MS

In-Depth Notes on Lipids

Overview of Lipids

  • Definition: Lipids are biomolecules that contain fatty acids or a steroid nucleus, soluble in organic solvents but insoluble in water.

    • Originates from Greek word "lipos" meaning fat.

    • Play a crucial role in cell membranes, fat-soluble vitamins, and steroid hormones.

General Structure of Lipids

  • Lipids are organic compounds that are not soluble in water, emphasizing their hydrophobic nature.

Fatty Acids

  • Definition: Long, unbranched carbon chains with a carboxylic acid group at the end.

    • Length: Typically contain 12-18 carbon atoms.

    • Insolubility: Long carbon chain makes them insoluble in water.

    • Types:

    • Saturated: No C=C double bonds present.

    • Unsaturated: Contains C=C double bonds.

Drawing Fatty Acids

  • In skeletal formulas, ends and bends of lines represent carbon atoms.

    • Example: Lauric acid can be depicted in various structural forms.

Types of Fatty Acids

  • Saturated Fatty Acids: Only single C—C bonds present, generally solid at room temperature with higher melting points.

  • Monounsaturated Fatty Acids: Contain one C=C double bond.

    • Example: Oleic acid found in olives.

  • Polyunsaturated Fatty Acids: Contain at least two C=C double bonds.

Cis and Trans Unsaturated Fatty Acids

  • Unsaturated fatty acids have two isomeric forms: cis and trans.

  • Most naturally occurring unsaturated fatty acids are cis isomers and are oils at room temperature.

Properties of Saturated Fatty Acids

  • Saturated fatty acids fit closely together due to regular pattern, enduring higher melting points and remaining solid at room temperature.

Chemistry Link to Health: Omega-6 Fatty Acids

  • Unsaturated fats (from vegetable oils and fish) are healthier than saturated fats.

  • Omega-6 fatty acids, like linoleic and arachidonic acids, initiate their first double bond at the sixth carbon from the methyl end.

Waxes

  • Waxes are long-chain fatty acid esters with alcohols.

    • Structure: Composed of 14-30 carbon atoms.

    • Function: Serve as protective coatings to prevent water loss in plants.

  • Examples:

    • Beeswax and Carnauba wax (Brazilian palm tree).

Triacylglycerols (Triglycerides)

  • Definition: Esters of glycerol (a trihydroxy alcohol) and fatty acids formed by dehydration reaction.

    • Generally, three hydroxyl groups in glycerol react with three fatty acids.

    • Names are derived by changing "glycerol" to "glyceryl."

    • Example: Glyceryl tristearate is the compound formed from three stearic acids, commonly known as tristearin.

Mixed Triacylglycerols

  • Can contain different fatty acids (e.g., stearic, oleic, and palmitic acids).

Hydrogenation: Trans Fatty Acids

  • Process where unsaturated fats are converted into saturated fats, potentially forming trans fats, which can be unhealthy.

Hydrolysis of Triacylglycerols

  • Hydrolysis breaks down triacylglycerols into glycerol and three fatty acids, requiring strong acids (HCl or H2SO4) or enzymes (lipases).

Saponification and Soap

  • Definition: Reaction of fats with strong bases like NaOH in heat, yielding glycerol and sodium salts of fatty acids (soaps).

    • Produces solid soaps with NaOH and softer liquid soaps with KOH.