Lipids
L. Scheffler
IB Chemistry 1-2
Lincoln High School
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Lipids
• Lipids are organic molecules with long
hydrocarbon chains that are soluble in
non-polar organic solvents
• Lipids are generally divided into three
classes
• 1.Triglycerides – Fats and Oils
• 2. Phospholipids – lecithin
• 3 Steroids -- Cholesterol
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Fats and Oils
• Fats and oils are triesters formed from the
condensation reaction of glycerol (1,2,3,propanetriol)
with long chain fatty acids
• Example:
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Fats and Oils
• Fats are generally solids at room
temperature, while oils are usually
liquids
• Fats contain saturated hydrocarbon
chains
• Oils contain unsaturated hydrocarbon
chains, with at least 1 C=C. Frequently
there are several C=C. They are known
as polyunsaturated.
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Fatty Acids
• Stearic acid and linoleic acid have the same
number of carbon atoms but very different
melting points.
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Common Fatty Acids
Name
Formula
Source
Saturated Fatty Acids
Lauric Acid
CH3-(CH2)10-COOH
Coconut Oil
Palmitic Acid
CH3-(CH2)14-COOH
Palm Oil
Stearic Acid
CH3-(CH2)16-COOH
Animal and
vegetable fats
Arachidic Acid
CH3-(CH2)18-COOH
Peanut Oil
Unsaturated Fatty Acids
Oleic
CH3-(CH2)7CH=CH-(CH2)7COOH
Corn Oil
Acid
Linoleic CH3-(CH2)4 CH=CH-CH2-CH=CH –
Linseed Oil
Acid
(CH2)7COOH
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Differences in Melting Points
• The carbon atoms in the hydrocarbon chain form a
succession of tetrahedrons
• This regular tetrahedral arrangement of carbon
atoms makes it possible for it to pack with parallel
chains fairly closely together
• Although the attractions between the chains are only
the rather weak van der Waals attractions the large
surface area in the long carbon chains groups result
in attractive forces that are strong enough to sustain
a solid state
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Unsaturated Fatty Acids
• The presence of the C=C in the unsatruated
fatty acid chain changes the bond angle from
about 109 oC to around 120 oC.
• This “kink” in the carbon chain keeps the
fatty acids from packing as closely together.
• As a result the van der Waals forces are
weaker and less energy is required to
separate them.
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Saturated and Saturated Fats
and Nutrition
• Saturated and unsaturated fats are terms
most commonly used in the context of
nutrition.
• Most animal fats are saturated fats. They are
usually solids at room temperature.
• Vegetable oils are more unsaturated. They
are liquids at room temperature.
• Oils with one C=C double bond per fatty acid
chain are called “monounsaturated oils”
• Oils with more than one C=C double bond
per fatty acid chain are called
“polyunsaturated oils”.
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Hydrogenated Fats and Oils
• Unsaturated oils can be hydrogenated to
form solid, saturated fats by the reaction with
hydrogen gas in the presence of nickel or
platinum as a catalyst.
• Margarine is an example of a hydrogenated
oil.
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The Iodine Index
• The degree of unsaturation can be measured
by measuring the amount of iodine that can
react with the unsaturated fat or oil. Each
mole of C=C requires one mole of I2 to react.
• The haloalkane chain is nearly colorless
Therefore unsaturated hydrocarbon chains
will destroy purple brown color of iodine
solutions as long as there are C=C bonds
present.
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Iodine Index of Common Fats/ Oils
Oil or fat
Butter fat
Percent Percent of
saturated monounsaturated
fats
fats
67%
29%
Percent of
Iodine
polyunsaturated Index
fats
4%
34
Beef
Tallow
52%
44%
4%
50
Olive Oil
15%
75%
10%
81
Peanut Oil
18%
49%
33%
93
Canola Oil
7%
10%
62%
13%
31%
77%
130
125
Sunflower
oil
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Essential Fatty Acids
• Most naturally occuring fats are a mixture of
saturated, monounsaturated and
polyunsaturated fatty acids
• Essential fatty acids are those that the body
cannot synthesize on its own.
• They must be acquired from the foods we
eat.
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Essential Unsaturated Fatty
Acids
w-6 linoleic acid is an example of an essential
fatty acid. It is a cis isomer. The w-6
indicates that there is a C=C on the 6th
carbon from the end of the carbon chain
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Essential Unsaturated Fatty
Acids
w-3 linolenic acid is another example of an
essential fatty acid. It is a cis isomer. The w3 indicates that there is a C=C on the 3rd
carbon from the end of the carbon chain
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Trans Fatty Acids
• When fatty acids are made synthetically by
partially hydrogenating other polyunsaturated
fatty acids, some trans isomers may be
formed.
• Trans fatty acids are found in fried foods and
in some margarines.
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Trans Fatty Acids
• Trans fatty acids are generally considered
undesirable since they increase the
formation of LDL Cholesterol and hence the
risk of heart disease.
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Fat Metabolism
• Fats metabolism occurs more slowly than
carbohydrates metabolism but fats provide more
energy than carbohydrates.
• Fats require greater degree of oxidation to become
CO2 and H2O than carbohydrates because
carbohydrates already have one oxygen for every
carbon atom
• The number of oxygen molecules needed to oxidize a
fat is greater than for carbohydrates., The oxidation of
fats takes longer, but it also generates more energy.
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Hydrolysis of Fats
• In the body triglycerides, fats and oils, are
hydrolyzed to fatty acids by the action of
enzymes known as lipases
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Hydrolysis of Fats
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Phospholipids
• A phospholipid has one of the three carbon chains of
a triglyceride is replaced with a more polar
phosphate-containing group.
Four parts of a phospholipid
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Phospholipids
• In a phospholipids are one of the essential components
of cell membranes.
• Phosphatidyl Choline, an example of a phospholipid, has
this structure:
• Phosphatidyl choline is a major component of lecithin
found in egg yolk,
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Phospholipid Functions
• Phospholipids form a significant part of cell
membranes.
• The cell membrane must protect the cell form the
intercellular fluids around it. At the same time it must
allow cell nutrients to enter the cell and waste
products to leave.
• Phospholipids tend to form
bilayers in aqueous solutions.
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Phospholipid Functions
• The polar heads interface
with water and the non-polar
tails are attracted to nonpolar tissues.
• The larger phospholipids
can open and close to form
vesicles. It is believed that
this behavior is important to
the functioning of the porous
cell membranes
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Cholesterol
• Cholesterol has the characteristic four ring structure
that is common to all steroids.
• Cholesterol exists in esterified form in fatty acids
and in a free form.
• Cholesterol is created by the liver, but is also
available through food.
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Cholesterol Functions
• Cholesterol is the most common, important and
necessary steroid in the human body.
• It is component of all tissues and is found in the
blood, brain and the spinal cord.
• It also acts as a building block to create other
steroids such as sex hormones and adrenocorticoid
hormones as well as essential substances such as
vitamin D.
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LDL and HDL
• Cholesterol is transported around the body by
lipoproteins.
• Low density lipoproteins (LDL) range from 18-25nm
• LDL transport cholesterol to the arteries where it can
build up and cause cardiovascular disease
• LDL result from saturated fats, especially lauric (C12),
myristic (C14) and palmitic (C16) acids.
• High density lipoproteins (HDL) are smaller, ranging
from 8-11 nm.
• HDL can remove cholesterol from the arteries and
transport it back to the liver.
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Lipid Functions in the Body
• Energy storage
Lipids are highly efficient
energy stores for most higher animals. Fats are
stored in the adipose tissues. Because they have
less oxygen per molecule, lipids are oxidized more
slowly, but release more energy.
• Thermal insulation and protection
Fats
provide thermal insulation for the body.
• Cell Structure Lipids, especially phospholipids,
form a significant part of most cell membranes.
They protect the cell from the intercellular fluids
around it and play an important role in the
transport of fluids into and out of the cell.
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The end
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