Essential Biomolecules: Definitions of Key Biological Compounds and Properties

Biomolecules and Bioelements: Fundamental Definitions

Biomolecules are compounds (molecules) that are part of living systems. They are classified into two main kinds: inorganic and organic.

Bioelements (or biogenic elements) are the simple substances (elements) that make up biomolecules.

Key Properties of Aqueous Solutions

Molecular Polarity and pH Regulation

• Dipole: Any substance that exhibits a skewed distribution of its electrical charges, generating a negative pole and a positive pole.
• Polar Character: The property of a substance that possesses an electric dipole.
• pH: The negative logarithm (changed sign) of the concentration of hydrogen ions ($H^+$).
• Hydronium Ion ($H_3O^+$): The ionized form of water.
• Buffer System: A substance or group of substances whose primary function is to maintain a constant pH level within a biological system.

Osmosis

Osmosis is the passive diffusion of the solvent (typically water in living matter) through a semipermeable membrane. The movement occurs from the more dilute solution (lower solute concentration) into the more concentrated solution (higher solute concentration).

Carbohydrates: Structure and Function

Carbohydrates are ternary organic molecules, consisting mainly of Carbon (C), Hydrogen (H), and Oxygen (O), often in an approximate ratio of $C_n(H_2O)_n$. They usually have a sweet flavor, and their primary functions are Energy storage and/or Structural support.

Types of Carbohydrates

• Monosaccharides: These are the smallest structural units of carbohydrates. They are small molecules with a number of carbon atoms ranging from 3 to 7 (e.g., trioses, tetroses, pentoses, hexoses).
• Disaccharides: Carbohydrates formed by the joining of two monosaccharides.
• Polysaccharides: High molecular weight carbohydrates, formed by the polymerization of hundreds or thousands of monosaccharides.

Lipids: Diversity and Biological Roles

Lipids are a heterogeneous group of substances characterized by having a large hydrocarbon portion in their molecule. This characteristic makes them insoluble in water (hydrophobic) but soluble in nonpolar organic solvents (e.g., benzene, alcohol, ether, chloroform).

Classes of Lipids

Storage and Protective Lipids

• Glycerides (Neutral Fats): Lipids formed by the combination of fatty acids and glycerol. Triglycerides are the most important and abundant, constituting the major energy reserves in plant and animal cells.
• Waxes: Lipids composed of fatty acids and long-chain alcohols. They serve as protective covers for the skin, hair, feathers, and exoskeleton in animals, and for the leaves and fruits of higher plants.

Membrane and Derived Lipids

• Glycerolipids and Sphingolipids: Both constitute the majority of so-called membrane lipids because, due to their amphipathic nature, they are the main constituents of biological membranes.
• Terpenes (Isoprenoids): A very heterogeneous group of unsaponifiable lipids formed by the polymerization of the structural unit isoprene (2-methylbutadiene). They can have a linear structure (e.g., phytol) or a cyclical structure (e.g., carotene).
• Steroids: Unsaponifiable lipids derived from steranes. The most important is cholesterol, which is a crucial part of the plasma membranes of animal cells (more rarely found in higher plants), conferring fluidity and stability. Cholesterol is also part of some lipoproteins in blood plasma.