Biochemistry Foundations: Monomers, Polymers, Lipids, Nucleotides, and Plant Signaling

Monomers, Polymers, and Macromolecules

  • The lecture focuses on four foundational areas:
    • Monomers and polymers
    • Carbohydrates (sugars and polysaccharides)
    • Lipids and the lipid bilayer
    • Nucleotides, nucleic acids, and energy currency (ATP)

Monomers and Polymers

  • Monomers are building blocks that join to form polymers, typically defined as chains of repeating units.
    • Example: Monosaccharides (like glucose) are monomers that form polysaccharides (like starch).
    • An example disaccharide: Glucose + Glucose \%26#8594 Maltose + H_2O.

Carbohydrates: Monosaccharides, Disaccharides, and Polysaccharides

  • Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose).
  • Polysaccharides: Long carbohydrate polymers (e.g., starch, glycogen).
  • Linking sugars: Dehydration synthesis (loss of water) forms polymers.
    • \text{Monosaccharide} + \text{Monosaccharide} \rightarrow \text{Disaccharide} + \text{H}_2\text{O}.
    • (\text{Monosaccharide})*n \rightarrow \text{Polysaccharide} + (n-1) \text{H}_2\text{O}.
  • Breaking polymers: Hydrolysis (addition of water) breaks bonds.
    • \text{Polysaccharide} + \text{H}_2\text{O} \rightarrow \text{Monosaccharides}.
  • Metabolic water is generated during digestion.

Lipids and the Lipid Bilayer

  • Basic structure of cellular membranes composed of phospholipids.
    • Have hydrophilic heads and hydrophobic tails.
    • Not considered true polymers due to their non-chain arrangement.
  • Amphipathic nature of phospholipids is crucial for stable bilayer formation.
  • Saturated fatty acids: Straight chains, pack tightly, more solid at room temperature.
  • Unsaturated fatty acids: Double bonds create kinks, prevent tight packing, more fluid.

Macromolecular Composition of the Body

  • Approx. 70\% water.
  • Approx. 30\% other chemicals:
    • About 6\% are macromolecules (polysaccharides, fats, proteins, nucleic acids).
    • About 6\% are small molecules.
  • Life's chemistry occurs primarily in an aqueous environment.

Dehydration Synthesis and Hydrolysis: Building and Breaking Polymers

  • Dehydration synthesis (condensation): Monomers join by removing a water molecule, forming a covalent bond.
    • Example: \text{Monosaccharide} + \text{Monosaccharide} \rightarrow \text{Disaccharide} + \text{H}_2\text{O}.
  • Hydrolysis: Water is added to break bonds, yielding smaller units.
    • Example: \text{Polysaccharide} + \text{H}_2\text{O} \rightarrow \text{Monosaccharides}.
  • Dehydration synthesis builds energy-storing macromolecules; hydrolysis releases monomers for energy.

Nucleotides, Nucleic Acids, and Energy Currency (ATP)

  • Nucleotide composition: Nitrogenous base + sugar + phosphate group.
  • RNA vs. DNA sugars:
    • RNA: Ribose (2'-OH).
    • DNA: Deoxyribose (lacks 2'-OH).
  • ATP (adenosine triphosphate): A nucleotide that stores energy in its phosphate bonds.
    • \text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{Energy (}\Delta G^{\circ'} \approx -30.5\text{ kJ/mol)}.
  • Phosphodiester backbone: Nucleotides link in nucleic acids (RNA/DNA) via 3' hydroxyl to 5' phosphate bonds.
    • \text{Nucleotide}_i \rightarrow \text{Nucleotide}_{i+1} \text{ via a phosphodiester bond (5'-P\%26#82113' linkage).}

Plant Chemical Communication and Human Chemosensation

  • Plants communicate chemically (e.g., in response to herbivores).
  • Humans rely less on chemosensation, often underestimating chemical signals.

Common Misconceptions and Exam Strategy

  • Misconceptions:
    • Mitochondria are not the brain's literal powerhouse.
    • Lipid bilayers are not polymers like proteins or nucleic acids.
  • Learning approach: Participate, understand core concepts and relationships (monomers, polymers, macromolecules) over rote memorization.

Quick Reference: Key Formulas and Concepts

  • Dehydration synthesis (sugar): \text{Monosaccharide} + \text{Monosaccharide} \rightarrow \text{Disaccharide} + \text{H}_2\text{O}.
  • Polymerization (sugar): ( \text{Monosaccharide} )*n \rightarrow \text{Polysaccharide} + (n-1) \text{H}_2\text{O}.
  • Hydrolysis: \text{Polysaccharide} + \text{H}_2\text{O} \rightarrow \text{Monosaccharides}.
  • Nucleotide: \text{Nitrogenous base} + \text{Sugar} + \text{Phosphate}.
  • ATP hydrolysis: \text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{Energy (}\Delta G^{\circ'} \approx -30.5\text{ kJ/mol)}.