Biochemistry Chapter 19: Lipids

Chapter 19: Lipids

• Lipids are organic compounds found in living organisms
• Lipids are generally insoluble in water but soluble in nonpolar organic solvents
• Lipids are diverse in structure, not unified by a common structural feature
• Five main categories of lipids are defined based on their function
  • Energy-storage lipids (triacylglycerols)
  • Membrane lipids (phospholipids, sphingoglycolipids, cholesterol)
  • Emulsification lipids (bile acids)
  • Chemical messenger lipids (steroid hormones, eicosanoids)
  • Protective-coating lipids (biological waxes)

19.1 Structure and Classification of Lipids

• Lipids are classified based on their solubility
  • Insoluble or sparingly soluble in water
  • Soluble in nonpolar organic solvents

19.2 Types of Fatty Acids

• Fatty acids are naturally occurring monocarboxylic acids
• Saturated fatty acids have only single C-C bonds
• Unsaturated fatty acids have one or more C=C double bonds
  • Monounsaturated have one double bond
  • Polyunsaturated have two or more double bonds
• Fatty acid chains are usually linear (unbranched)
• Number of carbon atoms is often even
• The location of the double bonds (i.e., omega 3, omega 6) is important in their function

19.3 Physical Properties of Fatty Acids

• Water solubility varies with chain length; short chains are somewhat soluble, long chains are insoluble
• Melting point depends on chain length and degree of unsaturation; shorter chains and more unsaturated chains have lower melting points

19.4 Energy-Storage Lipids: Triacylglycerols

• Triacylglycerols (triglycerides) are the main energy storage lipids of animals
  • Glycerol molecule esterified with 3 fatty acid chains.
• They are stored in specialized cells called adipocytes.

19.5 Dietary Considerations and Triacylglycerols

• Diets high in fats/oils are linked to increased heart disease and certain cancers
• Americans are encouraged to reduce their fat intake.
• Recommendations are given on portion amounts of unsaturated, saturated and polyunsaturated fats for different nutrients.

19.6 Chemical Reactions of Triacylglycerols

• Hydrolysis is the partial breakdown of triacylglycerols
  • Breaking of ester bonds to yield mono- or diacylglycerols and fatty acids
• Saponification is the complete hydrolysis of a triacylglycerol in a basic solution
  • Produces soap (a salt of a fatty acid) and glycerol.
• Hydrogenation adds hydrogen to unsaturated fatty acids to increase the degree of saturation
  • Converts oils into solid fats

19.7 Membrane Lipids: Phospholipids

• Phospholipids are major components of cell membranes.
  • Contain a glycerol backbone, two fatty acid chains, a phosphate group, and a polar group.
  • Form bilayers in cell membranes.

19.8 Membrane Lipids: Sphingolipids

• Sphingolipids are structurally related to sphingosine, an 18 carbon long unsaturated amino alcohol.
• Often contain a carbohydrate chain.
• Types: Cerebrosides, gangliosides - Important components of nerve tissue and cell membranes, particularly in the brain.

19.9 Membrane Lipids: Cholesterol

• Cholesterol is a steroid lipid.
• Important component of cell membranes, and in the synthesis of hormones and vitamins.
• A lipid with a fused ring structure that is crucial for normal function in animals.

19.10 Cell Membranes

• Cell membranes are composed of a phospholipid bilayer, which is a double layer of phospholipids.
• The membrane also contains proteins for active transport
• Cholesterol molecules help regulate the fluidity of cell membranes.

19.11 Emulsification Lipids: Bile Acids

• Bile acids are cholesterol derivatives that function as emulsifiers
• They aid in the digestion of fats by dispersing them in aqueous solutions.

19.12 Messenger Lipids: Steroid Hormones

• Steroid hormones are derived from cholesterol
• These hormones regulate various processes in the body (sexual and metabolic processes).
• Types: Estrogens, androgens, progestins

19.13 Messenger Lipids: Eicosanoids

• Eicosanoids are a diverse group of molecules derived from fatty acids.
• Involved in inflammation, pain, fever, blood clotting, reproduction, and other functions.
• Types: Prostaglandins, thromboxanes, leukotrienes.

19.14 Protective-Coating Lipids: Biological Waxes

• Waxes are esters of long-chain fatty acids and long-chain alcohols.
• Repellent to water and protect surfaces of plants and animals in various ways.

Explore the fascinating world of lipids in this quiz based on Chapter 19. Learn about their structures, classifications, and functional categories such as energy-storage and membrane lipids. Test your knowledge on fatty acids and their roles in living organisms.