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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
1
Lipids
Types of Lipids
Fatty Acids
Fats, and Oils
Chemical Properties of Triglycerides
2
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)
3
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
4
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
5
Types of Lipids
• Lipids with fatty acids
Waxes
Fats and oils (trigycerides)
Phospholipids
Sphingolipids
• Lipids without fatty acids
Steroids
6
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
7
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
8
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
9
Properties of Saturated
Fatty Acids
• Contain only single C–C bonds
• Closely packed
• Strong attractions between chains
• High melting points
• Solids at room temperature
10
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
11
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)
12
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
13
Typical fish oil supplements
14
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
15
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
16
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)
17
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
18
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
19
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
20
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
21
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
22
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
23
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.
24
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
25
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
26
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
27
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
28
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
29
Solution L3
What are the products obtained from the
complete hydrogenation of glyceryl
trioleate?
2. Glyceryltristearate
30
Lipids
Phospholipids
Steroids and Cholesterol
Plasma (Cell)Membranes
31
Phosphoglycerides
• Most abundant lipids in cell membranes
• Control cell permeability
FATTY ACID
FATTY ACID
glycerol
PO4
Amino
alcohol
32
Steroids
• Steroid nucleus
• 3 cyclohexane rings
• 1 cyclopentane ring
steroid nucleus
33
Cholesterol
• Most abundant steroid in the body
• Add methyl CH3- groups, alkyl chain, and OH to steroid nucleus
CH3
CH3
CH3
CH3
CH3
HO
34
Cholesterol in the Body
• Cellular membranes
• Myelin sheath, brain, and nerve tissue
• Bile salts
• Hormones
• Vitamin D
35
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
36
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
37
Sex Hormones
CH3 OH
CH3
O
CH3 OH
CH3
HO
t e st ost e r on e
e st r ad iol
38
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
39
Diagram of a Plasma
Membrane
Polar sections
Nonpolar tails
40