Chem 20: Ch. 15 Lipids Study Guide

Drawing Fatty Acids P. 3

-In a skeletal formula of a fatty acid, the ends and bends of the line are the carbon atoms. -The structural formula of lauric acid can be drawn in several forms

Cis and Trans Unsaturated Fatty Acids P. 4

-Unsaturated fatty acids can be drawn as CIS and TRANS isomers -OLEIC ACID is a monounsaturated fatty acid found in olives, with one double bond at carbon 9.

Melting Points of Fats and Oils

A FAT -is usually solid at room temperature -usually comes from animal sources such as meat, whole milk, butter, and cheese. An OIL -is usually liquid at room temperature -is usually obtained from a plant source such as palm oil and coconut oil.

Steroid Nucleus P. 22

A STEROID NUCLEUS consists of -three cyclohexane rings and one cyclopentane ring, fused together -rings designated as A, B, C, and D -numbered carbon atoms beginning in ring A -two methyl groups at positions 18 and 19.

Study Check: Consider the condensed structural formula for oleic acid. P. 5-6 A. Why is this molecule an acid? B. How many total carbon atoms are in oleic acid? C. Is this a saturated, monounsaturated, or polyunsaturated fatty acid? D. Is it likely to be a solid or liquid at room temperature? E. Would it be soluble in water?

A. It contains a carboxylic acid functional group B. Oleic acid contains 18 carbon atoms. C. Oleic acid is a monounsaturated fatty acid. D. It is a liquid at room temperature E. The long carbon chain makes it insoluble in water.

Study Check: Label each of the following fatty acids as saturated, monounsaturated, or polyunsaturated. A. linolenic acid B. palmitoleic acid C. stearic acid

A. POLYUNSATURATED. B. MONOUNSATURATED C. SATURATED

Study Check: Lipids are characterized by the presence of fatty acids or a steroid nucleus. Which type is described by the following? P. 2 A. contains a fused-four membered ring system B. contains long carbon chains C. includes carbonyl groups

A. STEROID B. FATTY ACIDS C. FATTY ACIDS

Study Check: Identify each of the following as a fatty acid, a triacylglycerol, an amino alcohol, or a glycerophospholipid. A. glyceryl trioleate B. cephalin C. choline D. palmitic acid.

A. TRIACYLGLYCEROL B. GLYCEROPHOSPHOLIPID C. AMINO ALCOHOL D. FATTY ACID

Study Check: Which of the following statements are true and which are 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.

A. TRUE B. FALSE. C. TRUE D. TRUE

Amino Alcohols P. 18

Amino alcohols found in GLYCEROPHOSPHOLIPIDS -are chlorine, erine, and ethanolamine -are ionized at physiological pH of 7.4.

Bile Salts

BILE SALTS -are synthesized in the liver from cholesterol and stored in the gallbladder -have polar and nonpolar regions that act like soaps to make fat soluble in water. -help in absorption of cholesterol When large amounts of cholesterol accumulate in the gallbladder, gallstones are formed.

Study Check: Which of the following is NOT a characteristic of lipids? P. 2-3 A. may contain a carboxylic acid group B. may contain a four-ring structure C. soluble in water D. mostly nonpolar

C. Lipids are nonpolar and therefore are NOT soluble in water.

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.

Cholesterol in Foods

CHOLESTEROL -is considered elevated if plasma cholesterol exceeds 200 mg/dL -is synthesized in the liver and obtained from foods A diet that is low in foods containing cholesterol and saturated fats appears to be helpful in reducing the serum cholesterol level.

Cholesterol in the Body

CHOLESTEROL -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. Cross-sections of arteries show how plaque clogs the arteries.

Cholesterol P. 22

CHOLESTEROL -is the most important and abundant steroid in the body -has a hydroxyl group (-OH) on (carbon 3) -has a double bond between carbons 5 and 6 -has methyl groups at carbons 10 and 13 -has an alkyl chain at carbon 17

Study Check: the transport of particles across a cell membrane from high concentration to low concentration is called?

DIFFUSION.

Hydrogenation: Trans Fatty Acids P. 14-15

During hydrogenation, -double bonds are converted to C-C single bonds. -a small number of the cis double bonds are converted to more stable trans double bonds, causing a change in the overall structure of the fatty acids. In the body, trans fatty acids -behave like saturated fatty acids -are estimated to be 2-4% of our total calories. -raise LDL-cholesterol and lower HDL-cholesterol.

Fatty Acids

FATTY ACIDS are -long, unbranched carbon chains with a carboxylic acid group at the end. -typically 12-to-18 carbon atoms long -insoluble in water b/c of the long carbon chain -SATURATED when they do not contain C=C double bonds in the carbon chain. -UNSATURATED when they contain C=C double bonds in the carbon chain.

Monounsaturated Fatty Acids P. 4 Table 15.1

Fatty acids can be MONOUNSATURATED, with only one double C=C bond in the carbon chain.

Polyunsaturated Fatty Acids P. 4 Table 15.1

Fatty acids can be POLYUNSATURATED, with at least two double C=C bonds in the carbon chain.

Saturated Fatty Acids P. 4 Table 15.1

Fatty acids can be SATURATED, with only C-C single bonds in the carbon chain.

Trans Fatty Acids in Foods

Foods containing naturally occurring trans fatty acids include milk, eggs, and beef. Foods that contain trans fatty acids from the hydrogenation process include -deep fried foods -bread, baked goods, and cookies -crackers and chips -stick and soft margarine -vegetable shortening

Glycerophospholipids P. 18

GLYCEROPHOSPHOLIPIDS contain -two fatty acids that form ester bonds with the first and second hydroxyl groups of glycerol. -a hydroxyl group that forms an ester with phosphoric acid, which forms another phosphoester bond with an amino alcohol.

Study Check: What products are obtained from the complete hydrogenation of glyceryl trioleate? A. glycerol and three oleic acids B. glyceryltristearate C. glycerol and three stearic acids

GLYCERYLTRISTEARATE

Structure and Polarity of a Glycerophospholipid P. 19

Glycerophospholipids -have both polar and nonpolar regions that allow them to interact with polar and nonpolar substances. -have a POLAR HEAD containing the ionized amino alcohol and phosphate portion, which is strongly attracted to water. -have a nonpolar HYDROCARBON TAIL portion soluble only in nonpolar substances such as lipids. -are the most abundant lipids in cell membranes and play an important role in cellular permeability.

15.6 Steroids: Cholesterol, Bile Salts, and Steroid Hormones

High- and low-density lipoproteins transport cholesterol between the tissues and the liver.

Essential Fatty Acids

Humans -are capable of synthesizing some fatty acids from carbohydrates or other fatty acids. -cannot synthesize sufficient amounts of polyunsaturated fatty acids such as linoleic acid, linolenic acid, and arachidonic acid. Because these polyunsaturated fatty acids must be obtained from the diet, they are known as essential fatty acids.

Triacylglycerols: Hydrogenation

In HYDROGENATION REACTIONS, -double bonds in unsaturated fatty acids react with hydrogen gas to produce carbon-carbon single bonds. -hydrogen gas is bubbled through the heated oil, typically in the presence of a nickel catalyst.

Hydrolysis P. 16

In HYDROLYSIS, -triacylglycerols split into glycerol and three fatty acids -a strong acid, HCl or H2SO4, or digestive enzymes called lipases are required.

Transport of Lipoproteins in the Body

Lipoproteins such as HDLs and LDLs transport nonpolar lipids and cholesterol to cells and the liver.

Sphingomyelin P.21

In a sphingomyelin, -the amine group of sphingosine forms an amide bond to a fatty acid. -the hydroxyl group forms an ester bond with phosphate, which forms another phosphoester bond to choline or ethanolamine. Sphingomyelins are abundant in the white matter of the myelin sheath, a coating surrounding the nerve cells that increases the speed of nerve impulses and insulates and protects the nerve cells.

Triacylglycerols

In the body, fatty acids are stored as TRIACYLGLYCEROLS (triglycerides), which are -esters of glycerol (a trihydroxy alcohol) and fatty acids -formed when three hydroxyl groups of glycerol react with the carboxyl groups of three fatty acids -named by changing GLYCEROL to GLYCERYL and naming the fatty acids as carboxylates.

Fluid Mosaic Model: Cell Membranes

In the fluid mosaic model of a cell membrane, -proteins and cholesterol are embedded in a lipid bilayer of phospholipids. -the bilayer forms a membrane-type barrier with polar heads at the membrane surfaces and the nonpolar tails in the center away from the water. 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.

Properties of Saturated Fatty Acids P. 5 (continued)

In unsaturated fatty acids, the cis double bonds cause the carbon chain to bend or kink, giving the molecules an irregular shape and allowing fewer interactions between molecules.

Lecithin and Cephalin P. 19

LECITHIN and CEPHALIN are types of glycerophospholipids that are -abundant in brain and nerve tissues. -found in egg yolk, wheat germ, and yeast.

15.1: Lipids P. 1

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" -an important feature in cell membranes, fat-soluble vitamins, and steroid hormones.

Types of Lipoproteins P. 25 Table 15.5

LIPOPROTEINS -differ in density, composition, and function. -include low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs)

Lipoproteins

LIPOPROTEINS -surround nonpolar lipids with polar lipids and protein for transport to cells. -are soluble in water because the surface consists of polar lipids.

Types of Lipids P. 1

Lipids are characterized by their structures. 1. Lipids such as waxes, fats, oils, and phospholipids are esters that can be hydrolyzed to give fatty acids and other molecules. 2. Steroids, also lipids, do not contain fatty acids and cannot be hydrolyzed. They are characterized by the steroid nucleus of four fused carbon rings.

General Structure of Lipids P. 2

Lipids are naturally occurring compounds that are soluble in organic solvents but not in water.

Lipoproteins: Lipid Transport P. 24

Lipids are nonpolar and made more soluble by combining them with glycerophospholipids and proteins to form water-soluble complexes called lipoproteins.

15.4 Chemical Properties of Triacylglycerols

Many soft margarines, stick margarines, and solid shortenings are produced by the partial hydrogenation of vegetable oils.

15.3 Waxes and Triacylglycerols

Natural waxes are found on the surface of fruits and on the leaves and stems of plants, where they help prevent loss of water and damage from pests. Waxes on the skin, fur, and feathers of animals provide a waterproof coating.

Prostaglandins: NSAIDs P. 7

Non-steroidal anti-inflammatory drugs (NSAIDs) block production of prostaglandins, decreasing pain and inflammation. NSAIDs include naproxen (Aleve and Naprosyn), ketoprofen (Actron), and nabumetone (Relafen)

Oils with Unsaturated Fatty Acids

OILS from -olive and peanut are monounsaturated; they contain large amounts of oleic acid -corn, cottonseed, safflower seed, and sunflower seed are polyunsaturated because they contain large amounts of fatty acids with two or more double bonds. -palm and coconut are solids at room temperature because they consist mostly of saturated fatty acids.

Prostaglandins P. 6

PROSTAGLANDINS -are hormone-like substances produced in cells -are also known as eicosanoids, formed from arachidonic acid, a polyunsaturated fatty acid with 20 carbon atoms. -differ by the substituents attached to the five-carbon ring. When tissues are injured, arachidonic acid is converted to prostaglandins that produce inflammation and pain in the area. Non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin, block the production of prostaglandins.

Saponification and Soap P. 16-17

SAPONIFICATION -is the reaction of a fat with a strong base such as NaOH in the presence of heat. -splits triacylglycerols into glycerol and the sodium salts of fatty acids. -is the process of forming "soaps" (salts of fatty acids) -with NaOH gives solid soaps that can be molded into different shapes. -with KOH gives softer, liquid soaps.

Properties of Saturated Fatty Acids P. 5

SATURATED FATTY ACIDS -contain only single C-C bonds and fit close together in a regular pattern. -have strong dispersion forces between long carbon chains. -have higher melting points and are usually solids at room temperature.

Study Check: Draw the condensed structural formula for the product of a glyceryl tripalmoleate that undergoes hydrogenation. P. 16

SOLUTION:

Study Check: Draw the condensed structural formula for the triacylglycerol containing three molecules of myristic acid (14:0). P.11

SOLUTION:

Study Check: Draw the condensed structural formula of a cephalin that contains stearic acid and serine. P. 20

SOLUTION:

Study Check: What are the fatty acids in the following triacylglycerol? P. 10

SOLUTION:

Study Check: Write the equation for the reaction catalyzed by the enzyme lipase that hydrolyzes glyceryl trilaurate (trilaurin) during the digestion process. P. 17

SOLUTION:

Study Check: palmitic acid, the 16-carbon saturated fatty acid, is the most common fatty acid found along with the ionized amino alcohol choline in the sphingomyelin of eggs. Draw the condensed structural formula for this sphingomyelin. P. 21

SOLUTION:

Study Check: match the components of the cholesterol molecule with the following: P. 23 _________ carbon chain ________________ hydroxyl group __________ steroid nucleus ________________ methyl group

SOLUTION: D carbon chain A hydroxyl group C steroid nucleus B methyl group

Study Check: Identify each of the following as a fatty acid, steroid nucleus, or triacylglycerol. P. 26-27 A. cholesterol B. stearic acid C. glyceryl tristearate D. estradiol E. contains no fatty acids.

SOLUTION: A. STEROID B. FATTY ACID C. TRIACLGLYCEROL D. STEROID E. STEROID

Drawing the Structure of a Triacylglycerol: Draw the condensed structural formula for glyceryl tripalmitoleate (tripalmitolein). P. 11

SOLUTION: Glyceryl tripalmitoleate (tripalmitolein) is the triacylglycerol that contains ester bonds between glycerol and three palmitoleic acids acid molecules. ANALYZE THE PROBLEM: Name of Lipid: glyceryl tripalmitoleate (tripalmitolein) Type of Lipid: triacylglycerol Type of Alcohol: glycerol Fatty Acids: three; palmitoleic acid (16:1) Type of Bond: ester

Sphingomyelin P. 18

SPHINGOMYELIN -contains sphingosine instead of glycerol. -contains a fatty acid, phosphate, and an amino alcohol.

Steroid Hormones

STEROID HORMONES are -chemical messengers that serve as a communication system for the body. -produced from cholesterol. -adrenal corticosteroids from adrenal glands -mineralocorticoids (electrolyte balance) -glucocorticoids (regulate glucose level)

Saturated and Unsaturated Melting Points P. 12

Saturated fatty acids -have higher melting points than unsaturated fatty acids because they pack together more tightly. -are usually found in animal fats and in coconut and palm oils.

Adrenal Corticosteroids P. 26

Steroid hormones called ADRENAL CORTICOSTEROIDS -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.

15.7 Cell Membranes

Substances are transported across a cell membrane by either diffusion, facilitated transport, or active transport.

15.5 Phospholipids P. 18

The PHOSPHOLIPIDS are the family of lipids similar in structure to triacylglycerols; they include GLYCEROPHOSPHOLIPIDS and SPHINGOMYELIN.

Triacylglycerol: Glyceryl Tristearate P. 9

The name of the fatty acid formed with three stearic acids becomes glyceryl tristearate. The common name of this compound is tristearin.

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 agains a concentration gradient.

Mixed Triacylglycerols P. 9

Triacylglycerol may contain different fatty acids, such as the triacylglycerol made from stearic, oleic, and palmetic acids.

Triacylglycerols: Energy Storage

Triacylglycerols are the major form of energy storage for animals. -Animals that hibernate eat large quantities of plants, seeds, and nuts that are high in calories. -As the external temperature drops, the animal goes into hibernation and the body temperature drops to nearly freezing, reducing cellular activity, respiration, and heart rate. -During hibernation, the animal's stored fat in the form of triacylglycerols is its only source of energy.

Percent Saturated and Unsaturated Fatty Acids in Fats and Oils P. 12

Vegetable oils have low melting points because they have higher percentage of unsaturated fatty acids than do animal fats.

Waxes P. 8

WAXES are -esters of saturated fatty acids and long-chain alcohols, each containing from 14 to 30 carbon atoms. -coatings that prevent loss of water by leaves of plants.

15.2 Fatty Acids

We might think of saturated fatty acids as chips with regular shapes that stack closely together in a can. Similarly, irregularly shaped chips would be like unsaturated fatty acids that do not fit closely together.

Hydrogenation Reactions P. 13

When hydrogen adds to all of the double bonds of glyceryl trioleate (triolein) using a nickel catalyst, the product is the saturated fat glyceryl tristearate (tristearin). In commercial HYDROGENATION, -the addition of hydrogen is stopped before all the double bonds in a liquid vegetable oil become completely saturated. -the partial hydrogenation of a liquid vegetable oil changes it to a soft, semisolid fat. -the more saturated product has a higher melting point.