3.1

Introduction to Organic Compounds

3.1 Life's Molecular Diversity

  • Carbon: central to biological molecules due to its ability to form stable bonds with many elements.

    • Roles: Carbon forms complex structures that are crucial for life processes.

    • Organic Compounds: primarily consist of carbon and hydrogen, with functional groups influencing reactivity.

Carbon's Chemical Properties


  • Valence Electrons: Carbon has 4 electrons in its outer shell, enabling it to form 4 covalent bonds, leading to diversity in functionality and structure.

  • Isomers: compounds with the same chemical formula but different structures, impacting their physical and chemical properties (e.g., Methane (CH₄) vs. Ethane (C₂H₆)).

Hydrocarbons

  • Composed entirely of carbon and hydrogen atoms, hydrocarbons are significant as they are the primary constituents of petroleum.


  • Though rare in living organisms, the presence of hydrocarbons in lipids is crucial as they store energy efficiently.

Carbon Skeletons

  • Carbon compounds can be arranged in straight chains, branched chains, or ring structures.


    • Implications: The structural diversity leads to varied chemical properties and biological activities, highlighted in the development of pharmaceuticals.

Cells' Molecular Complexity

3.3 Large Molecules from Small Building Blocks

  • Macromolecules: consist of carbohydrates, lipids, proteins, and nucleic acids, formed from smaller units via dehydration reactions (polymerization).

    • Diversity: Cells can synthesize diverse macromolecules from a limited set of monomers (e.g., 20 amino acids). The unique structures they form confer specialized functions.

Polymers and Monomers


  • Polymers: large structures made of many identical smaller units (e.g., a train of cars).

  • Dehydration Reaction: linking monomers together releases a water molecule, essential for forming complex molecules.

  • Hydrolysis: the process of breaking down polymers into monomers using water; crucial for digestion and metabolism.

Carbohydrates

3.4 Monosaccharides: Simplest Carbohydrates

  • Monosaccharides: single sugar units (e.g., glucose, fructose) that serve as building blocks for larger carbohydrates.

    • General Formula: defined by CH₂O (e.g., glucose's molecular formula is C₆H₁₂O₆).


  • Molecular Structure: Isomers such as glucose and fructose share the same molecular formula but differ in arrangement. They often form ring structures in aqueous solutions, increasing reactivity.

Cellular Function

  • Role of Carbohydrates: they serve as the primary energy source for cells; glucose is used immediately for cellular respiration and energy production.

Disaccharides and Polysaccharides

3.5 Formation of Disaccharides

  • Formed when two monosaccharides combine through dehydration synthesis, e.g., maltose (glucose + glucose) and sucrose (glucose + fructose).

    • Function in Plants: sucrose not only provides energy but also serves structural roles within plant cells.

3.7 Polysaccharides Overview

  • Polysaccharides: long chains of monosaccharide units (e.g., starch, glycogen, cellulose) that serve various functions in organisms.

    • Starch: primary energy storage polysaccharide in plants.

    • Glycogen: energy storage in animals characterized by a highly branched structure, facilitating rapid energy release.


    • Cellulose: serves as a structural component in plant cell walls, providing rigidity.

Fiber and Nutritional Impact

  • Cellulose: while not digestible by humans, it is essential for digestive health, acting as fiber.

  • Chitin: another structural polysaccharide found in the exoskeletons of arthropods.

  • Importance of Dietary Fiber: promotes digestive health and aids in nutrient absorption, highlighting the value of incorporating fiber-rich foods in diets.