chem: chap 14

Chapter 14: Lipids

Chapter Objectives (1 of 2)

  • 14.1 List two major functions of lipids.

  • 14.2 Classify lipids as saponifiable or nonsaponifiable.

  • 14.3 Describe four general characteristics of fatty acids.

  • 14.4 Draw structural formulas of triglycerides given the component parts.

  • 14.5 Describe the structural similarities and differences of fats and oils.

  • 14.6 Write key reactions for fats and oils.

  • 14.7 Compare and contrast the structures of fats and waxes.

Chapter Objectives (2 of 2)

  • 14.8 Draw structural formulas for phosphoglycerides.

  • 14.9 Describe two uses for phosphoglycerides.

  • 14.10 Draw structural formulas for sphingolipids.

  • 14.11 Describe two uses for sphingolipids.

  • 14.12 Describe the major features of cell membrane structure.

  • 14.13 Identify the structural characteristic typical of steroids.

  • 14.14 List five important groups of steroids in the body.

What Are Lipids?

  • Definition: Biologically compounds soluble only in nonpolar solvents.

  • Types:

    • Simple Lipid: Contains an ester with two components: an alcohol and one or more fatty acids.

    • Complex Lipid: Contains an ester with more than two types of components: an alcohol, fatty acids, and other components.

Classification of Lipids

  • Saponifiable Lipids: Can be hydrolyzed; includes triglycerides, waxes, phospholipids, and sphingolipids.

  • Nonsaponifiable Lipids: Cannot be hydrolyzed; includes steroids and prostaglandins.

Section 14.2: Fatty Acids

  • Micelles:

    • Defined as spherical clusters with polar portions on the surface and nonpolar portions in the interior.

    • Nonpolar chains face away from water; polar carboxylate groups remain in contact with water.

Characteristics of Natural Fatty Acids

  1. Generally straight-chain carboxylic acids (no branching).

  2. Sizes typically range from 10 to 20 carbons.

  3. Usually contains an even number of carbon atoms, including the carboxyl carbon.

  4. Can be saturated (no double bonds) or unsaturated (one or more double bonds).

Unsaturated Fatty Acids

  • Cis Configuration: Both carbon chains on the same side of the double bond, creating a bend in the chain.

  • Trans Configuration: Carbon chains on opposite sides of the double bond, leading to a straighter chain structure.

Melting Points of Fatty Acids

  • Saturated fatty acids have higher melting points (MPs) compared to unsaturated fatty acids due to stronger intermolecular forces (IMFs).

  • Example:

    • Stearic acid (saturated, MP 71 °C) vs. oleic acid (unsaturated, MP 13 °C).

Essential Fatty Acids

  • Definition: Fatty acids that the body cannot synthesize on its own.

  • Examples: Linoleic acid and linolenic acid; play crucial roles in various body functions, including hormone production and inflammation response.

Triglycerides

  • Definition: Triesters derived from glycerol and three fatty acids.

  • Structural characteristics influence physical state (solid vs. liquid):

    • Fats (solid) contain higher proportions of saturated fatty acids.

    • Oils (liquid) typically consist of unsaturated fatty acids.

Section 14.4: Chemical Properties and Reactions of Fats and Oils

  • Acid Hydrolysis: The process of breaking down triglycerides into glycerol and fatty acids in the presence of water and an acid catalyst.

  • Lipase Hydrolysis: Enzymatic breakdown catalyzed by lipase enzymes during digestion, yielding glycerol and fatty acids.

  • Saponification: Reaction where triglycerides react with a strong base to produce glycerol and soap (salt of a fatty acid).

Hydrogenation

  • Process involving the addition of hydrogen to unsaturated triglycerides to convert them to more saturated forms.

  • Trans Fats: Produced during hydrogenation; may have health implications.

Waxes

  • Definition: Esters of long-chain fatty acids and long-chain alcohols, providing protective coatings in nature.

  • Examples: Beeswax and sebum in skin.

Phosphoglycerides

  • Definition: Complex lipids consisting of glycerol, fatty acids, phosphoric acid, and an aminoalcohol (e.g., choline).

  • Lecithin: An abundant phosphoglyceride, important for cell membranes.

Sphingolipids

  • Definition: Complex lipids containing sphingosine, a fatty acid, and additional components.

  • Sphingomyelin: Found extensively in brain and nerve tissues, playing a critical role in nerve sheaths.

Blood Type Antigens

  • Glycolipids on red blood cell surfaces function as antigens determining blood types (A, B, O).

  • Blood type compatibility is based on antigen presence; for example, individuals with type B cannot receive type A blood.

Diseases Related to Lipid Accumulation

  • Examples:

    • Tay-Sachs disease: Due to excessive glycolipids in the brain.

    • Gaucher's disease: Accumulation of ceramide glucosides in the spleen and liver.

    • Niemann-Pick disease: Accumulation of sphingomyelins, particularly in the liver.

Biological Membranes

  • Prokaryotic Cells: Simple cells without nucleus or membrane-bound organelles.

  • Eukaryotic Cells: Complex cells with organelles, including a nucleus.

  • Membrane structures include lipid bilayers formed by phosphoglycerides.

Steroids and Hormones

  • Steroids consist of four fused rings.Examples include cholesterol, influencing various bodily functions and associated with health risks like atherosclerosis.

  • Hormones: Chemical messengers that mediate bodily responses and functions (e.g., adrenal hormones affecting metabolism, sex hormones regulating reproductive functions).

Prostaglandins

  • Derived from unsaturated fatty acids, hence play critical roles in numerous physiological processes such as blood clotting and childbirth.

  • They possess therapeutic potential in medical applications, such as inducing labor or treating ulcers.