Transcript
Chapter 15
Lipids
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.
15.1 Lipids 15.2 Fatty Acids
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Types of Lipids
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Classes of Lipids
The types of lipids containing fatty acids are • waxes • fats and oils (triacylglycerols) • glycerophospholipids • prostaglandins The types of lipids that do not contain fatty acids are • steroids
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Saturated and Unsaturated Fatty Acids
Fatty Acids Fatty acids are • long-chain carboxylic acids. • typically 12-18 carbon atoms. • insoluble in water. • saturated or unsaturated.
Fatty acids are • saturated with all single C–C bonds. • unsaturated with one or more double C=C bonds. Olive oil contains 84% unsaturated fatty acids and 16% saturated fatty acids.
O C OH palmitic acid, a saturated acid O C OH
palmitoleic acid, an unsaturated acid
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Properties of Unsaturated Fatty Acids
Properties of Saturated Fatty Acids
Unsaturated fatty acids • contain one or more cis double C=C bonds. • 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.
Saturated fatty acids • contain only single C–C bonds. • are closely packed. • have strong attractions between chains. • have high melting points. • are solids at room temperature.
HOOC H
COOH
H C C
“kinks” in chain H
COOH COOH COOH
C C
H
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Melting Points of Some Saturated Fatty Acids
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Melting Points of Some Unsaturated Fatty Acids
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Learning Check
Solution
Assign the melting points of –17 °C, 13 °C, and 69 °C to the correct fatty acid. Explain. stearic acid (18 C) oleic acid (18 C) linoleic acid (18 C)
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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
saturated one double bond two double bonds
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Chapter 15
Lipids
Waxes Waxes are • esters of saturated fatty acids and long-chain alcohols. • coatings that prevent loss of water by leaves of plants.
15.3 Waxes, Fats, and Oils
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Fats and Oils: Triacylglycerols
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Triacylglycerols In a triacylglycerol, glycerol forms ester bonds with three fatty acids.
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.
Ester Bonds
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Formation of a Triacylglycerol Glycerol CH2
+
OH
CH
OH
CH2
OH
+
three fatty acids HO C O
(CH2)14CH3
HO C O
(CH2)14CH3
HO C
(CH2)14CH3
Learning Check What are the fatty acids in the following triacylglycerol?
triacylglycerol
O
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O CH2
O
CH2 O C
(CH2)14CH3
CH
(CH2)14CH3 + 3H O 2
CH2
O
O CH O C
C
(CH2)16CH3
O
O
O
C (CH2)7CH CH(CH2)7CH3 O C
(CH2)12CH3
O CH2 O C
(CH2)14CH3 17
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Solution
Melting Points of Fats and Oils
O CH2
O
CH
O
CH2
O
C
(CH2)16CH3
A fat • is usually solid at room temperature. • is prevalent in meats, whole milk, butter, and cheese. An oil • is usually liquid at room temperature. • is prevalent in plants such as olive and safflower.
Stearic acid
O C (CH2)7CH CH(CH2)7CH3 O C
(CH2)12CH3
Oleic acid
Myristic acid
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Diagram of Triacylglycerol with Unsaturated Fatty Acids
Oils with Unsaturated Fatty Acids Oils • have more unsaturated fats. • have cis double bonds that cause “kinks” in the fatty acid chains. • with “kinks” in the chains do not allow the triacylglycerol molecules to pack closely. • have lower melting points than saturated fatty acids. • are liquids at room temperature.
Unsaturated fatty acid chains with kinks cannot pack closely.
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Percent Saturated and Unsaturated Fatty Acids In Fats and Oils
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Chapter 15
Lipids
15.4 Chemical Properties of Triacylglycerols
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Chemical Properties of Triacylglycerols
Hydrogenation of Oils
The chemical reactions of triacylglycerols are similar to those of alkenes and esters.
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.
• 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
Learning Check What products are obtained from the complete hydrogenation of glyceryl trioleate?
O CH2
O
C
Ni
(CH2)5CH CH(CH2)7CH3
+ 3H2
O CH
O
CH2
O
C (CH2)5CH CH(CH2)7CH3 CH2 O C
(CH2)5CH CH(CH2)7CH3
Glyceryl tripalmitoleate (tripalmitolean)
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O
O C
(CH2)14CH3
O
CH
O
CH2
O
C (CH2)14CH3 O C
1. Glycerol and 3 oleic acids 2. Glyceryltristearate 3. Glycerol and 3 stearic acids
(CH2)14CH3
Glyceryl tripalmitate (tripalmitin) 27
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OlestraTM, a Fat Substitute
Solution
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.
What products are obtained from the complete hydrogenation of glyceryl trioleate? 2. Glyceryltristearate
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Hydrogenation and Trans Fatty Acids
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
Most naturally occurring fatty acids have cis double bonds. • During hydrogenation, some cis double bonds are converted to trans double bonds.
C=C H
• In the body, trans fatty acids behave like saturated fatty acids.
H
• It is estimated that 2-4% of our total Calories is in the form of trans fatty acid.
• trans have bulky groups on opposite sides of C=C. H CH3─ (CH2)5 C=C H
(CH2)7─ COOH
• Several studies reported that trans fatty acids raise LDLcholesterol and lower HDL-cholesterol.
trans
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Hydrogenation of Unsaturated Fats
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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.
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Solution
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Hydrolysis In hydrolysis, • triacylglycerols split into glycerol and three fatty acids. • an acid or enzyme catalyst is required.
(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.
O CH2
O
C O
CH
O
C (CH2)14CH3 + H2O O
CH2
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O
C
(CH2)14CH3
(CH2)14CH3
H+ CH2
OH
CH
OH
CH2
OH
O
+
HO C
(CH2)14CH3
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Saponification and Soap
Saponification O
Saponification • 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.
CH2 O C
(CH2)14CH3
O CH O C
(CH2)14CH3
+ 3NaOH
O CH2 O C
CH2 OH (CH2)14CH3
CH OH
O
+ 3Na+ -O C (CH2)14CH3 “soap” CH2 OH 37
Learning Check
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Solution
What products are obtained from the complete hydrolysis of glyceryl trioleate?
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
1. Glycerol and 3 oleic acids
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Learning Check
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Solution
Write the product of the following reaction:
O
O CH2 O C O
CH2
O
C (CH2)14CH3 O
CH
O
C (CH2)14CH3 O
(CH2)5CH CH(CH2)7CH3
CH
O
C (CH2)5CH CH(CH2)7CH3 + 3H2 O
CH2
O
C
(CH2)5CH
Ni
CH2
CH(CH2)7CH3
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O
C
(CH2)14CH3
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Chapter 15
Lipids
Glycerophospholipids
15.5 Glycerophospholipids
Glycerophospholipids are • the most abundant lipids in cell membranes. • composed of glycerol, two fatty acids, phosphate, and an amino alcohol.
Fatty acid
Fatty acid
Fatty acid
Glycerol
Glycerol PO4
Fatty acid
Amino alcohol PO4
Amino alcohol
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Structure and Polarity of a Glycerophospholipid
Polarity of Glycerophospholipids A glycerophospholipid has • two nonpolar fatty acid chains. • a phosphate group and a polar amino alcohol. CH3 │+ HO−CH2−CH2−N−CH3 │ Choline CH3
+
HO−CH2−CH2−NH3 Ethanolamine
+
NH3 │ HO−CH2−CH−COO− Serine
Amino alcohols
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Lecithin and Cephalin
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Learning Check Identify each as A. fatty acid C. amino alcohol
Lecithin and cephalin are glycerophospholipids • abundant in brain and nerve tissues. • found in egg yolk, wheat germ, and yeast.
B. triacylglycerol D. glycerophospholipid
1. glyceryl trioleate 2. cephalin 3. choline 4. palmitic acid
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Solution Identify each as A. fatty acid C. amino alcohol 1. glyceryl trioleate 2. cephalin 3. choline 4. palmitic acid
Chapter 15
Lipids
15.6 Steroids: Cholesterol and Steroid Hormones
B. triacylglycerol D. glycerophospholipid B. triacylglycerol D. Glycerophospholipid C. amino alcohol A. fatty acid
CH3 CH3
CH3 CH3
CH3
HO Copyright © 2009 by Pearson Education, Inc.
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Steroid Nucleus
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Cholesterol Cholesterol • is the most abundant steroid in the body. • has methyl CH3- groups, alkyl chain, and -OH attached to the steroid nucleus.
A steroid nucleus consists of
• 3 cyclohexane rings. • 1 cyclopentane ring. • no fatty acids.
CH3 CH3 CH3
CH3 CH3
steroid nucleus
HO 51
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.
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Cholesterol in Foods A normal, open artery.
An artery clogged by cholesterol plaque 53
Cholesterol • is considered elevated if plasma cholesterol exceeds 200 mg/dL. • is synthesized in the liver and obtained from foods.
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Learning Check
Solution
Match the components of the cholesterol molecule with the following: ___ carbon chain ___hydroxyl group ___ steroid nucleus ___methyl group CH3 CH3
Match the components of the cholesterol molecule with the following: _D carbon chain _A_hydroxyl group _C steroid nucleus _B_methyl group
D
CH3 CH3
CH3 CH3
B
CH3
CH3 CH3
B
CH3
A
D
A
HO
C
HO
C
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Lipoproteins
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Types of Lipoproteins Lipoproteins • differ in density, composition, and function. • include low-density lipoproteins (LDLs) and highdensity lipoproteins (HDLs).
Lipoproteins • combine lipids with proteins and phospholipids.
• are soluble in water because the surface consists of polar lipids. 57
Transport of Lipoproteins in the Body
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Steroid Hormones Steroid hormones are • chemical messengers in cells. • sex hormones. - androgens in males (testosterone) - estrogens in females (estradiol) • Adrenocortical hormones from adrenal glands. - mineralocorticoids (electrolyte balance) - glucocorticoids (regulate glucose level)
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Steroid Hormones
Adrenal Corticosteroids
Steroid hormones • are produced from cholesterol.
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.
• include sex hormones such as androgens (testosterone) in males and estrogens (estradiol) in females. Copyright © 2009 by Pearson Education, Inc.
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Anabolic Steroids
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Adrenal Corticosteroids
Anabolic 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.
Copyright © 2009 by Pearson Education, Inc.
Copyright © 2009 by Pearson Education, Inc.
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Learning Check
Solution
Identify each lipid as a (1) fatty acid, (2) steroid, or (3) triacylglycerol. A. B. C. D. E.
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Identify each lipid as a (1) fatty acid, (2) steroid, or (3) triacylglycerol. A. 2 cholesterol B. 1 stearic acid C. 3 glyceryl tristearate D. 2 estradiol E. 2 contains no fatty acids
cholesterol stearic acid glyceryl tristearate estradiol contains no fatty acids
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Chapter 15
Lipids
Cell Membranes
15.7 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
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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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Transport Pathways Through Cell Membranes
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.
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Learning Check
Solution
The transport of particles across a cell membrane from
The transport of particles across a cell membrane from high concentration to low concentration is called
high concentration to low concentration is called
2. diffusion.
1. facilitated transport. 2. diffusion. 3. active transport.
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