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Chem 150 Unit 5 - Biological Molecules I Lipids 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. 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. 2 Introduction The types of lipids that we will look at include. • Fatty Acids • • • • • • 3 • 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 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. nonpolar 4 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. nonpolar 5 polar Fatty Acids Melting Temperature {°C} Melting points for saturated fatty acids: No. of Carbons 6 Fatty Acids Some fatty acids contain double bonds 7 • unsaturated • monounsaturated • polyunsaturated • polyunsaturated 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. 8 Fatty Acids Melting Temperature {°C} Normally the double bonds are cis • This lowers the melting points for fatty acids containing double bonds. No. of Double Bonds 9 Fatty Acids The cis double bonds produce kinks, which disrupt the London forces by preventing the tails from packing close to one another. 10 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 11 Fatty Acids The negative charge makes the polar head portion of the the fatty acid even more more polar and hydrophilic. 12 Questions (Clickers) What is the name used to describe molecules that contain both a hydrophobic and and hydrophilic part? 13 A) Amphiprotic B) Amphoteric C) Amphipathic D) Psychopathic 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. • 14 In Unit 3 we discussed how amphipathic molecules form interesting structures when exposed to water. 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. 15 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. • 16 In Unit 3 we discussed how amphipathic molecules form interesting structures when exposed to water. 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. 17 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: O CH3 CH2 Carboxylic acid part C O CH2 CH3 Alcohol part Ethyl propanoate 18 Waxes Waxes are esters. 14-36 carbons 19 16-30 carbons 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. came from the fatty acid 20 came from the alcohol Waxes Waxes are very hydrophobic and are used by plants and animals for protective, water-proof coatings 21 Questions Draw the skeletal structures for the products formed when beeswax undergoes base-catalzyed hydrolysis (saponification). 22 Reactions Involving Water (Unit 4) Hydrolysis • Hydrolysis can also be catalyzed using a base (OH-):. O CH3 CH2 CH2 C O O CH2 CH3 ethylbutanoate (an ester) 23 H2O OH- CH3 CH2 CH2 C O butanoate ion (a carobxylate ion) + HO CH2 CH3 ethanol (an alcohol) • 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 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 24 Triglycerides Triglycerides are a combination of three 3 fatty acid molecules with a glycerol molecule. 25 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. HO CH2 HO CH HO CH2 glycerol 26 Triglycerides For triglycerides, all three hydroxyls of the glycerol have a fatty acid residue attached to it. O CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2C O CH2 O CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2C O CH O CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2C O fatty acid residues 27 CH2 glycerol residue Figure 8.6 from Raymond 28 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. 29 • 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. 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. • 30 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. Triglycerides Reactions that involve triglycerides include: • • • 31 Hydrogenation Oxidation Base-catalyzed hydrolysis (saponification) Transport of fats: LDL transfers cholesterol to tissues from liver. Dietary fat 32 VLDL moves triglycerides from liver to tissues. 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) Fun Topic !: Fake Fats Side effects? 33 Olestra: sucrose fatty acid ester(s) Fat : glycerol fatty acid ester(s) 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. 34 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. ‣ • 35 H H H H This isCconsidered reduction, because the hydrogenHis bringing in additional + H C C C H 2 platinum electrons to the molecule. H H catalyst H H The alkane that is produced in this reaction is considered “saturated” because it can no longer absorb any more hydrogen atoms. unsaturated saturated 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. 36 Triglycerides Hydrogenation of triglycerides • Total hydrogenation liquid 37 solid Triglycerides Hydrogenation of triglycerides • Partial hydrogenation liquid 38 solid Triglycerides Hydrogenation of triglycerides • Partial hydrogenation cab produce trans fats. • Trans fats have been found to lower your HDL (“Good cholesterol”) levels. 39 Triglycerides Saturated vs Unsaturated Fats 40 Triglycerides Saturated vs Unsaturated Fats 41 Triglycerides Saturated vs Unsaturated Fats 42 Triglycerides Saturated vs Unsaturated Fats 43 Triglycerides Saturated vs Unsaturated Fats saturated fat O C trans unsaturated fat H O CH2 O C O CH H cis unsaturated fat H H 44 O C O CH2 Fat (Triacylglyceride) Triglycerides Oxidation of triglycerides • • 45 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. Triglycerides Oxidation of triglycerides These stink ! 46 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 • 47 We saw this on an earlier slide Reactions With Water (Unit 4) Hydrolysis example: • The base catalyzed hydrolysis of fats produces soap and glycerol O C H O CH2 O C 3 H2O O CH H H H O C Fat 48 O CH2 OH- Reactions With Water (Unit 4) Hydrolysis example: • The base catalyzed hydrolysis of fats produces soap and glycerol O C O HO CH2 HO CH HO CH2 O H 3 H2O C O OH- + H H O H C O Soap 49 Glycerol Phospholipids and Glycolipids Phospholipids and Glycolipids are the stuff that biological membranes are made of. • 50 Like the soaps, these molecules are highly aphipathic, and when mixed with water spontaneously form membranes that are described as lipid bilayers. Phospholipids and Glycolipids Soaps form Micelles 51 Phospholipids form Lipid Bilayers Phospholipids and Glycolipids Phospholipids and Glycolipids are the stuff that biological membranes are made of. • 52 Like the soaps, these molecules are highly aphipathic, and when mixed with water spontaneously form membranes that are described as lipid bilayers. Phospholipids and Glycolipids Phosphospholipids • 53 There a are two types of phospholipids • Glycerophospholipids Phospholipids and Glycolipids Phosphospholipids • 54 There a are two types of phospholipids • Sphingolipids Phospholipids and Glycolipids Phosphospholipids • The Glycerophospholipids have a structure similar to triglycerides, with one of the fatty acids replaced with a phosphate. There is usually an additional alcohol attached to the other side of the phosphate 55 Phospholipids and Glycolipids Phosphospholipids • The Glycerophospholipids have a structure similar to triglycerides, with one of the fatty acids replaced with a phosphate. phosphoester 56 bonds Phospholipids and Glycolipids Phosphospholipids • The Glycerophospholipids have a structure similar to triglycerides, with one of the fatty acids replaced with a phosphate. “Phosphotidyl-” refers to everything but the X 57 Phospholipids and Glycolipids Phosphospholipids • Phospholipids are used commercially as emulsifying agents. • An emulsifying agent stabilizes an emulsion. • An emulsion is a colloidal suspension of one liquid in another. ‣ An example is mayonnaise, which is a colloidal suspension of oil and water. • 58 Lecithin, which is another name for the phospholipid phosphotidylcholine, is used as an emulsifying agent in mayonnaise and other prepared foods. Phospholipids and Glycolipids Phosphospholipids • The sphingolipids function similarly to the glycerophospholipids, but structurally they are different. • There is not glycerol core • The glycerol and one of the fatty acids found in glycerophospholipids is replaced with a molecule called sphingosine. 59 Phospholipids and Glycolipids Phosphospholipids 60 • The sphingolipids are found in the myelin membranes that insulate the nerve cells. • Some sphingolipids use sugars for the alcohol portion of the molecule • These are called glycolipids. Steroids Steroids are a type of lipid that is not derived form a fatty acid. • They are based instead on a system of five cycloalkane rings that are fused together. 61 Steroids Steroids are a type of lipid that is not derived form a fatty acid. • They are based instead on a system of five cycloalkane rings that are fused together. 62 Steroids Cholesterol is the steroid that used as the starting point for the synthesis of other steroids. Note the fused ring system 63 Steroids • • Cholesterol is only found in animals Besides being used to synthesize the other steroids, cholesterol is dissolved in membranes to keep them fluid. • Plants use the alternative strategy of using polyunsaturated fatty acids to make their phospholipids. 64 Lipoproteins Lipoproteins are used to transport the water insoluble lipids such as triglycerides, phospholipids and cholesterol, in the blood. • Lipoproteins contain lipids and proteins. • They include: • Chylomicrons transport primarily • • 65 triglycerides from the digestive track. LDLs (low density lipoproteins) transport cholesterol, triglycerides and phospholipids from the liver to other tissues. HDLs (high density lipoproteins) transport cholesterol and phospholipids back to the liver. Lipoproteins The HDL and LDL levels in the blood can be used to assess ones risk for atherosclerosis. • • 66 High levels of HDL is considered good • This is why HDL is sometimes referred to as “good cholesterol” • > 40 mg/dL is good. High levels of LDL is considered bad • This is why LDL is sometimes referred to as “bad cholesterol” • > 100 mg/dL is bad. 67 Eicosanoids Eicosanoids are derived from arachidonic acid: 68 Membranes Fluid mosaic model 69 Membranes Transport across membranes 70 The End