Biochemistry in Anatomy & Physiology

Introduction to Biochemistry

Biochemistry is the study of the chemical composition and reactions of living matter. Understanding biochemistry is essential for comprehending the structure and function of the human body at the molecular level.

• Organic compounds: Contain carbon, are usually large, and are covalently bonded. Examples include carbohydrates, fats, proteins, and nucleic acids.

• Inorganic compounds: Do not contain carbon (with some exceptions such as CO2 and CO). Examples include water, salts, and many acids and bases.

Inorganic Compounds

Water

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

• High heat capacity: Absorbs and releases heat with little temperature change, preventing sudden changes in body temperature.

• High heat of vaporization: Requires large amounts of heat to evaporate, providing a useful cooling mechanism (e.g., sweating).

• Polar solvent properties: Dissolves and dissociates ionic substances, forms hydration layers around large charged molecules (such as proteins), and serves as the body's major transport medium.

• Reactivity: Participates in chemical reactions (e.g., hydrolysis and dehydration synthesis).

• Cushioning: Protects organs by providing a resilient cushion.

Salts

Salts are ionic compounds that dissociate into separate ions in water. They are essential for various physiological processes.

• Separate into cations (positively charged ions) and anions (negatively charged ions), excluding H+ and OH- ions.

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

• Ions such as sodium (Na+), potassium (K+), calcium (Ca2+), and iron (Fe2+/3+) play specialized roles in body functions.

• Ionic balance is vital for homeostasis.

• Common salts in the body: NaCl (sodium chloride), CaCO3 (calcium carbonate), KCl (potassium chloride), and calcium phosphates.

Example: Dissociation of NaCl in water releases Na+ and Cl- ions, which are surrounded by water molecules due to their polar nature.

Acids and Bases

Definitions and Properties

• Acids: Proton donors; they release hydrogen ions (H+) in solution. Example: HCl → H+ + Cl-

• Bases: Proton acceptors; they pick up H+ ions or release hydroxyl ions (OH-) in solution. Example: NaOH → Na+ + OH-

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

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

pH Scale and Acid-Base Balance

The pH scale measures the concentration of hydrogen ions (H+) in a solution, ranging from 0 (most acidic) to 14 (most basic).

• pH is the negative logarithm of [H+] in moles per liter:

• The scale is logarithmic: each pH unit represents a tenfold difference in [H+].

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

• Neutral solutions: Equal [H+] and [OH-], pH = 7 (e.g., pure water)

• 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: Representative pH Values

Clinical Relevance

• Enzymes in the body function within a narrow pH range.

• Significant deviations in blood pH (e.g., arterial pH < 7.0) can be life-threatening.