Basic Principles of Chemistry

Introduction to Chemistry in Biological Systems

Chemistry is fundamental to understanding physiological processes in living organisms. All body functions, from movement to digestion, are governed by chemical reactions. Chemistry relevant to biology can be divided into basic chemistry and biochemistry, with a focus on organic and inorganic compounds.

Key Terms in Basic Chemistry

Matter and Its States

• Matter: Anything that has mass and occupies space.

• States of Matter:

  • Solid: Definite shape and volume.

  • Liquid: Changeable shape, definite volume.

  • Gas: Changeable shape and volume.

Elements and Atoms

• Elements: Substances that cannot be broken down into simpler substances by ordinary chemical methods. Four elements (C, O, H, N) make up 96% of body weight.

• Atoms: The smallest units of elements, combining to form molecules and compounds.

Molecules and Compounds

• Molecule: Two or more atoms bonded together (e.g., O2).

• Compound: Molecule with two or more different kinds of atoms (e.g., C6H12O6).

Mixtures

• Mixtures: Physical combinations of two or more components.

• Three types:

  • Solutions: Homogeneous mixtures; solute particles are very tiny and do not settle out or scatter light.

  • Colloids: Heterogeneous mixtures; larger particles that do not settle out and scatter light (e.g., Jell-O).

  • Suspensions: Heterogeneous mixtures with large, visible solutes that settle out (e.g., blood).

Differences Between Mixtures and Compounds

• Mixtures do not involve chemical bonding; compounds do.

• Mixtures can be separated by physical means; compounds require chemical methods.

• Mixtures can be heterogeneous or homogeneous; compounds are always homogeneous.

Chemical Bonds and Reactions

Chemical Bonds

• "Energy relationships" between electrons of reacting atoms.

• Not physical structures, but determine how atoms interact in compounds.

Chemical Reactions

• Synthesis (Combination): Atoms/molecules combine to form larger molecules (anabolic processes).

• Decomposition: Molecules are broken down into smaller molecules or atoms (catabolic processes).

• Exchange (Displacement): Bonds are both made and broken; atoms are exchanged between molecules.

Energy in Chemical Reactions

• Exergonic: Release energy (catabolic).

• Endergonic: Absorb energy (anabolic).

Factors Affecting Reaction Rates

• Temperature (higher increases rate)

• Concentration (higher increases rate)

• Particle size (smaller increases rate)

• Catalysts: Increase reaction rate without being changed; enzymes are biological catalysts.

Organic and Inorganic Chemistry

Inorganic Compounds

• Do not contain carbon (exceptions: CO2, CO).

• Include water, salts, acids, and bases.

Water

• Most abundant inorganic compound in living cells (60–80% of cell volume).

• Key properties:

  1. High heat capacity

  2. High heat of vaporization

  3. Polar solvent properties

  4. Reactivity

  5. Cushioning

Salts

• Ionic compounds that dissociate in water to form electrolytes (conduct electricity).

• Vital for nerve impulse transmission, muscle contraction, and water balance.

Acids and Bases

• Acids: Release H+ ions in solution (e.g., HCl).

• Bases: Accept H+ ions or release OH– (e.g., NaOH).

• Both are electrolytes and affect pH.

pH Scale

• Measures hydrogen ion concentration.

• pH 7 is neutral; below 7 is acidic; above 7 is basic (alkaline).

Buffers

• Help maintain acid-base homeostasis by releasing or binding H+ as needed.

Organic Compounds

• Contain carbon, usually large, covalently bonded molecules.

• Include carbohydrates, lipids, proteins, and nucleic acids.

• Most are polymers made by dehydration synthesis and broken down by hydrolysis.

Major Classes of Organic Compounds

Carbohydrates

• Include sugars and starches; contain C, H, O (2:1 ratio of H:O).

• Major source of cellular fuel.

• Three classes:

  • Monosaccharides: Single sugars (e.g., glucose, fructose, galactose, ribose, deoxyribose).

  • Disaccharides: Two sugars (e.g., sucrose, maltose, lactose).

  • Polysaccharides: Many sugars (e.g., starch, glycogen, cellulose).

Important Polysaccharides

• Starch: Storage form in plants; must be digested to glucose.

• Glycogen: Storage form in animals; stored in liver and muscle.

• Cellulose: Indigestible fiber in plants; aids digestive movement.

Lipids

• Contain C, H, O (less O than carbohydrates), sometimes P.

• Insoluble in water; main types include triglycerides, phospholipids, steroids, and eicosanoids.

Triglycerides

• Fats (solid) and oils (liquid); composed of three fatty acids and glycerol.

• Main functions: energy storage, insulation, protection.

Phospholipids

• Modified triglycerides with a phosphate group; have polar (hydrophilic) heads and nonpolar (hydrophobic) tails.

• Major component of cell membranes.

Steroids

• Four interlocking hydrocarbon rings; cholesterol is the most important steroid.

• Precursor for vitamin D, steroid hormones, and bile salts.

Eicosanoids

• Derived from arachidonic acid; include prostaglandins, which regulate inflammation, blood pressure, and clotting.

Proteins

• Composed of C, H, O, N (sometimes S and P); 10–30% of cell mass.

• Made of amino acids linked by peptide bonds.

• Functions: structural, enzymatic, transport, contractile, communication, defensive.

Levels of Protein Structure

• Primary: Sequence of amino acids.

• Secondary: Alpha-helix or beta-sheet formed by hydrogen bonds.

• Tertiary: 3D folding due to side chain interactions.

• Quaternary: Multiple polypeptide chains form a functional protein.

Nucleic Acids

• Composed of C, H, O, N, P; largest molecules in the body.

• Polymers of nucleotides (nitrogen base, pentose sugar, phosphate group).

• Two types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

ATP (Adenosine Triphosphate)

• Primary energy-transferring molecule in cells.

• Energy from glucose breakdown is stored in ATP and used for cellular work.

Additional info: This guide covers foundational chemistry concepts essential for understanding organic chemistry and biochemistry, including the structure and function of biomolecules, chemical reactions, and the importance of water, acids, bases, and buffers in biological systems.