Biological Macromolecules and Their Chemistry

Biological Macromolecules

General Overview

  • Transition from general organic chemistry (OCHEM) to biochemistry.
  • Focus of Chapter 3: Biological macromolecules.
  • Biological macromolecules consist of high-energy large molecules essential for life.
  • Four main classes: carbohydrates, proteins, lipids, and nucleic acids (nucleic acids to be discussed in Chapter 9).

Definitions

  • Polymer: Large molecules made up of repeating units called monomers.
    • Mer: A piece or bit (Greek origin).
    • Poly: Many bits (Greek origin).
    • Example: A long chain formed by covalent bonds between monomers.

Chemical Mechanisms

  • Covalent Bonds: Bonds that connect monomers to form polymers.
  • Dehydration Synthesis (Condensation Reaction):
    • Process of joining two monomers:
    • One monomer has a hydroxyl (-OH) group and the other has a hydrogen (-H) group.
    • The enzyme removes -OH from one monomer and -H from the other, releasing a water molecule (H₂O).
    • A covalent bond forms between the two monomers.
    • Diagram Explanation:
    • Two generic monomers join, water liberated, and a covalent bond forms.
  • Hydrolysis:
    • Process of breaking a polymer into monomers:
    • A water molecule is used to break the covalent bond, incorporating -OH into one monomer and -H into the other.
    • Definition: Hydrolysis means "water splitting".

Key Points of Dehydration Synthesis and Hydrolysis

  • Used to form and break down biological macromolecules.
  • Described enzymatically; specific enzymes for specific reactions (e.g. amylase for starch, protease for proteins).

Carbohydrates

Definition
  • Carbohydrate: Composed of carbon and water, generally represented by the formula: Cn(H2O)nC_n(H_2O)_n.
    • For every carbon atom, there are two hydrogens and one oxygen.
Monosaccharides
  • Basic unit: Monosaccharide (one sugar).
    • Examples: Glucose (C₆H₁₂O₆), Fructose, Galactose (all C₆H₁₂O₆ isomers).
Significance of Monosaccharides
  • Glucose: Primary energy source for most cells, often referred to as blood sugar or dextrose.
    • Very short-term energy storage.
  • Fructose: Found in fruits, sweeter than glucose, energy storage in plants.
Disaccharides
  • Formed by the combination of two monosaccharides via dehydration synthesis into a single molecule:
    1. Maltose: Two glucose units (alpha 1,4 glycosidic linkage).
    2. Sucrose: Glucose + Fructose (common sugar).
    3. Lactose: Glucose + Galactose (milk sugar).
  • Disaccharides characterized by their glycosidic linkages (alpha or beta).
Polysaccharides
  • Large, complex carbohydrates made up of many monosaccharides.
  • Amylose: Continuous chain of glucose units connected by alpha 1,4 linkages (fewer branches).
  • Amylopectin: A more branched form of starch (more branches).
  • Glycogen: Highly branched polysaccharide (energy storage in animals).
  • Cellulose: Composed of beta 1,4 linkages (structural component of plant cell walls, not digestible by humans).
  • Polysaccharides are critical for long-term energy storage and structural integrity in plants and animals.

Lipids

Definition
  • Lipids: Diverse hydrophobic molecules that include fats, phospholipids, and steroids.
  • Characteristics: Generally insoluble in water.
Types of Lipids

  1. Fats/Triglycerides

    • Composed of glycerol and fatty acids.
      • Glycerol: A three-carbon molecule with hydroxyl groups.
      • Fatty Acids: Long hydrocarbon chains (can be saturated or unsaturated).
      • Saturated: No double bonds; solid at room temperature (animal fats).
      • Unsaturated: One or more double bonds; liquid at room temperature (oils).
    • Function: Energy storage.

  2. Phospholipids

    • Similar to fats but contain a phosphate group instead of one fatty acid.
    • Structure: Glycerol, two fatty acids, and a phosphate group; forms cellular membranes.
    • Characteristics:
      • Hydrophobic tails (fatty acids) and hydrophilic heads (phosphate group).
      • Forms bilayers in aqueous environments, critical for cell membrane structure and function.

  3. Steroids

    • Characterized by a four-ring structure of carbon atoms.
    • Function: Many biological roles, including acting as hormones (e.g., testosterone, estrogen) and contributing to cell membrane structure (cholesterol).
Conclusion
  • This section covers carbohydrates and lipids, their structures, processes of formation and breakdown (dehydration synthesis and hydrolysis), main types, and functions.
  • Understanding the chemistry of these biomolecules is fundamental for future studies in biology and biochemistry.