What are amino acids? Chemical Structure
Amino acids (or amino acids) are the primary structural unit of proteins. We can therefore imagine amino acids as building blocks which, joined by a glue called a peptide bond, form a long sequence that gives rise to a protein.
Inside the stomach and duodenum these bonds are broken and the individual amino acids reach the small intestine where they are absorbed as such and used by the body.
From a chemical point of view, the amino acid is an organic compound containing a carboxylic group (COOH) and an amino group (NH2). In addition to these two groups, each amino acid is distinguished from the others by the presence of a residue (R) also known as the side chain name of the amino acid.
Classification of amino acids
Only twenty of the different amino acids existing in nature (currently over five hundred) are involved in protein synthesis. From a nutritional point of view, these amino acids can in turn be divided into two large groups: that of essential amino acids and that of non-essential amino acids.
Essential are those amino acids that the human body is unable to synthesize in sufficient quantities to meet its needs. For adults there are eight and more precisely: phenylalanine, isoleucine, lysine, leucine, methionine, threonine, tryptophan and valine. During the period of growth, a ninth one must be added to the eight mentioned, histidine, in consideration of the fact that in this period the requirements of this amino acid are higher than the synthesis capacity.
They are considerate semi-essential amino acids cysteine and tyrosine, as the body can synthesize them starting from methionine and phenylalanine.
They are defined conditionally essential amino acids (arginine, glycine, glutamine, proline and taurine) those amino acids that play a fundamental role in maintaining homeostasis and the functions of the organism in certain physiological situations. In some pathological conditions these amino acids may not be synthesized at a sufficient speed to meet the real needs of the organism.
Arginine is assuming considerable importance, as a precursor of nitric oxide, due to the many functions that the latter carries out in cellular activity, in the transduction of biological signals and in immune defense.
CONTENT IN ESSENTIAL AMINO ACIDS: proteins that contain all essential AAs in balanced quantities and ratios can be defined as complete or noble. In general, animal proteins are complete and vegetable proteins are incomplete. The term noble associated with vegetable proteins is incorrect and was introduced to counter the saying according to which "legumes are the meat of the poor". In reality, taking a good source of vegetable proteins in the diet is very important and to further enhance this concept the term "noble" has been improperly introduced. In any case, these deficiencies can be overcome simply by using appropriate food associations such as PASTA and BEANS. In this case we speak of mutual integration because the amino acids that the pasta is lacking are supplied by the beans and vice versa.
LIMITING AMINO ACID: of a protein or a protein mixture is the amino acid essential deficient or completely absent, which limits the use of all other amino acids even if present in excess of the needs. As we have seen in proteins of vegetable origin, this amino acid is generally not sufficient to guarantee the need and must be introduced through the "pairing with other foods.
CHEMICAL INDEX: it is given by the ratio between the quantity of a given amino acid in one gram of the protein under examination and the quantity of the same amino acid in one gram of the biological reference protein (of the egg). The higher this index, the greater the percentage of essential amino acids.
BRANCHED AMINO ACIDS: o BCAAs are three essential amino acids (Valine, Isoleucine and Leucine) which in particular conditions, such as intense physical effort, are used as an auxiliary energy substrate for fats and carbohydrates.
Branched chain amino acids in food Vs branched chain amino acids in supplements
Functions of amino acids
The primary function of amino acids is to intervene in protein synthesis, necessary to cope with the cell renewal processes of the organism. In addition to this function, called "plastic", amino acids also have a modest but not negligible importance in energy production ( branched chain amino acids)
Some amino acids are also precursors of compounds that perform important biological functions.
From tryptophan we obtain niacin (vitamin PP), serotonin (neurotransmitter) and melatonin (regulator of the circadian rhythms of the sleep / wake cycle).
From the sulfur amino acids (methionine and cysteine) glutathione is obtained, an important antioxidant useful for fighting free radicals and keratin, an essential protein for the health of hair, hair and nails.
In addition to those involved in protein synthesis, many other amino acids perform very important functions. Among these, the best known in the sports field are creatine (useful for increasing alactacid and lactacid anaerobic capacity and power) and carnitine which facilitates the transport of lipids within the mitochondrion).
MORE: Functions of amino acids "
