Lecture on Lipids and Nucleic Acids

Lipids

• Definition: Hydrophobic molecules due to non-polar covalent bonds. Non-polarity results from hydrocarbon chains.
• Properties:
  • Not considered polymers as they do not form covalent bonds.
  • Interactions are non-covalent (van der Waals interactions), similar to hydrophobic interactions.
  • Different types in the body with varied functions due to different structures.
• Types and Functions:
  • Fats and Oils: Used for energy.
  • Phospholipids: Structure, form plasma membranes or lipid bilayers.
  • Carotenoids and Chlorophylls: In plants, aid in photosynthesis.
  • Steroids: Hormones signaling different body responses.
  • Vitamins: Essential for metabolizing food sources.
  • Myelin: Fat layer around nerves and on skin.
• Triglycerides:
  • Stored energy form.
  • Composed of three fatty acids attached to a glycerol molecule.
  • Highly hydrophobic due to non-polarity in fatty acid tails.
  • Formed through condensation reactions.
  • Differ in length: short, medium, long chain fatty acids.
• Saturated vs. Unsaturated Fatty Acids:
  • Saturated Fatty Acids:
    • Fully saturated with hydrogen, no double bonds.
    • Pack tightly, solid at room temperature (e.g., butter).
  • Unsaturated Fatty Acids:
    • Contain double bonds, cause kinks, less tightly packed.
    • Liquid at room temperature (e.g., oils).
• Phospholipids:
  • Glycerol backbone with attached fatty acids and phosphate.
  • Amphipathic molecules (hydrophilic phosphate and hydrophobic tails).
  • Form lipid bilayers with hydrophilic ends facing aqueous solutions and hydrophobic tails in the center.
• Steroids and Cholesterol:
  • Predominantly carbon and hydrogen.
  • Amphipathic due to hydroxyl group.
  • Cholesterol is a hormone precursor and important in lipid bilayers.
• Vitamins: Some, like Vitamin A, are hydrophobic and categorized as lipids.

Nucleic Acids

• Central Dogma: DNA -> RNA -> Protein.
• DNA:
  • Blueprint for genes and phenotype.
  • Can undergo replication or transcription to RNA.
  • Double-stranded, held together by hydrogen bonds between bases.
    • Guanine-Cytosine have 3 hydrogen bonds.
    • Adenine-Thymine have 2 hydrogen bonds.
    • Thymine in DNA and Uracil in RNA.
• RNA:
  • Single-stranded, ribonucleic acid.
  • Transcribed from DNA and translated at ribosomes to make polypeptides.
• Nucleotides:
  • Composed of phosphate group, sugar (ribose or deoxyribose), and base.
  • Bases: Cytosine, Thymine (DNA), Uracil (RNA), Adenine, Guanine.
  • DNA uses deoxyribose sugar, RNA uses ribose sugar.
  • RNA has phosphodiester bonds for covalent connections.

Important Concepts

• Saturated vs. Unsaturated Fatty Acids: Affects packing and physical state at room temperature.
• Phospholipid Bilayers: Essential for cell membrane structure.
• Central Dogma and Nucleic Acids: Key to understanding genetic information flow.

Review Questions: Engage with questions to ensure understanding.