1 © 2013 pearson education, inc. chapter 17, section 1 general, organic, and biological chemistry...

General, Organic, and Biological Chemistry

Fourth EditionKaren Timberlake

17.1Lipids

Chapter 17Lipids

Lectures

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 nonpolar organic solvents. natural components of cell membranes, fat-soluble

vitamins, and steroid hormones.

Lipids

There are 2 types of lipids; those that contain the structural component of a fatty

acid; and

those that contain the structural component of a four member steroid molecule.

Types of Lipids

The lipids that contain fatty acids are waxes, fats and oils (triacylglycerols), glycerophospholipids, and prostaglandins.

The types of lipids that do not contain fatty acid chainsare steroids.

Types of Fatty Acid Lipids

Learning Check

Which lipids contain the alcohol glycerol?

A. steroids and waxes

B. triacylglycerols and glycerophospholipids

C. sphingolipids and glycerophospholipids

D. glycerophospholipids and waxes

Solution

Which lipids contain the alcohol glycerol?

A. steroids and waxes

B. triacylglycerols and glycerophospholipids

C. sphingolipids and glycerophospholipids

D. glycerophospholipids and waxes

Answer is B. Triacylglycerols and glycerophospholipidscontain the alcohol glycerol.

17.2Fatty Acids

Chapter 17Lipids

Lectures

Fatty Acids

Fatty acids contain long-chain

hydrocarbons with a carboxylic acid.

typically contain 12 to 18 carbon atoms.

are insoluble in water. can be saturated or

unsaturated.

Fatty Acid Formulas

The formulas for fatty acids are written as condensed structural formulas. skeletal formulas.

Insert structures of lauric acid pg 600, both condensed structural formula and skeletal formulas

Saturated fatty acids have only single C—C bonds. molecules that fit closely together

in a regular pattern. have properties similar to alkanes.

Saturated Fatty Acids

Unsaturated Fatty Acids

Unsaturated fatty acids have one or more double bond. that are naturally occurring have one or more cis

double bond

insert picture of cis and trans fatty acid from top of pg 602

Monounsaturated Fatty Acids

Unsaturated fatty acids with one double bond are called monounsaturated fatty acids.

Insert table 17.1 monounsaturated fatty acids.

Polyunsaturated Fatty Acids

Unsaturated fatty acids with more than one double bond are called polyunsaturated fatty acids.

Insert table 17.1 polyunsaturated fatty acids.

Properties of Saturated Fatty AcidsSaturated fatty acids fit closely together in a

regular pattern. have significant

dispersion forces between chains.

have higher melting points.

are solids at room temperature.

Properties of Unsaturated Fatty AcidsUnsaturated fatty acids have “kinks” in the fatty

acid chains. do not pack closely. have fewer attractions

between chains. have lower melting points. are liquids at room

temperature.

“kinks” in chain

Learning Check

Assign the melting point (mp) of −17°C, 13°C, or 69°C to each one of the following 18-carbon fatty acids, and list the fatty acids in order from highest to lowest melting point. Explain.

A. oleic acid

B. stearic acid

C. linoleic acid

Solution

Stearic acid is saturated and would have a higher melting point than the unsaturated fatty acids. Oleic acid, which has one double bond, has a higher mp than linoleic acid, which has two double bonds.

B. stearic acid mp 69°C saturatedA. oleic acid mp 13°C unsaturated with one

double bond C. linoleic acid mp −17°C unsaturated with two

double bonds

Prostaglandins

Prostaglandins have 20 carbon atoms in their fatty acid chains. differ by the substituents attached to the 5-carbon

Prostaglandins and Physiological Effects

Prostaglandins have potent physiological effects. Some increase blood pressure. Some lower blood pressure. Some stimulate contractions and relaxation of smooth

muscle in the uterus during the birth process and menstrual cycle.

When tissues are injured, arachidonic acid in the bloodis converted to PGE1 and PGF2 that produceinflammation and pain in the area.

NSAIDs and Prostaglandins

Several nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin, block production of prostaglandins decreasing pain, inflammation, and fever.

Insert Picture of arachidonic acid conversion, top page 605.

NSAIDs and Prostaglandins

Other NSAIDs include naproxen (Aleve and Naprosyn), ketoprofen (Actron), and nabumetone (Relafen).

Long-term use of such products can result in liver, kidney, and gastrointestinal damage.

Omega-3 and Omega-6 Fatty Acids

Fish and vegetable oils have high levels of unsaturated fats. In vegetable oils, they are mostly omega-6 with

the first at C6.

Linoleic acid

In fish oils, they are mostly omega-3 with the first at C3. CH3─CH2─(CH═CH─CH2)3─(CH2)6─COOH 1 3

Linolenic acid

Omega-6 and Omega-3 Fatty Acids

Omega-3 Fatty Acids

Omega-3 fatty acids lower the tendency of blood platelets to stick

together, thereby reducing the possibility of blood clots.

can help reduce risk of heart disease. are found in salmon, tuna, and herring.

Learning Check

Draw the condensed structural formulas for each of the fatty acids with 10 carbon atoms that follow.

A. saturated

B. monounsaturated omega-3

C. monounsaturated omega-6

Solution

Draw the condensed structural formulas for each of the fatty acids with 10 carbon atoms that follow.

A. saturated

CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—CH2—COOH

B. monounsaturated omega-3

C. monounsaturated omega-6

17.3Waxes and

Triacylglycerols

Chapter 17Lipids

Lectures

Waxes are esters of saturated fatty acids and long-chain alcohols

each containing 14 to 30 carbon atoms. coatings that prevent loss of water from leaves of plants.

Typical Waxes

Fats and Oils: Triacylglycerols

Fats and oils are also called triacylglycerols. triesters of glycerol. produced by esterification. formed when the hydroxyl

groups of glycerol react with the carboxyl groups of fatty acids.

a major form of energy storage for animals.

Insert picture of polar bear pg 608

In a triacylglycerol, glycerol forms ester bonds with three fatty acids.

Triacylglycerols

Insert structure top pg 608 as shown:

Formation of a Triacylglycerol

Most naturally occurring fats and oils are mixed triacylglycerols that contain glycerol bonded by ester bonds to two or three different fatty acids, typically palmitic acid, linoleic acid, and stearic acid.

One possible structure follows.

Learning Check

What are the fatty acids in the following triacylglycerol?

CH2 (CH2)12 CH3

CH CH CH (CH2)7 CH3O (CH2)7C

O (CH2)16 CH3C

Solution

Stearic acid

Oleic acid

Myristic acidCH2 (CH2)12 CH3

CH CH CH (CH2)7 CH3O (CH2)7C

O (CH2)16 CH3C

Learning Check

Draw the condensed structural formula for glyceryl tripalmitoleate (tripalmitolein).

Solution

Draw the condensed structural formula for glyceryl tripalmitoleate (tripalmitolein).

Melting Points of Fats and Oils

A triacylglycerol that is usually called a fat is solid at room temperature. is prevalent in meats, whole milk, butter, and cheese.

A triacylglycerol that is usually called an oil is liquid at room temperature. is prevalent in plants, such as olive and safflower.

Oils with Unsaturated Fatty Acids

Oils have more unsaturated fats. have cis double bonds that cause “kinks” in the fatty

acid chains. cannot pack triacylglycerol molecules as closely

together as in fats. have lower melting points than do saturated fats. are liquids at room temperature.

Triacylglycerol with Unsaturated Fatty AcidsUnsaturated fatty acid chains have kinks that do not allow close packing, such as those in olive oil.

Saturated and Unsaturated Fatty Acids In Fats and Oils

Vegetable oils are liquids at room temperature because they have a higher percentage of unsaturated fatty acids than do animal fats.

17.4Chemical Properties of

Triacylglycerols

Chapter 17Lipids

Lectures

The chemical reactions of triacylglycerols are similarto 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.

Chemical Properties of Triacylglycerols

Hydrogenation of Glyceryl Trioleate

In a hydrogenation reaction, H2 adds across the double bond to form a carbon–carbon single bond.

Hydrogenation of Oils

The hydrogenation of oils converts double bonds to single bonds, adds hydrogen (H2) to the carbon atoms of double

bonds, increases the melting point, and produces solids, such as margarine and shortening

Learning Check

Which of the following products is obtained from the complete hydrogenation of glyceryl trioleate?

A. glycerol and 3 oleic acids

B. glyceryltristearate

C. glycerol and 3 stearic acids

Which of the following products is obtained from the complete hydrogenation of glyceryl trioleate?

B. glyceryltristearate

Solution

Olestra, a Fat Substitute

Olestra is used in foods as an artificial fat. composed of 6–8 long-chain fatty acids attached by

ester links to a sucrose (not glycerol) molecule. not broken down in the intestinal tract.

Unsaturated fatty acids can be cis with bulky groups on the same side of , or

trans with bulky groups on opposite sides of .

Cis and Trans Fatty Acids

Trans Fatty Acids and Hydrogenation Trans fatty acids are formed during hydrogenation when cis double

bonds are converted to an undesirable side product with a trans double bond.

in the body behave like saturated fatty acids. are estimated to make up 2–4% of our total

calories.

The American Heart Association recommends the use of soft margarine, which is only slightly hydrogenated and therefore has fewer trans fatty acids.

Trans Fats

In vegetable oils, the unsaturated fats usually contain cis double

bonds. during hydrogenation, some cis double bonds are

converted to trans double bonds (more stable), causing a change in the fatty acid structure.

Formation of Trans Fats

Learning Check

Identify each statement as true (T) or false (F).

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

Identify each statement as true (T) or false (F).

T A. There are more unsaturated fats in vegetable oils.

F B. Vegetable oils have higher melting points than fats.

T C. Hydrogenation of oils converts some cis-double bonds to trans-double bonds.

T D. Animal fats have more saturated fats.

Hydrolysis

In acid or enzyme hydrolysis, water adds to the ester bonds. triacylglycerols hydrolyze forming glycerol and three

fatty acids. a strong acid, such as HCl or H2SO4, or an enzyme

catalyst is required.

Base Hydrolysis (Saponification )

In base hydrolysis (saponification), a triacylglycerol reacts with heat and a strong base. a triacylglycerol splits into glycerol and the salts of

fatty acids (soap). a solid soap that can be molded into a desired shape

is produced when NaOH is used. a softer, liquid soap is produced when KOH is used. polyunsaturated oils produce softer soaps.

Saponification

glycerol + salts of fatty acids (soap)Fat or oil + strong base

Summary of Organic and Lipid Reactions

What products are obtained from the complete hydrolysis of glyceryl trioleate?

B. glyceryl tristearate

C. glycerol and 3 stearic acids

Learning Check

What products are obtained from the complete hydrolysis of glyceryl trioleate?

Solution

Learning Check

Draw the condensed structural formula of theproduct of the following reaction.

(CH2)7 CH CH

CHCH(CH2)7

(CH2)5 CH3

Solution

CH2 (CH2)14

CH O C

(CH2)14 CH3

17.5Phospholipids

Chapter 17Lipids

Lectures

Glycerophospholipids, themost abundant lipids in cellmembranes, contain two fatty acids, which form ester

bonds with the first and second hydroxyl group of glycerol.

a third hydroxyl group, which forms an ester with phosphoric acid, which then forms another phosphoester bond with an amino alcohol.

Glycerophospholipids

Insert pictureof glycerophospholipidpg 618

Lecithin and cephalin are glycerophospholipids that are abundant in brain and nerve tissues. are found in egg yolk, wheat germ, and yeast. contain choline (in lecithins) or either ethanolamine or

serine (in cephalins).

Lecithin and Cephalin

Glycerophospholipids Contain Amino Alcohols. Three amino alcohols found in glycerophospholipids

are choline, serine, and ethanolamine. In the body, at a physiological pH of 7.4, these amino

alcohols are ionized.

Insert structures of amino alcohols pg 618 bottom

Glycerophospholipids are Polar and Nonpolar. Glycerophospholipids have both polar and nonpolar regions that allow them to

interact with polar and nonpolar substances. an ionized amino alcohol and phosphate portion,

called “the head,” which is polar and strongly attracted to water.

a hydrocarbon chain known as “the tail,” which is soluble in nonpolar substances.

Formation of GlycerophospholipidsThe formation of a glycerophospholipid occurs when ester bonds form between glycerol and two fatty acids, and two phosphoester bonds form between phosphoric acid and an ionized amino alcohol and glycerol, such as palmitic acid.

Components of GlycerophospholipidsThe components of a glycerophospholipid are choline, phosphoric acid, glycerol, and two fatty acids.

Insert structure from figure 17.6a

Components of GlycerophospholipidsIn a glycerophospholipid, a polar “head” contains the ionized amino alcohol and phosphate, while the hydrocarbon chains of two fatty acids make up the nonpolar “tails.”

Insert structure from figure 17.6b

Learning Check

Identify each as a fatty acid, triacylglycerol, amino alcohol or glycerophospholipid.

A. glyceryl trioleate

B. cephalin

C. choline

D. palmitic acid

Solution

Identify each as a fatty acid, triacylglycerol, amino alcohol or glycerophospholipid.

A. glyceryl trioleate triacylglycerol

B. cephalin glycerophospholipid

C. choline amino alcohol

D. palmitic acid fatty acid

Learning Check

Identify the components and type of glycerophospholipid. O ║CH2—O—C— (CH2)16—CH3

O ║CH2—O—C— (CH2)16—CH3

║ │CH2—O—P—O—CH2—CH−COO –

│ O–

Solution

Identify the components and type of glycerophospholipid. O ║CH2—O—C— (CH2)16—CH3

O 2 Stearic acids

║CH2—O—C— (CH2)16—CH3

║ │ Type = cephalinCH2—O—P—O—CH2—CH−COO –

│ Serine O– Phosphate Amino alcohol

Sphingosine

Sphingosine is an 18-carbon unsaturated amino alcohol.

Insert structure top pg 621

Sphingolipids

Sphingolipids are phospholipids that contain a long-chain amino alcohol called sphingosine, rather than glycerol.

Sphingomyelins

Sphingomyelins, are a group of sphingolipids in which the amine group forms an amide bond to a fatty acid,

and the hydroxyl group of sphingosine forms an ester

bond with phosphate forming another phosphoester bond to an amino alcohol, such as choline.

Sphingomyelins

Sphingomyelins, are abundant in the white matter of the myelin sheath, a coating

surrounding the nerve. cells that increase the speed of nerve impulses and

insulate and protect the nerve cells.

Multiple Sclerosis

In multiple sclerosis, sphingomyelin is lost from the myelin sheath, which

protects the neurons in the brain and spinal cord. scars form on the neurons and impair the

transmission of nerve signals.

17.6Steroids

Chapter 17Lipids

Lectures

Steroid Nucleus

Steroid molecules contain a steroid nucleus with3 cyclohexane rings, 1 cyclopentane ring,no fatty acids, anda total of four rings A, B, C, D.

The steroid nucleus is numbered from the carbon atoms in ring A to two methyl groups at 18 and 19.

Cholesterol

Cholesterol is the most important and abundant steroid in

the body. is a sterol because it contains an oxygen atom

as a hydroxyl group, –OH on carbon 3. has a double bond between carbon 5 and

carbon 6. has methyl –CH3 groups, at carbon 10 and 13.

has a carbon chain at carbon 17.

Cholesterol

Cholesterol is a component of cellular membranes, myelin sheaths, and brain and nerve tissues.

Cholesterol in the Body

Cholesterol in the body

is obtained from meats, milk, and eggs and synthesized in the liver.

clogs arteries when high levels form plaque.

A normal, open artery.

An artery clogged by cholesterol plaque

Cholesterol in Foods

A typical American diet includes 400–500 mg of cholesterol per day.

The American Heart Association has recommended no more than 300 mg of cholesterol per day.

Saturated fats in the diet may stimulate the production of cholesterol by the liver.

Learning Check

Match the components of the cholesterol molecule witheach of the following:

alkyl chain hydroxyl group

steroid nucleus methyl group

CH3CH3

Solution

Match the components of the cholesterol molecule witheach of the following:

alkyl chain hydroxyl group

steroid nucleus methyl group

CH3CH3

Bile Salts

Bile salts are synthesized from cholesterol in the liver. are stored in the gallbladder and secreted into the

small intestine. have a polar and a nonpolar region. help in the absorption of cholesterol into the intestinal

mucosa.

Sodium Glycocholate, a Bile Salt

Nonpolar region

Polar region

Gallstones

Gallstones are formed when large amounts of cholesterol

accumulate in the gallbladder. composed of almost 100% cholesterol, with some

calcium salts, fatty acids, and glycerophospholipids.

Lipoproteins

Lipoproteins are spherical particles with an outer surface of polar

proteins and glycerophospholipids that surround hundreds of nonpolar molecules of triacylglycerols and cholesteryl esters.

combine lipids with proteins and phospholipids. are soluble in water because the surface consists of

polar lipids.

Lipoproteins

A spherical lipoprotein particle surrounds nonpolar lipids with polar lipids and protein for transport to body cells.

Types of Lipoproteins

Lipoproteins differ in density, composition, and function

and include chylomicrons, very low-density lipoprotein (VLDLs); low-density lipoproteins (LDLs), which carry

cholesterol to the tissues; and high-density lipoproteins (HDLs) that pick up

cholesterol from the tissues and carry it to the liver.

LDLs transport cholesterol to tissues where it can be used

for synthesis of cell membranes and steroid hormones.

deposit cholesterol in the arteries in the form of plaque when cholesterol levels exceed levels needed by tissues.

called “bad” cholesterol for their contribution to heart disease.

HDLs are more dense than LDLs due to the increased

amount of protein present. pick up cholesterol from the tissues and carry it to the

liver, where it can be converted to bile salts, which are eliminated from the body,

are called “good” cholesterol.

VLDLs carry the triacylglycerols synthesized in the liver to the adipose tissues for storage.

Insert fig 17.10 pg 626

Lipid Panel

A lipid panel is a blood test that measures serum lipidlevels including cholesterol triglycerides high-density lipoprotein (HDL) low-density lipoprotein (LDL)

The results of a lipid panel are used to evaluate apatient’s risk of heart disease.

Lipid Panel

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.

Steroid Hormones

Adrenal Corticosteroids

Adrenal corticosteroids are steroid hormonesproduced by the adrenal glands located on the topof each kidney and include aldosterone, which regulates electrolytes and

water balance by the kidneys; cortisol, released under stress to increase blood

sugar and regulate carbohydrate, fat, and protein metabolism; and

prednisone, a synthetic corticosteroid, derived from cortisone, used for reducing inflammation, treating asthma and rheumatoid arthritis.

Adrenal Corticosteroids

Learning Check

Identify each of the following as a steroid, triacylglycerol, phospholipid, or 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 steroid

B. glycerol, 2 fatty acids, phospholipid

phosphate, and choline

C. glyceryl tristearate triacylglycerol

D. sphingosine, fatty acid, sphingolipid

phosphate, and choline

E. estradiol steroid

F. bile salts steroid

G. lipids in plasma phospholipid

membranes sphingolipid

17.7Cell Membranes

Chapter 17Lipids

Lectures

Cell Membranes

Cell membranes have a lipid bilayer that separates cellular contents from the external

environment. contains two layers of glycerophospholipids arranged

with their hydrophilic heads at the outer and inner membrane surfaces and their hydrophobic tails in the center.

Fluid Mosaic Model of Cell MembranesThe 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.

Fluid Mosaic Model

Transport Pathways Through Cell MembranesThe transport of substances through cell membranesinvolves 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; and active transport, which moves ions against a

concentration gradient.

Transport Pathways Through Cell Membranes

Learning Check

What is the transport of particles across a cell membranefrom high concentration to low concentration called?

A. facilitated transport

B. diffusion (passive transport)

C. active transport

Solution

What is the transport of particles across a cell membranefrom high concentration to low concentration called?

A. facilitated transport

B. diffusion (passive transport)

C. active transport

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