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Chapter 5

LIFESCI 2N03 Chapter Notes - Chapter 5: Lipoprotein Lipase, Unsaturated Fat, Polyunsaturated Fat


Department
Life Sciences
Course Code
LIFESCI 2N03
Professor
Janet Pritchard
Chapter
5

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Saturday, February 27, 2016
Chapter 5: Lipids (Triglycerides, Phospholipids, and Sterols)
-Lipids: A family of compounds that includes triglycerides, phospholipids, and sterols.
-Characterized b their insolubility in water.
-Triglycerides are most abundant, both in foods and in the body.
5.1 The Chemist’s View of Fatty Acids and Triglycerides
-Like carbohydrates, lipids are composed of carbon, hydrogen, and oxygen.
-Because they have more carbon and hydrogen than oxygen, they can supply more energy per
gram than carbohydrates.
1. Every triglyceride contains one molecule of glycerol and three fatty acids (basically, chains
of carbon atoms).
2. Fatty acids may be 4 to 24 (even numbers of) carbons long, the 18-carbon ones being the
most common in foods and especially noteworthy in nutrition.
3. Fatty acids may be saturated or unsaturated. Unsaturated fatty acids may have one or more
points of unsaturation (mono or poly).
4. Of special importance in nutrition are the polyunsaturated fatty acids whose first point of
unsaturation is next to the third carbon (omega-3) or next to the sixth carbon (omega-6).
5. The 18-carbon fatty acids that fit this description are linolenic acid (omega-3) and linoleic
acid (omega-6). Each is the primary member of a family of longer-chain fatty acids that help
to regulate blood pressure, blood clotting, and other body functions important to health.
Fatty Acids
-A fatty acid is an organic acid–a chain of carbon atoms with hydrogens attached–that has an
acid group (COOH) at one end and a methyl group (CH3) at the other end.
-Most natural fatty acids contain even numbers of carbons (2-24).
-18-carbon fatty acids are most abundant in our foods.
Acetic acid: Stearic acid:
- Shortest fatty acid (2C chain) - Simplest of the 18C fatty acids
-A saturated fatty acid (i.e., stearic acid) is fully loaded with hydrogen atoms and contains
only single bonds between its C atoms.
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Saturday, February 27, 2016
-A double bond is a point of unsaturation; this becomes an unsaturated fatty acid.
-A monounsaturated fatty acid (i.e., oleic acid) only has one double bond with two
missing hydrogens.
-A polyunsaturated fatty acid (i.e., linoleic acid linolenic acid) has two or more double
bonds.
-Chemists identify polyunsaturated fatty acids by the position of the double bond
nearest the methyl (CH3) end of the carbon chain.
-An omega-3 fatty acid (i.e., linolenic acid) has its first double bond three carbons
away from the methyl end.
-An omega-6 fatty acid (i.e., linoleic acid) has its first double bond six carbons
away.
-Oleic acid = omega-9, like most monounsaturated fatty acids.
Triglycerides
-Triglycerides are lipids composed of three fatty acids attached to a glycerol (3C chain)
molecule.
-A series of condensation reactions combine a H atom from the glycerol and a OH group from
a fatty acid, forming a molecule of water and leaving a bond between the two molecules.
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Glycerol + three fatty acids Triglyceride + three water molecules

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Saturday, February 27, 2016
Degree of Unsaturation Revisited
-The degree of unsaturation influences the firmness of fats at room temperature.
-Most oils (polyunsaturated) are liquid at room temperature, and fats (saturated) are solid.
-Shorter carbon chains are softer at room temperature.
-Saturation also influences stability.
-All fats become spoiled when exposed to oxygen.
-Polyunsaturated fats spoil faster because their double bonds are unstable.
-Saturated fats are most resistant to oxidation and thus least likely to spoil.
-Manufacturers can protect fat-containing products against spoiling in three ways (none
perfect):
-Sealing products in air-tight, nonmetallic containers, protected from light, and
refrigerated–expensive and inconvenient.
-Adding antioxidants to compete for the oxygen and thus protect the oil.
-Hydrogenation
-During hydrogenation, some or all of the points of unsaturation are saturated by adding
hydrogen molecules.
-Advantages:
-Protects against oxidation (prolonging shelf-life).
-Alters the texture of foods by making liquid vegetable oils more solid
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