Lipids - Fatty Acids, Triglycerides, Phospholipids, Terpenes, Waxes, Eicosanoids

Overview of Lipids

  • Lipids: Fats and oils in everyday life.

  • Types of Lipids:

    • Fatty acids

    • Triglycerides

    • Phospholipids

    • Steroids

    • Waxes

    • Terpenes

    • Prostaglandins

  • Key Property: Nonpolar, mostly hydrophobic, do not mix well with water.

Structure of Lipids

  • Composed mainly of carbon-hydrogen bonds (hydrocarbons).

  • May include other elements such as:

    • Oxygen (e.g., in phospholipids)

    • Nitrogen (e.g., in phospholipids)

    • Phosphorus (e.g., in phospholipids)

  • Carbon-hydrogen bonds contribute to hydrophobic nature.

Functions of Lipids

  • Energy Storage:

    • Triglycerides provide long-term energy storage.

    • Utilized during fasting; enzymes (lipase) break down triglycerides into fatty acids and glycerol for energy.

    • Store more than twice the energy compared to carbohydrates.

  • Cell Membrane Structure:

    • Composed primarily of phospholipids.

  • Thermal Insulation and Protection:

    • Useful in cold climates.

Fatty Acids

  • Definition: Long hydrocarbon chains with a carboxylic acid functional group.

  • Structure:

    • Carbon atoms connected by hydrogen; maximum hydrogen connected results in saturated fatty acids.

    • Saturated Fatty Acids:

      • No double bonds, solid at room temperature (e.g., butter).

    • Unsaturated Fatty Acids:

      • One or more double bonds; liquid at room temperature (e.g., vegetable oils).

      • Trans Fatty Acids:

        • Hydrogens on opposite sides of the double bond.

Triglycerides

  • Composition:

    • Glycerol (three-carbon molecule with three hydroxyl groups) + three fatty acids.

  • Formation:

    • Dehydration Synthesis:

      • Loses water to create triglycerides.

    • Function:

      • Significant energy storage, nonpolar nature makes them hydrophobic.

  • Breakdown:

    • Hydrolysis:

      • Water is used to split triglycerides back into glycerol and fatty acids.

Phospholipids

  • Composition:

    • Phosphate group + glycerol + two fatty acid chains.

  • Structure:

    • Polar head (hydrophilic, faces water) and two non-polar tails (hydrophobic).

    • Make up the cell membrane, forming a bilayer.

Steroids

  • Characteristic Structure: Four fused rings.

  • Examples:

    • Cholesterol: Maintains membrane fluidity.

    • Estradiol: Primary female sex hormone.

    • Testosterone: Primary male sex hormone.

    • Cortisol: Reduces inflammation during stress (hydrocortisone when used as medication).

Waxes

  • Composition: Long chains of hydrocarbons, often containing functional groups.

  • Characteristics:

    • Nonpolar, high melting and boiling points.

    • Examples include beeswax and paraffin wax.

Terpenes

  • Basic Unit: Isoprene (five carbon atoms, diene).

  • Types:

    • Dienes: Two double bonds; examples - limonene (found in citrus) and beta-carotene (found in carrots).

    • Beta-carotene consists of 40 carbon atoms (8 isoprene units); limonene has 10 carbon atoms (2 isoprene units).

    • Cyclic Terpene: Limonene has a ring structure.

Icosanoids

  • Categories:

    • Prostaglandins: 20 carbon atoms; involved in vasodilation and platelet inhibition.

    • Thromboxanes: Facilitate platelet aggregation and vasoconstriction.

    • Leukotrienes: Serve as inflammatory mediators.

Conclusion

  • Lipids play essential roles in energy storage, membrane structure, and signaling within organisms.