Biomolecules and the Role of Water in Living Matter

Biological Molecules and Biomolecules

Inorganic: H₂O, O₂, CO

Organic (Macromolecules): Proteins, Nucleic Acids, Carbohydrates, Lipids

Structure and Function of Macromolecules

• Polysaccharides: Polymers with structural functions (cellulose) or energy storage (glycogen).
• Nucleic Acids: Polymers of 4 nucleotides. Function associated with the storage, transmission, and expression of genetic information.
• Proteins: Combinations of 20 amino acids. Different functions (catalytic, structural, transport, hormones, antibodies, receptors).
• Lipids: Do not polymerize, they associate. Structural or functional roles.

Characteristics of Living Matter

Living things are made of chemical molecules interacting in an aqueous fluid, acquiring new physicochemical properties that give rise to vital phenomena.

Complexity, order, matter and energy exchange with the environment, and replication (self-replicating life).

Water in Biological Processes

Water provides a fluid environment that allows the mobility of molecules and their interaction in metabolic processes.

• Structure and properties
• Water as a solvent
• Ionization
• Buffer solutions

Solvent Action of Water

Water is the universal solvent in intracellular and extracellular media due to its polar nature and its tendency to form hydrogen bonds.

Hydrophobic Molecules: Relatively insoluble in water. Aliphatic and aromatic hydrocarbons or their derivatives that cannot form hydrogen bonds.

Approximate Body Composition (%)

• 60% Water
• 5.5% Minerals
• 20% Lipids
• >1% Nucleic Acids
• 1% Carbohydrates
• 14% Proteins

Ionic Equilibria

Practically all chemical reactions that occur in the body take place in an aqueous medium in which the behavior of molecules depends on their ionization state.

It is therefore important to understand:

• Acid-base equilibria
• Water ionization
• Importance of buffer solutions

Buffer Solutions

Maintain physiological pH; they are formed by weak acids and their conjugate bases.

• Bicarbonate Buffer: Maintains the pH of extracellular fluid close to values of 7.4.

Other Physiological Buffers

• H₂PO₄^- / HPO₄^2- (pKa = 6.86): Maintains intracellular pH.
• Proteins (pKa close to 7)
• NH₄⁺ / NH₃: Buffers urine.