1. Chem 1152: Ch. 18
Lipids

2. Lipids Biomolecules defined in terms of solubility:
Insoluble in water but soluble in nonpolar solvents.
Waxy, greasy or oily compounds.
Biological Functions:
Energy Storage
Structural component of cell membranes
Signaling molecules
Two major classes 
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

3. Saponifiable Lipids
Saponification: base hydrolysis of esters to produce carboxylic acid salt and alcohol
Simple Lipids:
Contain fatty acids and alcohols
Complex Lipids:
Contain multiple fatty acids, alcohol, something else
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

4. Fatty Acids Building blocks of many lipids Long chain carboxylic acids
Carboxyl group hydrophilic at physiological pH (7.4)
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

5. Micelles
In aqueous solutions, ionized fatty acids form spherical clusters
Polar head is facing out towards water (hydrophilic)
Long alkane chains associate in interior (hydrophobic) through weak dispersion forces
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

6. Characteristics of Fatty Acids
Straight chain (unbranched) carboxylic acids
Comprised of carbons
Usually have even number of carbons
Can be saturated or unsaturated
Usually no other functional groups
unsaturated
saturated
Unsaturated fatty acids usually contain double bonds in the cis configuration
This creates kink or bend in chain that prevents unsaturated fatty acids from packing together closely unlike saturated fatty acids
Results in weaker intermolecular forces, lower MP’s
Usually liquid at room temp
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

7. Properties of Unsaturated Fatty Acids
The kink or bend in chain of unsaturated fatty acids prevents from packing together closely unlike saturated fatty acids
Results in weaker intermolecular forces, lower MP’s
Increases fluidity of biological membranes
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

8. Properties of Unsaturated Fatty Acids
Phospholipids form bilayer in cell membrane
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

9. Essential Fatty Acids
The human body can synthesize all but two of the necessary fatty acids
Linoleic acid (omega-6 fatty acid)
Linolenic acid (omega-3 fatty acid)
Must be obtained from diet (plant and fish oils)
Polyunsaturated (multiple double bonds)
18 Carbons in chain
Diets rich in omega-3 fatty acids may:
decrease serum cholesterol, triglycerides
reduce risk of heart disease
Sources of omega-3 fatty acids:
Fish
Nuts
Kidney Beans
Spinach
Broccoli and cauliflower
Oils
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

10. Structures of Fats and Oils
Fats: Triglycerides from animal (saturated)
Oils: Triglycerides from vegetables (unsaturated)
These are esters (alcohol + acid)
Alcohol derived from glycerol
Acid from fatty acids
Most common lipids
triglyceride
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

11. Reactions of Triglycerides
Ester of 3 alcohols, 3 acids
triglyceride
hydrogenation
hydrolysis
saponification
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

12. Chemical Properties of Fats and Oils
Triglycerides exhibit chemical properties of esters and alkenes
Rxn: Hydrolysis
Breakdown of cellular fats to supply energy begins with lipase catalyzed hydrolysis reaction
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

13. Chemical Properties of Fats and Oils
Rxn: Saponification
Soapmaking (up to AD 500), by adding base (lye or aqueous extract of wood ash) to animal fat
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

14. Chemical Properties of Fats and Oils
Rxn: Hydrogenation
Results in partial hydrogenation (partially-hydrogenated vegetable oils)
Semi-solids that don’t separate
 Crisco
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

15. Waxes
Simple, saponifiable lipids (long chain fatty acid + alcohol = ester)
Alcohol derived from long chain alcohols (12-32 carbons) not glycerols
Water insoluble
Occur in nature as protective coatings on:
Feathers
Fur
Skin
Leaves
Fruits
Beeswax
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

16. Phosphoglycerides Complex lipids
Serve as major components of cell membranes
Also known as phospholipids
Structure similar to triglycerides
triglyceride
phosphoglyceride
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

17. Phosphoglycerides
The most common phosphoglycerides have choline, ehanolamine, or serine attached to the phosphate group.
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

18. Phosphatidylcholine (lecithin)
Phosphoglycerides
Lecithins
Phospholglycerides that contain choline
Soy lecithin used to provide smooth texture to margarine, chocolate
Cephalins
Phospholglycerides that contain ethanolamine or serine
Functions:
structural components of cell membranes
micelle forming agents
Functions:
Cell membranes
Blood-clotting
Phosphatidylcholine (lecithin)
Cephalin
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

19. Sphingolipids Complex lipid found in cell membrane
Contain sphingosine instead of glycerol
These are found in brain and nerve tissue, and in myelin sheath that surrounds nerves
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

20. Glycolipids Another type sphingolipid Contain carbohydrates
AKA cerebrosides due to abundance in brain tissue
No phosphate linkage
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

21. Related Diseases
Some human diseases are related to abnormal accumulation of sphingomyelins and glycolipids
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

22. Fluid-mosaic Model of Biological Membranes
Cell membranes for both prokaryotic and eukaryotic cells comprised of lipids organized in a bilayer
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

23. Steroids
Exhibit feature of other lipids (e.g., soluble in non-polar solvents)
Cholesterol is most abundant steroid in human body
Essential component of cell membranes
Precursor for other steroids:
Bile salts
Sex hormones
Vitamin D
Adrenocorticoid hormones
Synthesized in liver or obtained from food
May contribute to atherosclerosis
Steroid
Cholesterol
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

24. Bile Salts Yellow-brown or green liver secretion stored in gallbladder
Bile salts are released into intestine to separate large globules of lipids into smaller droplets
Bile salts also emulsify (mix immiscibles) cholesterol found in the bile for excretion
Gallstones may occur if cholesterol too high and/or bile salts too low
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011;

25. Steroid Hormones
Hormone: Chemical produced in the cell or gland that delivers a message affecting cells in another part of the organism
Steroid hormones derived from cholesterol
Two Major Steroid Hormones:
Adrenocorticoid Hormones
Male and Female Sex Hormones
Steroid hormones diffuse through the cell membrane and combine with receptor proteins in the cytoplasm
Hormone-receptor complex cause cell to respond to hormone by interacting with cell DNA and stimulating protein synthesis

26. Adrenocorticoid Hormones
Produced in adrenal glands located at top of kidneys
Classified into 2 functional groups:
Mineralocorticoids: Regulate concentration of ions (Na+) in body fluids
Aldosterone: most important mineralocorticoid
Promotes absorption of Na+ and Cl- in kidney tubules
Glucorticoids: Enhance carbohydrate metabolism
Cortisol is major glucocorticoid in human body
Increases glucose and glycogen concentration in body
Cortisol, cortisone and prednisolone exert anti-inflammatory effects
Used to treat rheumatoid arthritis, bronchial asthma
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

27. Male Sex Hormones Male sex hormones (androgens) produced in testes
Testosterone: Most important
Promotes normal growth of male genitalia and aids in development of secondary sex characteristics
Anabolic steroids banned for use by athletes include testosterone and derivatives
Use of these can lead to:
Liver tumors
Testicular atrophy
Decreased sperm count
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011;

28. Female Sex Hormones
Female sex hormones promote development of secondary sex characteristics
Increase in voice pitch
Increased breast size
Inhibition of facial hair
Estrogens:
Primary female sex hormones, play important roles in reproduction:
Estradiol
Estrone
Progesterone
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

29. Prostaglandins First identified in secretions from male prostate gland
Currently about 20 known prostaglandins in both men and women
Cyclic compounds derived from arachidonic acid
Hormone-like
Functions:
Regulate menstruation
Prevent conception
Induce uterine contractions during childbirth
Therapeutic applications:
Induce labor
Treat asthma
Treat peptic ulcers
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011