Lipids
Lipids are the hydrophobic compounds of C, H and O
With 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
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•
•
•
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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
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•
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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
palmitic acid, a saturated acid
COOH
palmitoleic acid, an unsaturated fatty acid
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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
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Properties of Saturated
Fatty 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 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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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
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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)
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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
+ H 2O
(CH2)14CH3 +
H 2O
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Learning Check L2
What are the fatty acids in the following
triglyceride?
O
CH2
O
C
(CH2)16CH3
O
CH
CH2
O
O
C (CH2)7CH CH(CH2)7CH3
O
C
(CH2)12CH3
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Solutions L2
What are the fatty acids in the following
triglyceride?
O
CH2
O
C
O
CH
CH2
Stearic acid
(CH2)16CH3
Oleic acid
O
C (CH2)7CH CH(CH2)7CH3
O
Myristic acid
O C (CH2)12CH3
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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
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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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
O
CH2
O
C
(CH2)14CH3
O
CH
CH2
O
O
C (CH2)14CH3
O
C
(CH2)14CH3
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
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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
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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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
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salts –these insolubilize soaps)
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 ACID
glycerol
PO4
Amino
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
CH3
CH3
CH3
CH3
HO
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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
CH3 OH
CH3
O
CH3 OH
CH3
HO
t e st ost e r on e
e st r ad iol
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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
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Diagram of a Plasma
Membrane
Polar sections
Nonpolar tails
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