Classification of elements by quantitative content
Depending on their percentage in biological structures, biogenic elements are generally divided into three main groups:
- Macroelements (about 98%). This group includes oxygen (O), carbon (C), hydrogen (H), and nitrogen (N). They are often called organogens. Carbon and hydrogen serve as the structural basis of water and all organic substances—proteins, nucleic acids, lipids, and carbohydrates. Oxygen and nitrogen are essential for the biosynthesis of organic compounds and the realization of their functions.
- Microelements (about 1.9%). These include potassium (K), phosphorus (P), sulfur (S), magnesium (Mg), chlorine (Cl), calcium (Ca), sodium (Na), and iron (Fe). Despite their smaller proportion, they are critical for enzymatic activity and tissue excitability.
- Ultramicroelements (less than 0.01%). Represented by iodine (I), copper (Cu), cobalt (Co), zinc (Zn), molybdenum (Mo), bromine (Br), manganese (Mn), boron (B), and others. They are part of specific hormones, vitamins, and enzymes.
Physiological role of macro- and microelements
Each biogenic element performs strictly defined functions, sustaining vital processes:
- Sodium (Na) and Potassium (K): ensure the processes of excitation and nerve impulse conduction (especially in nervous and muscular tissues). Sodium also maintains osmotic pressure and pH, while potassium is essential for muscle contractions.
- Calcium (Ca): a crucial structural component of bone tissue. Blood clotting and adequate muscle contraction are impossible without it.
- Chlorine (Cl): participates in the regulation of water-salt metabolism (along with sodium and potassium), maintains plasma osmotic pressure and gastric juice pH.
- Phosphorus (P): is part of the structure of teeth and bones, and is also an essential component of ATP, NADP, and phospholipids.
- Iron (Fe): a structural element of hemoglobin (in the blood) and myoglobin (in the muscles), and is part of respiratory chain enzymes.
- Magnesium (Mg): a component of chlorophyll and coenzymes, activates DNA synthesis and energy metabolism.
- Sulfur (S): an essential component of amino acids, proteins (e.g., insulin), and vitamins (B₁).
Functions of ultramicroelements
Elements present in trace amounts determine the function of the endocrine system and complex biochemical cascades:
- Iodine (I): the basic component of thyroid hormones.
- Copper (Cu): ensures hematopoiesis processes, hemoglobin synthesis, and the function of respiratory enzymes.
- Cobalt (Co): a structural part of vitamin B₁₂.
- Zinc (Zn): necessary for normal growth, acts as a component of enzymes.
- Fluorine (F): forms the structure of dental tissue.
- Manganese (Mn): participates in fatty acid oxidation, cellular respiration, and photosynthesis.
Ratio of chemical compounds
Chemical elements combine into molecules, forming inorganic and organic substances. The percentage is calculated based on wet mass:
Inorganic substances:
- Water (70–80%). A polar solvent that creates an optimal environment for biochemical reactions.
- Mineral salts (1–1.5%).
Organic substances:
- Proteins (10–20%). Biopolymers that perform structural and catalytic (enzymatic) functions.
- Fats (1–5%). Form the basis of all biological membranes.
- Nucleic acids (1–2%). Primarily DNA—a biopolymer whose monomer is a nucleotide. It stores hereditary information and transmits it during replication.
- Carbohydrates (0.2–2%). Act as a source of energy. Certain polysaccharides (e.g., cellulose) build the cell walls of prokaryotes and plants.
Briefly: answers to topical questions
What functions do carbohydrates perform in an animal cell?
In an animal cell, carbohydrates perform energetic, reserve, protective, receptor, and immunological functions.
- Energetic — oxidation of 1 g releases 17.6 kJ of energy.
- Reserve — stored in the form of the animal polysaccharide glycogen.
- Receptor — as part of the glycocalyx, they ensure intercellular recognition and contacts.
- Immunological — form specific surface antigens, determining the genetic individuality of the cell.
- Protective — participate in the formation of histocompatibility receptors.
- Constituent — are components of DNA, RNA, ATP, FAD, NAD+, NADP+.
What types of RNA are present in the cell and what are their functions?
In prokaryotic and eukaryotic cells, sources indicate:
- Messenger / template RNAs (iRNA / mRNA) — serve as a template for protein synthesis; iRNA transforms into mRNA during maturation.
- Ribosomal RNAs (rRNA) — are part of ribosomes, performing structural and catalytic functions.
- Transfer RNAs (tRNA) — transport amino acids to the ribosomes.
Additionally:
- Small nuclear RNAs (snRNA) — present only in eukaryotic cells; participate in splicing (removal of introns and joining of exons).
- Small nucleolar RNAs (snoRNA) — participate in the chemical modification of rRNA, tRNA, and snRNA.
- Ribozymes / catalytic RNAs (cRNA) — possess catalytic activity, cleaving all types of RNA.
- Transfer-messenger RNAs (tmRNA) — a rare type; found in many bacteria and in plant plastids; control the destruction of mRNAs lacking stop codons.
For quick memorization of the four main organogen macroelements, use the word CHON: C (carbon), H (hydrogen), O (oxygen), N (nitrogen). They make up 98% of the cell contents.
Class and exam questions
Which chemical elements are responsible for nerve impulse conduction?
In the processes of cell excitation and impulse conduction in nervous and muscular tissues, sodium (Na) and potassium (K) ions play the main role.
What structures contain iron and magnesium?
Iron is a component of hemoglobin, myoglobin, and respiratory chain enzymes. Magnesium is part of chlorophyll, coenzymes, and activates energy metabolism.
What proportion of the cell mass does water account for, and what is its function?
Water makes up 70 to 80% of the wet mass. It acts as the primary polar solvent and medium for all biochemical reactions to take place.
What else to study on this topic
- Organization of the genetic apparatus: structure of the DNA molecule and replication process
- Comparison of prokaryotic and eukaryotic cell structure
- Metabolism: stages of anabolism (assimilation) and catabolism (dissimilarity)
- Cell theory: key principles and exceptions (viruses and bacteriophages)
- Cell cycle and the significance of mitosis
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