2
Outline
Types of LipidsStructures of Lipids
Fatty AcidsFats, and Oils
Chemical Properties of Triglycerides
3
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.
Lipids
• Hydrophobic, non-polar molecules• energy storage
– a lot of calories in a small space• generally insoluble in water
– stored in special ways in the body• also function as structural components of cells
5
Types of Lipids
Lipids with fatty acids Waxes. Fats and oils (triacylglycerols). Glycerophospholipids. Prostaglandins.
Lipids without fatty acids Steroids
Fatty Acids
• made up of carbon, hydrogen, oxygen– more carbon and hydrogen so they supply more
energy/gram• common building block for most lipids
fatty acids
8
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
the determining factor in whether to call a fatty acid saturated, unsaturated, monounsaturated, polyunsaturated, or trans fatty is determined by its chemical bonds and structure
Fatty Acids
10
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
11
Structures
Saturated fatty acids• Fit closely in regular pattern
Unsaturated fatty acids• Cis double bonds
COOHCOOHCOOH
C CH H
COOHcis double bond
Properties of SaturatedFatty Acids
• Contain only single C–C bonds• Closely packed • Strong attractions between chains• High melting points• Solids at room temperature
13
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
15
Waxes
Waxes are Esters of saturated fatty acids and long-chain alcohols. Coatings that prevent loss of water by leaves of plants.
TABLE 17.2
16
Fats and Oils: Triacylglycerols
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.
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
Esterification
• When glycerol combines with each fatty acid, a condensation reaction (dehydration synthesis) takes place
• An acid reacting with an alcohol produces an ester linkage, hence this process is called as esterification.
Triglycerides• the form of lipid most found in food
– 3 fatty acids + glycerol– Glycerol is an alcohol, while the
fatty acids are an acidic carboxyl group combined with long hydrocarbon chain.
– major class of dietary lipid– flabby stuff most of us have is
cells filled with triglycerides
19
Melting Points of Fats and Oils
A triacylglycerol that is a fat Is solid at room temperature. Is prevalent in meats, whole milk, butter, and cheese.
A triacylglycerol that is an oil Is liquid at room temperature. Is prevalent in plants such as olive and safflower.
20
Chemical Properties of Triacylglycerols
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
21
The chemical reactions of triacylglycerols are similarto 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.
Chemical Properties of Triacylglycerols
22
Hydrogenation
Adds hydrogen (H2) to the carbon atoms of double bonds. Converts double bonds to single bonds. The process is done using an enzyme and hydrogen gas TRANS fatty acids or Trans fat Produces solids such as margarine and shortening.
23
Hydrogenation
Ni + 3H2
glyceryl tripalmitoleate (tripalmitolean)
glyceryl tripalmitate(tripalmitin)
O
(CH2)14CH3C
O
(CH2)14CH3C
O
(CH2)14CH3C
O
O
OCH2
CH2
CH
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
Trans-Fatty Acids
hydrogenated fatty acids more saturated than natural vegetable oils able to pack together more tightly more solid are room temperature behave more like saturated fatty acids
hidden in the reporting levels for unsaturated fatty acids
25
HydrolysisIn hydrolysis, Triacylglycerols split into glycerol and three 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++3
+ 3
26
Glycerophospholipids are The most abundant lipids in cell membranes. Composed of glycerol, two fatty acids, phosphate
and an amino alcohol.
Glycerol
PO4Amino alcohol
Glycerophospholipids
Fatty acid
Fatty acid
27
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
Sterols (Steroids)
Lipids without fatty acids Highly hydrophobic important players: bile, sex hormones, Vit D
cholesterol is starting material cholesterol
only found in food derived from animals “good” or “bad “ cholesterol is not a type of cholesterol
found in food refers to the transportation of cholesterol in the blood
made in liver from carbs, protein, fat 800-1500 milligrams/day