Structure of proteins
Proteins are macromolecules formed by a series of amino acids, joined together through a bond called peptide. The sequence of the individual amino acids is genetically dictated and determines the function of the protein itself.
The peptide bond involves the removal of a water molecule and can therefore be broken up by hydrolysis, ie by providing water and a specific enzyme that catalyzes the reaction.
In addition to Carbon, Hydrogen and Oxygen, protein molecules contain nitrogen, which is present at 16% of the total molecular weight.
Proteins represent 10-15% of the body mass. However, the various tissues are characterized by a different protein content. In nerve cells, for example, proteins represent 10% of the cell mass, while in muscle cells this share rises to 20%.
Contractile proteins make up 65% of the body's protein mass, although, since muscle mass can increase or decrease, this share varies slightly from individual to individual.
Functions of proteins and nitrogen balance
In the organism, proteins play a double role: structural on the one hand (they enter into the composition of the various cellular components) and functional on the other (they intervene in the performance of innumerable bodily functions). Enzymes, receptors, hormones and immunoglobulins are just some of the many protein molecules present in the body.
Proteins also participate in the regulation of the acid-base balance of body fluids, are responsible for the molecular mechanism of contraction and participate in the blood clotting process.
The proteins of the organism are not stable entities, but are subject to a continuous change, called turnover. They are in fact continuously demolished and replaced by new and similar protein molecules. The speed of this turnover decreases with age and is different in the cells. of the different fabrics. This continuous process of renewal has a considerable energy cost, which alone represents as much as 20% of the energy expended daily to support the basal metabolism.
Due to the turnover of proteins, a certain quantity of free amino acids is always present in the cells of the organism, called an amino acid pool. This pool should not be understood as a real reserve of nitrogenous substances, but as a quantity of amino acids present in one dynamic state, with one flow in and one out.
A + B = C + D
condition of
maintenance
in physiological conditions the incoming flow is the same as the outgoing one and the amino acid pool is in equilibrium;
A + D> B + C
increased protein
of the organism
During growth, during pregnancy and during convalescence from a debilitating disease, an increase in body proteins is recorded; this situation is also recorded when muscle masses increase following intense sporting activity;
B + C> A + D
decreased protein
bodily
Debilitating diseases, aging and overly restrictive diets promote the loss of muscle mass and protein.
This scheme allows to make a balance between the supply and the elimination of proteins from the organism. This balance, called nitrogen, is expressed in terms of nitrogen.
Nitrogen balance = Nitrogen taken with food proteins - nitrogen eliminated
The nitrogen balance can be positive, negative or in balance
The nitrogen balance is positive during: growth, pregnancy, breastfeeding and intense physical activity. On the other hand, it is negative during absolute or protein fasting and in the presence of debilitating pathologies.
CONTINUE: Second part "
