(1) Monosaccharides are called the "simple sugars" because they cannot be
further broken down into simpler molecules. The monosaccharide glucose is the major
carbohydrate used for fuel by the cells.
Disaccharides are two monosaccharides that are joined chemically.
(3) Polysaccharides are a group of five or more monosaccharides that are
d. Proteins are complex molecules of chemically linked chains of amino acids.
Proteins are essential components of all cells in the body and have many functions
within the human body. Some proteins function as enzymes, some as antibodies, and
some are used for nutrition. The diet must contain sufficient protein to replace the
protein broken down during normal body functions and growth. Proteins are broken
down into their constituent amino acids to be absorbed from the digestive tract. These
amino acids are transported to the body's cells, where they are recombined to form
(synthesize) new protein molecules.
(1) All proteins are synthesized from combinations of the naturally occurring
amino acids. A great variety of proteins are made possible with only a limited number of
amino acids because a different protein is created with each variation in the number and
arrangement of the amino acids. This can be likened to the alphabet and words. The
letters (amino acids) can be combined in a multitude of ways to form different words
(2) Ten of these amino acids are termed "essential" amino acids. This is
due to the fact that these amino acids cannot be synthesized within the body, but must
be consumed as food for growth and survival. Other amino acids can be synthesized
within the body from other molecules present within the cells. A food protein that
contains all the essential amino acids is referred to as a "complete" protein.
e. Fat is primarily an energy source. In addition to its value as an energy
source, fat serves as a carrier for the fat-soluble vitamins (A, D, E, and K) and adds
flavor to the diet. Fats are emulsified in the intestine and split into fatty acids and
glycerol for absorption. If not used as immediate energy sources, fatty acids are re-
synthesized into body fat and stored in the many fat cells of the body for future use.
Metabolism refers to all the chemical activity within the body. All chemical
reactions either release or require energy. Metabolism has two phases: an energy-
generating process called catabolism and an energy-requiring process called
anabolism. Both processes occur simultaneously within the cells, but they are regulated
independently. For this reason, the body's metabolism can be thought of as energy