Function of proteins

A common idea is that each protein fulfills only one function in general. However any function of a protein at least requires a connection with a substrate, there is thus a function of recognition, then from this connection rises one or more events, which can have effects on various scales in the organization. The concept of function of a protein is a very vague concept. This is why one tends more and more to try to have a hierachic vision of the function of proteins by breaking up the function according to the following levels of description:

phenotypical
cellular
molecular

In a very general way, these functions can be distributed in six great groups.

There exist four levels of structure at proteins. A protein is a chain of amino-acids.

Catalyze

Certain proteins are catalysts of chemical reactions: they make it possible chemical reactions to quickly be held under the conditions of temperature and pressure in conformity with the life. These proteins are then called Enzyme S. For example, the degradation of the Glucose in order to extract the energy contained in this molecule, is made by the combined action of ten enzymes in a called metabolic way Glycolyse. A piece of sugar left on a table with an infinitesimal probability break up into carbonic gas and water, one can accelerate this reaction by strongly heating sugar. Subjected to the action of the glycolytic enzymes, this reaction takes only a few seconds with 37° C and a pressure of 1 atmosphere.

The metabolic Maladie occur when one of the enzymes of a metabolic Voie is transferred and has a functionality different from the normal.

Cellular structure

The shape of the cells and fabrics as their strength to the physical constraints is gotten by proteins of structure, like the Collagène or the proteins of the Cytosquelette.

Cellular mobility

The contractile proteins composing the muscle, Actine and Myosine, are at the origin of the cellular movements, as well as Mitose. The proteins are also constitutive of the Flagelle S of locomotion of the Spermatozoïde S and some Bactérie S.

Cellular communication

The intercellular communication is of an crucial importance for the development and the coordinated operation of the organization. One finds proteins having a function of Récepteur of hormone. In the case of Hormone S absorbent (not being able to cross the cellular Membrane), the receiver is a membrane protein integrated in the membrane and having a site of fixing on the side external with the cell, while its intracellular part makes it possible to transmit the information convoyed by the hormone. In the case of lipophilic hormones, therefore crossing the membrane freely, such as for example the estrogen S, the protein receiver is cytosolic. Fixing induces a change of conformation of the receiver (its three-dimensional structure is modifée), then enabling him to fix itself at its effector target, which in the case of the estrogen is a sequence of DNA.

A whole series of proteins make it possible to convoy information since the origin to the final target. They are the enzymes of cellular indication. One of the mechanisms most often met is the Phosphorylation targets carried out by a group of proteins called proteins kinases. The dephosphorylation, quite as important, is the fact of Phosphatase S.

Immune system

The Immunoglobuline S which make it possible to recognize it to oneself not-oneself are proteins; they are often called Anticorps. One estimates at several billion the number of different immunoglobulins, each one synthesized by a different cell (clone), called Lymphocyte B. During the Vaccination, a lymphocyte B recognizes the Antigène introduced and multiplies by Mitose S, thus multiplying the number of sites of manufacture of the anticorp.

Transport

Several proteins have a function of transport: hemoglobin for the transport of dioxygene, the transferrine for the transport of iron. Another type of transport is ensured by the ionic channels. They allow the transport of ions through the cellular membrane, which is differently impermeable for them. These channels are at the origin of the electric activities measured in the Cerveau and ensure the contraction of the muscle. They are also at the origin of the filtration of blood on the level of the Rein and the reabsorption of the ions contained in the primitive urine, which is the blood deprived of the illustrated elements (cells). Another type of transmembrane transport is ensured by the conveyers, who, contrary to the ionic channels, require an energy contribution to fulfill their function. Transport of electrons is ensured by the enzymes of the cellular Respiration and the Photosynthèse.

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