Biochemistry: The Chemical Basis of Life

Introduction to Biochemistry

Biochemistry is the study of the chemical composition and reactions of living matter. All living organisms are composed of chemicals, which can be classified as either organic or inorganic compounds. Both types are essential for life and play distinct roles in cellular structure and function.

• Inorganic compounds: Include water, salts, and many acids and bases. These compounds generally do not contain carbon.

• Organic compounds: Include carbohydrates, fats (lipids), proteins, and nucleic acids. These compounds always contain carbon, are usually large, and are covalently bonded.

Inorganic Compounds

Water: The Most Abundant Inorganic Compound

Water is the most abundant inorganic compound in living cells, accounting for 60%–80% of their volume. Its unique properties make it vital for life.

• High heat capacity: Water can absorb and release large amounts of heat with little temperature change, helping to prevent sudden changes in body temperature.

• High heat of vaporization: Evaporation of water requires significant energy, making sweating an effective cooling mechanism.

• Polar solvent properties: Water dissolves and dissociates ionic substances, forming hydration layers around large charged molecules (e.g., proteins). It is the body's major transport medium.

• Reactivity: Water is involved in many chemical reactions, including hydrolysis and dehydration synthesis.

Salts and Electrolytes

Salts are ionic compounds that dissociate in water to form ions. These ions are essential for various physiological processes.

• Salts separate into cations (positively charged ions) and anions (negatively charged ions) in water.

• All ions are called electrolytes because they conduct electrical currents in solution.

• Electrolytes play specialized roles in body functions, such as nerve impulse transmission and muscle contraction.

• Common body salts: Sodium chloride (NaCl), calcium carbonate (CaCO3), potassium chloride (KCl).

• Ionic balance is vital for maintaining homeostasis.

Acids and Bases

Definitions and Properties

• Acids: Proton donors that release hydrogen ions (H+) in solution. Example:

• Bases: Proton acceptors that pick up H+ ions in solution. Example:

• When a base dissolves in water, it releases a hydroxyl ion (OH-).

• Important acids: Hydrochloric acid (HCl), acetic acid (HC2H3O2), carbonic acid (H2CO3).

• Important bases: Bicarbonate ion (HCO3-), ammonia (NH3).

Acid-Base Concentration and the pH Scale

The pH scale measures the concentration of hydrogen ions (H+) in a solution. It is a logarithmic scale ranging from 0 to 14, where each pH unit represents a tenfold difference in H+ concentration.

• pH formula:

• Acidic solutions: High [H+], low pH (0–6.99)

• Neutral solutions: Equal numbers of H+ and OH- ions; pH = 7 (e.g., pure water: M)

• Alkaline (basic) solutions: Low [H+], high pH (7.01–14)

• Example: A solution with pH 5 is 10 times more acidic than a solution with pH 6.

Table: Classification of Solutions by pH

Summary

• Biochemistry underpins all physiological processes in the body.

• Inorganic compounds such as water, salts, acids, and bases are essential for maintaining cellular environment and function.

• The pH scale is a critical concept for understanding acid-base balance in biological systems.

Additional info: Understanding the chemical properties of water, electrolytes, acids, and bases is foundational for topics such as cellular metabolism, nerve impulse transmission, and muscle contraction, which are covered in later chapters of Anatomy & Physiology.