Chapter 2
Chemistry Comes Alive
45
2
and
glycerol
(glis
9
er-ol), in a 3:1 ratio of fatty acids to glycerol
(Figure 2.16a)
. Fatty acids are linear chains of carbon and hy-
drogen atoms (hydrocarbon chains) with an organic acid group
(
¬
COOH) at one end. Glycerol is a modified simple sugar
(a sugar alcohol).
Fat synthesis involves attaching three fatty acid chains to a
single glycerol molecule by dehydration synthesis. Te result is
an E-shaped molecule. Te glycerol backbone is the same in all
triglycerides, but the fatty acid chains vary, resulting in different
kinds of fats and oils.
Tese are large molecules, o±en consisting of hundreds of
atoms, and ingested fats and oils must be broken down to their
building blocks before they can be absorbed. Teir hydrocarbon
chains make the triglycerides nonpolar molecules. Because po-
lar and nonpolar molecules do not interact, oil (or fats) and wa-
ter do not mix. Consequently, triglycerides provide the body’s
Triglycerides (Neutral Fats)
Triglycerides
(tri-glis
9
er-īdz), also called
neutral fats
, are com-
monly known as
fats
when solid or
oils
when liquid. A triglyc-
eride is composed of two types of building blocks,
fatty acids
H
O
H
Glycerol
H
HO
HO
HO
C
CH
2
CH
2
H
H
C
C
O
H +
3H
2
O
+
O
H
CH
3
CH
3
HO
CH
2
CH
2
CH
2
CH
2
O
C
O
CH
CH
3
CH
3
N
+
C
H
O
CH
2
O
O
P
O
O
H
H
H
H
C
C
O
O
H
C
O
Phosphorus-containing
group (polar “head”)
Example
Phosphatidylcholine
Example
Cholesterol (cholesterol is the
basis for all steroids formed in the body)
Glycerol
backbone
2 fatty acid chains
(nonpolar “tail”)
Polar “head”
Nonpolar “tail”
(schematic phospholipid)
3 fatty acid chains
Triglyceride, or neutral fat
3 water
molecules
CH
2
CH
2
CH
3
O
C
CH
2
CH
2
CH
2
CH
2
CH
3
O
C
CH
2
CH
2
CH
2
CH
2
CH
3
O
C
CH
2
CH
2
CH
2
CH
2
CH
3
O
C
CH
2
CH
2
CH
2
CH
2
CH
3
O
C
CH
2
CH
2
CH
2
CH
2
CH
3
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
3
CH
2
O
C
O
CH
2
CH
2
CH
2
CH
2
CH
3
C
H
C
H
CH
3
CH
3
CH
3
H
3
C
(c)
Simplified structure of a steroid
Four interlocking hydrocarbon rings form a steroid.
(b)
“Typical” structure of a phospholipid molecule
Two fatty acid chains and a phosphorus-containing group are attached to the glycerol backbone.
(a)
Triglyceride formation
Three fatty acid chains are bound to glycerol by dehydration synthesis.
Figure 2.16
Lipids.
The general structure of
(a)
triglycerides, or
neutral fats,
(b)
phospholipids, and
(c)
cholesterol.
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