1. Chapter 18: Lipids

2. IMPORTANT FUNCTIONS OF LIPIDS
Protective wax coatings found on some plants
Energy-rich compounds with low densities
Storage form of energy for plants and animals
Structural components, especially in cellular membrane formation

3. LIPID A biological compound that is soluble only in nonpolar solvents.

4. FATTY ACIDS Building blocks of many lipids Long chain carboxylic acids

5. FATTY ACIDS, cont. In water, fatty acids will form micelles.

6. FATTY ACIDS – COMMON CHARACTERISTICS
Usually straight chains (no branching)
Sizes usually range from C10 to C20
Usually have an even number of carbons
Can be saturated (no C=C bonds) or unsaturated (has C=C bonds, usually in the cis configuration)
Examples of saturated, monounsaturated, and polyunsaturated fatty acids containing 18 carbon atoms:

7. FATTY ACID – MOLECULAR SHAPES C=C causes “kinking” of the carbon chain

8. FATTY ACIDS – MOLECULAR SHAPES, cont.
Fatty acids with C=C bonds cannot pack closely together because of shape. This leads to decreased intermolecular attractions and lower melting points.
Fatty acid melting points decrease as the number of C=C bonds increases.
Most unsaturated fatty acids are liquids at room temperature.

9. ESSENTIAL FATTY ACIDS
Those needed by the body, but not synthesized within the body in adequate amounts.
For humans, linoleic and linolenic acid are essential, but easily obtainable from plant and fish oils.

10. STRUCTURE OF FATS AND OILS
Fats Usually from animal sources Solids at room temperature Contain a high degree of saturated fatty acids
Oils Usually from plant and fish sources Liquids at room temperature Contain more unsaturated fatty acids

11. STRUCTURE, cont.
Fats and oils are triglycerides (triglycerols) which are triesters of glycerol.

12. STRUCTURE, cont. An example of the esterification process:

13. REACTIONS OF FATS AND OILS
Hydrolysis – important for fat and oil digestion

14. REACTIONS, cont.
Saponification – the commercial production of the salts of fatty acids (soaps)

15. REACTIONS, cont.
Hydrogenation – decreases the degree of unsaturation, used to make margarines from oils

16. WAXES
Esters of fatty acids and long chain alcohols Water insoluble and not easily hydrolyzed Often found in protective coatings

17. PHOSPHOGLYCERIDES
A phospholipid that contains an alcohol (usually an amino alcohol)

18. IMPORTANT PHOSPHOGLYCERIDES
Lecithins Contain the amino alcohol choline Important cell membrane component Emulsifying agent
Cephalins Contain ethanolamine or serine as the alcohol Found in most cell membranes, especially brain tissue

19. SPHINGOLIPIDS Sphingolipids contain sphingosine rather than glycerol.
Two types of sphingolipids exist:
Sphingomyelin contains a phosphate and choline group. It is found in the myelin sheath surrounding nerve cells.
Glycolipids contain carbohydrates unit. They are often called cerebrosides because of their abundance in brain tissue.

20. SPHINGOLIPID STRUCTURE

21. CELL MEMBRANES
Prokaryotic Cells – simple unicellular organisms with no internal membrane structures
Eukaryotic Cells – cells containing membrane-enclosed organelles, particularly a nucleus

22. MEMBRANE STRUCTURE Most are 60% lipid, 40% protein
Lipids in membranes: phosphoglycerides, sphingomyelin, and cholesterol
Lipids are organized in a bilayer with hydrophobic (long carbon chain) portions inside and hydrophilic (polar groups) exposed to the water environment.

23. FLUID MOSAIC MODEL OF MEMBRANE STRUCTURE

24. Like all lipids, steroids are soluble in nonpolar solvents.
A broad class of compounds that have the same structural feature:
Like all lipids, steroids are soluble in nonpolar solvents.

25. STEROIDS, cont.
Cholesterol – the most abundant steroid in the human body Essential component of cell membranes Precursor of other important steroids Synthesized by liver and present in foods Strong correlation between cholesterol blood levels and atherosclerosis

26. STEROIDS, cont.
Bile salts – bile is produced by the liver, stored in the gallbladder, and emptied into the intestine Bile salts emulsify lipids in the intestine, breaking
apart lipid globules Increased surface area allows lipids to be more easily hydrolyzed

27. STEROID HORMONES
Hormone – a chemical messenger secreted by specific glands and carried through the blood to a target tissue, where it triggers a particular response
There are two major categories of steroid hormones: adrenocorticoid hormones and sex hormones.

28. ADRENOCORTICOID HORMONES
Produced by the adrenal glands
Two classes:
Mineralocorticoids – regulate the concentration of ions in bodily fluids Aldosterone – increases absorption of Na+ and Cl-
Glucocortiocids – enhance carbohydrate metabolism Cortisol – increases glucose and glycogen concentrations in the body

29. SEX HORMONES
Androgens – Male sex hormones produced by testes, including testosterone
Estrogen and Progesterone – female sex hormones produced by ovaries, including estradiol and estrone (the most important estrogens)

30. PROSTAGLANDINS Cyclical compounds synthesized from arachidonic acid
Similar to hormones in that they are intimately involved in a host of body processes
Involved in almost every phase of reproduction
Participate in blood clotting

31. THERAPEUTIC POTENTIAL OF PROSTAGLANDINS
PGE2 and PGF2 induce labor and used for therapeutic abortion in early pregnancy
PGE2 in aerosol form used to treat asthma - opens up bronchial tubes by relaxing the surrounding muscles
Others inhibit gastric secretions and used to treat peptic ulcers
Many researchers believe that when they are fully understood, prostaglandins will be found useful for treating a much wider variety of ailments