Chem 150 Unit 5 - Biological Molecules I Lipids

1. Chem 150Unit 5 - Biological Molecules ILipids • Like organic molecules, biological molecules are grouped into families. There are four major families of biological molecules, including proteins, nucleic acids, carbohydrates, and lipids. The lipids are the subject of this unit. Of these four families, the lipids are the structurally the most diverse. This is because unlike members of the other three families, members of this families do no share a common structural feature, but rather share a common physical property; the are hydrophobic.

2. Introduction • Lipids are hydrophobic, nonpolar molelcules. • They are soluble in nonpolar solvent. • They are insoluble in polar solvents, such as water • They are isolated from the other biological molecules by extracting them with nonpolar solvents.

3. Introduction • The types of lipids that we will look at include. • Fatty Acids • In the carboxylic acid family • Waxes • Fatty Acids + Alcohols • Triglycerides • 3 Fatty acids + glycerol • Phospholipids and glycolipids • 2 fatty acids + glycerol + phosphate + X • Steroids • Derivatives of cholesterol • Eicosanoids • Derivatives of the Fatty acid arachidonic acid • Membranes • Formed from phospholipids and glycolipids

4. nonpolar polar Fatty Acids • Fatty acids contain a carboxylic acid group • This should make them quite polar • However, they also contain a long hydrocarbon tail • Which overall, makes them nonpolar.

5. nonpolar polar Fatty Acids • Fatty acids typically contain between 12 and 20 carbons • The number is usually always even. • The nonpolar tails interact with London forces.

6. Fatty Acids • Melting points for saturated fatty acids: Melting Temperature {°C} No. of Carbons

7. Fatty Acids • Some fatty acids contain double bonds • unsaturated • monounsaturated • polyunsaturated • polyunsaturated

8. Fatty Acids • The common fatty acids found in biological systems are shown in Table 8.1 of Raymond. Text Linolenic acid is one of the omega-3 fatty acids.

9. Fatty Acids • Normally the double bonds are cis • This lowers the melting points for fatty acids containing double bonds. Melting Temperature {°C} No. of Double Bonds

10. Fatty Acids • The cis double bonds produce kinks, which disrupt the London forces by preventing the tails from packing close to one another.

11. Fatty Acids • As acids, the carboxylic acid group in fatty acids can react with a base to produce a carboxylate ion • By donating its proton (H+) to the base the fatty acid becomes negatively charged. • We will talk more about acids and bases in Unit 6

12. Fatty Acids • The negative charge makes the polar head portion of the the fatty acid even more more polar and hydrophilic.

13. Questions (Clickers) • What is the name used to describe molecules that contain both a hydrophobic and and hydrophilic part? • Amphiprotic • Amphoteric • Amphipathic • Psychopathic

14. Fatty Acids • The salts of fatty acids are also called soaps, and are considered amphipathic, meaning they have a part that is very hydrophobic along with a part that is very hydrophilic. • In Unit 3 we discussed how amphipathic molecules form interesting structures when exposed to water.

15. Biochemical Compounds &Their Interactions with Water (Unit 3) • When placed in water, amphipathic molecules, form structures, such as micelles, which attempt to address the conflict.

16. Fatty Acids • The salts of fatty acids are also called soaps, and are considered amphipathic, meaning they have a part that is very hydrophobic along with a part that is very hydrophilic. • In Unit 3 we discussed how amphipathic molecules form interesting structures when exposed to water.

17. Waxes • Waxes are made by combining fatty acids with long chain alcohols. • In Unit 2 we discussed how carboxylic acids react with alcohols to from esters.

18. Alcohols, Carboxylic Acids & Esters (Unit 2) • We look now at three families that are distinguished by a functional group that contains the element oxygen. • Esters • Chemically, esters can be synthesize by reacting a carboxylic acid with and alcohol: Ethyl propanoate

19. 14-36 carbons 16-30 carbons Waxes • Waxes are esters.

20. came from the fatty acid came from the alcohol Waxes • When two more molecules combine to form a larger molecule, the word residue is used to indicate which molecule that part of the the larger molecule came from.

21. Waxes • Waxes are very hydrophobic and are used by plants and animals for protective, water-proof coatings

22. Questions • Draw the skeletal structures for the products formed when beeswax undergoes base-catalzyed hydrolysis (saponification).

23. Reactions Involving Water (Unit 4) • Hydrolysis • Hydrolysis can also be catalyzed using a base (OH-):. • Because one of the products of the hydrolysis is a carboxylic acid, in base catalyzed hydrolysis the base undergoes a second acid/base reaction with the carboxylic acid to produce a carboxylate ion. • The base catalyzed hydrolysis of esters is also called saponification • We will be discussing acids and bases in Unit 6

24. Triglycerides • Triglycerides are a storage form of fatty acids in mammals. • Often when blood tests are done, they measure your triglycyeride levels. • High triglyceride levels in the blood are a risk indicator for artherosclerosis. *American Heart Association

25. Triglycerides • Triglycerides are a combination of three 3 fatty acid molecules with a glycerol molecule.

26. Triglycerides • Glycerol, which is also called glycerin, is an alcohol with three hydroxyl groups. • As with the waxes, the fatty acids can react with the hydroxyl groups to form esters. • Since there are three hydroxyl groups, three fatty acids can react to form three esters.

27. Triglycerides • For triglycerides, all three hydroxyls of the glycerol have a fatty acid residue attached to it.

28. Figure 8.6 from Raymond

29. Triglycerides • Just as with fatty acids, where the presence of cis double bonds lower the melting points, triglycerides made from unsaturated fatty acids have lower melting points than those made from saturated fatty acids. • Triglycerides from animals tend to have a higher proportion of saturated fatty acids. • Most are solids at room temperature and are called fats. • Examples include: butter, lard and bacon grease • Triglycerides from plants tend to have a higher proportion of unsaturated fatty acids. • Most are liquids at room temperature and are called oils. • Examples include: corn oil, canola oil, peanut oil and olive oil.

30. Triglycerides • Triglycerides as primarily used as a form of stored energy. • This is why when you eat more than you need to meet your energy requirements, the excess energy is stored in the form of fat. • Fat can store almost twice as much energy per gram as carbohydrates and proteins • In mammals the fats are stored in the adipose tissue. • Adipose tissue also functions to protect organs from shock and cold.

31. Triglycerides • Reactions that involve triglycerides include: • Hydrogenation • Oxidation • Base-catalyzed hydrolysis (saponification)

32. Transport of fats: VLDL moves triglycerides from liver to tissues. LDL transfers cholesterol to tissues from liver. HDL carries cholesterol from tissues to liver. Monoglycerides and fatty acids are absorbed by intestines - transported as chylomicrons in lymph system to blood.-Fat Blocker-Xenical (orlistat) Dietary fat

33. Olestra: sucrose fatty acid ester(s) Fat : glycerol fatty acid ester(s) Fun Topic !: Fake Fats Side effects?

34. Triglycerides • Hydrogenation of triglycerides • This is the same reaction that we saw in Unit 4 with the hydrogenation of alkenes. • Unsaturated fats and oils contain alkenes and can be hydrogenated to produce saturated fats. • Commercially, vegetable oils are often hydrogenated to produce a solid product that has better qualities for making baked goods. • Animal fats, such as butter and lard, which are naturally saturated, can also be used, but unlike the vegetable oils, they come with cholesterol, which is undesirable for health reasons.

35. Oxidation and Reduction (Unit 4) • Hydrogenation • Another type of oxidation/reduction reaction is the hydrogenation reaction: • In this example, an alkene is reduced to an alkane. • This is considered reduction, because the hydrogen is bringing in additional electrons to the molecule. • The alkane that is produced in this reaction is considered “saturated” because it can no longer absorb any more hydrogen atoms. unsaturated saturated

36. Triglycerides • Hydrogenation of triglycerides • This is the same reaction that we saw in Unit 4 with the hydrogenation of alkenes. • Unsaturated fats and oils contain alkenes and can be hydrogenated to produce saturated fats. • Commercially, vegetable oils are often hydrogenated to produce a solid product that has better qualities for making baked goods. • Animal fats, such as butter and lard, which are naturally saturated, can also be used in baking, but unlike the vegetable oils, they come with cholesterol, which is undesirable for health reasons.

37. Triglycerides • Hydrogenation of triglycerides • Total hydrogenation liquid solid

38. Triglycerides • Hydrogenation of triglycerides • Partial hydrogenation liquid solid

39. Triglycerides • Hydrogenation of triglycerides • Partial hydrogenation cab produce trans fats. • Trans fats have been found to lower your HDL (“Good cholesterol”) levels.

40. Triglycerides • Saturated vs Unsaturated Fats

41. Triglycerides • Saturated vs Unsaturated Fats

42. Triglycerides • Saturated vs Unsaturated Fats

43. Triglycerides • Saturated vs Unsaturated Fats

44. Triglycerides • Saturated vs Unsaturated Fats Fat (Triacylglyceride)

45. Triglycerides • Oxidation of triglycerides • Unsaturated triglycerides can react with oxygen to produce small change fatty acids another small molecules. • These often do not smell very good • This is what happens when butter goes rancid. • This makes solid fats and oils more stable than liquid oils and is why the solid fats are preferred for deep frying.

46. Triglycerides • Oxidation of triglycerides These stink !

47. Triglycerides • Saponification of triglycerides • Saponification is the base-catalyzed hydrolysis of the ester bonds in a triglyceride. • We also discussed this reaction in Unit 4 • This cleaves the esters back into carboxylic acids (fatty acids) and an alcohol (glycerol). • Because the reaction is base-catalyzed, the base also reacts with the carboxylic acids to from carboxylate ions • We saw this on an earlier slide

48. Reactions With Water (Unit 4) • Hydrolysis example: • The base catalyzed hydrolysis of fats produces soap and glycerol Fat

49. Reactions With Water (Unit 4) • Hydrolysis example: • The base catalyzed hydrolysis of fats produces soap and glycerol Soap Glycerol

50. Phospholipids and Glycolipids • Phospholipids and Glycolipids are the stuff that biological membranes are made of. • Like the soaps, these molecules are highly aphipathic, and when mixed with water spontaneously form membranes that are described as lipid bilayers.