Water: Biomedical Importance and Properties

Water: Biomedical Importance

• Water is the most prevalent chemical component in living organisms
• Its unique properties, including solvation of diverse molecules, stem from its dipolar structure and hydrogen bonding capability
• Water interacts with solvated biomolecules, influencing their structures
• Water acts as a crucial reactant or product in many metabolic processes due to its excellent nucleophilic properties
• Water's slight dissociation into hydroxide and proton ions determines the acidity of an aqueous solution, generally measured using the logarithmic pH scale
• Bicarbonate and other buffers maintain the pH of extracellular fluid within a narrow range (7.35 to 7.45)
• Measuring the pH of arterial blood and the CO2 content of venous blood confirms acid-base balance disturbances

Water, an Ideal Biological Solvent

• A water molecule forms an irregular, slightly skewed tetrahedron with oxygen at its center
• Hydrogen atoms and unshared electrons of the remaining orbitals occupy the corners
• The 105-degree angle between the hydrogen atoms deviates slightly from the ideal tetrahedral angle (109.5 degrees)
• Water's asymmetrical electrical charge distribution creates a dipole
• Oxygen's high electronegativity pulls electrons away from the hydrogen nuclei, leaving them with partial positive charges
• Unshared electron pairs on oxygen create a region of local negative charge

Water: General Properties

• Water is the most abundant substance in living systems, comprising 70% or more of the weight of most organisms
• Water is the universal solvent of life
• All chemical reactions within organisms occur in liquid water
• Water's polarity gives it unique properties, including its role as a solvent, a chemical reactant, and a factor regulating temperature

Water Quality

• Chemical water: pure water, containing only H₂O
• Portable water: contains no harmful substances, suitable for drinking
• Palatable water: aesthetically pleasing
• Wholesome water: not chemically pure but contains harmless substances
• Polluted water: contains harmful substances, but not necessarily pathogens
• Contaminated water: contains pathogens
• Mineral water: contains minerals like calcium, iron, and manganese

Assessing Water Quality

• Physical Parameters: Turbidity, color, odor/taste, temperature, conductivity
• Chemical/Biological Parameters: Total solids, pH, hardness, presence of chemicals such as chloride, nitrate, and sulfate; biological parameters like bacteria, viruses, and protozoa

Properties of Water

• Surface Tension: Water molecules stick together and to other surfaces, providing protection and cohesion crucial to the integrity of cell and biological tissues
• Cohesion and Adhesion: Water molecules stick to each other (cohesion) and other polar substances (adhesion), such as glass and plastics via hydrogen bonding
• High Specific Heat: Water absorbs or releases large amounts of heat energy with minimal temperature change, helping to regulate cellular and environmental temperatures
• High Heat of Vaporization: Water requires a significant amount of energy to change from a liquid to a gaseous state, influencing the regulation of body temperature
• Lower Density of Ice: Water molecules in ice crystals are spaced further apart compared to liquid water, thus ice floats and providing insulation in aquatic environments
• Polarity: Water is a polar molecule, making it a good solvent for polar substances like ions, carbohydrates and proteins

Solvent Properties of Water

• Water is a polar solvent that readily dissolves a wide array of biologically important molecules, including charged and polar compounds
• Nonpolar molecules like lipids do not dissolve easily in water
• Hydrophobic interactions occur: Water molecules constrain their orientations around nonpolar solutes
• Hydration shells form to stabilize ions (like Sodium and Chloride) weakening their attraction, thereby dissolving the ions
• Water forms hydrogen bonds with non-ionic, but polar compounds

Water as a Reactant

• Water is a direct participant in many biochemical reactions
• Hydrolysis reactions involve breaking the bonds of a molecule with water
• Condensation reactions involve forming a larger molecule by removing water
• ATP (adenosine triphosphate) synthesis, which is a key biochemical reaction involves the removal of water from a large molecule, forming a new molecule with a high energy bond

Biomedical Importance of Water

• Water is essential for all forms of life.
• Water serves as the medium for all cellular events.
• Water is required to transport solutes in the body
• Water aids in the folding of complex biomolecules like proteins and nucleic acids.
• Water's semi-fluid nature governs the structure of cellular components.
• Water regulates body temperature.
• Water accelerates biochemical reactions by supplying ions

Maintenance of Water Balance

• Water intake and output balance is crucial for homeostasis
• Two key factors maintaining homeostasis include thirst response and antidiuretic hormone (ADH) action
• ADH regulates water reabsorption by the kidneys
• Mechanisms for water intake and output are opposite in nature when water content is imbalanced
• Water intake and output homeostasis is maintained by a complex combination of hormonal and other processes

Diseases of Water Balance

• Edema: Excess water in the body causes swelling (edema) from conditions like water intoxication; cancer or reaction from high doses of intravenous fluids
• Dehydration: Inadequate water intake causes dehydration from various triggers, including vomiting, diarrhea, and disruption of the hypothalamus

Ionization of Water

• Water has a slight tendency to ionize into hydrogen ions (H+) and hydroxide ions (OH-)
• Free protons (H+) do not exist in solution, but form hydronium ions (H3O+)

The pH Scale

• pH measures the hydrogen ion concentration of a solution
• pH is a logarithmic scale, meaning a change in one whole number on the pH scale, represents a tenfold difference in H+ concentration
• pH values range from 0 to 14
• A neutral solution has a pH of 7
• pH values below 7 indicate acidic solutions
• pH values above 7 indicate basic or alkaline solutions
• Water's ionization influences pH profoundly
• Various factors can alter the pH value of a solution, such as acid rain that lowers pH

Importance of pH

• Organisms must maintain pH within a narrow range
• Stomach acids aid digestion; excess can trigger pain and discomfort
• Mouth bacteria lower pH causing decay (mouthwash is often basic to mitigate this)
• Bee stings contain methanoic acid that can trigger pain; baking soda can be applied as a counter
• Proper pH is required for enzyme function, transport of solutes and maintenance of the structure of key biomolecules

Functions of Body Normal pH

• Enzyme function and body homeostasis rely on proper pH
• Solutes transport also needs the appropriate pH.
• Folding or biological shape of proteins, enzymes and nucleic acids require proper pH
• Coenzymes and metabolites structure depends on proper pH

Acid-Base Balance Disturbances

• Acidosis: Occurs due to elevated acidity in the body from conditions such as diabetes, loss of bicarbonate due to diarrhea, and disruption of the kidneys' proper elimination of acids
• Respiratory Acidosis: Results from depressed respiration and abnormal lung function
• Alkalosis: Occurs due to high blood pH that may be due to loss of HCl, excess bicarbonate due to vomiting, or hyperventilation triggered by a variety of physiological factors

Strong Acids and Strong Bases

• Strong acids readily donate H+ ions when dissociating in solution
• Strong bases readily donate OH- ions or react with H+ ions in solution
• Strong acids (like hydrochloric acid) completely dissociate into ions
• Weak acids (like in tomato juice) do not completely dissociate.
• Strong bases (such as sodium hydroxide) largely dissociate

Buffers

• Buffers help maintain a stable pH range within biological systems
• Buffers typically consist of a weak acid and its conjugate base
• They readily absorb excessive H+ or OH- ions, preventing drastic shifts in pH
• Bicarbonate buffer system in the blood is a crucial buffer system
• The buffer system assists in moderating pH changes by absorbing excessive ions, or exhaling excess carbon dioxide, preventing fluctuations in pH.

Explore the critical role of water in biology through this quiz. Understand its unique properties, including how it influences biomolecular structures and participates in metabolic processes. Dive into concepts such as pH balance and the significance of buffers in maintaining physiological conditions.