Macromolecules

Chapter 3: Macromolecules

Definition: Macromolecules are large, complex molecules that are fundamental components of all living organisms. They are composed of smaller units called monomers, which link together to form polymers.

Key Concepts:

  • Organic Compounds: Contain carbon atoms. All macromolecules are organic.

    • Exception: Carbon dioxide (CO₂) is inorganic despite having carbon.

  • Carbon: The central element in organic chemistry, capable of forming four covalent bonds, leading to a variety of complex structures.

  • Structure Begets Function: The way monomers are assembled into polymers affects the structure and function of the macromolecule (similar to how letters form words).

  • Directionality: The orientation of monomers in a polymer influences the properties and function of the macromolecule.

Types of Macromolecules

1. Carbohydrates

  • Elements: Carbon (C), Hydrogen (H), Oxygen (O)

    • Note: If any other element is present, it’s not a carbohydrate.

  • Monomers: Monosaccharides (simple sugars)

    • Example: Glucose (C₆H₁₂O₆) — must know its structure and chemical formula.

  • Polymers: Polysaccharides

    • Function: Energy storage, structural support

      • Energy Storage:

        • Glycogen: Found in animals (stored in the liver and muscles).

        • Starch: Found in plants, can coil and branch, making it compact and efficient for energy storage.

      • Structure:

        • Cellulose: Found in plant cell walls, uses beta glucose (fiber), not easily digested by humans.

        • Chitin: Found in exoskeletons of insects and crustaceans, similar to cellulose but with nitrogen-containing groups.

    • Structure and Branching: Both starch and glycogen are branched. Branching allows faster energy release because enzymes can break down multiple points simultaneously.

  • Bond Name: Glycosidic linkage (formed through dehydration synthesis, broken by hydrolysis).

2. Proteins (Polypeptides)

  • Elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N)

  • Monomers: Amino acids (20 different types)

    1. Structure: Central (alpha) carbon, amino group (NH₂), carboxyl group (COOH), and variable R group (side chain).

    2. R Group: Determines the chemical properties and function of the amino acid.

  • Polymers: Polypeptides, which fold into functional proteins.

  • Bond Name: Peptide bond (formed through dehydration synthesis between the amino group of one amino acid and the carboxyl group of another).

  • Protein Structure Levels:

    1. Primary Structure: Sequence of amino acids.

    2. Secondary Structure: Hydrogen bonding forms alpha-helices and beta-pleated sheets (not involving R groups).

    3. Tertiary Structure: 3D shape formed by interactions between R groups (hydrogen bonds, ionic bonds, disulfide bridges).

    4. Quaternary Structure: Multiple polypeptide chains interact to form a functional protein (e.g., hemoglobin).

  • Function: Enzymatic activity, structural support, transport, signaling, immune response.

  • Mutation Impact: Changes in amino acid sequence can alter protein structure and function, potentially leading to loss of function or disease.

3. Nucleic Acids

  • Elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P)

  • Monomers: Nucleotides

    • Components: A phosphate group, a five-carbon sugar (ribose in RNA, deoxyribose in DNA), and a nitrogenous base.

    • Nitrogenous Bases:

      • Purines (2 rings): Adenine (A), Guanine (G)

      • Pyrimidines (1 ring): Cytosine (C), Thymine (T, only in DNA), Uracil (U, only in RNA)

  • Polymers: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)

    • Structure of DNA: Double helix, antiparallel strands (one 3’ to 5’, the other 5’ to 3’), base pairing (A with T, C with G).

    • Structure of RNA: Single-stranded, contains ribose sugar, uses uracil instead of thymine.

  • Bond Name: Phosphodiester bond (links nucleotides together).

  • Function: Storage, transmission, and expression of genetic information.

4. Lipids

  • Elements: Carbon (C), Hydrogen (H), Oxygen (O) (lower oxygen content than carbohydrates)

  • Structure: Hydrophobic, mix poorly with water due to nonpolar regions.

  • Monomers: Not true monomers, but often include glycerol and fatty acids.

  • Types:

    1. Triglycerides (fats and oils)

      • Structure: One glycerol molecule and three fatty acids.

      • Types of Fatty Acids:

        • Saturated: No double bonds, solid at room temperature (e.g., butter).

        • Unsaturated: One or more double bonds, liquid at room temperature (e.g., olive oil).

        • Trans fats: Artificially hydrogenated unsaturated fats, solid at room temperature.

    2. Phospholipids

      • Structure: Glycerol backbone, two fatty acids, and a phosphate group.

      • Properties: Amphipathic (hydrophilic head and hydrophobic tails).

      • Function: Form the phospholipid bilayer of cell membranes.

    3. Steroids

      • Structure: Four fused carbon rings with various functional groups.

      • Examples: Cholesterol (membrane component), hormones (testosterone, estrogen).

    4. Waxes

      • Structure: Long-chain fatty acids esterified to long-chain alcohols.

      • Function: Protective coatings on plants and animals (e.g., beeswax, cuticle on leaves).

  • Bond Name: Ester bond (between glycerol and fatty acids).

  • Function: Energy storage, insulation, protection, hormone synthesis, structural components of membranes.


Key Reactions Involving Macromolecules

  • Dehydration Synthesis (Condensation Reaction): Joins monomers into polymers by removing a water molecule.

  • Hydrolysis: Breaks polymers into monomers by adding a water molecule.