The Structure and Function of Large Biological Macromolecules

Chapter 5: The Structure and Function of Large Biological Macromolecules

Learning Objectives

The Molecules of Life

  • Four Major Classes of Macromolecules:

    • Carbohydrates
    • Lipids
    • Proteins
    • Nucleic Acids

  • Monomers and Polymers:

    • Monomers: Individual subunits that can link to form polymers.
    • Polymers: Long chains made up of repeated monomers.

  • Condensation and Hydrolysis Reactions:

    • Condensation Reaction (Dehydration Synthesis): Joins monomers by removing water.
    • Hydrolysis: Breaks polymers into monomers by adding water.

Carbohydrates Serve as Fuel and Building Material

  • Types of Carbohydrates:

    • Monosaccharides: Simple sugars (e.g., glucose).
    • Disaccharides: Two monosaccharides linked (e.g., sucrose).
    • Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen).

  • Glycosidic Linkage:

    • Type of covalent bond that links monosaccharides.

  • Comparative Structure, Function, and Location:

    • Starch: Plant storage form of glucose.
    • Glycogen: Animal storage form, highly branched.
    • Cellulose: Structural component of plant cell walls.
    • Chitin: Structural component in fungal cell walls and arthropod exoskeletons.

Lipids are a Diverse Group of Hydrophobic Molecules

  • Building-block Molecules: Glycerol and fatty acids.

  • Types of Lipids:

    • Fats (Triglycerides): Made from glycerol and three fatty acids, linked by an ester linkage.
    • Phospholipids: Two fatty acids and a phosphate group attached to glycerol; form cell membranes.
    • Steroids: Characterized by a four-ring carbon skeleton (e.g., cholesterol).

  • Saturated vs. Unsaturated Fats:

    • Saturated: No double bonds (solid at room temperature).
    • Unsaturated: One or more double bonds (liquid at room temperature).
    • Cis and Trans Fats: - Cis: Kinked structure due to double bonds. - Trans: Straight structure, often found in processed foods.

Proteins Have Many Structures, Resulting in a Wide Range of Functions

  • Proteins vs. Polypeptides:

    • Polypeptides: Unbranched chains of amino acids.
    • Proteins: Functionally active polypeptides.

  • Amino Acids Structure:

    • Composed of amino group, carboxyl group, hydrogen atom, and R group (side chain).
    • Grouped based on R group properties (nonpolar, polar, electrically charged).

  • Peptide Bond Formation:

    • Formed between the amino group of one amino acid and the carboxyl group of another, resulting in the release of water (condensation).

  • Protein Structure Levels:

    • Primary: Sequence of amino acids.
    • Secondary: Coils (alpha helix) and folds (beta pleated sheet) stabilized by hydrogen bonds.
    • Tertiary: Overall shape, shaped by interactions of R groups (hydrophobic interactions, hydrogen bonds, ionic bonds, van der Waals interactions, disulfide bridges).
    • Quaternary: Multi-polypeptide complexes (e.g., hemoglobin).

  • Protein Denaturation:

    • Loss of native structure and function due to environmental changes (pH, temperature).

  • Chaperonins: Assist in correct protein folding.

  • Methods to Determine Protein Structure:

    • X-ray crystallography
    • Nuclear magnetic resonance (NMR) spectroscopy
    • Bioinformatics to predict structures.

Nucleic Acids Store and Transmit Hereditary Information

  • Components of Nucleotides:

    • Nitrogenous base, pentose sugar, phosphate group.

  • Nucleic Acid Types:

    • DNA (Deoxyribonucleic Acid): Double-stranded, stores genetic information.
    • RNA (Ribonucleic Acid): Single-stranded, involved in protein synthesis.

  • Nucleotide Bonding:

    • Phosphodiester Linkage: Bond between nucleotides.

  • Base Pairing:

    • A pairs with T (or U in RNA), C pairs with G.
    • Chargaff's rules: % of A = % of T, % of G = % of C.

  • Flow of Genetic Information: DNA -> RNA -> Protein (Central Dogma).

  • Mutations:

    • Changes in nucleotide sequence can affect protein structure and function.
    • Point mutations: A change in a single base pair can result in genetic disorders (e.g., sickle-cell disease).

Summary of Macromolecules

  • Carbohydrates:

    • Composition: Carbon, hydrogen, oxygen (CH2O)n.
    • Classes: Monosaccharides, disaccharides, oligosaccharides, polysaccharides.

  • Lipids:

    • General Features: Vary in structure, primarily hydrophobic due to nonpolar bonds.

  • Proteins:

    • Functions: Diverse roles in cells, including catalysis (enzymes), structure, transport, signaling, defense.

  • Nucleic Acids:

    • Role in Genetics: Storage and transmission of genetic information; templates for protein synthesis.