INORGANIC BIOMOLECULES: CHARACTERISTICS, FUNCTIONS, TYPES - BIOLOGY - 2025

The inorganic biomolecules are a large group of molecular configurations present in living beings. By definition, the basic structure of inorganic molecules is not composed of a carbon skeleton or bonded carbon atoms.

However, this does not mean that inorganic compounds must be completely devoid of carbon to be included in this great category, but rather that carbon must not be the main and most abundant atom in the molecule. The inorganic compounds that are part of living beings are mainly water and a series of solid or solution minerals.

Source: I, Splette

Water - the most abundant inorganic biomolecule in organisms - has a series of characteristics that make it an essential element for life, such as a high boiling point, high dielectric constant, ability to buffer changes in temperature and pH, among others.

Ions and gases, on the other hand, are restricted to very specific functions within organic beings, such as the nervous impulse, blood coagulation, osmotic regulation, among others. In addition, they are important cofactors of certain enzymes.

characteristics

The distinguishing feature of inorganic molecules found in living matter is the absence of carbon-hydrogen bonds.

These biomolecules are relatively small and include water, gases, and a number of anions and cations that actively participate in metabolism.

Classification and functions

The most relevant inorganic molecule in living matter is, without a doubt, water. In addition to this, other inorganic components are present and are classified into gases, anions and cations.

Within the gases we have oxygen, carbon dioxide and nitrogen. In the anions are chlorides, phosphates, carbonates, among others. And in the cations are sodium, potassium, ammonium, calcium, magnesium and other positive ions.

Below we will describe each of these groups, with their most outstanding characteristics and their function within living beings.

-Water

Water is the most abundant inorganic component in living beings. It is widely known that life develops in a watery environment. Although there are organisms that do not live in a body of water, the internal environment of these individuals is mostly hydric. Living things are composed of between 60% and 90% water.

The composition of water in the same organism can vary, depending on the type of cell studied. For example, a cell in a bone has, on average, 20% water, while a brain cell can easily reach 85%.

Water is so important because the vast majority of the biochemical reactions that make up the metabolism of individuals take place in an aqueous environment.

For example, photosynthesis begins with the breakdown of the components of water by the action of light energy. Cellular respiration results in the production of water by cleaving glucose molecules for energy extraction.

Other lesser known metabolic pathways also involve the production of water. The synthesis of amino acids is produced by water.

Properties of water

Water has a series of characteristics that make it an irreplaceable element on planet earth, allowing the wonderful event of life. Among these properties we have:

Water as a solvent: structurally, water is made up of two hydrogen atoms attached to an oxygen atom, sharing their electrons through a polar covalent bond. Thus, this molecule has charged ends, one positive and one negative.

Thanks to this conformation, the substance is called polar. In this way, water can dissolve substances with the same polar tendency, since the positive portions attract the negative portions of the molecule to dissolve and vice versa. The molecules that water dissolves are called hydrophilic.

Remember that in chemistry, we have the rule that "the same dissolves the same." This means that polar substances dissolve exclusively in other substances that are also polar.

For example, ionic compounds, such as carbohydrates and chlorides, amino acids, gases, and other compounds with hydroxyl groups, can easily dissolve in water.

Dielectric constant : the high dielectric constant of the vital liquid is also a factor that contributes to dissolving inorganic salts within it. The dielectric constant is the factor by which two charges of opposite sign are separated with respect to vacuum.

Specific heat of water: damping violent changes in temperature is an essential characteristic for the development of life. Thanks to the high specific heat of water, temperature changes stabilize, creating an environment suitable for life.

A high specific heat means that a cell can receive significant amounts of heat and the cell temperature does not increase significantly.

Cohesion: Cohesion is another property that prevents sudden changes in temperature. Thanks to the opposite charges of the water molecules, they attract each other, creating what is called cohesion.

Cohesion allows the temperature of living matter not to increase too much. Heat energy breaks the hydrogen bonds between molecules, instead of accelerating individual molecules.

PH control: in addition to regulating and keeping the temperature constant, water is capable of doing the same with the pH. There are certain metabolic reactions that require a specific pH in order to take place. In the same way, enzymes also require specific pH to work with maximum efficiency.

The regulation of pH occurs thanks to the hydroxyl groups (-OH) that are used together with the hydrogen ions (H ⁺). The former is related to the formation of an alkaline medium, while the latter contributes to the formation of an acid medium.

Boiling point : the boiling point of water is 100 ° C. This property allows water to exist in a liquid state at a wide temperature range, from 0 ° C to 100 ° C.

The high boiling point is explained by the ability to form four hydrogen bonds for each molecule of water. This characteristic also explains the high melting points and heat of vaporization, if we compare them with other hydrides, such as NH ₃, HF or H ₂ S.

This allows the existence of some Extremophilic organisms. For example, there are organisms that develop near 0 ° C and are called psychrophiles. In the same way, thermophilic ones develop around 70 or 80 ° C.

Density variation: the density of water varies in a very particular way as the ambient temperature changes. Ice presents an open crystalline lattice, in contrast to water in a liquid state it presents a more random, tighter and denser molecular organization.

This property allows the ice to float on the water, act as a term insulator and allow the stability of large ocean masses.

If this were not so, the ice would be sunk in the depths of the seas, and life, as we know it, would be an extremely unlikely event, how could life arise in large masses of ice?

Ecological role of water

To finish with the topic of water, it is necessary to mention that the vital liquid not only has a relevant role inside living beings, it also shapes the environment where they live.

The ocean is the largest reservoir of water on earth, which is affected by temperatures, favoring evaporation processes. Huge amounts of water are in a constant cycle of evaporation and precipitation of water, creating what is known as the water cycle.

-Gas

If we compare the extensive functions of water in biological systems, the role of the rest of the inorganic molecules is restricted only to very specific roles.

In general, gases pass through cells in aqueous dilutions. Sometimes they are used as substrates for chemical reactions, and in other cases they are the waste product of the metabolic pathway. The most relevant are oxygen, carbon dioxide and nitrogen.

Oxygen is the final electron acceptor in the transport chains of aerobically-respired organisms. Also, carbon dioxide is a waste product in animals and a substrate for plants (for photosynthetic processes).

-Ions

Like gases, the role of ions in living organisms appears restricted to very particular events, but essential for the proper functioning of an individual. They are classified depending on their charge into anions, ions with negative charges, and cations, ions with positive charges.

Some of these are only required in very small amounts, such as the metal components of enzymes. Others are needed in higher amounts, such as sodium chloride, potassium, magnesium, iron, iodine, among others.

The human body is constantly losing these minerals, through urine, feces, and sweat. These components must be re-entered into the system through food, mainly fruits, vegetables, and meats.

Ion functions

Cofactors: Ions can act as cofactors of chemical reactions. The chlorine ion participates in the hydrolysis of starch by amylases. Potassium and magnesium are essential ions for the functioning of enzymes that are very important in metabolism.

Maintenance of osmolarity: another function of great importance is the maintenance of optimal osmotic conditions for the development of biological processes.

The amount of dissolved metabolites must be regulated in an exceptional way, since if this system fails, the cell could explode or could lose significant amounts of water.

In humans, for example, sodium and chlorine are important elements that contribute to the maintenance of osmotic balance. These same ions also promote acid-base balance.

Membrane potential: in animals, ions actively participate in the generation of the membrane potential in the membrane of excitable cells.

The electrical properties of membranes affect crucial events, such as the ability of neurons to transmit information.

In these cases, the membrane acts analogously to an electrical capacitor, where charges accumulate and store thanks to the electrostatic interactions between cations and anions on both sides of the membrane.

The asymmetric distribution of ions in solution on each side of the membrane is translated into an electrical potential - depending on the permeability of the membrane to the ions present. The magnitude of the potential can be calculated by following the Nernst or Goldman equation.

Structural: some ions perform structural functions. For example, hydroxyapatite conditions the crystalline microstructure of bones. Calcium and phosphorus, meanwhile, is a necessary element for the formation of bones and teeth.

Other functions: finally, ions participate in such heterogeneous functions as blood clotting (by calcium ions), vision and muscle contraction.

Differences between organic and inorganic biomolecules

Approximately 99% of the composition of living things include only four atoms: hydrogen, oxygen, carbon and nitrogen. These atoms function as pieces or blocks, which can be arranged in a wide range of three-dimensional configurations, forming the molecules that allow life.

While inorganic compounds tend to be small, simple and not very diverse, organic compounds tend to be more notable and varied.

In addition to this, the complexity of organic biomolecules increases since, in addition to the carbon skeleton, they have functional groups that determine the chemical characteristics.

However, both are equally necessary for the optimal development of living beings.

Use of the terms organic and inorganic in everyday life

Now that we describe the difference between both types of biomolecules, it is necessary to clarify that we use these terms in a vague and imprecise way in everyday life.

When we designate fruits and vegetables as "organic" - which is very popular today - it does not mean that the rest of the products are "inorganic." As the structure of these edible elements is a carbon skeleton, the definition of organic is considered redundant.

In fact, the term organic arises from the ability of organisms to synthesize these compounds.

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