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Macromolecules - Chapter 3.2

Carbohydrates

  • Macromolecule category: Carbohydrates
  • Key roles: simple sugar chains; energy source
  • Context: part of the four major macromolecules discussed (Carbohydrates, Lipids, Proteins, Nucleic Acids)
  • Real-world relevance: provide quick energy for cells and form structural components in some organisms

Lipids

  • Macromolecule category: Lipids
  • Key properties: hydrophobic
  • Key roles: energy source, cell membrane structure, hormones
  • Relevance: lipid components contribute to membrane integrity and signaling molecules

Proteins

  • Macromolecule category: Proteins
  • Subunits: amino acids (~20 in humans) per protein
  • Monomer: amino acids
  • Linkage: amino acids are connected by a special covalent bond called a peptide bond
  • Backbone: all proteins share a common backbone N-C-C
  • R-group (side chain):R-groups have unique chemical properties that determine behavior and interactions

Protein Functions (Table 5.1: An Overview of Protein Functions)

  • Structural proteins
    • Function: Support
    • Examples: Collagen and elastin provide a fibrous framework in connective tissues; Keratin in hair, horns, feathers; Silk fibers in insect/spider cocoons and webs
  • Storage proteins
    • Function: Storage of amino acids
    • Examples: Ovalbumin (egg white) as amino acid source for developing embryo; Casein (milk) as major amino acid source for baby mammals
  • Transport of other substances
    • Examples: Hemoglobin (transports oxygen in blood); other proteins transport molecules across cell membranes
  • Coordination of an organism's activities
    • Examples: Hormonal proteins (e.g., insulin) regulate blood sugar; Receptors detect signals
  • Response of cell to chemical stimuli
    • Examples: Receptor proteins in membranes detect chemical signals from other cells
  • Movement
    • Examples: Actin and myosin drive muscle movement; Contractile proteins contribute to undulations of cilia/flagella
  • Transport proteins
    • Function: Transport substances across membranes and within organisms
  • Hormonal proteins
    • Function: Regulate physiological processes via signaling molecules
  • Receptor proteins
    • Function: Detect and respond to chemical signals
  • Contractile proteins
    • Function: Generate movement in cells and tissues
  • Defensive proteins
    • Function: Protect against disease (e.g., antibodies)
  • Enzymatic proteins
    • Function: Selectively accelerate chemical reactions (catalysis)
  • Overall note: These categories illustrate how diverse protein functions are, from structural support to catalysis to signaling and defense
  • Examples (summarized):
    • Structural: Collagen, Elastin, Keratin, Silk
    • Storage: Ovalbumin, Casein
    • Transport: Hemoglobin, membrane transport proteins
    • Hormonal: Insulin
    • Receptors: Membrane receptors in nerve cells
    • Movement/Contractile: Actin, Myosin; cilia/flagella motion
    • Defensive: Antibodies
    • Enzymatic: Digestive enzymes that hydrolyze dietary polymers

Peptide Bonds

  • A sequence of linked amino acids forms a polypeptide chain
  • The order of amino acids determines the resulting protein's shape and function
  • Visual: …N-C-C---N-C-C---N-C-C… (peptide-bonded backbone)
  • Implication: Small changes in sequence can have large effects on function (e.g., genetic mutations altering structure)

Importance of Shape – Conformation

  • 3-D shape (Native Conformation) is essential for function
  • Shape enables interactions with other molecules and proper activity
  • Shape is formed as the protein assembles and is self-stabilizing via bonds
  • Consequence: Misfolding or incorrect conformation can disrupt function

Protein Structures

1) Primary Structure

  • Definition: The actual order of amino acids in the chain
  • Determined by DNA sequence (gene)
  • Significance: Small changes can have big impacts (e.g., sickle cell anemia; Glu
    ightarrow Val substitution)

2) Secondary Structure

  • Definition: Small, regular, repeated foldings/coiling of the protein backbone
  • Contribution: Stabilizes overall structure
  • Stabilized by: Hydrogen bonds (H-bonds)
  • Common forms: ext{α-helix}, ext{β-sheets}

3) Tertiary Structure

  • Definition: Final bending and folding of the protein
  • Driver: Interactions among side chains (R groups) and with surrounding water
  • Result: 3-D shape that determines function

4) Quaternary Structure

  • Definition: Structural arrangement between multiple subunits of a protein
  • Occurs only in proteins with multiple subunits
  • Examples: Collagen (multi-subunit), Hemoglobin (multi-subunit)

Nucleic Acids

  • M hyp: Molecules of inheritance; job is information storage
  • Monomer: Nucleotides
  • Backbone: sugar-phosphate framework with nitrogenous bases
  • Structure hints:
    • Nitrogen-containing bases: Cytosine (C), Guanine (G), Adenine (A), Uracil (U) in RNA; Thymine (T) in DNA
    • Base pairing and polymer backbone establish genetic information storage
  • Nucleotides consist of:
    • Sugar (backbone component)
    • Phosphate group
    • Nitrogenous base
  • DNA (deoxyribonucleic acid)
    • Contains coded information for making proteins
    • Directs its own replication; copied and passed during cell division
    • Divided into genes (short DNA sequences coding for a single protein)
    • Every cell contains DNA

RNA (ribonucleic acid)

  • Functions in making proteins (acts as intermediary and more)
  • Characteristics: single-stranded
  • Types of RNA:
    • mRNA (messenger)
    • tRNA (transfer)
    • rRNA (ribosomal)

Summary

  • Macromolecules: Carbohydrates, Lipids, Proteins, Nucleic Acids
  • Carbohydrates, Proteins, and Nucleic Acids are polymers; Lipids are not built from monomers in the same way
  • All play essential roles in cellular function and structure
  • Proteins exhibit a hierarchy from primary to quaternary structure, with conformation driving function
  • Nucleic acids store and transmit genetic information; DNA and RNA have distinct roles and structures

Next: Cells, Structure and Function