CHE110 Chapter 19 PPT

Chapter 19: Lipids

19.1 Introduction to Lipids

  • Definition of Lipids: Biomolecules soluble in organic solvents and insoluble in water; characterized by physical properties rather than specific functional groups.

  • Chemical Structure: Contain many nonpolar C—C and C—H bonds with few polar bonds, leading to water insolubility.

19.2 Fatty Acids

Hydrolyzable Lipids

  • Derived from fatty acids (RCOOH) with chains of 12 to 20 carbon atoms.

  • Saturated Fatty Acids: No double bonds; higher melting points.

  • Unsaturated Fatty Acids: One or more double bonds (usually cis); lower melting points as the number of double bonds increases.

Common Saturated and Unsaturated Fatty Acids

  • Examples:

    • Stearic Acid (mp 71°C) - saturated

    • Oleic Acid (mp 16°C) - unsaturated

Table 19.2: Common Fatty Acids

  • Saturated Fatty Acids:

    • Lauric acid (12C, 0 double bonds, Mp 44°C)

    • Myristic acid (14C, 0 double bonds, Mp 58°C)

    • Palmitic acid (16C, 0 double bonds, Mp 63°C)

    • Stearic acid (18C, 0 double bonds, Mp 71°C)

  • Unsaturated Fatty Acids:

    • Palmitoleic acid (16C, 1 double bond, Mp 1°C)

    • Oleic acid (18C, 1 double bond, Mp 16°C)

    • Linoleic acid (18C, 2 double bonds, Mp -5°C)

    • Linolenic acid (18C, 3 double bonds, Mp -11°C)

    • Arachidonic acid (20C, 4 double bonds, Mp -49°C)

  • Omega Fatty Acids:

    • Linoleic acid: Omega-6 (first C=C at C6 from methyl end).

    • Linolenic acid: Omega-3 (first C=C at C3 from methyl end).

19.3 Waxes

  • Definition: Esters formed between a fatty acid and high molecular weight alcohol.

  • Characteristics: Highly hydrophobic due to long nonpolar C chains.

  • Uses: Form protective coatings (e.g., bird feathers, sheep wool, beeswax).

19.4 Triacylglycerols (Fats and Oils)

  • Definition: Three esters formed from glycerol and three molecules of fatty acids.

  • Types:

    • Simple Triacylglycerols: Three identical fatty acid chains.

    • Mixed Triacylglycerols: Two or three different fatty acids.

    • Saturated Triacylglycerols: Only saturated fatty acids; solid at room temperature.

    • Unsaturated Triacylglycerols: At least one unsaturated fatty acid; liquid at room temperature.

  • Health Implications: Avoid high saturated fat intake to reduce heart disease risk.

19.5 Hydrolysis of Triacylglycerols

  • Process: Hydrolyzed with water in the presence of acid, base, or enzymes (lipases).

  • Energy Storage in Humans: Stored in adipose cells; constant number of cells, volume changes with weight gain/loss.

  • Soap Synthesis: Result from basic hydrolysis of triacylglycerols producing metal salts of fatty acids.

19.6 Phospholipids

  • Definition: Lipids containing a phosphate atom; key components of cell membranes.

  • Two main types: Phosphoacylglycerols and sphingomyelins.

19.7 Cell Membranes

  • Cell Membrane Structure: Composed of phospholipids forming a bilayer; selectively permeable.

  • Transport Mechanisms:

    • Simple Diffusion: Small molecules pass through the membrane.

    • Facilitated Transport: Requires integral protein channels for larger polar molecules.

    • Active Transport: Movement against concentration gradients requiring energy input.

19.8 Cholesterol and Steroid Hormones

  • Cholesterol: A key steroid, synthesized in the liver, important for cell membranes.

  • Health Effects: High levels can lead to coronary artery disease; transported by LDLs and HDLs.

  • Steroid Hormones: Include estrogens, progestins, and androgens, involved in various physiological processes.

19.10 Fat-Soluble Vitamins

  • Vitamins A, D, E, and K are critical organic compounds stored in adipose cells.

  • Vitamins Functions:

    • Vitamin A: Vision, mucous membrane health; deficiency can lead to night blindness.

    • Vitamin D: Regulates calcium metabolism; deficiency can cause rickets.

    • Vitamin E: Antioxidant; protects unsaturated fats from oxidation.

    • Vitamin K: Clotting protein synthesis; deficiency can lead to bleeding issues.