SPHINGOLIPIDS

1. SPHINGOLIPIDS • Sphingolipids are complex lipids that 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 a carbohydrate unit. They are often called cerebrosides because of their abundance in brain tissue.

2. SPHINGOLIPIDS(continued) • Sphingomyelin:

3. SPHINGOLIPIDS(continued) • Glycolipid:

4. SPHINGOLIPIDS(continued) • Several human diseases are known to result from an abnormal accumulation of sphingomyelins and glycolipids in the body. • Each of these diseases is the result of an inherited absence of an enzyme needed to break down these complex lipids.

5. CELL MEMBRANES • Prokaryotic cells are simple unicellular organisms without a nucleus or membrane-enclosed organelles. • Eukaryotic Cells are cells containing membrane-enclosed organelles, particularly a nucleus. • An organelleis a specialized structure within a cell that performs a specific function. • The roles of membrane include: • external cell membrane function as a selective barrier between the living cell and its environment; • internal membranes surround some organelles, create cellular compartments that have separate organization and functions.

6. CELL MEMBRANES (continued)

7. MEMBRANE STRUCTURE • Most membranes are 60% lipid and 40% protein. • The lipids in membranes are phosphoglycerides, sphingomyelin, and cholesterol. • Lipids are organized in a lipid bilayer with hydrophobic (long carbon chain) portions inside and hydrophilic (polar groups) exposed to the water environment. • When a lipid bilayer is broken and the tails are exposed to water, the resulting repulsion causes the bilayer to reform and the break seals spontaneously.

8. FLUID MOSAIC MODELOF MEMBRANE STRUCTURE

9. MEMBRANE STRUCTURE (continued) • Membrane lipids usually contain unsaturated fatty acid chains. • They fit into bilayers more loosely than saturated fatty acids. • This increases flexibility or fluidity of the membrane. • Proteins float in the lipid bilayer like icebergs in the sea, some extend completely through the bilayer. • Lipid molecules are free to move laterally within the bilayer like dancers on a crowded dance floor.

10. STEROIDS • Steroids are a broad class of compounds that have the same structural feature: • Like all lipids, steroids are soluble in nonpolar solvents.

11. STEROIDS(continued) • Cholesterol is: • the most abundant steroid in the human body. • an essential component of cell membranes. • a precursor of other important steroids. • synthesized by liver and present in foods. • A strong correlation exists between cholesterol blood levels and atherosclerosis (hardening of arteries).

12. STEROIDS(continued) • Bile is yellowish-brown or green, produced by the liver, stored in the gallbladder, and emptied into the intestine. • Bile salts emulsify lipids in the intestine by breaking apart lipid globules. • The increased surface area allows lipids to be more easily hydrolyzed.

13. STEROIDS(continued) • Bile salts emulsify cholesterol found in the bile. • Gallstones (80% cholesterol, colored by bile pigments) form when: • the cholesterol level in bile is too high. • the concentration of bile salts is too low.

14. STEROIDS(continued) • The passage of a gallstone: • causes excruciating pain. • can allow stones to lodge in the duct and prevent bile from passing into the duodenum and prevents fats from being digested normally. • The result is great pain, feeling nauseated and ill, skin taking on yellow color as bile pigments are absorbed into the blood, and stool becoming gray-colored because of the lack of excreted bile pigments. • Both the gallbladder and the stones can be surgically removed.

15. STEROID HORMONES • A hormone is 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.

16. ADRENOCORTICOID HORMONES • Adrenocorticoid hormones are produced by the adrenal glands. • The two classes of adrenocorticoid hormones are: • mineralocorticoids, which regulate the concentration of ions in bodily fluids. • Example: Aldosterone, which increases absorption of Na+ and Cl- • glucocorticoids, which enhance carbohydrate metabolism. • Example: Cortisol, which increases glucose and glycogen concentrations in the body and has powerful anti-inflammatory effects in the body

17. SEX HORMONES • Androgens are male sex hormones produced by testes, including testosterone. • Estrogen and progesterone are female sex hormones produced by ovaries, including estradiol and estrone (the most important estrogens).

18. PROSTAGLANDINS • Prostaglandins are: • 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. • involved in blood clotting.

19. THERAPEUTIC POTENTIAL OF PROSTAGLANDINS • PGE2 and PGF2 induce labor and are used for therapeutic abortion in early pregnancy. • PGE2 in aerosol form is used to treat asthma because it opens up bronchial tubes by relaxing the surrounding muscles. • Other prostaglandins 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.