lipids 1. lipids are biomolecules that are nonpolar soluble in organic solvents but not in water....
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Structures of Lipids 3TRANSCRIPT
Lipids
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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
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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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Fats and Other Lipids
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
Fats and Other Lipids
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.
Fats and Other Lipids
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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Fluid Mosaic Model
77Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
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
© 2013 Pearson Education, Inc.
a. Polyglyceridesb. Monoglycerides c. Diglyceridesd. Triglyceridese. Tetraglycerides
Learning Check
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Learning Check
CH3(CH2CH=CH)5(CH2)3COOH
Eicosapentanoic acid (EPA)an Omega-3 fatty acid
cis-oleic acid
© 2013 Pearson Education, Inc.
a. Trans fatty acids b. Unsaturated fatty
acids c. Omega-3 fatty acidsd. Both a and be. Both b and c
Solution