus drastiquement simplify the modeling of complex systems while using of this concept of modularity.

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