Lipids Lecture Notes

Overview of Lipids

• Lipids include fatty acids, triglycerides, phospholipids, steroids, waxes, terpenes, prostaglandins.
• Characteristics:
  • Nonpolar and mostly hydrophobic.
  • Comprised mostly of hydrocarbon (carbon-hydrogen) bonds.
  • Can contain oxygen, nitrogen, phosphorus (especially in phospholipids).

Functions of Lipids

• Energy Storage: Triglycerides are major for long-term energy storage.
  • Lipase breaks down triglycerides into fatty acids and glycerol for energy.
  • Triglycerides store more than twice the energy of carbohydrates.
• Cellular Membrane: Phospholipids form the cell membrane structure.
• Thermal Insulation & Protection: Key in maintaining body temperature.

Types of Lipids

Fatty Acids

• Long chains of hydrocarbons ending in a carboxylic acid group.
• Saturated Fatty Acids: No double bonds, solid at room temp (e.g., butter).
• Unsaturated Fatty Acids: Have double bonds, liquid at room temp (e.g., oils).
  • Trans Fatty Acids: Hydrogen atoms are opposite sides of the double bond.

Triglycerides

• Composed of glycerol and three fatty acids.
• Formation involves dehydration synthesis (loss of water molecules).
• Can be broken down by hydrolysis (adding water to split molecules).

Phospholipids

• Made of a phosphate group, glycerol, and two fatty acid chains.
• Essential for the cell membrane (phospholipid bilayer).
• Polar head (hydrophilic) and non-polar tails (hydrophobic).

Steroids

• Characterized by four fused rings.
• Examples: Cholesterol (cell membrane fluidity), Estradiol (estrogen), Testosterone (androgen), Cortisol (anti-inflammatory).

Waxes

• Nonpolar, high in long alkyl chains.
• Examples: Beeswax, plant waxes, paraffin wax (candles).
• High melting (e.g., paraffin wax melts at 99°F).

Terpenes

• Basic unit: Isoprene (5 carbons, two double bonds).
• Examples: Myrcene, Limonene (citrus peels), Beta-carotene (carrots).

Icosanoids

• Include prostaglandins, thromboxanes, leukotrienes.
  • Prostaglandins: Vasodilators, inhibit platelet aggregation.
  • Thromboxanes: Facilitate platelet aggregation, vasoconstrictors.
  • Leukotrienes: Inflammatory mediators.

Summary

Lipids serve crucial roles in energy storage, cell membrane structure, and physiological processes like insulation and hormone function. Understanding the structure and function of different lipids is essential for comprehending their biological significance.