Lecture Notes: Lipids

Overview

• Lipids are macromolecules not grouped by structure but by characteristic:
  • Nonpolar & hydrophobic (do not mix well with water).
• Three major categories of lipids:
  • Fats
  • Sterols
  • Phospholipids

Fats

• Functions:
  • Long-term energy storage.
  • Provide insulation and help with temperature regulation.
• Energy Storage:
  • Fats have many carbon-hydrogen bonds, which store a lot of energy.
  • More energy than proteins or carbohydrates.
• Structure of Fats:
  • Made up of carbon, hydrogen, and oxygen.
  • Also known as triglycerides.
  • Consist of a glycerol "head" and three fatty acid chain "tails".
  • Linked by ester linkages formed through dehydration synthesis.
• Types of Fats:
  • Saturated Fats:
    • Maximum number of hydrogen atoms, no double bonds.
    • Straight fatty acid chains allow them to be more compact.
    • Solid at room temperature (e.g., butter).
  • Unsaturated Fats:
    • Have double bonds, less hydrogen atoms.
    • Bent fatty acid chains, less dense.
    • Liquid at room temperature (e.g., fish oils).
  • Trans Fats:
    • Mostly artificially produced through hydrogenation.
    • Convert cis bonds to trans bonds, partially straightening the chain.
    • Desirable for long shelf life, good texture, and taste, but have negative health impacts.

Sterols

• Function:
  • Act as hormones, chemical messengers for long-term changes, growth, and development.
• Structure:
  • Four carbon rings fused together.
  • Variations occur in attached groups, but the ring structure is constant.
  • Examples: Testosterone, estradiol, cholesterol.

Phospholipids

• Function:
  • Form cellular membranes, acting as barriers.
• Structure:
  • Consist of a glycerol "head" and two fatty acid "tails".
  • One carbon in glycerol is attached to a phosphate group, not a fatty acid chain.
  • Amphipathic: Part hydrophilic (water-loving) and part hydrophobic (water-fearing).
• Properties:
  • Form micelles or bilayers in water.
  • Micelles: Heads face outward, tails inward, forming a circle.
  • Liposomes: Double layer with tails facing inward, creating a bilayer.
  • Phospholipid bilayers are crucial for the formation of cellular membranes.