Lipids 1. Lipids are Biomolecules that are nonpolar Soluble in organic solvents but not in water....

Lipids

1

LipidsLipids are• Biomolecules that are nonpolar

– Soluble in organic solvents but not in water.• Named for the Greek word lipos, (means “fat”)

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Types of lipids we’ll look at:• Fatty acids.• Waxes.• Fats and oils (triglycerides = triacylglycerols).• Glycerophospholipids.• Steroids.

Structures of Lipids

3

Fatty AcidsFatty acids • Are long-chain

carboxylic acids.• Typically contain 12-

18 carbon atoms.• Are insoluble in

water.• Can be saturated or

unsaturated.

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Fatty Acid FormulasThe 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

5

OH

O

Palmitic Acid

Fatty Acid Formulas

Saturated Fatty AcidsSaturated 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.

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Some Saturated Fatty Acids

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Fats and Other Lipids

Saturated fatty acids have no carbon-to-carbon double bonds.

Monounsaturated fatty acids have one carbon-to-carbon double bond.

Polyunsaturated fatty acids have two or more carbon-to-carbon double bonds.

Unsaturated Fatty AcidsUnsaturated fatty acids • Have one or more double C=C bond• Typically contain cis double bonds.

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Unsaturated Fatty AcidsUnsaturated 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.

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“kinks” in chain

Unsaturated Fatty Acids

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Melting Points of Some Fatty Acids

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Learning Check

Assign the melting points of –17°C, 13°C, and 69°C to the correct fatty acid. Explain.

stearic acid (18 C’s) saturatedoleic acid (18 C’s) one double bondlinoleic acid (18 C’s) two double

bonds

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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 saturatedoleic acid mp 13°C

linoleic acid mp -17°C most unsaturated

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Omega-6 and Omega 3- Fatty Acids

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Fatty acids In vegetable oils are mostly omega-6 with the first C=C at C6 from the end. 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 from the end. linolenic acid CH3─CH2─(CH=CH─CH2)3─(CH2)6─COOH 3

Some Omega-6 and Omega-3 Fatty Acids

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Learning CheckMatch the following fatty acids with a term that best

describes them:A. Polyunsaturated D. SaturatedB. monounsaturated omega-6 E. monounsaturatedC. monounsaturated omega-3

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

CH3—CH2—CH2—CH2—CH2—CH2—CH=CH—CH2—COOH

CH3—CH2—CH2—CH2—CH2—CH=CH—CH2—CH2—COOH

CH3—CH2—CH2—CH2—CH2—CH=CH—CH2—CH=CH—CH2—CH=CH—CH2—COOH

SolutionMatch the following fatty acids with a term that best

describes them:A. Polyunsaturated D. SaturatedB. monounsaturated omega-6 E. monounsaturatedC. monounsaturated omega-3

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

CH3—CH2—CH2—CH2—CH2—CH2—CH=CH—CH2—COOH

CH3—CH2—CH2—CH2—CH2—CH=CH—CH2—CH2—COOH

CH3—CH2—CH2—CH2—CH2—CH=CH—CH2—CH=CH—CH2—CH=CH—CH2—COOH A

B

E

D

Waxes, Fats, and Oils

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WaxesWaxes are• Esters of saturated fatty acids and long-chain

alcohols.• Coatings that prevent loss of water by leaves of

plants.

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Fats and Oils: TriacylglycerolsFats and oils are• Also called triglycerides or

triacylglycerols.• Esters of glycerol.• Produced by esterification.• Formed when the hydroxyl

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

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TriglyceridesIn a triglyceride (triacylglycerol), • Glycerol forms ester bonds with three

fatty acids.

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Triglycerides are triesters of glycerol and fatty acids.

Formation of a Triacylglycerolglycerol + 3 fatty acids triacylglycerol

OHCH2

OH

OHCH2

CHO

(CH2)14CH3CHO

O

(CH2)14CH3CHO

O

(CH2)14CH3CHO

O

O

C (CH2)14CH3

CH O

O

C (CH2)14CH3

CH2 O

O

C (CH2)14CH3

CH2

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+ 3H2O

+

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

(CH2)12CH3

O

C

CH(CH2)7CH3(CH2)7CH

O

C

O

(CH2)16CH3C

O

O

OCH2

CH2

CH

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A. Palmitic Acid, Oleic Acid, Lauric AcidB. Stearic Acid, Oleic Acid, Lauric AcidC.Stearic Acid, Oleic Acid, Myristic AcidD.Palmitic Acid, Oleic Acid, Lauric AcidE. None of these

Solution

(CH2)12CH3

O

C

CH(CH2)7CH3(CH2)7CH

O

C

O

(CH2)16CH3C

O

O

OCH2

CH2

CH

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Stearic acid

Oleic acid

Myristic acidA. Palmitic Acid, Oleic Acid, Lauric AcidB. Stearic Acid, Oleic Acid, Lauric AcidC.Stearic Acid, Oleic Acid, Myristic AcidD.Palmitic Acid, Oleic Acid, Lauric AcidE. None of these

Melting Points of Fats and OilsA triacylglycerol that is a fat • Is solid at room temperature.• Solid fats have a high proportion of saturated fatty

acids.• Is prevalent in meats, whole milk, butter, and cheese.

A triacylglycerol that is an oil• Is liquid at room temperature.• Liquid oils have a high proportion of unsaturated fatty

acids.• Is prevalent in plants such as olive and safflower.

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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 close

together as in fats.• Have lower melting points than saturated fats.• Are liquids at room temperature.

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Olive OilContains a high percentage of oleic acid, which is a monounsaturated fatty acid with one cis double bond.

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Unsaturated fatty acid chains have kinks that do not allow close packing.

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Saturated & Unsaturated FAs In Fats and Oils


Iodine number is a measure of the degree of unsaturation of a fat or oil. Iodine number is the number of grams of I2 that are consumed by 100 g of a fat or oil.


Iodine Number

Learning Check Which of the following fats or Oils would have the highest

Iodine number (consume the most I2 or Br2)?

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A. Olive OilB. ButterC. Coconut OilD. Canola OilE. Corn Oil

SolutionWhich of the following fats or Oils would have the highest

Iodine number (consume the most I2 or Br2)?

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A. Olive OilB. ButterC. Coconut OilD. Canola OilE. Corn Oil

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.

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Hydrogenation of Oils• Adds hydrogen (H2) to the C’s of double bonds.• Converts C=C’s to C-C’s. • Increases the melting point.• Produces solids (ie margarine and shortening).

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Ni + 3H2

glyceryl tripalmitoleate

(tripalmitolean)

glyceryl tripalmitate

(tripalmitin)

Hydrogenation

CH(CH2)7CH3(CH2)5CH

O

C

CH(CH2)7CH3(CH2)5CH

O

C

CH(CH2)7CH3(CH2)5CH

O

C

O

O

OCH2

CH2

CH

O

(CH2)14CH3C

O

(CH2)14CH3C

O

(CH2)14CH3C

O

O

OCH2

CH2

CH

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Learning CheckWhat product(s) is obtained from the completehydrogenation of glyceryl trioleate?

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1. Glycerol and 3 oleic acids2. Glyceryltristearate3. Glycerol and 3 stearic acids

C

O

C

C

CH

H

H

H

H

O

O

O

C

O

C

O

glyceryl trioleate

1. Glycerol and 3 oleic acids2. Glyceryltristearate3. Glycerol and 3 stearic acids

C

O

C

C

CH

H

H

H

H

O

O

O

C

O

C

O

glyceryl trioleate C

O

C

C

CH

H

H

H

H

O

O

O

C

O

C

O

H2, Ni

glyceryl tristerate

SolutionWhat product(s) is obtained from the completehydrogenation of glyceryl trioleate?

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Olestra, A Fat SubstituteOlestra 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.

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Trans Fatty Acids and Hydrogenation Trans fatty acids• Formed during hydrogenation when cis double bonds trans.• In the body behave like saturated fatty acids. • Estimated to make up 2-4% of our total Calories. • Reported to raise LDL-cholesterol and lower HDL-cholesterol.

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C

O

C

C

CH

H

H

H

H

O

O

O

C

O

C

O

4 H2, Ni

C

O

C

C

CH

H

H

H

H

O

O

O

C

O

C

O

Learning Check

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(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. 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.

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T

T

T

F

HydrolysisIn hydrolysis, • Triacylglycerols split into glycerol and 3 fatty acids.• An acid or enzyme catalyst is required.

OCH2

OCH

OCH2

OHCH2

OHCH

OHCH2

O

(CH2)14CH3CHO

H2OO

(CH2)14CH3C

O

(CH2)14CH3C

O

(CH2)14CH3C

H+

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+3

+ 3

HydrolysisIn hydrolysis, • Triacylglycerols split into glycerol and 3 fatty acids.• An acid or enzyme catalyst is required.

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C

O

C

C

CH

H

H

H

H

O

O

O

C

O

C

O

glyceryl trioleate

H+, H2O

C

C

CH

H

H

H

H

O

O

O H

H

H

C

O

+ 3 HO

Saponification and SoapSaponification = Basic Hydrolysis• 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).

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C

O

C

C

CH

H

H

H

H

O

O

O

C

O

C

O

glyceryl trioleate

NaOH

C

C

CH

H

H

H

H

O

O

O H

H

H

C

O

+ 3 Na+ -O

Sodium OleateA “soap”

Saponification

Na+ -O

O

C (CH2)14CH3

O

O

C (CH2)14CH3

CH O

O

C (CH2)14CH3

CH2 O

O

C (CH2)14CH3

CH2

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+ 3NaOH

3

OH

CH OH

CH2 OH

CH2

+“soap”

Learning Check

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What products are obtained from the complete hydrolysis of glyceryl tripalmitoleate?1. Glycerol and 3 palmitoleic acids2. Glyceryl tripamitate3. Glycerol and 3 palmitic acids

Solution

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What products are obtained from the complete hydrolysis of glyceryl tripalmitoleate?1. Glycerol and 3 palmitoleic acids2. Glyceryl tripamitate3. Glycerol and 3 palmitic acids

Learning CheckWrite the product of the following reaction.

OCH2

O

O

CH2

CH

CH(CH2)7CH3(CH2)5CH

O

CO

CH(CH2)7CH3(CH2)5CHCO

C CH(CH2)7CH3(CH2)5CH

H2Ni

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+ 3

SolutionWrite the product of the following reaction.

OCH2

O

O

CH2

CH

CH(CH2)7CH3(CH2)5CH

O

CO

CH(CH2)7CH3(CH2)5CHCO

C CH(CH2)7CH3(CH2)5CH

H2Ni

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+ 3

O

O

C (CH2)14CH3

CH O

O

C (CH2)14CH3

CH2 O

O

C (CH2)14CH3

CH2

GlycerophospholipidsGlycerophospholipids are• The most abundant lipids in cell membranes. • Composed of glycerol, two fatty acids, phosphate

and an amino alcohol.

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Glycerol

PO4Amino alcohol

Fatty acid

Fatty acid

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 54

Structure and Polarity of A Glycerophospholipid

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Lecithin and CephalinLecithin and cephalin are glycerophospholipids• Abundant in brain and nerve tissues.• Found in egg yolk, wheat germ, and yeast.

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Learning CheckIdentify each as a

A. fatty acid B. triacylglycerolC. amino alcohol D. glycerophospholipid

1. glyceryl trioleate 2. cephalin 3. choline4. palmitic acid

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SolutionIdentify each as a

A. fatty acid B. triacylglycerolC. amino alcohol D. glycerophospholipid

1. glyceryl trioleate2. cephalin3. choline4. palmitic acid

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B. triacylglycerol D. glycerophospholipid C. amino alcohol A. fatty acid

Learning CheckIdentify the components and type of glycerophospholipid O ║CH2−O −C −(CH2)16 −CH3

O ║CH−O −C −(CH2)16 −CH3

+

O NH3

│║CH2−O −P −O − CH2−CH−COO-

│ O-

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SolutionIdentify the components and type of glycerophospholipid O ║CH2−O −C −(CH2)16 −CH3

O 2 stearic acids ║CH−O −C −(CH2)16 −CH3

+

O NH3

│║ type = cephalinCH2−O −P −O − CH2−CH−COO-

│ serine O-

phosphate amino alcohol

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Steroid NucleusA steroid nucleus consists of• 3 cyclohexane rings.• 1 cyclopentane ring.• No fatty acids.

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steroid nucleus

CholesterolCholesterol• Is the most abundant steroid in the body. • Has methyl CH3- groups, alkyl chain, and -OH

attached to the steroid nucleus.

CH3

CH3CH3

CH3

HO

CH3

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Cholesterol in the BodyCholesterol 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.

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A normal, open artery.

An artery clogged by cholesterol plaque

Cholesterol in FoodsCholesterol is • Synthesized in the

liver. • Obtained from

foods. • Considered

elevated if plasma cholesterol exceeds 200 mg/dL.

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Learning Check

CH3

CH3CH3

CH3

HO

CH3

AC

B

D

Match the components of the cholesterol molecule withthe following:1. ___ carbon chain 3. ___hydroxyl group2. ___ steroid nucleus 4. ___methyl group

SolutionMatch the components of the cholesterol molecule withthe following:1. ___ carbon chain 3. ___hydroxyl group2. ___ steroid nucleus 4. ___methyl group

CH3

CH3CH3

CH3

HO

CH3

AC

B

D

ABC

D

Bile SaltsBile salts• Synthesized in the liver from cholesterol.• Stored in the gallbladder and secreted into the small intestine.• Have a polar and a nonpolar region• Mix with fats to break them part (Emulsify fat particles)

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OH

COO- Na+CH2

H

N

O

COHCH3

CH3

HO

CH3

glycine, an amino acid cholic acid, a bile acid

sodium glycocholate, a bile salt

LipoproteinsLipoproteins• Combine lipids with proteins and phospholipids.• Are soluble in water because the surface consists

of polar lipids.

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Types of LipoproteinsLipoproteins• Differ in density, composition, and function.• Include low-density lipoprotein (LDLs) and high-

density lipoprotein (HDLs).

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Transport of Lipoproteins in the Body

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Steroid HormonesSteroid hormones• Are chemical

messengers in cells.• Are produced from

cholesterol. • Include sex hormones

such as androgens (testosterone) in males and estrogens (estradiol) in females.

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Anabolic SteroidsAnabolic steroids• Are derivatives of testosterone.• Are used illegally to increase muscle mass.• Have side effects including fluid retention, hair

growth, sleep disturbance, and liver damage.

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Learning Check Identify each as a 1. fatty acid 2. steroid 3. triacylglycerol4. phospholipid

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A. ____ cholesterolB. ____ glycerol, 2 fatty acids, phosphate, & cholineC. ____ glyceryl tristearateD. ____estradiolE. _____bile saltsF. ____ lipids in plasma membranes

SolutionIdentify each as a A. fatty acid B. steroid C. triacylglycerolD. phospholipid

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1. ____ cholesterol2. ____glycerol, 2 fatty acids, phosphate, & choline3. ____glyceryl tristearate4. ____estradiol5. ____bile salts6. ____ reacts with lye to make soap

CB

DB

BA or C

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.

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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.

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Eleventh Edition

Nancy Gardner

CHEMISTRYAN INTRODUCTION TO GENERAL, ORGANIC,

AND BIOLOGICAL CHEMISTRY

CRS “Clicker” QuestionsChapter 15

Lipids

© 2012 Pearson Education, Inc.

15.1 All of the following lipids can be hydrolyzed to form fatty acids except ________.

A. waxesB. oilsC. glycerophospholipidsD. steroids

Learning Check

15.2 Which of the following fatty acids is saturated?

A. linolenic acidB. palmitoleic acidC. steric acidD. oleic acid

Learning Check

15.3 What characterizes a triacylglycerol?

A. the presence of three –OH groupsB. long-chain fatty acids with double bondsC. three fatty acids connected to glycerol by

ester bondsD. the presence of a benzene ring

Learning Check

15.4 Hydrogenation of unsaturated fatty acids produces what undesired side product?

A. cis-fatty acidsB. trans-fatty acidsC. saturated fatty acidsD. unsaturated fatty acids

Learning Check

15.5 What groups replace a fatty acid in a glycerophospholipid?

A. phosphate and an alcoholB. phosphate and a ketoneC. phosphate and an amino alcoholD. phosphate and an aldehyde

Learning Check

15.6 What characterizes a steroid compound?

A. amino groupsB. three fused ringsC. four fused ringsD. long carbon chains linked by an ester

Learning Check

15.7 Where are the hydrophobic ends of the glycerophospholipids found in the cell?

A. facing each other inside the cell wallB. facing outward on the cell wallC. in the cytoplasmD. in the nucleus

Learning Check

15.10 Which fatty acid is not an essential fatty acid?

A. oleic acidB. linoleic acidC. linolenic acidD. arachidonic acid

Learning Check

15.11 Of the following, which one is NOT an omega-3 fatty acid?

A. linoleic acidB. linolenic acidC. eicosapentaenoic acidD. docosahexaenoic acid

Learning Check

15.12 Which of the following is the correct structure for a 10-carbon fatty acid called capric acid?

A.

B.

C.

D.

OH

O

OH

O

OH

O

O

O

Learning Check

15.13 What is the major form of energy storage for animals that hibernate?

A. triacylglycerolsB. steroidsC. alkenesD. carbohydrates

Learning Check

15.14 Which lipid in plasma has the most “bad” cholesterol?

A. triacylglycerolB. phospholipidsC. cholesterolD. cholesteryl esters

Learning Check


a. Polyglyceridesb. Monoglycerides c. Diglyceridesd. Triglyceridese. Tetraglycerides

Learning Check


a. Polyglyceridesb. Monoglycerides c. Diglyceridesd. Triglyceridese. Tetraglycerides

Solution

a. Trans fatty acids b. Unsaturated fatty acids c. Omega-3 fatty acidsd. Both a and be. Both b and c

CH3(CH2CH=CH)5(CH2)3COOH


Learning Check

CH3(CH2CH=CH)5(CH2)3COOH

Eicosapentanoic acid (EPA)an Omega-3 fatty acid

cis-oleic acid


a. Trans fatty acids b. Unsaturated fatty

acids c. Omega-3 fatty acidsd. Both a and be. Both b and c

Solution

Lipids 1. Lipids are Biomolecules that are nonpolar Soluble in organic solvents but not in water....

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Transcript of Lipids 1. Lipids are Biomolecules that are nonpolar Soluble in organic solvents but not in water....