The Chemistry of Life 23
CH 2 OH (^)
H O H OHCH 2 O H (^)
H
H
(^) HO 1 H 2 O
OH (^) O H^
CH 2 OH
HO
OH H
H^ OH^
Sucrose
H
HO
(^)
CH 2 OH (^)
(^) O H HO^1 CH (^2) O H
H
H
(^2) H HO 5
OH 1
OH^ HO^3 4 CH 6 2 OH^
H OH OH H (^)
Glucose Fructose (^)
(^) ®
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Figure 2- 6 The chemical structure of the six-carbon sugars, glucose and fructose. When combined,
they produce the disaccharide sucrose.
result in another series of sugars such as common table
sugar or sucrose, a disaccharide.
Carbohydrates have two important functions: -energy
storage (sugars, starch, glycogen) and cell strengthening
(cellulose of plant cell walls and chitin in the external
skeleton of arthropod animals). Energy production is the
more common function of carbohydrates.
Lipids
There are a number of different kinds of lipids. Lipids are
substances that are insoluble in water. Fats, phospholip-ids,
steroids, and prostaglandins are examples of these different
kinds of molecules. We will concentrate on fats, which are
a major kind of lipid. Of the fats in the human body, 95%
are triglycerides, now called -triacylglycerols (try-ass-il-
GLISS-er-allz). They consist of two types of building
blocks: glycerol and fatty acids. Glycerol is a simple
molecule similar to a sugar except that it has only a three-
carbon chain. Each carbon of the chain is bonded to a
hydrogen and a hydroxyl (^2 OH) group as well as to the
carbons of the chain (Figure 2-7). Fatty acids are composed
of long chains of carbon atoms of
different lengths. All the carbon atoms are bonded to hy-
drogen atoms except the carbon at one end of the chain.
This carbon atom is bonded to the carboxyl (^2 COOH)
group, which makes these molecules slightly acidic. Most
naturally occurring fatty acids contain an even number of
carbon atoms, 14 to 18. A fatty acid is saturated if it
contains only single covalent bonds such as those found in
whole milk, butter, eggs, beef, pork, and coconut and palm
oils. Too much of these fatty acids contributes to
cardiovascular disease. Saturated fats tend to be solids at
room temperature. However, if the carbon chain has one or
more double covalent bonds between the carbon atoms, it is
an unsaturated fatty acid. These fatty acids are good for
you and are found in sunflower, corn, and fish oils.
Unsaturated fats tend to be liquids at room tem-perature.
Fats have a number of major roles in the body. Like
carbohydrates they contain stored chemical energy. Fat
found under the skin acts as an insulator to prevent heat
loss. Any animal that lives in the Arctic or Antarc-tic
region (polar bears, seals, whales, or penguins) has a thick
layer of insulatory fat. The camel’s hump is a thick deposit
of fat to protect its internal organs from excessive rises in
temperature in the hot desert. Fat also protects
(^)
H O H H H H H (^)
(^)
H C OH HO C C C C C C H (^)
(^)
H H H H H (^)
O H H H H H (^)
(^)
H C OH HO C C C C C C H (^)
(^)
H H H H H (^)
O H H H H H (^)
HO
H
(^)
H C OH C C C C C C (^)
(^)
H H H H H H (^)
Glycerol Fatty acids (^)
(^)
H O H H H H H (^)
H
O
H
C^ C^ C^ C^ C^ C^ C^
(^)
H H H H H (^)
O H H H H H (^)
Enzymes
H
O
H
C^ C^ C^ C^ C^ C^ C^
(^) H H H H H (^)
3H 2 O O^ H^ H^ H^ H^ H^
H
O
H
C^ C^ C^ C^ C^ C^ C^
(^)
H H H H H H (^)
(^) Triacylglycerol molecule (^)
(^) ®
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Figure 2- 7 The structure of a fat like triacylglycerol is -composed of a glycerol molecule and fatty
acids.