The structure of lipids and it's components

A learning material about lipids

1. LIPIDS

2. Lipids are heterogeneous group of compounds including fats, oils, steriods , waxes, and related compounds. They are related by their physical rather than by their chemical properties. These properties are: They are relatively insoluble in water; and They are soluble in nonpolar solvents

3. 4 MAIN GROUPS OF LIPIDS Fatty acids ( un saturated and saturated) Glycerides (glycerol-containing lipids) Nonglyceride lipids ( sphingolipids . Steroids, waxes) Complex lipids

4. IMPORTANCE OF LIPIDS IN BIOLOGICAL PROCESS Energy source – Excellent source of energy for the body. When oxidized, each gram of fat releases 9 kilocalories (kcal) of energy, or more than twice the energy released by oxidation of a gram of carbohydrate. Energy storage – Most of the energy stored in the body is in the form of lipids (triglycerides). Stored in fat cells called, adipocytes, these fats are a particularly rich source of energy for the body.

5. Cell membrane structural components – Phosphogycerides , sphingolipids , and steroids make up the basic structure of all cell structure of all cell membranes. These membranes control the flow of molecules into and out of cells and allow cell-to-cell communication. Hormones – The steroid hormones are critical chemical messengers that allow tissues of the body to communicate with one another. The hormone like prostaglandins exert strong biological effects on both the cells that produce them and other cells of the body. Vitamins – The lipid-soluble vitamins, A, D, E, and K, play a major role in the regulation of several critical biological processes, including blood clotting and vision.

6. Vitamin absorption – Dietary fat serves as a carrier of the lipid-soluble vitamins. All are transported into cells of the small intestine in association with fat molecules. Therefore, a diet that is too low in fat (less than 20% of calories) can result in a deficiency of these four vitamins. Protection – Fats serve as a shock absorber, or protective layer, for the vital organs. About 4% of the total body fat is reserved for this critical function. Insulation – Fat stored beneath the skin (subcutaneous fat) serves to insulate the body from extremes of cold temperatures.

7. ROLES OF LIPIDS

8. Fatty acids – Metabolic fuel; Building blocks for other lipids Triacylglycerides – Main storage form of fatty acids and chemical energy. Phospholipids – Component of membranes; Sources of arachidonic acid, inositol triphosphate, and diglyceride for signal transduction. Sphingolipids – Component of membranes Cholesterol – Component of membranes; Precursor of bile salts and steroid humans. Bile salts – Lipid digestion and absorption; Main product of cholesterol metabolism.

9. Steroid hormones – Intracellular signals that regulate gene expression in target cells Eicosanoids – Regulators of physiological functions. Vitamins – Vision, Calcium metabolism, Antioxidants, blood coagulation. Ketone bodies – Metabolic fuel

10. STRUCTURE OF LIPIDS FATTY ACIDS – monocarboxylic acids that typically contain hydrocarbon chains of variable lengths (usually 12 to 20 carbons long). Saturated fatty acids – only contain C-C single bonds. Unsaturated fatty acids – contain one or more C=C double bonds MONOUNSATURATED FATTY ACIDS – contains only one C=C double bond. POLYUNSATURATED FATTY ACIDS – contains two or mo re C=C double bonds.

11. Melting points of saturated fatty acids increase with increasing and number, as is the case with alkanes. Saturated fatty acids containing ten or more carbons are solids at room temperature. The melting point of a saturated fatty acid is greater than that of an unsaturated fatty acid of the same chain length. The reason is that saturated fatty acid chains tend to be fully extended and to stack in a regular structure, thereby causing increased intermolecular attraction.

12. CIS AND TRANS ISOMERISM Unsaturated fatty acids can exhibit cis and trans isomerism. Nearly all naturally occurring fatty acids are in the cis configuration. Trans double bonds are formed from the catalytic hydrogenation of vegetable oils to make margarine. Cis -fatty acids possess a bent (120◦) structure while trans-fatty acids are linear.

13. CHEMICAL REACTIONS OF FATTY ACIDS

14. ESTERIFICATION ACID HYDROLYSIS SAPONIFICATION REACTION AT THE DOUBLE BOND (UNSATURATED FATTY ACIDS)

15. DIETARY FATTY ACIDS Nonessential fatty acids – can be synthesized in the body. Essential fatty acids – cannot be synthesized and must be obtained from the diet (e.g., linoleic acid, linoleric acid)

16. 2. EICOSANOIDS Derived from either arachidonic acid or EPA; they are a diverse group of hormonelike molecules produced in mammalian tissue. Prostaglandin – involved in inflammation, reproduction, and digestion; contain a cyclopentane ring and hydroxy groups at C11 and C15.

17. Thromboxane – involved in platelet aggregation and vasoconstriction; contain a cyclic ether. Leukotrienes – attract immune system cells to damaged tissue ( chemostatic agents); have linear structures.

18. BRIEF SUMMARY OF BIOLOGICAL PROCESSES THAT ARE THOUGHT TO BE REGULATED BY PROSTAGLANDINS, LEUKOTRIENES, AND THROMBOXANES

19. BLOD CLOTTING Thromboxane A2 is produced by platelets in the blood and stimulates constriction of the blood vessels and aggregation of the platelets. PGI2 (prostacyclin) is produced by the cells lining the blood vessels and has precisely the opposite effect of thromboxane A2.

20. THE INFLAMMATORY RESPONSE Prostaglandins are thought to promote certain aspects of the inflammatory response, especially pain and fever. Drugs such as aspirin block prostaglandin synthesis and help to relieve the symptoms.

21. REPRODUCTIVE SYSTEM PGE2 stimulates smooth muscle contraction, particularly uterine contractions. An increase in the level of prostaglandins has been noted immediately before the onset of labor . PGE2 has also been used to induce second trimester abortions.

22. GASTROINTESTINAL TRACT Prostaglandins have been shown to both inhibit the secretion of acid and increase the secretion of a protective mucus layer into the stomach. Prostaglandins help to protect the stomach lining.

23. KIDNEYS Prostaglandins produced in the kidneys cause the renal blood vessels to dilate. The greater the flow of blood through the kidney results in increased water and electrolyte secretion.

24. RESPIRATORY TRACT Eicosanoids produced by certain white blood cells, the leukotrienes , promote the constriction of the bronchi associated with asthma. Other prostaglandins promote bronchodilation .

25. OMEGA-3 FATTY ACIDS According to American Heart Association (AHA), they issued a dietary guidelines that it is recommended to eat at least two servings of “oily” fish in our diet each week. Salmon, albacore tuna, sardines, lake trout, and mackerel. These fish contain high levels of two omega-3 fatty acids called eicosapentanoic acid (EPA) and the docosahexanoic acid (DHA).

26. GLYCERIDES

27. NEUTRAL GLYCERIDES Are lipid esters that contain the glycerol molecule and fatty acids. Neutral glycerides and phosphoglyceride . Neutral glycerides are non - ionic and nonpolar Phosphoglyceride molecules have a polar region.

28. Esterification of glycerol with a fatty acid produces a neutral glyceride. Monoglycerides , diglycerides , or triglycerides.

29. 3. TRIGLYCEROLS Main storage forms of fatty acids. (TAGs) esters of fatty acids bound to glycerol; sometimes referred to as neutral fats. Depending on the number of bound fatty acids to glycerol, they may be called as monoacylglycerols , diacyglycerols , or triacylglycerols .

30. Depending on their fatty acid compositions, TAGs may be classified as: Fats – contain a large proportion of saturated fatty acids; solids at room temperature. Oils – contain a large proportion of unsaturated fatty acids; liquids at room temperature.

31. 4. WAX ESTERS Waxes are complex mixtures of lipids which serve as protective coatings on plant surfaces, and the skin and fur of animals. Wax esters – esters of long-chain fatty acids and long-chain alcohols

32. 5. PHOSPHOLIPIDS Amphipathic molecules; contain a polar head (phosphate or other charged polar groups) and a hydrophobic tail (hydrocarbon chains of fatty acids). All phospholipids may be considered as derivatives of phosphatic acid. Upon suspension in water, phospholipids naturally arrange to form bilayers. Hydrophobic groups are placed in the interior to exclude water, while hydrophilic groups are oriented so that they are exposed to water. Because of this, phospholipids are the major components of cellular membranes.

33. NONGLYCERIDE LIPIDS

34. 4. SPHINGOLIPIDS Contains sphingosine Similar to phospholipids, they are important components of cellular membranes, instead of glycerol, they are based on a long-chain amino alcohol known as sphingosine .

35. TYPES OF SPHINGOLIPIDS Sphingomyelin – ceramide is esterified to a phosphate group (from phosphorylcholine or phosphorylethanolamine ); found in greatest abundance in the myelin sheath of nerve cells. Its role is essential to proper cerebral function and nerve transmission. Glycolipids (or glycosphingolipids ) – do not contain phosphate; has a carbohydrate attached via O- glycosidic linkage to ceramide .

36. 7. STEROIDS Triterpene derivatives with four fused rings; resembles phenanthrene . Cholesterol – essential component of animal cell membranes; important precursor of other important steroids such as bile acids, adrenocortical hormones, sex hormones, D vitamins, cardiac glycosides, sitosterols in plants, and some alkaloids.

37. STEROIDS Naturally occuring family of organic molecules of biochemical and medical interest. The bile salts that aid in the emulsification and digestion of lipids are steroid molecules, as are sex hormones, testosterone and estrone .

38. The steroids are members of a large, diverse collection of lipids called the isoprenoids . All of these compounds are built from one or more five-carbon units called isoprene.

39. ISOPRENOIDS A large group of biomolecules which contain repeating 5-carbon structural units known as isoprene units. Subclassified into steroids and terpenes .

40. 8. TERPENES Isoprenols which are found largely in the essential oils of plants and animals. General term of lipids that are synthesized from isoprene units. Examples are, steroids, bile salts, the lipid-soluble vitamins, chlorophyll, and certain plant hormones.

41. CHOLESTEROL A common steroid is found in the membranes of most animal cells. It is an amphipathic molecule and is readily soluble in the hydrophobic region of membranes. Cholesterol, in combination, with other substances, contributes to a narrowing of the artery passageway. As narrowing increases, more pressure is necessary to ensure adequate blood flow, and high blood pressure (hypertension) develops. Hypertension is also linked to heart disease.

42. In series of chemical reactions, cholesterol is converted to the steroid progesterone, the most important hormone associated with pregnancy. Produced in the ovaries and in the placenta, progesterone is responsible for both the successful initiation and the successful completion of pregnancy.

43. WAXES Are derived from many different sources and have a variety of chemical compositions, depending on the source. Paraffin wax, composed of a mixture of solid hydrocarbons (usually the straight chain compounds). Natural waxes generally are composed of a long-chain fatty acid esterified to a long-chain alcohol. Long hydrocarbon tails are extremely hydrophobic, waxes are completely insoluble in water.

44. COMPLEX LIPIDS Are lipids that are bonded to other types of molecules. The most common and important complex lipids are plasma lipoproteins, which are responsible for the transport of other lipids in the body. Lipoprotein particles consist of a core of hydrophobic lipids surrounded by amphipatic proteins, phospholipids, and cholesterol.

45. 4 MAJOR CLASSES OF HUMAN PLASMA LIPOPROTEINS: CHYLOMICRONS – which have a density of less than 0.95 g/mL, carry dietary triglycerides from the intestine to other tissues. The remaining lipoproteins are classified by their densities. VERY LOW DENSITY LIPOPROTEINS (VLDL) – have a density of 0.95-1.019 g/ mL. They bind triglycerides synthesized in the liver and carry them to adipose and other tissues for storage.

46. LOW-DENSITY LIPOPROTEINS (LDL) – are characterized by a density of 1.019-1.063 g/ mL. They carry cholesterol to peripheral issues and help regulate cholesterol levels in those tissues. These are richest in cholesterol, frequently carrying 40% of the plasma cholesterol. HIGH-DENSITY LIPOPROTEINS (HDL) – have a density of 1.063-1.210 g/ mL. They are bound to plasma cholesterol; however, they transport cholesterol from peripheral tissues to the liver.

47. 9. LIPID VITAMINS Vitamin A – participates in the visual cycle in rod cells; active molecule is retinal. Vitamin D – involved in the regulation of calcium and phosphorus metabolism; most abundant form in the circulatory system is vitamin D3. Vitamin E – antioxidant which traps radicals formed as a result of phospholipid hydrocarbon chain oxidation by oxygen gas; active molecule is a - tocopherol . Vitamin K – plays an important role in the blood-clotting process; long unsaturated hydrocarbon side consists of repeating isoprene units.

48. 10. KETONE BODIES Molecules formed when fatty acid breakdown predominates over carbohydrate breakdown. Include acetoacetate, B - hydroxybutyrate , and acetone.

49. LIPOPROTEINS Any protein linked to a lipid group; most often applied to a group of structures found in the plasma of mammals which transport lipid molecules through the blood. Lipoprotein are classified according to density.

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