Chemical Composition of Living Beings: Bioelements and Biomolecules

Molecular Level: Chemical Composition of Living Beings

1.1. Bioelements

Bioelements are all chemical elements that, in greater or lesser proportions, form living matter. There are six that qualify as the primary bioelements: C (Carbon), H (Hydrogen), O (Oxygen), N (Nitrogen), P (Phosphorus), and S (Sulfur). These make up most of living matter.

Others are involved in smaller quantities but are still essential for cellular metabolism. These are called secondary bioelements, which include Mg (Magnesium), Ca (Calcium), K (Potassium), Na (Sodium), and Cl (Chlorine).

Even smaller quantities of other elements are essential for living beings. These are called trace elements, and their lack causes serious illness and even death. Examples include Fe (Iron), I (Iodine), Co (Cobalt), and Li (Lithium).

Biomolecules

Biomolecules are molecules that are part of living matter. They are classified into two groups:

• Inorganic: Water and mineral salts, present in both living and nonliving matter.
• Organic: Carbohydrates, lipids, proteins, and nucleic acids, present only in living matter.

Mineral Salts

Mineral salts are inorganic molecules that easily dissociate in living things. They can be precipitated or dissolved.

Dissolved Salts: These are dissociated in aqueous solutions into cations (Na+, K+, Fe2+, etc.) or anions (Cl-, HCO3-, etc.).

General Functions:

1. Maintain salinity and allow intra- and extracellular media to be isotonic.
2. Maintain the pH of the media inside and outside within an optimum range, through buffer systems.
3. Create electrochemical gradients and lead to membrane potentials essential for nerve impulse transmission.

Specific Functions:

1. Na+, K+: Involved in nerve impulse transmission.
2. Ca2+: Important in blood clotting.
3. Mg2+: Component of chlorophyll, a cofactor in many enzymes involved in cellular respiration and DNA duplication.
4. Fe2+, Fe3+: Part of hemoglobin and myoglobin, responsible for transporting oxygen in blood and muscles.

Precipitated Salts: These form solid structures with skeletal and protective functions. For example, calcium carbonate leads to the formation of bones, and calcium fluoride gives enamel its hardness.

Water and Its Biological Significance

Water is the largest component of living beings, making up about 75% of their composition. This percentage varies among organisms and is also related to age and type of organism. The importance of water for living cells reflects its physical and chemical properties, which lie in its molecular structure.

Properties:

1. Solvent Action: Water is a universal solvent. This property is the most important for life, due to its ability to form hydrogen bonds with other polar substances, causing them to dissolve when interacting with polar water molecules. This property is responsible for two important functions:
   • It is the medium where the majority of metabolic reactions occur.
   • The contribution of nutrients and the removal of waste products are accomplished through aqueous transport, where all these substances are previously dissolved.
2. High Cohesion Force: Hydrogen bonds keep water molecules firmly united, forming a compact structure. This makes water nearly incompressible and able to act as a hydrostatic skeleton in some animals.
3. High Adhesion Force: This relates to the hydrogen bonds established between water molecules and other polar molecules. Along with cohesion, it is responsible for the phenomenon of capillarity.
4. High Specific Heat: Water can absorb large amounts of heat while its temperature increases only proportionally, and vice versa.
5. High Thermal Conductivity: Water has a high thermal conductivity.
6. High Latent Heat of Vaporization: To go from liquid to gaseous state, it is necessary to break the hydrogen bonds, which requires an input of energy. This energy is taken from the surroundings, causing the temperature to fall.