Download Chapter 21 - Bakersfield College

Chemistry B11
Chapter 21
Lipids
Lipids
- Family of bimolecules.
- They are not defined by a particular functional
group, thus they have a variety of structures and
functions.
- They are soluble in organic solvents but not in water (nonpolar).
- They contain many nonpolar C—C and C—H
bonds and few polar bonds resulting in their water
insolubility.
Lipids
1. Store energy: fat cells
2. Chemical messengers: find in nerve fibers and hormones.
3. Parts of membranes: insoluble in water
Lipids
1. Simple lipids: (Waxes, Fats & Oils)
2. Complex lipids (Glycerophospholipids)
Store energy, insulation
Cell membrane
3. Steroid (Cholesterol & steroid hormones)
4. Eicosanoids
Pain, fever, inflammation
Chemical messenger
Cell membrane
Fatty acids
Fatty acids are:
• Long-chain unbranched carbon
attached to a carboxyl group.
• Typically 12-18 carbon atoms.
• Insoluble in water.
• Saturated or unsaturated.
COOH Stea
COOH Steari
(m
COOH Olei
COOH Oleic (a
(mp
Cis
COOH Lino
COOH Linole
Saturated and unsaturated Fatty acids
Saturated fatty acids are solids at room temperature.
Packed together  Maximum London dispersion forces
COOH
COOH
COOH
COOH
COOH
Unsaturated fatty acids are liquids at room temperature.
Can not pack together  London dispersion forces 
COOH
COOH
COOH
COOH
COOH
Fatty acids
• The human body is capable of synthesizing most fatty acids from
carbohydrates or other fatty acids.
• Humans do not synthesize sufficient amounts of fatty acids that
have more than one double bond.
• More than one double bond fatty acids are called essential fatty
acids and they must be provided by the diet.
Waxes
- are found in many plants and animals (or humans).
- In plants, they help prevent loss of water and damage from pests.
- In humans and animals, provide waterproof coating on skin and fur.
Wax is an ester of saturated fatty acid and long chain alcohol.
Long-chain alcohol
Ester bond
Fatty acid
Waxes
For example, shown below is the formation of spermaceti wax,
isolated from the heads of sperm whales.
Acid
Beeswax
Carnauba
Coating
Jojoba
Lanolin from wool
lotions
Triacylglycerols (Triglycerides)
Triacylglycerols are:
• Fats and oils (are stored in the body).
• Triesters of glycerol.
• Produced by Fischer esterification.
• Formed when the hydroxyl groups of
glycerol react with the carboxyl groups
of fatty acids.
Esterification
glycerol
three fatty acids
triacylglycerol
O
CH2
OH
HO C
O
(CH2)14CH3
CH
OH
HO C
O
(CH2)14CH3
CH2
OH
HO C
(CH2)14CH3
O
CH2 O C
(CH2)14CH3
O
Acid
CH O C
(CH2)14CH3 + 3H2O
O
CH2 O C
(CH2)14CH3
Triacylglycerols (Triglycerides)
CH2
OH
CH
OH
CH2
OH
Glycerol
O
CH2
O
C
(CH2)5CH CH(CH2)7CH3
O
CH
O
CH2
O
C (CH2)5CH CH(CH2)7CH3
O
C
(CH2)5CH CH(CH2)7CH3
G
L
Y
C
E
R
O
L
Fatty acid
Fatty acid
Fatty acid
Produced by esterification of glycerol (a trihydroxyl alcohol).
Triacylglycerols (Triglycerides)
Fat: is a triacylglycerol that is solid at room temperature.
Made by more saturated fatty acids (Saturated triacylglycerols).
Meat, milk, butter and cheese (animal sources).
Oil: is a triacylglycerol that is liquid at room temperature.
Made by more unsaturated fatty acids (Unsaturated triacylglycerols).
Corn, cotton seed, safflower and sunflower (plant sources).
Both are colorless, odorless, and tasteless.
Hydrogenation
- Hydrogen adds to the double bonds of unsaturated fats (using transition
metal catalyst such as Ni).
H H
_
- Melting point is increased.
- Liquid oils are converted to semisolid fats.
H H
Ni
C=C + H2 → _C_C_
_
H H
1- Hydrogenation
O
CH2
O
C
(CH2)5CH CH(CH2)7CH3
Ni
O
CH
O
CH2
O
C (CH2)5CH CH(CH2)7CH3
O
C
+ 3H2
(CH2)5CH CH(CH2)7CH3
glyceryl Trioleate
(triolein)
O
CH2
O
C
(CH2)14CH3
O
CH
CH2
O
O
C (CH2)14CH3
O
C
(CH2)14CH3
glyceryl tristearate
(tristearin)
2- Hydrolysis
Triacylglycerols are hydrolysis (split by water) in the presence of strong acid
or lipase (digestive enzyme).
O
CH2 O C
(CH2)14CH3
O
CH O C
(CH2)14CH3
+ 3H2O
O
CH2 O C
(CH2)14CH3
CH2 OH
O
CH OH
H+ or Lipase
CH2 OH
+O C (CH2)14CH3
+Na3HO
3- Saponification
• Is the process of forming “soaps” (salts of fatty acids).
• Is the reaction of a fat with a strong base (NaOH).
• Splits triacylglycerols into glycerol and the salts of fatty
acids.
• With KOH or the oils that are polyunsaturated gives
softer soaps (liquid soaps).
• Name of soap gives the source of the oil.
Like coconut or avocado soap
3- Saponification (Basic Hydrolysis)
O
CH2 O C
(CH2)14CH3
O
CH O C
(CH2)14CH3
+ 3NaOH
O
CH2 O C
(CH2)14CH3
CH2 OH
O
Heat
CH OH
+ 3Na+ -O C (CH2)14CH3
“soap”
Salt of fatty acid
CH2 OH
Glycerophospholipids
G
L
Y
C
E
R
O
L
Fatty acid
Fatty acid
CH3
phosphate
O
O
P
O
_
Amino
alcohol
HO – CH2 _ CH2
Choline
N+
CH3
CH3
O
Polar part (polar head) and nonpolar part (nonpolar tail)
Interact with both polar and nonpolar substances.
1. Most abundant lipids in cell membranes (semipermeable).
2. Combine with less polar triglycerides and cholesterol to make them soluble.
Steroids
Steroids have:
• A steroid nucleus which is
4 carbon rings.
• Attached groups that make the
different types of compounds.
steroid nucleus
• No fatty acids.
Cholesterol
Cholesterol:
• Is the most abundant steroid in the body.
• Insoluble in water (need a water soluble carrier).
• Has methyl CH3- groups, alkyl chain, and -OH
attached to the steroid nucleus.
CH3
CH3
CH3
HO
CH3
CH3
Cholesterol
Cholesterol:
• Is obtained from meats, milk, and eggs.
• Is synthesized in the liver from fats,
carbohydrates and proteins.
• Is needed for cell membranes, brain and
nerve tissue, steroid hormones, and
Vitamin D.
At artery clogged by
cholesterol plaque
• Clogs arteries when high levels form
plaque.
• No cholesterol in vegetable and plants.
Gallstones form in gallbladder
Steroids
Steroid hormones are:
Chemical messengers in body
Sex hormones
Testosterone & androsterone in males
Estrogen & progesterone in females
CH3 OH
CH3
O
Testosterone (androgen)
Male sex hormone
CH3 OH
CH3
HO
Estrogen
Female sex hormone
Lipoproteins
Triacylglycerols
Water-soluble form of lipids
(soluble in blood)
Spherical particles
Polar surface and nonpolar inner
Transporting lipids through the bloodstream to tissues where they are stored,
Used for energy, or to make hormones.
Lipoproteins
VLDL: very-low-density lipoprotein
Triglycerides and Cholesterol
LDL: low-density lipoprotein (bad Cholesterol)
Cholesterol
HDL: high-density lipoprotein (good Cholesterol)
Cholesterol
Recommended levels are: HDL > 40 mg/dL, LDL < 100 mg/dL, total serum cholesterol < 200 mg/dL.
Chylomicrons
Triglycerides and Cholesterol
VLDL
Liver
Intestine
and
elimination
Heart and
muscles
Fat storage
cells
HDL
LDL
Energy
Cell Membrane
Carbohydrate
Phospholipid
bilayer
Nonpolar
Polar
Semipermeable: nutrients can enter and waste products can leave.
Fluid mosaic model