Chapter 19 Lipids

1. Chemistry 203 Chapter 19 Lipids

2. Lipids • - Family of bimolecules. - They are not defined by a particular functional group, thus they have a variety of structures and functions. - They are soluble in organic solvents but not in water (nonpolar). - They contain many nonpolar C—C and C—H bonds and few polar bonds resulting in their water insolubility.

3. Lipids 1. Store energy: fat cells 2. Chemical messengers: find in nerve fibers and hormones. 3. Parts of membranes: insoluble in water

4. Store energy, insulation Cell membrane Chemical messenger Cell membrane Pain, fever, inflammation Lipids 1. Simple lipids: (Waxes, Fats & Oils) 2. Complex lipids (Glycerophospholipids) 3.Steroid (Cholesterol & steroid hormones) 4. Prostaglandins

5. Lipids Lipids can be categorized as: • Hydrolyzable lipids can be converted into small molecules by aqueous hydrolysis.

6. Lipids Lipids can be categorized as: • Nonhydrolyzable lipids cannot be cleaved into smaller molecules by aqueous hydrolysis.

7. R C O R ' O O = = - + ' R C - O H H O R + H2O An alcohol A carboxylic acid An ester Hydrolysis Most hydrolyzable lipids contain an ester. Hydrolysis: reaction with water. (breaking a bond and adding the elements of water) Heat H+ or enzyme

8. Fatty acids Hydrolyzable lipids are derived from fatty acids. • Fatty acids are: • Long-chain unbranched carbon attached to a carboxyl group (-COOH). • Typically 12-20 carbon atoms. • They have an even number of C atoms. • Insoluble in water. Cis

9. Fatty acids CH3(CH2)14COOH (palmitic acid) polar portion = hydrophillic nonpolar portion = hydrophobic Hydrophobic portion is much bigger than hydrophilic portion. Insoluble in water

10. Saturated and unsaturated Fatty acids Saturated fatty acids have no double bonds in their long hydrocarbon chains. Stearic acid: CH3(CH2)16COOH They are solids at room temperature. Packed together  Maximum London dispersion forces

11. Saturated and unsaturated Fatty acids Unsaturated fatty acids have 1 or more double bonds (generally cis) in their long hydrocarbon chains. Oleic acid: CH3(CH2)7CH=CH(CH2)7COOH They are liquids at room temperature. They can not pack together  London dispersion forces 

12. Fatty acids • The human body is capable of synthesizing most fatty acids from carbohydrates or other fatty acids. • Humans do not synthesize sufficient amounts of fatty acids that have more than one double bond. • More than one double bond fatty acids are called essential fatty acids and they must be provided by the diet. Linoleic acid linolenic acid

13. Essential Fatty acids Omega-n acids n: the position of the first double bond Linoleic acid is called an omega-6 acid, because of the position of the first C=C in the nonpolar chain.

14. Essential Fatty acids Linolenic acid is called an omega-3 acid, because of the position of the first C=C in the nonpolar chain.

15. Ester bond Fatty acid Long-chain alcohol Waxes Wax is an ester of saturated fatty acid and long chain alcohol.

16. Waxes For example, shown below is the formation of spermaceti wax, isolated from the heads of sperm whales.

17. Waxes Because of their long nonpolar C chains, waxes are very hydrophobic. O Beeswax (myricyl palmitate) CH3(CH2)14 C O(CH2)29CH3 hydrophobic region hydrophobic region They form protective coatings: • In plants, they help prevent loss of water and damage from pests. • In humans and animals, provide waterproof coating on skin and fur.

18. Carnauba Beeswax Coating Jojoba Lanolin from wool lotions

19. Waxes Hydrolysis reaction: like other esters, waxes are hydrolyzed.

20. Triacylglycerols (Triglycerides) Triacylglycerols are: • Fats and oils (are stored in the body). • Triesters of glycerol. • Produced by Fischer esterification. • Formed when the hydroxyl groups of glycerol react with the carboxyl groups of fatty acids.

21. Esterification glycerol three fatty acids triacylglycerol + 3H2O Acid

22. OH CH2 CH OH G L Y C E R O L CH2 OH Fatty acid Fatty acid Fatty acid Triacylglycerols (Triglycerides) Glycerol Produced by esterification of glycerol (a trihydroxyl alcohol).

23. Triacylglycerols (Triglycerides) Simple triacylglycerols have three identical fatty acid side chains. Mixed triacylglycerols have two or three different fatty acids.

24. Triacylglycerols (Triglycerides) Saturated triacylglycerols contain only saturated fatty acids. Monounsaturated triacylglycerols have 1 C=C bond. Polyunsaturated triacylglycerols have many C=C bonds. Increasing the number of double bonds in the fatty acid chain decreases the melting point of the triacylglycerol.

25. Triacylglycerols (Triglycerides) Fat: is a triacylglycerol that is solid at room temperature. Made by more saturated fatty acids (Saturated triacylglycerols). Meat, milk, butter and cheese (animal sources). Oil: is a triacylglycerol that is liquid at room temperature. Made by more unsaturated fatty acids (Unsaturated triacylglycerols). Corn, cotton seed, safflower and sunflower (plant sources). Both are colorless, odorless, and tasteless.

26. Fat & Health - Fats are used to build cell membranes, insulate the body, and store energy for later use. - It is recommended that no more than 20-35% of a person’s caloric intake should come from lipids. - A high intake of saturated triacylglycerols is linked to heart disease. - Saturated fats stimulate cholesterol synthesis in the liver, which can lead to cholesterol plaques building up inside arteries. - The result is high blood pressure, heart attack, and even stroke. - Unlike other vegetable oils, oils from palm and coconut trees are very high in saturated fats.

27. Fat & Health - Unsaturated triacylglycerols (omega-3 fatty acids from fish) lower the risk of heart disease by decreasing the level of cholesterol in the blood. - However, if the double bond of the unsaturated triacylglycerol is trans, the beneficial effect is lost. - Trans fats, which are primarily synthesized instead of naturally occurring, act like saturated fats and increase the cholesterol levels in the blood.

28. H H H H Ni _C=C_ + H2→ _C_C_ H H 1- Hydrogenation • Hydrogen adds to the double bonds of unsaturated fats (using transition metal catalyst such as Ni). • Melting point is increased. - Liquid oils are converted to semi-solid fats.

29. 1- Hydrogenation Ni + 3H2glyceryl Trioleate (triolein) glyceryl tristearate (tristearin) _ _

30. 2- Hydrolysis Triacylglycerols are hydrolysis (split by water) in the presence of strong acid or lipase (digestive enzyme). + 3H2O H 3H O H + H+ or Lipase H

31. Metabolism of tricaylglycerols - Humans store energy as triacylglycerols in adipose cells below the surface of the skin, in the breast area, and surrounding internal organs. - The number of adipose cells is constant; weight gained or lost causes them to swell or shrink, but not decrease or increase in number. - To metabolize triacylglycerols for energy, the esters are hydrolyzed by enzymes called lipases. - Complete metabolism of a triacylglycerol yields CO2, H2O, and a great deal of energy.

32. 3- Saponification (Basic Hydrolysis) - Is the process of forming “soaps” (salts of fatty acids). - Is the reaction of a fat with a strong base (NaOH). - Splits triacylglycerols into glycerol and the salts of fatty acids. - With KOH or the oils that are polyunsaturated gives softer soaps (liquid soaps). - Soaps are typically made from lard (from hogs), tallow (from cows or sheep), coconut oil, or palm oil. - All soaps work in the same way, but have different properties depending on the lipid source, length of C chain, and degree of unsaturation.

33. 3- Saponification (Basic Hydrolysis) + 3NaOH H Heat H + 3 Na+-O “soap” Salt of fatty acid H

34. Soaps Hydrophobic part: nonpolar Hydrophilic part: polar (remains in contact with environment)

35. Soaps When soap is mixed with dirt (grease, oil, and …), soap micelles “dissolve” these nonpolar, water-insoluble molecules.

36. phospholipids Phospholipids are lipids that contain a P atom. Two common types:

37. phospholipids 1. Phosphoacylglycerols: They are the main component of most cell membranes. Structurally, they resemble a triacylglycerol, except the third fatty acid has been replaced with a phosphodiester bonded to an alcohol. Fatty acid Fatty acid Amino alcohol

38. phospholipids 1. Phosphoacylglycerols: There are two types of phosphoacylglycerols: Ethanolamine Choline

39. phospholipids 2. Sphingomyelins: They differ in two ways: 1. They do not contain a glycerol backbone, they have a sphingosine backbone instead. sphingosine 2. They do not contain an ester; their single fatty acid is bonded to the backbone by an amide bond.

40. phospholipids 2. Sphingomyelins: The myelin sheath, the coating that surrounds nerve cells, is rich in sphingomyelins.

41. Interact with both polar and nonpolar substances. 1. Most abundant lipids in cell membranes (semipermeable). 2. Combine with less polar triglycerides and cholesterol to make them soluble. phosphoacylglycerols Nonpolar O R Polar

42. Carbohydrate Phospholipid bilayer Nonpolar Hydrophobic Polar Hydrophilic Cell Membrane Semipermeable: selected nutrients can enter and waste products can leave. Fluid mosaic model

43. Cell Membrane - Peripheral proteins are embedded within the membrane and extend outward on one side only. - Integral proteins extend through the entire bilayer. - Sometimes carbohydrates are attached to the exterior of the cell forming glycolipids and glycoproteins.

44. Transport Across a Cell Membrane Simple Diffusion: Small molecules like O2 and CO2 can diffuse through the cell membrane, traveling from higher to lower concentration. Facilitated Transport:Larger polar molecules (glucose) and ions (Cl- and HCO3-) travel through integral protein channels. Active Transport: Other ions, Na+, K+, and Ca2+, move against the concentration gradient; this required energy input.

45. Steroids Steroids have: • A steroid nucleus which is 4 carbon rings. • Attached groups that make the different types of compounds. • No fatty acids. (steroid nucleus)

46. Cholesterol Cholesterol: • Is the most abundant steroid in the body. • Insoluble in water (need a water soluble carrier). • Has methyl CH3- groups, alkyl chain, and -OH attached to the steroid nucleus.

47. Cholesterol Cholesterol: • Is obtained from meats, milk, and eggs. • Is synthesized in the liver from fats, carbohydrates and proteins. • Is needed for cell membranes, brain and nerve tissue, steroid hormones, and Vitamin D. • Clogs arteries when high levels form plaque (because it is insoluble in blood). • No cholesterol in vegetable and plants. At artery clogged by cholesterol plaque Gallstones form in gallbladder

48. Triacylglycerols Lipoproteins Water-soluble form of lipids (soluble in blood) Spherical particles Polar surface and nonpolar inner Transporting lipids through the bloodstream to tissues where they are stored, Used for energy, or to make hormones.

49. VLDL Liver Heart and muscles Fat storage cells Energy Intestine and elimination HDL LDL Lipoproteins VLDL: very-low-density lipoprotein Triglycerides and Cholesterol LDL:low-density lipoprotein (bad Cholesterol) Cholesterol HDL:high-density lipoprotein (good Cholesterol) Cholesterol Recommended levels are: HDL > 40 mg/dL, LDL < 100 mg/dL, total serum cholesterol < 200 mg/dL. Chylomicrons Triglycerides and Cholesterol

50. Steroid Hormones A hormone is a molecule that is synthesized in one part of an organism, which then elicits a response at a different site. Two types of steroids hormones: 1. Sex hormones 2. Adrenal Cortical Steroids Estrogens & progestins in females Androgens in males