BIOELEMENTS: CLASSIFICATION (PRIMARY AND SECONDARY) - BIOLOGY - 2025

" Bioelement " is a term used to refer to the main chemical elements that make up living beings. In some classifications, these are divided into primary elements and secondary elements.

Of the 87 known chemical elements, only 34 make up organic matter, and 17 of these 34 are known to be truly indispensable for life. In addition, of these 17 essential elements, five constitute more than 90% of the matter that makes up living organisms.

The periodic table of the elements, the primary and secondary bioelements are also indicated (Source: Alejandro Porto via Wikimedia Commons)

The six main elements in organic matter are hydrogen (H, 59%), oxygen (O, 24%), carbon (C, 11%), nitrogen (N, 4%), phosphorus (P, 1%) and sulfur (S, 0.1 to 1%).

These percentages reflect the number of atoms of each element with respect to the total number of atoms that make up living cells and these are what are known as "primary bioelements".

The secondary bioelements are found in a much smaller proportion and are potassium (K), magnesium (Mg), iron (Fe), calcium (Ca), molybdenum (Mo), fluorine (F), Chlorine (Cl), sodium (Na), iodine (I), copper (Cu) and Zinc (Zn).

Secondary elements are usually cofactors in catalytic reactions and participate in many of the biochemical and physiological processes inherent in the cells of organisms.

Primary bioelements

Carbon, hydrogen and oxygen atoms are the structural base of the molecules that make up organic matter, meanwhile nitrogen, phosphorus and sulfur interact with different biomolecules to provoke chemical reactions.

Hydrogen

Hydrogen is a chemical element that exists in gaseous form at room temperature (25ºC), it can only exist in a solid or liquid state at room temperature when it is bound to other molecules.

Hydrogen atoms are thought to be among the first atoms to make up the early universe. The theories that are handled propose that the protons contained in the nucleus of hydrogen atoms began to associate with the electrons of other elements to form more complex molecules.

Hydrogen can combine chemically with almost any other element to form molecules, among which are water, carbohydrates, hydrocarbons, etc.

This element is responsible for the formation of bonds known as “hydrogen bonds”, one of the most important weak interactions for biomolecules and the main force responsible for maintaining the three-dimensional structures of proteins and nucleic acids.

Carbon

Carbon forms the nucleus of many biomolecules. Its atoms can combine covalently with four other atoms of different chemical elements and also with themselves to form the structure of highly complex molecules.

Carbon, along with hydrogen, is one of the chemical elements that can form the largest number of different chemical compounds. So much so that all substances and compounds classified as "organic" contain carbon atoms in their main structure.

General structure of an amino acid (Source: User: Ppfk via Wikimedia Commons)

Among the main carbon molecules of living beings are carbohydrates (sugars or saccharides), proteins and their amino acids, nucleic acids (DNA and RNA), lipids and fatty acids, among others.

Oxygen

Oxygen is a gaseous element and is the most abundant in the entire earth's crust. It is present in many organic and inorganic components and forms compounds with almost all chemical elements.

It is responsible for the oxidation of chemical compounds and combustion, which are also different forms of oxidation. Oxygen is a very electronegative element, it is part of the water molecule and participates in the respiration process of a large part of living beings.

Reactive oxygen species are responsible for oxidative stress inside cells. It is very common to observe the damage caused by oxidative compounds to the macromolecules inside the cell, since they unbalance the reducing interior of the cells.

Nitrogen

Nitrogen is also predominantly gaseous, making up about 78% of the Earth's atmosphere. It is an important element in the nutrition of plants and animals.

In animals, nitrogen is a fundamental part of amino acids which, in turn, are the building blocks for proteins. Proteins structure tissues and many of them have the necessary enzymatic activity to accelerate many of the vital reactions for cells.

Nitrogen is a fundamental part of the nitrogenous bases that make up nucleic acids such as DNA and RNA (Source: File: Difference DNA RNA-DE.svg: Sponk / * translation: Sponk via Wikimedia Commons)

Nitrogen is present in the nitrogenous bases of DNA and RNA, essential molecules for the transfer of genetic information from parents to offspring and for the proper functioning of living organisms as cellular systems.

Match

The most abundant form of this element in nature is as solid phosphates in fertile soils, rivers and lakes. It is an important element for the functioning of animals and plants, but also of bacteria, fungi, protozoa and all living beings.

In animals, phosphorus is found in abundance in all bones in the form of calcium phosphate.

Phosphorus is essential for life, since it is also an element that is part of DNA, RNA, ATP and phospholipids (fundamental components of cell membranes).

This bioelement is always involved in energy transfer reactions, since it forms compounds with very energetic bonds, the hydrolysis of which is used to move different cellular systems.

Sulfur

Sulfur is commonly found in the form of sulfides and sulfates. It is especially abundant in volcanic areas and is present in the amino acid residues cysteine ​​and methionine.

In proteins, the sulfur atoms of cysteine ​​form a very strong intra- or intermolecular interaction known as the “disulfide bridge”, which is essential for the formation of the secondary, tertiary and quaternary structure of cellular proteins.

Coenzyme A, a metabolic intermediate with a wide variety of functions, has a sulfur atom in its structure.

This element is also fundamental in the structure of many enzymatic cofactors that participate in different important metabolic pathways.

Secondary bioelements

As mentioned above, the secondary bioelements are those that are found in a lower proportion than the primary ones and the most important are potassium, magnesium, iron, calcium, sodium and zinc.

Secondary bioelements or trace elements are involved in many of the physiological processes of plants, in photosynthesis, in respiration, in the cellular ionic balance of the vacuole and chloroplasts, in the transport of carbohydrates to the phloem, etc.

This is also true for animals and other organisms, where these elements, more or less dispensable and less abundant, are part of many cofactors necessary for the functioning of the entire cellular machinery.

Iron

Iron is one of the most important secondary bioelements since it has functions in multiple energy phenomena. It is very important in natural oxide reduction reactions.

In mammals, for example, iron is an essential part of hemoglobin, the protein that is responsible for the transport of oxygen in the blood within erythrocytes or red blood cells.

In plant cells this element is also part of some pigments such as chlorophyll, essential for photosynthetic processes. It is part of the cytochrome molecules, also essential for respiration.

Zinc

Scientists think that zinc was one of the key elements in the appearance of eukaryotic organisms millions of years ago, since many of the DNA-binding proteins for replication that made up the "primitive eukaryotes" used zinc as a motif of Union.

An example of this type of protein is zinc fingers, which are involved in gene transcription, protein translation, metabolism and protein assembly, etc.

Calcium

Calcium is one of the most abundant minerals on planet earth; in most animals it makes up teeth and bones in the form of calcium hydroxyphosphate. This element is essential for muscle contraction, transmission of nerve impulses, and blood clotting.

Magnesium

The highest proportion of magnesium in nature is found in solid form combined with other elements, it is not only found in the free state. Magnesium is a cofactor for more than 300 different enzyme systems in mammals.

The reactions in which it participates range from protein synthesis, muscle mobility, and nerve function, to regulation of blood glucose levels and blood pressure. Magnesium is necessary for energy production in living organisms, for oxidative phosphorylation and glycolysis.

It also contributes to the development of bones and is necessary for the synthesis of DNA, RNA, glutathione, among others.

Sodium and potassium

They are two very abundant ions in the cell interior and variations in their internal and external concentrations, as well as their transport, are determining factors for many physiological processes.

Potassium is the most abundant intracellular cation, it maintains the liquid volume inside the cell and the transmembrane electrochemical gradients.

Both sodium and potassium are actively involved in the transmission of nerve impulses, as they are transported by the sodium-potassium pump. Sodium also participates in muscle contraction and in the absorption of nutrients through the cell membrane.

The rest of the secondary bioelements: molybdenum (Mo), fluorine (F), Chlorine (Cl), iodine (I) and copper (Cu) play important roles in many physiological reactions. However, they are needed in a much smaller proportion than the six elements explained above.

References

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