General properties and Functions

• greasy or oily compounds, insoluble in water
• very diverse group: includes glycerides, waxes, steroids
• Variety of Functions
  1. Energy storage: typically as triglycerides (3 fatty acids + glycerol)
  2. Insulation
  3. Cushioning of organs and tissues; "shock absorbers"

Structure of Lipids

• Visit Properties of Lipids (Campbell website activity)
• Lipids are typically hydrocarbon; have lots of H-C-H

1. Fatty acids
   • Typically 12-24 C atoms long; see text Fig. 5.10 for examples
   • All hydrocarbon, except carboxyl group at one end; provides limited solubility, interaction with aqueous enzymes
   • View hydrocarbon and fatty acid
     
   • Some fatty acids contain 1 or 2 double bonds = unsaturated . These cause"kinks", can't pack as tightly as F.A. with no double bonds = saturated .
   • View saturated and unsaturated fatty acids
     
   • Fatty acids don't accumulate in cells. They are quickly converted into glycerides.
2. Glycerides
   • Glycerides: made of fatty acids + glycerol
   • Can be monoglycerides (rare) with one fatty acid; diglycerides (common in membrane lipids) with two fatty acids; or triglycerides (common in fat deposits, adipocytes or fat cells) with three fatty acids.
   • View glyceride formation
3. Triglycerides
   • Stored fat accumulates as triglyceride. Excess can deposit as plaque in arteries.
   • Animal fat = saturated triglyceride. Solid at room temperature (bacon, fat,lard, butter).
   • Plant fat = unsaturated triglyceride. Liquid at room temperature = oils (olive oil, peanut oil, safflower oil, etc.). Coconut fat (found in the white coconut"meat") is one of the few animal fats to be solid rather than oil.
   • View structure of triglyceride (aka "fat") (Campbell website activity)
   • Compare saturated and unsaturated fats (Campbell website activity)
   • View triglyceride globule in an adipocyte (fat cell)
   • build a triglyceride (Campbell website activity)
4. Diglycerides and Phospholipids
   • Diglycerides often are attached to a phosphate group to produce phospholipidmolecules (see text Fig. 5.12).
   • Phospholipids have very water-soluble (hydrophilic) groups at the phosphate end, but very water-insoluble (hydrophobic) groups at the fatty acid end.
   • When phospholipids are put in water, they spontaneously form membranes (more on this in Chap. 8).
   • View diglyceride
   • View lipid bilayer
     
5. Steroids
   • Steroids: still hydrocarbons, but instead of being linear molecules, these include ring-shaped molecules. See Fig. 5.14 in text for typical steroid.
   • Include cholesterol, testosterone (male sex hormone), estrogen and progesterone(female sex hormones).
   • Used in animals as hormones (chemical signals), also in membrane structure.
   • View steroid
6. Other lipids
   • Waxes, certain pigments are also members of the lipids.