2B: Biochemistry Foundations for Anatomy & Physiology: Inorganic Compounds, Acids, Bases, and pH

Biochemistry: The Chemical Basis of Life

Introduction to Biochemistry

Biochemistry is the study of the chemical composition and reactions of living matter. In anatomy and physiology, understanding biochemistry is essential for grasping how the body functions at the molecular level. Chemicals in the body are classified as either organic or inorganic compounds.

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

• Organic compounds: Include carbohydrates, fats, proteins, and nucleic acids. These compounds 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, separating into cations (positively charged ions) and anions (negatively charged ions), except for H+ and OH- ions. When dissolved, salts form electrolytes, which can conduct electrical currents in solution.

• Physiological roles: Ions such as sodium (Na+), potassium (K+), calcium (Ca2+), and iron (Fe2+/3+) are essential for nerve impulse transmission, muscle contraction, and maintaining fluid balance.

• Ionic balance: Maintaining the correct balance of ions is vital for homeostasis.

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

Acids and Bases

Definitions and Properties

• Acids: Substances that are proton donors; they release hydrogen ions (H+) in solution. Example: $\mathrm{HCl} \rightarrow \mathrm{H}^+ + \mathrm{Cl}^-$

• Bases: Substances that are proton acceptors; they pick up H+ ions in solution. Example: $\mathrm{NaOH} \rightarrow \mathrm{Na}^+ + \mathrm{OH}^-$

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

• Important acids: Hydrochloric acid (HCl), acetic acid (HC2H3O2 or HAc), 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. The more hydrogen ions present, the more acidic the solution. The pH scale is logarithmic and ranges from 0 to 14.

• pH formula: $\mathrm{pH} = -\log_{10}[\mathrm{H}^+]$

• Each pH unit represents a tenfold difference in H+ concentration.

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

• Neutral solutions: Equal numbers of H+ and OH- ions; pH 7 (e.g., pure water: $[\mathrm{H}^+] = 10^{-7}$ M).

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

Table: pH Ranges and Examples

pH Range	Type	Examples
0–6.99	Acidic	Gastric juice, lemon juice
7	Neutral	Pure water
7.01–14	Alkaline (Basic)	Blood (7.4), household bleach

Summary

• Biochemistry underpins all physiological processes in the body.

• Inorganic compounds such as water, salts, acids, and bases are essential for maintaining homeostasis and enabling biochemical reactions.

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

Additional info: These foundational concepts are essential for further study of organic molecules, cellular metabolism, and physiological regulation in anatomy and physiology.