In denaturation, biomolecules such as proteins and nucleic acids lose their biological activity due to structural changes. However, the primary structure of biomolecules remains intact. In the body, there are both necessary and harmful denaturation processes.
What is denaturation?
In the stomach, denaturation of food proteins occurs due to the influence of gastric acid. Denaturation refers to the destruction of the secondary, tertiary, and quaternary structure of proteins and nucleic acids by physical and chemical influences. Physical influences represent heat, pressure or high-energy radiation. Chemically, denaturations are caused by acids, alkalis, chaotropes, detergents, alcohol or other compounds. Despite these structural changes, however, the primary structure remains intact. The primary structure is characterized by the sequence of amino acids in proteins (albumen) or nitrogen bases in nucleic acids. The secondary structure describes the folding of biomolecules through the influence of hydrogen bonds, polar interactions, ionic bonds and hydrophobic interactions. Except for the formation of disulfide bonds between different sulfur-containing amino acids, the other covalent bonds are not changed. In the tertiary structure, spatial structures are formed within a biomolecule chain due to the foldings. The quaternary structure is characterized by the spatial structure formation with multiple chains. In this process, proteins and nucleic acids develop their biological activity only through the formation of the secondary, tertiary and quaternary structures. Denaturation destroys these structures by breaking the physical bonds between the individual atomic groups and the chemical bonds within the disulfide groups. Although the primary structure is retained, biological activity is lost. Denaturation occurs constantly both outside and inside the body. A typical example of denaturation is the hardness of the egg during cooking. In most cases, denaturations are irreversible. However, they can also be reversible.
Function and task
Denaturations occur constantly in animal and human organisms. For example, dietary proteins must first be prepared for chemical breakdown into the individual amino acids. This is not possible without digestion of the secondary, tertiary, or quaternary structures. The peptidases can only become active when the protein chain has been unfolded. In the stomach, the influence of gastric acid causes denaturation of the food proteins. After passing through the gastric portal, the processed food pulp is further chemically broken down by the digestive enzymes of the pancreas. Carbohydrates, fats and proteins are broken down into their corresponding monomers. Under the influence of peptidases, the individual amino acids are formed from the denatured dietary proteins, which are converted into endogenous proteins in the body. The agent for denaturation in the stomach is gastric acid, which consists mainly of hydrochloric acid. However, gastric acid does not only break down food proteins. It also destroys many of the food-borne pathogens by denaturing them. The denaturation of proteins and nucleic acids also plays an important role in immune defense. Thus, foreign protein particles (disease germs) and diseased or dead body cells are taken up and dissolved by so-called macrophages. Their digestion takes place in the so-called lysosomes. Lysosomes are cell organelles that break down foreign and endogenous substances with the help of enzymes. Macrophages contain a particularly large number of lysosomes. Inside the lysosomes, there is a low PH value (acidic environment). There, protein and nucleic acid components are first denatured and then digested by digestive enzymes. In addition, elevated temperatures often occur during an infection. In the case of fever, even sensitive disease germs are killed by denaturation due to the effect of heat. Lysosomes are present not only in macrophages, but also in all other body cells, because unusable waste products and protein components must be digested in every cell. The denaturation processes described so far are vital for the organism.
Diseases and ailments
However, in connection with denaturations that take place within the body, there are also pathological processes.In the case of infections, for example, the fever does not kill germs alone, because prolonged high temperatures can also destroy the body’s own proteins. This particularly affects the very sensitive enzymes. If the body temperature exceeds 40 degrees for a long time, many enzymes become ineffective. Therefore, very high fever has a potentially fatal effect on the organism. However, if the high temperature drops again within six hours, the damage is still reversible. Denaturations of proteins are also caused by heavy metal effects. Heavy metals can form complexes with proteins. This changes their tertiary and quaternary structures. Again, enzymes are particularly affected. This is why heavy metal accumulations in the organism lead to severe chronic and sometimes fatal diseases. Acid or alkali burns also involve denaturation of endogenous proteins in the skin. The death of the affected tissue initiates inflammatory processes that lead to itching and severe skin reactions. Furthermore, burns lead to denaturation of endogenous proteins of the skin and connective tissue. In medicine, severe bleeding is often treated with high-frequency current. In this process, the tissue temperature is briefly heated up to 80 degrees. As a result, tissue proteins and connective tissue fibers coagulate. This allows the wound to be effectively closed. Many age-related diseases are also associated with changes in the secondary and tertiary structure of proteins. Although complete denaturation does not occur in these cases, it does result in, among other things, refolding and the formation of plaques. A well-known example is the senile plaques in Alzheimer’s patients. Senile plaques are protein deposits in the brain that form as a result of folding in the tertiary structure. However, the causes of this process are not yet known. Among other things, an influence of aluminum on the structural changes of the tau protein is discussed.