Transcript Lipids - Karen Timberlake

Lipids
Types of Lipids
Fatty Acids
Fats, and Oils
Chemical Properties of Triglycerides
1
Types of Lipids
• Lipids with fatty acids
Waxes
Fats and oils (trigycerides)
Phospholipids
Sphingolipids
• Lipids without fatty acids
Steroids
2
Fatty Acids
•
•
•
•
Long-chain carboxylic acids
Insoluble in water
Typically 12-18 carbon atoms (even number)
Some contain double bonds
corn oil contains 86%
unsaturated fatty acids and
14% saturated fatty acids
3
Saturated and Unsaturated
Fatty Acids
Saturated = C–C bonds
Unsaturated = one or more C=C bonds
COOH
palmitic acid, a saturated acid
COOH
palmitoleic acid, an unsaturated fatty acid
4
Structures
Saturated fatty acids
• Fit closely in regular pattern
COOH
COOH
COOH
Unsaturated fatty acids
H
• Cis double bonds
H
C C
cis double bond
COOH
5
Properties of Saturated
Fatty Acids
• Contain only single C–C bonds
• Closely packed
• Strong attractions between chains
• High melting points
• Solids at room temperature
6
Properties of Unsaturated
Fatty Acids
• Contain one or more double C=C bonds
• Nonlinear chains do not allow molecules
to pack closely
• Few interactions between chains
• Low melting points
• Liquids at room temperature
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Learning Check L1
How would the melting point of stearic
acid compare to the melting points of oleic
acid and linoleic acid? Assign the melting
points of –17°C, 13°C, and 69°C to the
correct fatty acid. Explain.
stearic acid (18 C) saturated
oleic acid (18 C) one double bond
linoleic acid (18 C) two double bonds
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Solution L1
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
oleic acid mp 13°C
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linoleic acid mp -17°C
Fats and Oils
Formed from glycerol and fatty acids
O
CH2 OH
CH
OH
CH2
OH
glycerol
HO C
O
+
(CH2)14CH3
HO C (CH2)14CH3
O
HO C
(CH2)14CH3
palmitic acid (a fatty acid)
10
Triglycerides (triacylglcerols)
Esters of glycerol and fatty acids
ester bonds
O
CH2
O
C
(CH2)14CH3 + H2O
O
CH
CH2
O
O
C (CH2)14CH3
O
C
+ H2O
(CH2)14CH3 +
H 2O
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Learning Check L2
What are the fatty acids in the following
triglyceride?
O
CH 2
O
C
(CH 2)16CH 3
O
CH
CH 2
O
O
C (CH 2)7CH CH(CH 2)7CH 3
O
C
(CH 2)12CH 3
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Solutions L2
What are the fatty acids in the following
triglyceride?
O
CH 2
O
C
O
CH
CH 2
Stearic acid
(CH 2)16CH 3
Oleic acid
O
C (CH 2)7CH CH(CH 2)7CH 3
O
Myristic acid
O C (CH 2)12CH 3
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Properties of Triglycerides
Hydrogenation
• Unsaturated compounds react with H2
• Ni or Pt catalyst
• C=C bonds
C–C bonds
Hydrolysis
• Split by water and acid or enzyme catalyst
• Produce glycerol and 3 fatty acids
14
Hydrogenation
O
CH2
O
C
(CH2)5CH CH(CH2)7CH3
O
CH
CH2
O
O
C (CH2)5CH CH(CH2)7CH3
O
C
+ 3 H2
Ni
(CH2)5CH CH(CH2)7CH3
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Product of Hydrogenation
O
CH 2
O
C
(CH 2)14CH 3
O
CH
CH 2
O
O
C (CH 2)14CH 3
O
C
(CH 2)14CH 3
Hydrogenation converts double bonds in oils
to single bonds. The solid products are used
to make margarine and other hydrogenated
items.
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Hydrolysis
Triglycerides split into glycerol and three
fatty acids (H+ or enzyme catalyst)
O
CH2
O
C
(CH2)14CH3
O
CH
CH2
O
O
H
C (CH2)14CH3
O
C
+
+3 H2O
(CH2)14CH3
CH2 OH
CH
OH
CH2
OH
O
+
3 HO C
(CH2)14CH3
17
Saponification and Soap
• Hydrolysis with a strong base
• Triglycerides split into glycerol and the
salts of fatty acids
• The salts of fatty acids are “soaps”
• KOH gives softer soaps
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Saponification
O
CH2
O
C
(CH2)16CH3
O
CH
CH2
O
O
C
O
C
(CH2)16CH3 + 3 NaOH
(CH2)16CH3
CH2 OH
CH
CH2
O
+OH + 3 Na O C (CH2)14CH3
salts of fatty acids (soaps)
OH
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Learning Check L3
What are the products obtained from the
complete hydrogenation of glyceryl
trioleate?
(1) Glycerol and 3 oleic acids
(2) Glyceryltristearate
(3) Glycerol and 3 stearic acids
20
Solution L3
What are the products obtained from the
complete hydrogenation of glyceryl
trioleate?
2. Glyceryltristearate
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