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Biomolecules: Lipids
 
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Last revised: Friday, September 10, 1999
Reading: Ch. 5 in text
Note: These notes are provided as a guide to topics the instructor hopes to cover during lecture. Actual coverage will always differ somewhat from what is printed here. These notes are not a substitute for the actual lecture!
Copyright 1999. Thomas M. Terry

Monomers & Polymers

Other than water, biomolecules fall into 4 classes:

Each class contains small molecules (= monomers ), joined together to make large molecules (= polymers ); Only a few types of monomers; billions of different polymers

Condensation Reactions : involve release of water H 2 O, joining together of two monomers by covalent bond to form polymer. Occurs in biosynthesis .

General formula: A-OH + H-B ---------> A-B + H 2 O

Hydrolysis reactions : reverse of condensation. Involves adding water to split covalent bond, release of two smaller molecules. Occurs in digestion.

General formula: A-B + H 2 O --------> A-OH + H-B

Note: A-B could be amino acids, sugars, etc.
View animation of condensation and hydrolysis at The Biology Place.

Lipids

General properties and Functions

Structure of Lipids

  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 triglyceride
  4. Diglycerides
    • 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
    • Practice building glycerides at The Biology Place
  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.

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