lipid def: compounds which are relatively insoluble in water, but freely soluble in non polar...
TRANSCRIPT
Lipid
• Def: compounds which are relatively insoluble in water, but freely soluble in non polar organic solvents like benzene, ether, chloforom etc.
Function
1. Storage form of energy2. Structure component of biomembranes3. Insolution4. Shape and contour of body5. Protect internal organ6. Metabolic regulator7. Electric insulator in neurons8. Help in absorbtion of fat soluble vitamins9. Taste and palatability
Clinical importance of lipid
• Obesity• Artheroscreloris• Fatty liver• Lipid storage disorder• Lipoproteinimias
CLASSIFICATION OF LIPIDS
• Simple Lipids, exp: fat or oil, wax• Compound Lipid
– Phospholipid – lechitin– Glycolipids – cerebrosides– Sulpholipids – sulfated cerebrosides
• Derived lipids – exp. Fatty acids, prostaglandin, steroids, etc.
• Micellaneous lipids, exp. Carotenoids, squalene, etc.
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Types of Lipids
• Lipids with fatty acidsWaxesFats and oils (trigycerides)PhospholipidsSphingolipids
• Lipids without fatty acidsSteroids
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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
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Saturated and Unsaturated Fatty Acids
Saturated = C–C bondsUnsaturated = one or more C=C bonds
COOH
COOH
palmitoleic acid, an unsaturated fatty acid
palmitic acid, a saturated acid
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Structures
Saturated fatty acids• Fit closely in regular pattern
Unsaturated fatty acids• Cis double bonds
COOHCOOHCOOH
C CH H
COOHcis double bond
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Properties of SaturatedFatty Acids
• Contain only single C–C bonds
• Closely packed
• Strong attractions between chains
• High melting points
• Solids at room temperature
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Properties of UnsaturatedFatty 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) saturatedoleic acid (18 C) one double bondlinoleic 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°Coleic acid mp 13°Clinoleic acid mp -17°C
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Fats and Oils
Formed from glycerol and fatty acids
+
HO C (CH2)14CH3
O
HO C (CH2)14CH3
O
HO C (CH2)14CH3
O
glycerol palmitic acid (a fatty acid)
CH
CH2 OH
OH
CH2 OH
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Triglycerides (triacylglcerols)
Esters of glycerol and fatty acids
CH
CH2
CH2 O
O
O
C (CH2)14CH3
O
C (CH2)14CH3
O
C (CH2)14CH3
O
ester bonds
+
+
+
H2O
H2O
H2O
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Learning Check L2
What are the fatty acids in the following triglyceride?
CH
CH2
CH2 O
O
O
C (CH2)16CH3
O
C
O
(CH2)7CH CH(CH2)7CH3
C
O
(CH2)12CH3
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Solutions L2
What are the fatty acids in the following triglyceride?
CH
CH2
CH2 O
O
O
C (CH2)16CH3
O
C
O
(CH2)7CH CH(CH2)7CH3
C
O
(CH2)12CH3
Stearic acid
Oleic acid
Myristic acid
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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
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Hydrogenation
CH
CH2
CH2 O
O
O
C
O
(CH2)5CH CH(CH2)7CH3
C
O
(CH2)5CH CH(CH2)7CH3
C
O
+
(CH2)5CH CH(CH2)7CH3
H23Ni
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Product of Hydrogenation
Hydrogenation converts double bonds in oils to single bonds. The solid products are used to make margarine and other hydrogenated items.
CH
CH2
CH2 O
O
O
C (CH2)14CH3
O
C (CH2)14CH3
O
C (CH2)14CH3
O
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Hydrolysis
Triglycerides split into glycerol and three fatty acids (H+ or enzyme catalyst)
CH
CH2
CH2 O
O
O
C (CH2)14CH3
O
C (CH2)14CH3
O
C (CH2)14CH3
O H2O+3
3+ HO C (CH2)14CH3
O
CH
CH2 OH
OH
CH2 OH
H+
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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
3+ Na+ -O C (CH2)14CH3
O
CH
CH2 OH
OH
CH2 OH
CH
CH2
CH2 O
O
O
C (CH2)16CH3
O
C
O
(CH2)16CH3
(CH2)16CH3C
O
+ 3 NaOH
salts of fatty acids (soaps)
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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