What is an amino acid? Characteristics of this type of molecule

From a biological point of view, an amino acid is a molecule that contains an amino group and a carboxyl group in its physical structure. This organic compound is the basis of proteins.

If we look at the concept of amino acid from a purely physiological point of view, it may leave us a little cold, but the thing becomes interesting when we know that, for example, proteins are the most abundant molecules in the body. because they represent 50% of the dry weight of all our fabrics.

these nutrients they can be found in all cells, So that they constitute the organs, muscles, tissues, hair and skin. You could say that with nucleic acids (RNA and DNA), proteins are the basis of the life of all living things.

Thus, amino acids play an essential role in the concept of human “existence” and of all organisms as we know it today. If you want to know what an amino acid is and what are its types, keep reading.

    What is an amino acid? Coding of Life

    We have already defined the term from a purely physical point of view, but paying attention to a more functional approach, one could say that each amino acid is one more “brick” in the construction of the foundation of a building, in this case, each of the proteins that will later become part of the cells, which will form the tissues that will give rise to the very complex human body.

    These protein structures essential to existence are polymeric chains made up of amino acids linked by peptide bonds.That is, the amino group (-NH2) of one attached to the carboxyl group (-COOH) of another. The bond resulting from this union of the two molecules receives a chemical nomenclature CO-NH, and in the process a water molecule (H2O) is lost. Without going into the complex world of organic chemistry, we will limit ourselves to saying that this type of bond has characteristics intermediate between a double and a single.

    Once we have defined exactly how amino acids are combined to give rise to proteins, it is time to define the types of them found in nature.

    Types of amino acids

    It is assumed that all amino acids are part of proteins, which is why the simplest and quickest classification of them is between “essential” and “non-essential”. Yet many readers will be surprised to learn that not all amino acids are part of the protein complexes assumed by all. These require special mention.

    1. Non-protein amino acids

    Some metabolic intermediates and neurotransmitters have a characteristic amino acid structure, however they do not appear to be associated with the polymer chain that makes up proteins.

    Ornithine and citrulline, intermediate compounds in the urea cycle, or homocysteine ​​and homoserine, molecules essential to various metabolic processes are an example. Another precursor substrate to name is dihydroxyphenylalanine (DOPA), the initiator of metabolic pathways that give rise to neurotransmitters as important as dopamine and adrenaline.

    If these compounds act more “behind the scenes” compared to those directly associated with protein polymers, it is clear that one cannot imagine life without a hormone like adrenaline (and therefore DOPA), which increases the frequency. . fight and flight responses, thereby increasing the theoretical survival of the individual. Although they are not structural amino acids per se, their function is of course essential.

    After discussing this atypical group, it is clear that the thickness of the space and the informative importance are removed by the amino acids which are part of the proteins. We show them below.

    2. Protein amino acids

    When asked what an amino acid is, they are the first that come to mind. Canonical or codifiable protein amino acids are those encoded in the genome, i.e. the coupling instructions are stored in the DNA.

    Through processes such as transcription and translation (mediated by messenger and transfer RNAs), these synthetic instructions give rise to the desired protein, the basis for a concatenation of amino acids in a specific order. This is applicable when we operate in a field of “standard genetic code”.

    These amino acids common to all living things are: alanine, arginine, asparagine, aspartate, cysteine, phenylalanine, glycine, glutamate, glutamine, histidine, isoleucine, leucine, lysine, methionine, proline, serine, tyrosine, threonine, tryptophan and valine, that is, 20 organic molecules that are one of the essential pillars of life.

    As the classification of biological terms follows a clearly anthropocentric nomenclature, humans have divided these canonical amino acids into “essential” and “non-essential” according to the need for their consumption.

      2.1. essential amino acids

      These are the ones that the human body cannot produce on its own, and therefore must be consumed as protein with the diet.. These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine, or 9 of the 20 canons mentioned above .

      We are fortunate that these amino acids are found in the environment around us. For example, histidine is synthesized in abundant amounts by plants, fungi and bacteria. By concatenating the elements of the food chain of ecosystems, dairy products, beef and chicken contain histidine. We ingest it and this amino acid will be the precursor to histamine, a compound essential in mediating allergic responses by the immune system. Hence its name “essential”, because it is an example that we literally could not do without.

      Legumes and grains are generally considered foods rich in essential amino acids. It should be emphasized that this “essentiality” depends on the species that we observe, because naturally all living beings do not follow the same metabolic pathways.

      2.2. Non-essential amino acids

      In this case, the amino acids they are produced by metabolic pathways included in the physiology of human beings. These are: alanine, tyrosine, aspartate, cysteine, glutamate, glutamine, glycine, proline, serine, asparagine and arginine, or 11 of the 20 guns.

      As we mentioned earlier, the different metabolic pathways are different even in mammals themselves. For example, cats need an essential enzyme to synthesize taurine, which is an acid derived from cysteine. In this case, this compound would become essential for them even though humans can synthesize it for ourselves.

      However, the fact that amino acids can be synthesized by humans themselves this does not mean that they are not also ingested with the dietThey therefore naturally form the tissue of many other mammals on which we feed. For example, proline is found in both animal products (meat, fish, dairy, and eggs) and plant-based foods (legumes, seeds, whole grains, and fruits).

      2.3. conditional amino acids

      But did not the classification result in essential and non-essential elements? The question of what an amino acid is needs to be followed by certain assessments, and one of them is the existence of conditional amino acids.

      These are the ones who they are not essential in times of normality, but they may be necessary in the event of illness or special conditions. An example of this is certainly arginine (not essential in normal times), since its controlled intake in the diet is only necessary in the presence of certain diseases, such as obesity disorders and sickle cell anemia.


      As we have seen in these lines, the world of amino acids is large and complex, however its most widespread classification was made on the basis of the need (or not) of the intake by man in his diet.

      However, there are many other divisions based, for example, on the properties of its chain (neutral polar, neutral nonpolar, negatively or positively charged) or depending on the location of the amino group (alpha, beta or gamma amino acids) .). In short, we leave these classifications for another opportunity, because they are focused on a vision much more biochemical than functional.

      Thus, amino acids are organic molecules which constitute the most basic “pillar” of the human being: proteins, cells and tissues. Therefore, it is essential to know them and to know which ones should be correctly consumed in the daily diet.

      Bibliographical references:

      • What types of amino acids are there, aminoacidos.eu. Collected August 19 from https://www.aminoacido.eu/aminoacidos/que-tipos-de-aminoacidos-existen.html
      • Amino Acids, United States National Library of Medicine. Collected August 19 from https://medlineplus.gov/spanish/ency/article/002222.htm#:~:text=Los%20amino%C3%A1cidos%20no%20esenciales%20incluyen,%2C%20prolina%2C% 20serine % 20y% 20tyrosine.
      • Biomolecules (amino acids), University of the Basque Country. Retrieved August 19 from http://www.ehu.eus/biomoleculas/aa/tema8.htm#index

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