Chapter 25 Lipids

1
Chapter 25Lipids
Organic Chemistry, 6th EditionL. G. Wade, Jr.
Jo Blackburn Richland College, Dallas, TX Dallas
County Community College District ã 2006,
Prentice Hall
2
Introduction

• Classified by solubility, not structure.
• Can be extracted from cells by nonpolar organic
  solvents.
• Complex lipids are easily hydrolyzed.
• Waxes
• Triglycerides
• Simple lipids are not easily hydrolyzed.
• Steroids
• Prostaglandins
• Terpenes
  gt

3
Examples of Lipids
gt
4
Waxes

• Esters of long-chain fatty acids with long-chain
  alcohols.
• Spermaceti is found in the head of the sperm
  whale and is probably used to control buoyancy.
• Most natural waxes are protective coats for
  plants leaves, insects exoskeletons, mammals
  fur, and birds feathers. gt

5
Triglycerides

• Fatty acid esters of glycerol.
• Fats
• Solid at room temperature
• Most are derived from mammals
• Oils
• Liquid at room temperature
• Most are derived from plants or cold-blooded
  animals. gt

6
Fatty Acids

• Unbranched carboxylic acids with 12-20 carbons.
• Most contain an even number of carbons because
  they are built from acetic acid units.
• Melting points increase with increasing molecular
  weights.
• Unsaturation greatly lowers the melting point.
  gt

7
Melting Points

• A cis double bond bends the molecule so it cannot
  pack efficiently.
• A trans double bond has less effect.

8
Fats and Oils

• Most fats have saturated fatty acids.
• Most oils have unsaturated fatty acids.

9
Saponification

• Soap-making
• Base-catalyzed hydrolysis of ester linkages in
  fats and oils.

10
Soap Structure
gt
11
Grease in Soap Solution
gt
12
Detergents
gt
13
Phospholipids

• Contain a phosphate ester bond.
• Phosphoglycerides usually have one phosphoric
  acid group and two fatty acids.
• The phosphate may have an additional alcohol
  attached by an ester linkage.

14
Lipid Bilayer

• Cell membranes are a bilayer of phosphoglycerides

15
Steroids

• Polycyclic, usually all trans.
• Common structural features
• O or -OH at C3
• Side chain at C17
• Double bond from C5 to either C4 or C6.
  
  gt

16
A-B Ring Junction

• May be cis, but usually is trans.

17
Cholesterol

• Common biological intermediate.
• Probably a precursor to other steroids.
• Side chain at C17 and double bond C5-C6.
  
  gt

18
Sex Hormones

• Female hormone has an aromatic ring and one less
  methyl group than the male hormone.
• Testosterone is converted to estradiol in the
  ovaries.
  gt

19
Prostaglandins

• Biochemical regulators more powerful than
  steroids.
• Regulate functions such as
• Blood pressure
• Blood clotting
• Allergic response
• Digestive activity
• Labor onset
  gt

20
Structure of Prostaglandins

• Cyclopentane ring with two long side chains trans
  to each other.
• Most have 20 carbon atoms.
• Derived from arachidonic acid.

21
Terpenes

• Composed of 5-carbon isopentyl groups.
• Isolated from plants essential oils.
• CH ratio of 58, or close to that.
• Pleasant taste or fragrant aroma.
• Examples
• Anise oil
• Bay leaves
  gt

22
Structure of Terpenes

• Two or more isoprene units, 2-methyl-1,3-butadiene
  with some modification of the double bonds.

23
Classification

• Terpenes are classified by the number of carbons
  they contain, in groups of 10.
• A monoterpene has 10 Cs, 2 isoprenes.
• A diterpene has 20 Cs, 4 isoprenes.
• A sesquiterpene has 15 Cs, 3 isoprenes.
  
  gt

24
Terpenoids
gt
25
End of Chapter 25