What Is An Amino Acid? Characteristics Of This Type Of Molecules
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 things get interesting when we know that, for example, proteins are the most abundant molecules in the entire human body, as they represent the 50% of the dry weight of all our fabrics.
These nutrients can be found in all cells, so they make up organs, muscles, tissues, hair and skin. It could be said that, together with nucleic acids (RNA and DNA), proteins are the basis of the life of all living beings.
Thus, amino acids play an essential role in the concept of human “existence” and all organisms as we know it today. If you want to know what an amino acid is and what its types are, continue reading
We have already defined the term from a purely physical point of view, but paying attention to a more functional approach, it could be said that each amino acid is another “brick” in the construction of the foundations of a building, in this case, each of the proteins that will later form part of the cells, which will make up the tissues that will give rise to the very complex human body.
These protein structures essential for existence are polymer chains made up of amino acids linked by peptide bonds, that is, the amino group (-NH2) of one joined to the carboxyl group (-COOH) of another. The bond resulting from this union of both molecules receives a chemical nomenclature CO-NH, and in the process a molecule of water (H2O) is lost. Without entering into the complex world of organic chemistry, we will limit ourselves to saying that this type of bond has intermediate characteristics between a double and a single bond.
Once we have defined exactly how amino acids are associated to give rise to proteins, it is time for us to define the types of amino acids present in nature.
Types of amino acids
It is assumed that all amino acids are part of proteins, and therefore the simplest and quickest classification of them is between “essential” and “non-essential”. Still, 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, but They do not appear associated with the polymeric chain that makes up proteins
An example of this is Ornithine and Citrulline, intermediate compounds of the urea cycle, or Homocysteine and Homoserine, essential molecules for different metabolic processes. Another precursor substrate that needs to be mentioned is dihydroxyphenylalanine (DOPA), the initiator of the metabolic pathways that give rise to neurotransmitters as important as dopamine and adrenaline.
Although these compounds act more “behind the scenes” compared to those directly associated with protein polymers, it is clear that we cannot imagine life without a hormone such as adrenaline (and therefore DOPA), which increases the heart rate of living beings and promotes fight and flight responses, thus increasing the theoretical survival of the individual. Although they are not structural amino acids per se, their function is certainly essential.
Once this atypical group has been discussed, it is clear that the bulk of the space and informative importance goes to the amino acids that are part of proteins. We show them below.
2. Protein amino acids
When asked what an amino acid is, these are the first ones that come to mind. The canonical or codable protein amino acids are those that are encoded in the genome, that is, whose assembly instructions are stored in the DNA
Through processes such as transcription and translation (mediated by messenger and transfer RNAs) these synthesis instructions give rise to the desired protein, based on a concatenation of amino acids in a specific order. This is applicable when we are moving in “standard genetic code” terrain.
These common amino acids for all living beings are the following: alanine, arginine, asparagine, aspartate, cysteine, phenylalanine, glycine, glutamate, glutamine, histidine, isoleucine, leucine, lysine, methionine, proline, serine, tyrosine, threonine, tryptophan and valine, i.e. 20 organic molecules that are one of the essential pillars of life
As the classification of biological terms follows a clearly anthropocentric nomenclature, human beings have divided these canonical amino acids into “essential” and “non-essential” according to the need for their consumption.
2.1. Essential amino acids
They are those that the human body cannot produce on its own, and therefore, they must be consumed in the form of proteins with the diet These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine, that is, 9 of the 20 canonicals named above.
We are lucky that these amino acids are found in the environment that surrounds us. For example, histidine is synthesized in abundant quantities by plants, fungi and bacteria. By concatenation of 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 of histamine, an essential compound in mediating allergic responses by the immune system. That’s where its name “essential” comes from, as it is an example that, literally, we couldn’t live without it.
Legumes and cereals are generally assumed to be foods rich in essential amino acids It is necessary to emphasize that this “essentiality” depends on the species we focus on, since naturally not all living beings follow the same metabolic routes.
2.2. Non-essential amino acids
In this case, the amino acids They are produced through metabolic pathways included in the human being’s own physiology They are the following: alanine, tyrosine, aspartate, cysteine, glutamate, glutamine, glycine, proline, serine, asparagine and arginine, that is, 11 of the 20 canonicals.
As we have mentioned before, the different metabolic pathways are different even within mammals themselves. For example, cats lack 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 ourselves.
Even so, the fact that amino acids can be synthesized by the human being himself It does not mean that they are not also ingested with the diet, since they naturally make up the tissue of many other mammals on which we feed. For example, proline is found in both animal products (meat, fish, dairy products and eggs) and foods of plant origin (legumes, seeds, whole grains and fruits).
23. Conditional amino acids
But didn’t the classification end with essential and non-essential? The question of what an amino acid is must be followed by certain considerations, and one of them is that conditional amino acids exist.
These are those who They are not essential in a time of normality, but they may be required in case of illness or special conditions Undoubtedly an example of this is arginine (not essential at normal times), since its monitored ingestion in the diet is only needed in the presence of certain diseases, such as obesity disorders and sickle cell anemia.
Conclusions
As we have seen in these lines, the world of amino acids is extensive and complex, but Its most widespread classification has been made based on the need (or not) for human intake in their diet
Even so, there are many other divisions based, for example, on the properties of its chain (polar neutral, non-polar neutral, with a negative or positive charge) or according to the location of the amino group (alpha, beta or gamma amino acids). In any case, we leave these classifications for another opportunity, since they are focused on a much more biochemical than functional vision.
Thus, amino acids are organic molecules that make up the most basal “pillar” of the human being: proteins, cells and tissues. Therefore, it is essential to know them and know which ones must be consumed appropriately in the diet on a daily basis.
