Lipids Flashcards

Lipids Overview

• Biomolecules containing fatty acids or a steroid nucleus.

• Soluble in organic solvents, insoluble in water.

• Important in cell membranes, fat-soluble vitamins, and steroid hormones.

Types of Lipids

• Hydrolyzable: Waxes, fats, oils, and phospholipids (esters yielding fatty acids upon hydrolysis).

• Non-Hydrolyzable: Steroids (characterized by a four fused carbon ring steroid nucleus; do not contain fatty acids).

Fatty Acids

• Long, unbranched carbon chains with a carboxylic acid group at one end.

• Typically 12-18 carbon atoms long.

• Insoluble in water due to long carbon chain.

• Saturated (SFA): Contain only single C-C bonds.

• Unsaturated (UFA): Contain C-C double bonds; usually in cis configuration in naturally occurring fats.

  • Monounsaturated (MUFA): One C-C double bond.

  • Polyunsaturated (PUFA): More than one C-C double bond.

• Condensed notation: "18:1Δ9" (18 carbons, 1 double bond at carbon 9).

• Essential Fatty Acids: Must be obtained from diet (e.g., linoleic, linolenic, and arachidonic acids).

Properties of Fatty Acids

• Saturated Fatty Acids:

  • Single C-C bonds, pack closely.

  • Strong dispersion forces.

  • Higher melting points, solid at room temperature.

• Unsaturated Fatty Acids:

  • Cis double bonds cause kinks, reducing molecular interactions.

  • Lower melting points, liquid at room temperature.

Eicosanoids

• Derived from 20-carbon unsaturated fatty acids (eicosanoic acids).

• Act as short-lived local hormones.

  • Prostaglandins: Affect blood pressure, smooth muscle contraction; produced from arachidonic acid; inhibited by NSAIDs.

  • Leukotrienes:

Triacylglycerols (Triglycerides)

• Esters of glycerol and three fatty acids.

• Formed by reacting three hydroxyl groups of glycerol with carboxyl groups of three fatty acids.

• Major form of energy storage in animals.

Melting Points of Fats and Oils

• Fats: Solid at room temperature, from animal sources.

• Oils: Liquid at room temperature, from plant sources.

• Saturated fats have higher melting points than unsaturated fats.

Chemical Properties of Triacylglycerols

• Hydrogenation: Double bonds react with hydrogen gas (using a nickel catalyst) to form single bonds.

• Hydrolysis: Triacylglycerols split into glycerol and three fatty acids by strong acids or lipases.

• Saponification: Reaction with a strong base (NaOH or KOH) to form glycerol and salts of fatty acids (soaps).

Phospholipids

• Similar to triacylglycerols but include a phosphate group.

  • Glycerophospholipids: Two fatty acids, glycerol, phosphate, and an amino alcohol.

  • Sphingomyelin: Sphingosine instead of glycerol; contains a fatty acid, phosphate, and an amino alcohol.

• Polar and nonpolar regions allow interaction with both polar and nonpolar substances.

• Abundant in cell membranes, crucial for cellular permeability.

Steroids

• Characterized by a steroid nucleus: three cyclohexane rings and one cyclopentane ring fused together.

  • Cholesterol: Most abundant steroid; important for cell membranes, nerve tissue, steroid hormones, and vitamin D. Synthesized in the liver and obtained from food. High levels can form plaque in arteries.

  • Bile Salts: Synthesized from cholesterol in the liver; aid in fat absorption by making fats soluble in water; stored in the gallbladder.

  • Steroid Hormones:

Cell Membrane Lipids

• Cholesterol: Maintains membrane structure due to its rigidity.

• Glycolipids: Extend carbohydrate segments to recognize chemical messengers and pathogens.