chem 1204 test 2

1. Basic Lipid Functions and General Concepts

• Energy Storage: Lipids store energy (primarily as fat) and protect cells through the lipid bilayer of cell membranes. Fat layers also provide insulation and protection from physical trauma and electrical leakage.

• Other Functions:

  • Cell Protection: Subcutaneous fat protects against bruising, and waxy layers on fruits protect from environmental damage.

  • Insulation: Lipids insulate against cold and electrical leakage (e.g., myelin sheath around nerves).

  • Precursor to Hormones & Eicosanoids: Lipids are precursors to various hormones (e.g., steroid hormones) and eicosanoids (e.g., prostaglandins).

2. Functional Groups and Chemical Reactions

• Functional Groups:

  • Alcohols: Glycerol (memorable for lipids)

  • Carboxylic Acids: Important in fatty acids (FA) and ester formation.

  • Esters: Formed from reactions between acids and alcohols.

  • Phosphoric Acid Group: Involved in ATP, ADP, and cAMP.

  • Ester Hydrolysis: Process that releases alcohol and carboxylic acid.

• Reactions:

  • Ester Formation: Carboxylic acid + alcohol → ester.

  • Saponification: Hydrolysis of triglycerides (TAG) in base → soap.

  • Hydrogenation: Addition of hydrogen to unsaturated fats, making them more saturated.

  • Hydration: Addition of water to alkenes (unsaturated fats).

3. Types of Lipids

• Hydrolyzable vs Non-Hydrolyzable:

  1. Hydrolyzable lipids (e.g., triglycerides) can be broken down via hydrolysis.

  2. Non-hydrolyzable lipids (e.g., steroids) are not easily hydrolyzed.

• Classes of Lipids:

  1. Triglycerides (TAG): Hydrolyzed into glycerol and fatty acids.

  2. Phospholipids: Glycerophospholipids (e.g., lecithin, cephalins) and sphingolipids (sphingomyelins).

  3. Steroids: Cholesterol and bile salts.

  4. Waxes: Formed from long-chain alcohols and fatty acids.

  5. Sphingolipids: Unique backbone (sphingosine) with fatty acids attached to the nitrogen atom.

4. Lipid Structures and Naming

• Fatty Acids:

  • Saturated vs. Unsaturated: Saturated fatty acids have no double bonds (e.g., stearic acid), while unsaturated fatty acids have double bonds (e.g., oleic acid).

  • Cis vs. Trans Isomers: Natural unsaturated fatty acids are usually cis.

• Phospholipid Structures:

  • Glycerophospholipids: Glycerol backbone with phosphate and amino alcohol (e.g., lecithin and cephalins).

  • Sphingolipids: Sphingosine backbone with a fatty acid at the nitrogen atom.

5. Steroids

• Cholesterol:
  
  

  • Functions in cell membranes and myelin sheath.

  • Precursor to bile salts, steroid hormones, and vitamin D.

• Bile Salts: Derivatives of cholesterol that help emulsify fats in digestion.
  
  

• Steroid Hormones:
  
  

  • Sex Hormones: Estrogens, progesterone, and androgens.

  • Glucocorticoids: E.g., cortisol (affects glucose metabolism, immune response).

  • Mineralocorticoids: E.g., aldosterone (regulates electrolytes and blood pressure).

6. Omega-3 and Omega-6 Fatty Acids

• Omega-3 Fatty Acids: Found in fish oils (e.g., ALA, EPA, DHA), beneficial for reducing blood clotting and inflammation.

• Omega-6 Fatty Acids: Found in vegetable oils (e.g., linoleic acid, arachidonic acid), involved in inflammation and cell signaling.

7. Lipid-Related Diseases

• Atherosclerosis: Build-up of cholesterol plaques in blood vessels, leading to increased blood pressure and risk of heart attack.

• Gallstones: Formed from cholesterol aggregates in the gallbladder.

• Neonatal Respiratory Distress Syndrome (IRDS): Due to lack of surfactant in premature babies (phospholipids).

8. Membranes and Transport

• Phospholipid Bilayer: Composed of hydrophilic heads and hydrophobic tails. The bilayer is fluid, influenced by cholesterol.

• Types of Membrane Transport:

  • Passive Diffusion: Movement of small, non-polar molecules (e.g., O₂, CO₂) through the membrane.

  • Facilitated Diffusion: Movement of larger or polar molecules (e.g., glucose, Cl⁻) via protein channels.

  • Active Transport: Requires ATP, moves molecules against their concentration gradient (e.g., Na⁺/K⁺ pump).

  • Endocytosis and Exocytosis: Transport of large molecules into or out of the cell via vesicles.

• Lipoproteins:

  • Chylomicrons, VLDL, LDL, HDL: Lipoproteins responsible for transporting lipids throughout the body. HDL removes cholesterol from cells, while LDL delivers cholesterol to cells.

9. Clinical Relevance

• Pain and Inflammation: Arachidonic acid → Prostaglandins → Inflammation and pain. NSAIDs (e.g., aspirin) inhibit prostaglandin synthesis.

• Vitamin D: Synthesized in the skin from cholesterol, important for calcium and phosphorus regulation.

10. Key Points to Remember

• Memorize Structures: Know the structures of glycerol, fatty acids, cholesterol, and various lipids.

• Functional Groups: Recognize key functional groups (alcohol, carboxylic acid, phosphate, etc.) and their role in lipid reactions.

• Naming Systems: Understand ester, fatty acid, and phospholipid naming conventions.

• Disease Associations: Be aware of how lipids contribute to diseases like atherosclerosis and their role in inflammation.