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Chapter 18: Lipids
CHEM 1152
Dr. Sheppard
Spring 2015
2
Lipids
• One of 4 major classes of compounds found in living tissue– Nucleic acids, proteins, carbohydrates, lipids
• Specific types differ in structure• Includes fats, oils, cholesterol• Insoluble in water (large nonpolar section)• Soluble in organic solvents • Energy storage• Cell membranes• Insulation• Hormones/messengers• Some vitamins
3
18.1 Classification of lipids
Saponifiable = estersSimple = two components (fatty acid and alcohol)Complex = more than two components
4
Some example lipid structures
5
18.2 Fatty acids (FAs)
• Simplest type of lipid• Component of other more complex lipids• Carboxylic acid with long (10-20) carbon chain
– Even number of carbons– Typically unbranched
C C C C C C C C C C C C C C C OHC
OH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
OH
O
6
Fatty acids and micelle formation
7
Saturated vs. unsaturated fatty acids
• Saturated (“bad” fat)– Only C─C– Highly flexible– Pack together
• Unsaturated (“good” fat)– Contains C═C– Cis double bonds– “Kink” in chain reduces
possibility of heart disease• Don’t stick to walls of blood
vessels• Promote blood flow
– Monounsaturated – Polyunsaturated
8
Essential fatty acids
• Not synthesized by the body • Needed as precursors for essential molecules• Must be obtained from the diet• Plant and fish oils• Linoleic acid (18 carbons, 2 double bonds)• Linolenic acid (18 carbons, 3 double bonds)
9
Some important unsaturated fatty acids
• Oleic acid (18:1)– Olives– 18 carbons, C=C at C9
• Linoleic (18:2)– Corn, soybean oil– Essential FA– Omega-6 FA
• Linolenic acid (18:3)– Corn, fish oil– Essential FA– Omega-3 FA
1
18
9
O
OH
1
18
O
OH
1
18
O
OH
10
Physical properties of fatty acids
• Solubility– Insoluble in water– Soluble in organic solvents
(ether, chloroform)
• Melting point– Saturated = solid at room
temperature– MP increases with longer
chains– MP decreases with number
of unsaturations
11
12
18.3 Structure of Fats and oils
• Triglycerides/triacylglycerols (TAGs) – Most abundant class of lipids in animals – Fatty acid triesters of glycerol– Formed from esterification
13
Triglycerides
• Function– Energy reserves– Insulation
• Stored in adipocytes throughout the body– Hydrolyzed as needed by
enzymes called lipases
14
Triglycerides
• Mixed vs. simple• mp determined by degree of unsaturation
– More unsaturation in plants than in animals– “Fat” = mostly saturated
• Solid at room temperature• Meat, butter (animal sources other than fish)
– “Oil” = mostly unsaturated• Liquid at room temperature• Olive oil, peanut oil (fish and plants)
15
Triglycerides
16
Mixed or simple? Fat or oil?