Chapter 17 Lipids 17.1 Lipids Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

LIPID Lipids: 1. Fatty acids 2. Neutral fats and oils 3. Waxes   Lipids: 1. Fatty acids 2. Neutral fats and oils 3. Waxes 4. Phospholipid 5. Sterols 6. Fat soluble vitamins

Lipids Lipids are Biomolecules that contain fatty acids or a steroid nucleus. Soluble in organic solvents but not in water. Named for the Greek word lipos, which means “fat.” Extracted from cells using organic solvents.

Types of Lipids The types of lipids containing fatty acids are Waxes. Fats and oils (triacylglycerols). Glycerophospholipids. Prostaglandins. Not steroids, as they do not contain fatty acids.

Structures of Lipids Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Chapter 17 Lipids 17.2 Fatty Acids Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Lipids are non-polar (hydrophobic) compounds, soluble in organic solvents. Most membrane lipids are amphipathic, having a non-polar end and a polar end. Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end. A 16-C fatty acid: CH3(CH2)14-COO- Non-polar polar A 16-C fatty acid with one cis double bond between C atoms 9-10 may be represented as 16:1 cis D9.

Fatty Acid Formulas The formulas for fatty acids are written as Condensed formulas. Line-bond formulas. For example caprylic acid with 8 carbon atoms. CH3—(CH2)6—COOH CH3—CH2—CH2—CH2—CH2—CH2—CH2—COOH

Fatty Acids

Fatty Acids Fatty acids Are long-chain carboxylic acids. Typically contain 12-18 carbon atoms. Are insoluble in water. Can be saturated or unsaturated. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Saturated Fatty Acids Octanoic Acid

Unsaturated Fatty Acids 3 - Octenoic Acid 3, 6 - Octadienoic Acid Short hand: 8:1 (D3) 8:2 (D3,6)

Cis And Trans Fatty Acids Cis 9 - Octadecenoic Acid (oleic) Trans 9 - Octadecenoic Acid (elaidic acid)

Saturated Fatty Acids Saturated fatty acids have Single C–C bonds. Molecules that fit closely together in a regular pattern. Strong attractions between fatty acid chains. High melting points that make them solids at room temperature. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Some Saturated Fatty Acids TABLE 17.1 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Unsaturated Fatty Acids Have one or more double C=C bond Typically contain cis double bonds.

Properties of Unsaturated Fatty Acids Have “kinks” in the fatty acid chains. Do not pack closely. Have few attractions between chains. Have low melting points. Are liquids at room temperature. “kinks” in chain Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Polyunsaturated Fatty Acids Linoleic acid: Cis, cis, 9, 12 - Octadecadienoic acid Linolenic acid: Cis, cis, cis 9, 12, 15 - Octadecatrienoic acid Arachidonic acid: Cis, cis, cis, cis 5, 8, 11, 14 - Eicosatetraenoic acid   Linoleic Acid Linolenic Acid Arachidonic Acid

Some fatty acids and their common names: Double bonds in fatty acids usually have the cis configuration. Most naturally occurring fatty acids have an even number of carbon atoms. Some fatty acids and their common names: 14:0 myristic acid; 16:0 palmitic acid; 18:0 stearic acid; 18:1 cisD9  oleic acid 18:2 cisD9,12  linoleic acid 18:3 cisD9,12,15  a-linonenic acid 20:4 cisD5,8,11,14  arachidonic acid

Comparing Melting Points of Some Fatty Acids Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Effects of Double Bonds on the Melting Points 16:0   60 16:1 1 18:0 63 18:1 16 18:2 -5 18:3 -11 20:0 75 Fatty. Acids. Melting point. P. (0C) 20:4 -50

Melting Points and Solubility in Water of Fatty Acids

Learning Check stearic acid (18 C) saturated Assign the melting points of –17°C, 13°C, and 69°C to the correct fatty acid. Explain. stearic acid (18 C) saturated oleic acid (18 C) one double bond linoleic acid (18 C) two double bonds

Solution Stearic acid is saturated and would have a higher melting point than the unsaturated fatty acids. Because linoleic has two double bonds, it would have a lower mp than oleic acid, which has one double bond. stearic acid mp 69°C saturated oleic acid mp 13°C linoleic acid mp -17°C most unsaturated

Omega-6 and Omega 3- Fatty Acids In vegetable oils are mostly omega-6 with the first C=C at C6. linoleic acid CH3─(CH2)4─CH=CH─CH2─CH=CH─(CH2)7─COOH 6 In fish oils are mostly omega-3 with the first C=C at C3. linolenic acid CH3─CH2─(CH=CH─CH2)3─(CH2)6─COOH 3 Publishing as Benjamin Cummings Copyright © 2007 by Pearson Education, Inc.

Some Omega-6 and Omega-3 Fatty Acids

Learning Check Write a fatty acid with 10 carbon atoms that is: A. saturated B. monounsaturated omega-3 C. monounsaturated omega-6

Solution Write a fatty acid with 10 carbon atoms that is: A. saturated CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—CH2—COOH B. monounsaturated omega-3 CH3—CH2—CH=CH—CH2—CH2—CH2—CH2—CH2—COOH C. monounsaturated omega-6 CH3—CH2—CH2—CH2—CH2—CH=CH—CH2—CH2—COOH

Prostaglandin: One of a number of hormone-like substances that participate in a wide range of body functions such as the contraction and relaxation of smooth muscle, the dilation and constriction of blood vessels, control of blood pressure, and modulation of inflammation. Prostaglandins are derived from a chemical called arachidonic acid

Prostaglandins Prostaglandins have 20 carbon atoms in their fatty acid chains. An OH on carbon 11 and 15. A trans double bond at carbon 13. C 11 C 13 C 15 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Prostaglandins in the Body Prostaglandins are Produced by injured tissues. Involved in pain, fever, and inflammation. Not produced when anti-inflammatory drugs such as aspirin inhibit their synthesis. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Chapter 17 Lipids 17.3 Waxes, Fats, and Oils Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Waxes Waxes are Esters of saturated fatty acids and long-chain alcohols. Coatings that prevent loss of water by leaves of plants. TABLE 17.2

Fats and Oils: Triacylglycerols Fats and oils are Also called triacylglycerols. Esters of glycerol. Produced by esterification. Formed when the hydroxyl groups of glycerol react with the carboxyl groups of fatty acids. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Glycerophospholipids Glycerophospholipids (phosphoglycerides), are common constituents of cellular membranes. They have a glycerol backbone. Hydroxyls at C1 & C2 are esterified to fatty acids. An ester forms when a hydroxyl reacts with a carboxylic acid, with loss of H2O.

FAT AND OILS Mostly Triglycerides: Glycerol 3 Fatty Acids

Triacylglycerols In a triacylglycerol, Glycerol forms ester bonds with three fatty acids. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Formation of a Triacylglycerol glycerol + three fatty acids triacylglycerol + + 3H2O

Triglyceride (b - palmityl distearin) GLYCERIDES Monoglyceride (a - monostearin) Diglyceride (a, a' - distearin) Triglyceride (b - palmityl distearin)

Olive Oil Olive oil Contains a high percentage of oleic acid, which is a monounsaturated fatty acid with one cis double bond. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check What are the fatty acids in the following triacylglycerol?

Solution Stearic acid Oleic acid Myristic acid

MELTING POINTS OF TRIGLYCERIDES -15 C12 15 C14 33 C16 45 C18 55 C18:1 (cis) -32 Triglyceride Melting Point (°C) C18:1 (trans)

Melting Points of Fats and Oils A triacylglycerol that is a fat Is solid at room temperature. Is prevalent in meats, whole milk, butter, and cheese. A triacylglycerol that is an oil Is liquid at room temperature. Is prevalent in plants such as olive and safflower.

Oils with Unsaturated Fatty Acids Have more unsaturated fats. Have cis double bonds that cause “kinks” in the fatty acid chains. Cannot pack triacylglycerol molecules as close together as in fats. Have lower melting points than saturated fats. Are liquids at room temperature.

Diagram of Triacylglycerol with Unsaturated Fatty Acids Unsaturated fatty acid chains have kinks that do not allow close packing. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Saturated and Unsaturated Fatty Acids In Fats and Oils Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Chemical Properties of Triacylglycerols Chapter 17 Lipids 17.4 Chemical Properties of Triacylglycerols Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Chemical Properties of Triacylglycerols The chemical reactions of triacylglycerols are similar to those of alkenes and esters. In hydrogenation, double bonds in unsaturated fatty acids react with H2 in the presence of a Ni or Pt catalyst. In hydrolysis, ester bonds are split by water in the presence of an acid, a base, or an enzyme.

Hydrogenation of Oils The hydrogenation of oils Adds hydrogen (H2) to the carbon atoms of double bonds. Converts double bonds to single bonds. Increases the melting point. Produces solids such as margarine and shortening.

Hydrogenation Ni + 3H2 glyceryl tripalmitoleate glyceryl tripalmitate (tripalmitolean) glyceryl tripalmitate (tripalmitin)

Olestra, A Fat Substitute Olestra is Used in foods as an artificial fat. Sucrose linked by ester bonds to several long-chain fatty chains. Not broken down in the intestinal tract. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Cis and Trans Fatty Acids Unsaturated fatty acids can be Cis with bulky groups on same side of C=C. CH3─ (CH2)5 (CH2)7─ COOH cis C=C H H Trans have bulky groups on opposite sides of C=C. CH3─ (CH2)5 H C=C trans H (CH2)7─ COOH

Trans Fatty Acids and Hydrogenation Are formed during hydrogenation when cis double bonds are converted to trans double bonds. In the body behave like saturated fatty acids. Are estimated to make up 2-4% of our total Calories. Are reported in several studies reported to raise LDL-cholesterol and lower HDL-cholesterol.

Learning Check (1) True or (2) False A. There are more unsaturated fats in vegetable oils. B. Vegetable oils have higher melting points than fats. C. Hydrogenation of oils converts some cis-double bonds to trans- double bonds. D. Animal fats have more saturated fats.

Solution (1) True or (2) False A. T There are more unsaturated fats in vegetable oils. B. F Vegetable oils have higher melting points than fats. C. T Hydrogenation of oils converts some cis-double bonds to trans- double bonds. D. T Animal fats have more saturated fats.

Hydrolysis In hydrolysis, Triacylglycerols split into glycerol and three fatty acids. An acid or enzyme catalyst is required. +3 + 3

2. Saponification Value Saponification - hydrolysis of ester under alkaline condition.

Saponification and Soap Is the reaction of a fat with a strong base. Splits triacylglycerols into glycerol and the salts of fatty acids. Is the process of forming “soaps” (salts of fatty acids). With KOH gives softer soaps.

Saponification + 3NaOH + 3 “soap”

Saponification Value of Fats and Oils   Fat   Saponification # Milk Fat 210-233 Coconut Oil 250-264 Cotton Seed Oil 189-198 Soybean Oil 189-195 Lard 190-202  

2. Saponification Value Determination Saponification # --mgs of KOH required to saponify 1 g of fat. 1. 5 g in 250 ml Erlenmeyer. 2. 50 ml KOH in Erlenmeyer. 3. Boil for saponification. 4. Titrate with HCl using phenolphthalein. Conduct blank determination. B - ml of HCl required by Blank. S - ml of HCl required by Sample.

3. Iodine Number Number of iodine (g) absorbed by 100 g of oil. Molecular weight and iodine number can calculate the number of double bonds. 1 g of fat adsorbed 1.5 g of iodine value = 150.

Iodine Value Determination Iodine Value = (ml of Na2S2O3 volume for blank - ml of Na2S2O3 volume for sample)  N of Na2S2O3  0.127g/meq  100 Weight of Sample (g) Excess unreacted ICl

Iodine Numbers of Triglycerides Fatty Acids # of Double-bonds Iodine # Palmitoleic Acid 1 95 Oleic Acid 1 86 Linoleic Acid 2 173 Linolenic Acid 3 261 Arachidonic Acid 4 320

Learning Check 1. Glycerol and 3 oleic acids 2. Glyceryl tristearate What products are obtained from the complete hydrolysis of glyceryl trioleate? 1. Glycerol and 3 oleic acids 2. Glyceryl tristearate 3. Glycerol and 3 stearic acids

Solution What products are obtained from the complete hydrolysis of glyceryl trioleate? 1. Glycerol and 3 oleic acids

Learning Check Write the product of the following reaction. + 3

Solution

Glycerophospholipids Chapter 17 Lipids 17.5 Glycerophospholipids Fatty acid Glycerol Fatty acid PO4 Amino alcohol Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

PHOSPHOLIPID Lecithin (phosphatidyl choline)

Glycerophospholipids Glycerophospholipids are The most abundant lipids in cell membranes. Composed of glycerol, two fatty acids, phosphate and an amino alcohol. Fatty acid Glycerol Fatty acid PO4 Amino alcohol

Glycerophospholipids Are Polar A glycerophospholipid has Two nonpolar fatty acid chains. A phosphate group and a polar amino alcohol. CH3 │+ + HO−CH2−CH2−N−CH3 HO−CH2−CH2−NH3 │ choline CH3 ethanolamine + NH3 │ Amino alcohols HO−CH2−CH−COO− serine

Structure and Polarity of A Glycerophospholipid Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Lecithin and Cephalin Lecithin and cephalin are glycerophospholipids Abundant in brain and nerve tissues. Found in egg yolk, wheat germ, and yeast. Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

Lecithin Abundant in brain and nerve tissues Found in egg yolk, what germ, yeast

Chapter 17 Lipids 17.6 Sphingolipids Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Sphingolipids Sphingolipids Are similar to phospholipids. Contain sphingosine (a long-chain amino alcohol), a fatty acid, phosphate, and a small amino alcohol. Have polar and nonpolar regions. fatty acid sphingosine PO4 amino alcohol

Sphingosine Sphingosine is a long-chain unsaturated amino alcohol. CH3−(CH2)12 −CH=CH−CH−OH │ CH−NH2 CH2−OH sphingosine

Sphingolipids In sphingomyelin, a sphingolipid found in nerve cells There is an amide bond between a fatty acid and sphingosine, an 18-carbon alcohol. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Glycosphingolipids Glycosphingolipids contain monosaccharides bonded to the –OH of sphingosine by a glycosidic bond. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Glycosphingolipids and Cerebrosides Are sphingolipids that contain monosaccharides. Can be a cerebroside with galactose. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Steroid Nucleus A steroid nucleus consists of 3 cyclohexane rings. 1 cyclopentane ring. No fatty acids. steroid nucleus

Steroids: Cholesterol, Bile Salts, and Steroid Hormones Chapter 17 Lipids 17.7 Steroids: Cholesterol, Bile Salts, and Steroid Hormones Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

STEROLS Male & female sex hormones Bile acids Vitamin D Adrenal corticosteroids Cholesterol

Cholesterol Cholesterol Is the most abundant steroid in the body. Has methyl CH3- groups, alkyl chain, and -OH attached to the steroid nucleus.

Cholesterol, an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail. Cholesterol is largely hydrophobic. But it has one polar group, a hydroxyl, making it amphipathic.

Cholesterol inserts into bilayer membranes with its hydroxyl group oriented toward the aqueous phase & its hydrophobic ring system adjacent to fatty acid chains of phospholipids. The OH group of cholesterol forms hydrogen bonds with polar phospholipid head groups.

Cholesterol in the Body Cellular membranes Myelin sheath, brain, and nerve tissue Bile salts Hormones Vitamin D

Cholesterol in the Body A normal, open artery. Cholesterol in the body Is obtained from meats, milk, and eggs. Is synthesized in the liver. Is needed for cell membranes, brain and nerve tissue, steroid hormones, and Vitamin D. Clogs arteries when high levels form plaque. An artery clogged by cholesterol plaque Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Cholesterol in Foods Cholesterol is Synthesized in the liver. Obtained from foods. Considered elevated if plasma cholesterol exceeds 200 mg/dL. TABLE 17.4 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

FAT SOLUBLE VITAMINS Vitamin A:

Vitamin D2: Vitamin E:

Bile Salts Bile salts Are synthesized in the liver from cholesterol. Are stored in the gallbladder. Are secreted into the small intestine. Have a polar and a nonpolar region Mix with fats to break them part. Emulsify fat particles to provide large surface area.

Bile Salts Polar region Nonpolar region

Bile Salts Synthesized in the liver from cholesterol Stored in the gallbladder Secreted into small intestine Mix with fats to break them part Emsulsify fat particles

Sex Hormones

Lipoproteins Lipoproteins Combine lipids with proteins and phospholipids. Are soluble in water because the surface consists of polar lipids. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Types of Lipoproteins Lipoproteins Differ in density, composition, and function. Include low-density lipoprotein (LDLs) and high-density lipoprotein (HDLs). TABLE 17.5 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Steroid Hormones Steroid hormones Are chemical messengers in cells. Are produced from cholesterol. Include sex hormones such as androgens (testosterone) in males and estrogens (estradiol) in females. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Adrenal Corticosteroids Adrenal corticosteroids are steroid hormones that Are produced by the adrenal glands located on the top of each kidney. Include aldosterone, which regulates electrolytes and water balance by the kidneys. Include cortisone, a glucocorticoid, which increases blood glucose level and stimulates the synthesis of glycogen in the liver.

Adrenal Corticosteroids

Soxhlet Method.  

Learning Check Identify each as a 1. fatty acid 2. steroid 3. triacylglycerol 4. phospholipid 5. sphingolipid A. cholesterol B. glycerol, 2 fatty acids, phosphate, and choline C. glyceryl tristearate D. sphingosine, fatty acid, phosphate, and choline E. estradiol F. bile salts G. lipids in plasma membranes

Solution A. cholesterol 2 steroid B. glycerol, 2 fatty acids, phosphate, and choline 4 phospholipid C. glyceryl tristearate 3 triacylglycerol D. sphingosine, fatty acid, phosphate, and choline 5 sphingolipid E. estradiol 2 steroid F. bile salts 2 steroid G. lipids in plasma membranes 4 phospholipid, 5 sphingolipid .

Chapter 17 Lipids 17.8 Cell Membranes

Plasma Membranes Surround cells Lipid bilayer pf phospholipids Nonpolar hydrocarbon tails in center Polar (hydrophilic) sections on outside Some unsaturated fatty acids give flexibility Keep aqueous contents inside Allow certain biochemicals to pass through

Cell Membranes Cell membranes Separate cellular contents from the external environment. Consist of a lipid bilayer made of two rows of phospholipids. Have an inner portion made of the nonpolar tails of phospholipids with the polar heads at the outer and inner surfaces.

Fluid Mosaic Model of Cell Membranes The lipid bilayer Contains proteins, carbohydrates, and cholesterol. Has unsaturated fatty acids that make cell membranes fluid-like rather than rigid. Has proteins and carbohydrates on the surface that communicate with hormones and neurotransmitters.

Transport Through Cell Membranes The transport of substances through cell Membranes involves Diffusion (passive transport), which moves particles from a higher to a lower concentration. Facilitated transport, which uses protein channels to increase the rate of diffusion. Active transport, which moves ions against a concentration gradient.

Transport Pathways Through Cell Membranes Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Other Structures in Membranes Cholesterol molecules add strength Glycolipids on surface communicate with other cells Proteins embedded in bilayer move certain substances (water, K+, Cl-, HCO3-) across the cell membrane Proteins on surface act as receptors for hormones and other biochemicals

Diagram of a Plasma Membrane Polar sections Nonpolar tails

Learning Check The transport of particles across a cell membrane from high concentration to low concentration is called 1. Facilitated transport 2. Diffusion 3. Active transport

Solution The transport of particles across a cell membrane from high concentration to low concentration is called 2. Diffusion