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or sequence of these amino acid molecules determines the struc- Glucose (an aldehyde sugar)
ture that gives the protein its unique set of biochemical proper- H H H H OH H
ties. Insulin, for example, is a protein hormone that biochemically
regulates the blood sugar level. Insulin contains 86 amino acid H C C C C C C O
molecules in the chain. Hemoglobin is the protein that carries
O O O O H
oxygen in the bloodstream, and its biochemical characteristics are H H H H
determined by its chain of 146 amino acid molecules.
Fructose (a ketone sugar)
CONCEPTS Applied H H H OH H
H C C C C C C H
Fats Foods
O O O H O OH
Pick a food product and write the number of grams of fats, H H H
proteins, and carbohydrates per serving according to the
information on the label. Multiply the number of grams of FIGURE 12.20 Glucose (blood sugar) is an aldehyde, and
proteins and carbohydrates each by 4 Cal/g and the number fructose (fruit sugar) is a ketone. Both have a molecular formula
of grams of fat by 9 Cal/g. Add the total Calories per serving. of C 6 H 12 O 6 .
Does your total agree with the number of Calories per serving
given on the label? Also examine the given serving size. Is Both glucose and fructose have the same molecular formula,
this a reasonable amount to be consumed at one time, or but glucose is an aldehyde sugar and fructose is a ketone sugar
would you probably eat two or three times this amount? (Figure 12.20). A mixture of glucose and fructose is found in
Write the rest of the nutrition information (vitamins, minerals, honey. This mixture also is formed when table sugar (sucrose)
sodium content, etc.), and then write the list of ingredients. is reacted with water in the presence of an acid, a reaction that
Tell what ingredient you think is providing which nutrient. takes place in the preparation of canned fruit and candies. The
(Example: vegetable oil—source of fat; milk—provides mixture of glucose and fructose is called invert sugar. Thanks to
calcium and vitamin A; MSG—source of sodium.) fructose, invert sugar is about twice as sweet to the taste as the
same amount of sucrose.
Two monosaccharides are joined together to form disac-
charides with the loss of a water molecule, for example,
CARBOHYDRATES
C 6 H 12 O 6 + C 6 H 12 O 6 → C 12 H 22 O 11 + H 2 O

Carbohydrates are an important group of organic compounds
glucose fructose sucrose
that includes sugars, starches, and cellulose, and they are impor-
tant in plants and animals for structure, protection, and food. The most common disaccharide is sucrose, or ordinary table sugar.
Cellulose is the skeletal substance of plants and plant materials, Sucrose occurs in high concentrations in sugarcane and sugar
and chitin is a similar material that forms the hard, protective beets. It is extracted by crushing the plant materials, then dissolv-
covering of insects and shellfish such as crabs and lobsters. ing the sucrose from the materials with water. The water is evapo-
Glucose, C 6 H 12 O 6 , is the most abundant carbohydrate and serves rated, and the crystallized sugar is decolorized with charcoal to
as a food and a basic building block for other carbohydrates. produce white sugar. Other common disaccharides include lac-
Carbohydrates were named when early studies found that tose (milk sugar) and maltose (malt sugar). All three di saccharides
water vapor was given off and carbon remained when sugar was have similar properties, but maltose tastes only about one-third
heated. The name carbohydrate literally means “watered carbon,” as sweet as sucrose. Lactose tastes only about one-sixth as sweet
and the empirical formulas for most carbohydrates indeed indi- as sucrose. No matter which di saccharide sugar is consumed
cate carbon (C) and water (H 2 O). Glucose, for example, could be (sucrose, lactose, or maltose), it is converted into glucose and
considered to be six carbons with six waters, or C 6 (H 2 O) 6 . How- transported by the bloodstream for use by the body.
ever, carbohydrate molecules are more complex than just water Polysaccharides are polymers consisting of mono saccharide
attached to a carbon atom. They are polyhydroxyl aldehydes units joined together in straight or branched chains. Polysac-
and ketones, two of which are illustrated in Figure 12.20. The charides are the energy-storage molecules of plants and animals
two carbohydrates in this il lus tration belong to a group of car- (starch and glycogen) and the structural molecules of plants

bohydrates known as mono saccharides, or simple sugars. They (cellulose). Starches are a group of complex carbohydrates
are called simple sugars because they are the smallest units that composed of many glucose units that plants use as a stored food
have the characteristics of carbohydrates, and they can be com- source. Potatoes, rice, corn, and wheat store starch granules and
bined to make larger complex carbohydrates. There are many serve as an important source of food for humans. The human
kinds of simple sugars, but they are mostly 6-carbon molecules body breaks down the starch molecules to glucose, which is
such as glucose and fructose. Glucose (also called dextrose) is transported by the bloodstream and utilized just as any other
found in the sap of plants, and in the human bloodstream, it is glucose. This digestive process begins with enzymes secreted
called blood sugar. Corn syrup, which is often used as a sweet- with saliva in the mouth. You may have noticed a result of this
ener, is mostly glucose. Fructose, as its name implies, is the enzyme-catalyzed reaction as you eat bread. If you chew the
sugar that occurs in fruits, and it is sometimes called fruit sugar. bread for a while, it begins to taste sweet.

312 CHAPTER 12 Organic Chemistry 12-14