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The term link It has several uses: in this case we are interested in referring to its meaning as a union or a link between different elements. Peptide , on the other hand, is that related to peptides : the molecules that are formed by a covalent amino acid binding (organic substances whose molecular composition has a carboxyl group and an amino group).

Is called peptide bond to the Chemical bond that is established between the carboxyl group of an amino acid and the amino group of another amino acid . This kind of link, where a water molecule is lost , allows the formation of those mentioned peptides and of the protein .

By joining an amino group (-NH2 ) and a carboxyl group (-COOH ) with loss of a water molecule, a link is established CO-NH . The development of this link always needs the input of Energy ; in turn, when the peptide bond is broken, energy release occurs.

Breaking a peptide bond can occur through the hydrolysis : this is the name of the splitting that registers a molecule through water. Hydrolysis, in the natural environment, occurs in a very slow way, although it is possible to accelerate the process using various techniques .

In the presence of water, a peptide bond can be broken with an amount of free energy around 8-16 kilojoules / mol (which is equivalent to 2-4 kcal / mol). Unit kilojoule per mole , which can be symbolized as kJ / mol , is recognized by the International System of Units (YES ) and corresponds to the relationship between energy and the amount of matter : energy is expressed in kilojoules and matter is measured in moles.

The kilojoules are just thousands of joules, another unit of measure recognized by the International System, whose original name is joule and it is used for the measurement of heat, work and energy. In technical terms, its definition is "the amount of work carried out by a Newton with a constant force along a meter in the direction of that force." Unit mol , on the other hand, is used to measure the amount of a given substance, and is part of the seven fundamental physical quantities of the SI.

To accelerate the hydrolysis of a peptide bond, which in nature can take more than a millennium, scientists can choose one of the following methods :

* acid hydrolysis : It is achieved by leaving the protein in a boil for a long time with strong acid type solutions (H2SO4 and HCI). This path achieves the complete destruction of tryptophan and part of threonine and serine;

* basic hydrolysis : it is usually carried out using BaOH or NaOH, and does not destroy amino acids mentioned in the previous method;

* enzymatic hydrolysis : in living beings, this way of degrading peptide bonds is the most normal. In this case, some enzymes proteolytics that act slowly and often do not complete their work, although neither the destruction of amino acids nor racemization occurs (when an optically active compound becomes racemic). This type of hydrolysis is very specific;

* temperature hydrolysis : if the conditions are normal, the peptide bonds are not destroyed, but the protein can be denatured (that is to say that its structures secondary, tertiary and quaternary). On the other hand, if a temperature higher than 110 ° is applied for 48 hours, it is possible to destroy the links.

It should be noted that, in general, the peptide bond is represented as a single link . Anyway, it has several features that bring it closer to a double link. That is why specialists often mention that a peptide bond presents properties that place it halfway between a single link and a double link.

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