Biochemistry: The Chemical Basis of Life

Biochemistry: The Chemical Basis of Life

Introduction to Biochemistry

Biochemistry is the study of the chemical composition and reactions of living matter. It is foundational for understanding the structure and function of the human body at the molecular level. Compounds in the body are classified as either organic or inorganic.

• Organic Compounds: Contain carbon, are covalently bonded, often large, and essential for life (e.g., proteins, lipids, carbohydrates, nucleic acids).

• Inorganic Compounds: All other chemicals in the body, also essential for life (e.g., water, salts, acids, bases).

Inorganic Compounds

Water

Water is the most abundant and important inorganic compound in the body, making up 60-80% of cell volume. Its unique properties are vital for life.

• High Heat Capacity: Absorbs and releases large amounts of heat with little temperature change, helping maintain homeostasis.

• High Heat of Vaporization: Requires significant energy to evaporate, providing a cooling mechanism (e.g., sweating).

• Polar Solvent: Dissolves many substances, forms hydration layers, and serves as a transport medium for gases, wastes, and nutrients.

• Reactivity: Participates in hydrolysis (breaking down molecules with water) and dehydration synthesis (building molecules by removing water).

• Cushioning: Protects organs from trauma (e.g., cerebrospinal fluid protects the brain).

Salts

Salts are ionic compounds that dissociate into ions in water, forming electrolytes that conduct electrical currents. Examples include NaCl, KCl, CaCO3, and calcium phosphates.

• Functions: Nerve impulse transmission, muscle contraction, oxygen transport (hemoglobin), and enzyme activity.

Acids and Bases

Acids and bases are substances that affect the pH of body fluids. Acids release hydrogen ions (H+), while bases release hydroxide ions (OH-).

• Acids: Taste sour, react with metals, act as proton donors (e.g., HCl, H2SO4, acetic acid).

• Bases: Taste bitter, feel slippery, act as proton acceptors, produce OH- (e.g., NaOH).

Buffers

Buffers are weak acids and bases that regulate pH to maintain homeostasis. They bind or release H+ as needed to keep pH stable.

Organic Compounds

Overview of Biological Organic Molecules

Four major organic molecules are unique to living systems: carbohydrates, lipids, proteins, and nucleic acids. All contain carbon and covalent bonds.

Carbohydrates

Carbohydrates include sugars, starches, chitin, and cellulose. They are classified by size and solubility and are made of monosaccharide building blocks.

• Solubility: Larger carbohydrates are less soluble in water.

Lipids

Lipids are water-insoluble molecules that dissolve in other lipids and organic solvents. Examples include neutral fats, phospholipids, cholesterol, and eicosanoids.

Proteins

Proteins make up 10-30% of cell mass and are the basic structural material of the body. They are composed of amino acids and can be classified by shape and function.

• Fibrous Proteins: Extended, strand-like, insoluble, and stable (e.g., collagen, keratin, elastin).

• Globular Proteins: Compact, spherical, water-soluble, and chemically active (e.g., antibodies, enzymes, hormones).

Denatured Proteins

Excessive heat or pH changes can break hydrogen bonds, causing proteins to lose their shape and function (denaturation).

Active Sites of Proteins

Active sites are specific regions on proteins that interact with other molecules. The integrity of these sites is crucial for protein function (e.g., hemoglobin binding oxygen, enzyme-substrate interaction).

Enzymes

Enzymes are globular proteins that act as biological catalysts, increasing the speed of chemical reactions without being consumed or becoming part of the product.

• Specificity: Each enzyme acts on a specific substrate (e.g., proteases break down proteins).

Nucleic Acids

Nucleic acids are the largest molecules in the body, composed of nucleotide building blocks. The two main types are DNA and RNA.

• DNA: Contains instructions for building proteins, located in the nucleus.

• RNA: Carries out DNA's instructions, located outside the nucleus.

ATP (Adenosine Triphosphate)

ATP is an energy molecule derived from an adenine-containing RNA nucleotide. It is used for cellular work, including transport, mechanical, and chemical activities.