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LipidsLipids are the hydrophobic compounds of C, H and OWith much higher ratio of hydrogen to oxygen than carbohydrates
Most are insoluble in water but soluble in non polar compounds
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Lipids
Types of Lipids
Fatty Acids
Fats, and Oils
Chemical Properties of Triglycerides
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Properties of fats and oils
• fats are solids or semi solids• oils are liquids• melting points and boiling points are not
usually sharp (most fats/oils are mixtures)• when shaken with water, oils tend to emulsify• pure fats and oils are colorless and odorless
(color and odor is always a result of contaminants) – i.e. butter (bacteria give flavor, carotene gives color)
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Examples of oils
• Olive oil – from Oleo europa (olive tree)• Corn oil – from Zea mays• Peanut oil – from Arachis hypogaea• Cottonseed oil – from Gossypium• Sesame oil – from Sesamum indicum• Linseed oil – from Linum usitatissimum• Sunflower seed oil – from Helianthus annuus• Rapeseed oil – from Brassica rapa• Coconut oil – from Cocos nucifera
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Non-drying, semi-drying and drying oils
• based on the ease of autoxidation and polymerization of oils (important in paints and varnishes)
• the more unsaturation in the oil, the more likely the “drying” process– Non-drying oils:
• Castor, olive, peanut, rapeseed oils
– Semi-drying oils• Corn, sesame, cottonseed oils
– Drying oils• Soybean, sunflower, hemp, linseed, tung, oiticica oils
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Types of Lipids
• Lipids with fatty acids
Waxes
Fats and oils (trigycerides)
Phospholipids
Sphingolipids
• Lipids without fatty acids
Steroids
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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 bonds
Unsaturated = 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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Fatty acids
• Common fatty acids
n = 4 butyric acid (butanoic acid)
n = 6 caproic acid (hexanoic acid)
n = 8 caprylic acid (octanoic acid)
n = 10 capric acid (decanoic acid)
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Fatty acids
• common FA’s: n = 12: lauric acid (n-dodecanoic acid; C12:0)
n = 14: myristic acid (n-tetradecanoic acid; C14:0)
n = 16: palmitic acid (n-hexadecanoic acid; C16:0)
n = 18; stearic acid (n-octadecanoic acid; C18:0)
n = 20; arachidic (eicosanoic acid; C20:0)
n= 22; behenic acid
n = 24; lignoceric acid
n = 26; cerotic acid
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Typical fish oil supplements
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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
linoleic 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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Hydrogenated fats
• hydrogenation leads to either saturated fats and or trans fatty acids
• the purpose of hydrogenation is to make the oil/fat more stable to oxygen and temperature variation (increase shelf life)
• example of hydrogenated fats: Crisco, margarine
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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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Soaps• Process of formation is known as
saponification– Types of soaps:
• Sodium soap – ordinary hard soap• Potassium soap – soft soap (shaving soaps are
potassium soaps of coconut and palm oils)• Castile soap – sodium soap of olive oil• Green soap – mixture of sodium and potassium linseed
oil• Transparent soap – contains sucrose• Floating soap – contains air• Calcium and magnesium soaps are very poorly water
soluble (hard water contains calcium and magnesium salts –these insolubilize 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
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Solution L3
What are the products obtained from the complete hydrogenation of glyceryl trioleate?
2. Glyceryltristearate
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Lipids
Phospholipids
Steroids and Cholesterol
Plasma (Cell)Membranes
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Phosphoglycerides
• Most abundant lipids in cell membranes • Control cell permeability
FATTY ACID
FATTY ACIDglycerol
PO4Amino alcohol
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Steroids
• Steroid nucleus• 3 cyclohexane rings• 1 cyclopentane ring
steroid nucleus
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Cholesterol
• Most abundant steroid in the body
• Add methyl CH3- groups, alkyl chain, and -OH to steroid nucleus
CH3
HO
CH3
CH3 CH3
CH3
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Cholesterol in the Body
• Cellular membranes
• Myelin sheath, brain, and nerve tissue
• Bile salts
• Hormones
• Vitamin D
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Bile Salts
• Synthesized in the liver from cholesterol
• Stored in the gallbladder
• Secreted into small intestine
• Mix with fats to break them part
• Emsulsify fat particles
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Steroid Hormones
• Chemical messengers in cells• Sex hormones
Androgens in males (testosterone)
Estrogens in females (estradiol)• Adrenocorticosteroids from adrenal glands
mineralocorticoids (electrolyte balance)
glucocorticoids regulate glucose level
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Sex Hormones
O
CH3
CH3OH
HO
CH3
CH3OH
testosterone estradiol
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Plasma Membranes
• Surround cells
• Lipid bilayer pf phospholipids
• Nonpolar hydrocarbon tails in center
• Polar (hydrophilic) sections on outside
• Some unsaturated fatty acids give flexibility
• Keep aqueous contents inside
• Allow certain biochemicals to pass through
4040
Diagram of a Plasma Membrane
Polar sections
Nonpolar tails