WHAT IS THE CHEMICAL COMPOSITION OF LIVING THINGS? - BIOLOGY - 2025

The chemical composition of living beings is based on organic molecules and some inorganic elements, more or less in the same proportions and that perform similar functions in all of them.

Living organisms are made up of cells and these cells present different degrees of complexity in their organization. Some are relatively simple, such as bacteria, and others are characterized by more complex organization patterns, with many more elements in their internal organization, as is the case in most eukaryotic cells.

Photograph by «oblako3011» at www.pixabay.com

The structural elements of living matter are made up of biomolecules and the main constituents of most of these biomolecules are, in the case of humans, for example, carbon (50%), oxygen (20%), hydrogen (10%).), nitrogen (8.5%), calcium (4%) and phosphorus (2.5%) (all values ​​relative to dry weight).

These six elements represent approximately 95% of the total composition of organic matter, the remaining 5% corresponds to other elements such as: potassium, sulfur, sodium, chlorine, magnesium, iron, manganese and iodine.

It should be noted that most of the composition of organisms (more than 60% of body weight) is water in a liquid state, which is a fundamental element for life since both intracellular structures and cells themselves are immersed in it..

This liquid medium provides the cells with the most important necessary conditions and in it all the relevant biochemical reactions for survival take place.

chemical composition of living being

- Complex biomolecules

Several of the main elements that go into the composition of living matter combine in different proportions to form different sets of small organic molecules, which in turn serve as structural elements for the formation of more complex biomolecules.

The relationship between these structural elements and the main complex biomolecules of organisms is as follows:

- Deoxyribonucleotides and deoxyribonucleic acid (DNA)

- Ribonucleotides and ribonucleic acid (RNA)

- Amino acids and proteins

- Monosaccharides and polysaccharides

- Fatty acids and lipids

Deoxyribonucleotides and deoxyribonucleic acid

Deoxyribonucleic acid or DNA contains the hereditary information of all living things, prokaryotes and eukaryotes. This important biomolecule also determines the main characteristics of a cell, both from a morphological, metabolic, structural and developmental point of view.

DNA encodes the information necessary for protein synthesis, as well as that required to synthesize RNA, which is another important organic molecule necessary for the synthesis and control of many cellular processes.

It is a polymer composed of two strands of subunits called nucleotides, whose structures are formed by a molecule of deoxyribose (a monosaccharide with 5 carbon atoms), one or more phosphate groups and a nitrogenous base with one or two rings (purine or pyrimidine, respectively).

The puric bases of DNA are adenine (A) and guanine (G), while the pyrimidine bases are thymine (T) and cytosine (C).

Linearly, the nucleotides of the same DNA strand are joined to each other through phosphodiester bonds, which consist of the phosphate groups and the sugars to which they are covalently linked.

The bases present in one of the strands are complementary with those that are opposite these in the other strand by means of hydrogen bonds, always in the same way: adenine with thymine (AT) and guanine with cytosine (GC).

Different nitrogenous bases in DNA and RNA.

Source User: Sponktranslation: User: Jcfidy

Ribonucleotides and ribonucleic acid

Like DNA, ribonucleic acid is a biomolecule and is responsible for the binding process of amino acids that make up proteins, as well as other more complex processes of regulation and control of gene expression.

It is also a biopolymer, but the nucleotides that form it are called ribonucleotides, because the monosaccharide that structures them is not a deoxyribose, as in DNA, but a ribose. They also have one or more phosphate groups and their nitrogenous bases differ from those of DNA in that guanine is not present, but uracil (U).

Amino acids and proteins

Proteins are biomolecules that can reach varying degrees of complexity and are significantly versatile in terms of structure and function. They not only give structure and shape to cells, but can also have activities that allow the rapid development of essential biochemical reactions (enzymes).

Regardless of the type of protein in question, they are all made up of basic “building blocks” called amino acids, which are molecules that have an “asymmetric” carbon atom attached to an amino group (-NH2), to a carboxyl group (-COOH), a hydrogen atom (-H) and a group R that differentiates them.

Graphic representation of the structure of a ribosomal protein (Source: Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute via Wikimedia Commons)

The most common amino acids in nature are 20 and are classified according to the identity of the R group; these are:

- asparagine, glutamine, tyrosine, serine, threonine (polar ones)

- aspartic acid, glutamic acid, arginine, lysine, histidine (those with charge) and

- glycine, alanine, valine, leucine, isoleucine, tryptophan, proline, cysteine, methionine and phenylalanine (the apolar ones).

Once DNA is translated into an RNA molecule, each nucleotide triplet represents a code that tells the structure that synthesizes proteins (ribosomes) what type of amino acid to incorporate into the growing peptide chain.

The polypeptides that make up proteins are produced, then, thanks to the union between their amino acids, which consists of the establishment of a peptide bond between the carbon of the carboxyl group of an amino acid and the nitrogen of the amino group of the adjacent amino acid.

Monosaccharides and polysaccharides

Carbohydrates are one of the most abundant biomolecules in living beings. They fulfill basic functions such as structural, nutritional, signaling elements, etc. They are made up of chemical complexes of carbon, hydrogen and oxygen in different proportions.

Plants are one of the main natural carbohydrate producers of living beings and most animals depend on these for their subsistence, since they extract energy, water and carbon from these.

Cellulose, a structural biopolymer (Source: Vicente Neto via Wikimedia Commons)

The structural carbohydrates of vegetables (cellulose, lignin, etc.), as well as the reserve carbohydrates of plants (starch) and of many animals (glycogen), are more or less complex polysaccharides that consist of polymers of simple sugar units or monosaccharides (mainly glucose).

Fatty acids and lipids

Lipids are water-insoluble compounds that constitute the fundamental substance of biological membranes, elementary from the functional and structural point of view of all living cells.

They are amphipathic molecules, that is, molecules that have a hydrophilic and a hydrophobic end. They are made up of fatty acid chains attached to a carbon skeleton, generally glycerol, whose third “free” carbon atom is attached to a particular substituent that gives each molecule its identity.

Some of the most common lipids (Source: The original uploader was Lmaps at English Wikipedia. Via Wikimedia Commons)

Fatty acids are hydrocarbons, that is, they are composed solely of carbon and hydrogen atoms bound together.

The association of multiple lipids in the form of a bilayer is what makes the formation of a membrane possible and the hydrophobicity characteristics of this structure, as well as the presence of integral and peripheral proteins, make this a semi-permeable structure.

- Water

Photograph by José Manuel Suárez, via Wikimedia Commons

Water (H2O) is one of the most important chemical elements for living beings and the cells that make them up. Much of the body weight of animals and plants is made up of this colorless liquid.

Through photosynthesis carried out by plants, water is the main source of oxygen that animals breathe and also of hydrogen atoms that are part of organic compounds.

It is considered as the universal solvent and its properties make it especially important for the development of virtually all the biochemical reactions that characterize living organisms.

If viewed from a cellular point of view, water is divided into "compartments":

• The intracellular space, where the cytosol is formed by water with other substances mixed, a fluid in which the organelles of eukaryotic cells are suspended.
• The extracellular space, which consists of the environment that surrounds cells, either in a tissue or in a natural environment (unicellular organisms).

- Ions

Much of the chemical elements in cells are found in the form of the biomolecules mentioned above and many others omitted from this text. However, other important chemical elements are in the form of ions.

Cell membranes are generally impervious to ions dissolved in the internal or external environment of cells, so these can enter or leave these through transporters or special channels.

The ionic concentration of the extracellular medium or of the cytosol influences the osmotic and electrical characteristics of the cells, as well as the different cellular signaling processes that depend on these.

Among the most important ions for animal and plant tissues are calcium, potassium and sodium, chlorine and magnesium.

References

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