Lipids Overview and Types

Lipids

• Defined by low solubility in water
• Not polymers
• Major biological components: fats, phospholipids, and steroids

Types of Lipids

• Fatty Acids: Vary in length and number/location of double bonds
  • Short-chain (2-4 carbons)
  • Medium-chain (6-10 carbons)
  • Long-chain (12 or more carbons)
  • Saturated (no double bonds)
  • Unsaturated (one or more double bonds)
• Triglycerides: Composed of glycerol and three fatty acids
  • Sn1, Sn2, Sn3 positions
• Phosphoglycerides: Glycerol backbone with two fatty acids and a phosphate group
  • Hydrophilic head (polar)
  • Hydrophobic tail (non-polar)
• Waxes: Long-chain alcohols esterified to long-chain fatty acids
• Steroids: Four fused carbon rings (steroid nucleus)
  • Cholesterol (membrane sterol)
  • Cortisol (adrenal hormone)
  • Progesterone (hormone precursor)
  • Testosterone (male hormone)
  • Estradiol (female hormone)
• Sphingolipids: Sphingosine or 4-sphingonine backbone
  • Sphingomyelin (myelin sheath components)
  • Cerebrosides (brain & nervous tissue, glucose/galactose sugar)
  • Sulfatides (brain and nervous tissue, sulfate-esterified galactose sugar)
  • Gangliosides (three or more sugars, including sialic acid)

Hydrogenated Fats

• Polyunsaturated vegetable oils with added hydrogen, leading to solid form at room temperature
• Process called hydrogenation converts polyunsaturated oils to saturated fats
• Margarine and shortening are examples

Trans-Fatty Acids (TFAs)

• Produced when hydrogen is added to monounsaturated or polyunsaturated fats
• Raise low-density lipoproteins (LDL) and total cholesterol
• Found in baked goods and processed foods

Lipid Transport

• Lipoproteins transport lipids in the blood
  • Chylomicrons: largest and least dense, transport diet-derived lipids from intestines
  • VLDL: made by liver, transport lipids to tissues
  • LDL: composed primarily of cholesterol, transport lipids to tissues
  • HDL: composed primarily of protein, removes cholesterol from cells to liver

Number of Fat Cells

• Average human body has between 10 and 30 billion fat cells