Chapter 17- CHEM 1152k

Chapter 17: Lipids

Overview

• Lipids: Essential biomolecules characterized by their insolubility in water and presence of fatty acids or steroid structures.

• Lipids serve critical functions in cell membranes, fat-soluble vitamins, and steroid hormones.

Types of Lipids

• Lipids can be categorized based on structure into several classes:

  • Waxes: Esters of long-chain fatty acids and long-chain alcohols.

  • Triacylglycerols: Formed from glycerol and three fatty acids; major form of energy storage in animals.

  • Glycerophospholipids: Contain glycerol, two fatty acids, and a phosphate group; crucial in forming cellular membranes.

  • Sphingolipids: Composed of sphingosine, fatty acid, and phosphate.

  • Steroids: Characterized by a structure that includes four fused carbon rings; do not contain fatty acids.

Structure of Lipids

• Glycerol-containing lipids: Includes triacylglycerols and glycerophospholipids.

• Sphingolipids: Have sphingosine as a backbone rather than glycerol.

• Steroid structure: Consists of four fused rings (steroid nucleus), pivotal in hormones and cellular functions.

Fatty Acids

• Fatty acids are the simplest type of lipids, characterized by:

  • Long unbranched carbon chains with a carboxyl group at one end.

  • Saturated Fatty Acids: No double bonds between carbon atoms.

  • Unsaturated Fatty Acids: One or more double bonds present; categorized into monounsaturated and polyunsaturated.

Physical Properties of Fatty Acids

• Melting Points:

  • Saturated fatty acids have higher melting points than unsaturated due to tighter packing.

  • Unsaturated fatty acids possess kinks from double bonds, leading to lower melting points.

Essential Fatty Acids

• Essential fatty acids, such as linoleic and linolenic acid, must be obtained from the diet because the body cannot synthesize them.

Prostaglandins and NSAIDs

• Prostaglandins: Hormone-like substances derived from arachidonic acid; involved in various physiological functions including inflammation.

• NSAIDs: Nonsteroidal anti-inflammatory drugs that inhibit prostaglandins to alleviate pain and inflammation.

Waxes and Triacylglycerols

• Waxes: Protective coatings in plants and animals; you can find in fruits, leaves, and animal skins.

• Triacylglycerols: Main energy storage form; they consist of glycerol and three fatty acids.

Melting Points and Physical States of Fats and Oils

• Fats: Solid at room temperature, primarily sourced from animals.

• Oils: Liquid at room temperature, primarily sourced from plants.

Chemical Properties of Triacylglycerols

• Hydrogenation: The process of adding hydrogen to unsaturated fats to make them more solid.

• Hydrolysis: The splitting of fats into glycerol and fatty acids in the presence of water or enzymes.

• Saponification: The reaction of fats with strong bases to form soaps.

Phospholipids

• Phospholipids: Key components of cell membranes; consist of glycerol, fatty acids, and a phosphate group.

• Structure: Contains hydrophilic (polar) head and hydrophobic (non-polar) tails, crucial for forming lipid bilayers.

Cell Membranes

• Function: Semipermeable barriers that regulate nutrient entry and waste exit; composed of phospholipids and proteins in a fluid mosaic model.

• Transport Mechanisms:

  • Diffusion: Movement from high to low concentration.

  • Facilitated transport: Utilizes protein channels for ion transport.

  • Active transport: Movement against concentration gradients using energy.

Cholesterol and Steroid Hormones

• Cholesterol: A crucial steroid in the body, sourced from diet and synthesized in the liver; crucial for cell membrane fluidity and steroid hormones (e.g., estrogen, testosterone).

• Adrenal Corticosteroids: Hormones produced by adrenal glands regulating various bodily functions, including stress response and electrolyte balance.