Chapter 2 Lipids and Membranes

1
Chapter 2 Lipids and Membranes
2
Lipids

• Lipids a heterogeneous class of naturally
  occurring organic compounds classified together
  on the basis of common solubility properties
• insoluble in water, but soluble in aprotic
  organic solvents including diethyl ether,
  chloroform, methylene chloride, and acetone
• Lipids include
• fatty acids, triacylglycerols, sphingolipids,
  phosphoacylglycerols, glycolipids,
• lipid-soluble vitamins
• prostaglandins, leukotrienes, and thromboxanes
• cholesterol, steroid hormones, and bile acids

3
Fatty Acids

• Fatty acid an unbranched-chain carboxylic acid,
  most commonly of 12 - 20 carbons, derived from
  hydrolysis of animal fats, vegetable oils, or
  phosphodiacylglycerols of biological membranes
• In the shorthand notation for fatty acids
• the number of carbons and the number of double
  bonds in the chain are shown by two numbers,
  separated by a colon

4
Fatty Acids
5
Fatty Acids

• Among the fatty acids most abundant in plants and
  animals
• nearly all have an even number of carbon atoms,
  most between 12 and 20, in an unbranched chain
• the three most abundant are palmitic (160),
  stearic (180), and oleic (181) acids
• in most unsaturated fatty acids, the cis isomer
  predominates the trans isomer is rare
• unsaturated fatty acids have lower melting points
  than their saturated counterparts the greater
  the degree of unsaturation, the lower the melting
  point

6
Triacylglycerols

• Triacylglycerol (triglyceride) an ester of
  glycerol with three fatty acids
• natural soaps are prepared by boiling
  triglycerides (animal fats or vegetable oils)
  with NaOH, in a reaction called saponification
  (Latin, sapo, soap)

7
Soaps

• Soaps form water-insoluble salts when used in
  water containing Ca(II), Mg(II), and Fe(III) ions
  (hard water)

8
Phosphoacylglycerols

• Phosphoacylglycerols (phosphoglycerides) are the
  second most abundant group of naturally occurring
  lipids
• found almost exclusively in plant and animal
  membranes, which typically consist of 40 -50
  phosphoacylglycerols and 50 - 60 proteins
• the most abundant phosphoacylglycerols are
  derived from phosphatidic acid, a molecule in
  which glycerol is esterified with two molecules
  of fatty acid and one of phosphoric acid
• the three most abundant fatty acids in
  phosphatidic acids are palmitic (160), stearic
  (180), and oleic (181)

9
Phosphoacylglycerols

• A phosphatidic acid
• further esterification with a low-molecular-weight
  alcohol gives a phosphoacylglycerol
• the most common of these low-molecular-weight
  alcohols are

10
Phosphoacylglycerols
11
Phosphoacylglycerols
12
Phosphoacylglycerols

• A lecithin

13
Waxes

• An ester of a long-chain fatty acid and alcohol
• from the Old English word weax honeycomb

14
Sphingolipids

• contain sphingosine, a long-chain aminoalcohol
  from which this class is named

15
Glycolipids

• Glycolipid a compound in which a carbohydrate is
  bound to an -OH of the lipid
• many glycolipids are derived from ceramides

16
Steroids

• Steroids a group of plant and animal lipids that
  have this tetracyclic ring structure

17
Steroids

• The features common to the ring system of most
  naturally occurring steroids are illustrated here

18
Androgens

• Androgens male sex hormones
• synthesized in the testes
• responsible for the development of male secondary
  sex characteristics

19
Estrogens

• Estrogens female sex hormones
• synthesized in the ovaries
• responsible for the development of female
  secondary sex characteristics and control of the
  menstrual cycle

20
Cholesterol

• The steroid of most interest in our discussion of
  biological membranes is cholesterol

21
End