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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.
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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.
SPHINGOLIPIDS(continued) • Sphingomyelin:
SPHINGOLIPIDS(continued) • Glycolipid:
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.
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.
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.
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.
STEROIDS • Steroids are a broad class of compounds that have the same structural feature: • Like all lipids, steroids are soluble in nonpolar solvents.
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).
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.
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.
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.
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.
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
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).
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.
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.