TEKS 7.6C: Recognize how large molecules are broken down into smaller molecules such as
carbohydrates can be broken down into sugars.
Why do you need food?
• Food provides your body with materials to grow and
repair tissues. It provides energy for everything you do.
• Your body breaks down the food you eat into nutrients it
can use. Nutrients are the substances in food that
provide the raw materials and energy the body needs to
carry out life processes.
• People need six types of nutrients: carbohydrates, fats,
proteins, vitamins, minerals, and water. Of these,
carbohydrates, fats, and proteins must be broken down
into small molecules before the body can use them.
1. Identify List the six type of nutrients your body needs. Identify the three
that the body must break down before they can be used for life processes.
(contd.)
TEKS 7.6C: Recognize how large molecules are broken down into smaller molecules such as
carbohydrates can be broken down into sugars.
• Enzymes are biological catalysts. A catalyst speeds up, or even
simply makes possible, certain chemical reactions.
• Some of these reactions break down large nutrient molecules
into smaller ones. The diagram shows how this process works
during the digestion of carbohydrates (starch).
• The mouth, stomach, pancreas, and small intestine all make
enzymes that help digest food.
1. An enzyme molecule
becomes available.
2. A starch molecule fits the
chemical shape of the
enzyme.
3. The starch molecule binds
to the enzyme.
4. The starch molecule is
broken down into two sugar
molecules.
5. The enzyme and the
molecules separate.
TEKS 7.6C: Recognize how large molecules are broken down into smaller molecules such as
carbohydrates can be broken down into sugars.
How are carbohydrates broken down?
Carbohydrates are compounds that contain atoms of carbon,
hydrogen, and oxygen. These atoms are bonded to form
molecules of starches and sugars. There are several types of
carbohydrates:
• The sugars that provide your body with energy are called
monosaccharides. Mono means “one.” Saccharide means
“sugar.” A monosaccharide is made up of a single molecule
of simple sugar. The most common simple sugar is glucose.
• The carbohydrates you eat are mostly complex sugars,
such as disaccharides (two linked simple sugars) and
polysaccharides (many linked simple sugars). Complex
sugars must be broken down into simple sugars before your
body can use them.
(contd.)
TEKS 7.6C: Recognize how large molecules are broken down into smaller molecules such as
carbohydrates can be broken down into sugars.
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Enzymes break down carbohydrates.
The breakdown of large carbohydrate molecules begins in
the mouth. There, an enzyme in saliva breaks down starch
into smaller molecules.
No changes occur to carbohydrates in the stomach.
In the small intestine, a new set of enzymes acts on the
carbohydrates. Some enzymes are produced by the
pancreas; others are produced by the cells in the walls of the
small intestine. Together, these enzymes work to break down
the carbohydrates into simple sugars.
2. Sequence List the digestive organs that are involved in carbohydrate digestion in
order. Identify the organs in which enzymes act on complex carbohydrates to
eventually break them down into simple sugars.
TEKS 7.6C: Recognize how large molecules are broken down into smaller molecules such as
carbohydrates can be broken down into sugars.
How are proteins broken down?
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Proteins are large molecules that contain carbon,
hydrogen, nitrogen, and oxygen atoms. The simplest
unit in a protein is an amino acid. Proteins are made up
of long chains of 20 different amino acids bonded to one
another. Your body uses amino acids for life functions.
Two or more linked amino acids is known as a peptide.
The proteins you eat are polypeptides. They are made
of many, many peptides and thus many amino acids.
Enzymes in the stomach begin breaking large
polypeptides into smaller polypeptides.
In the small intestine, different enzymes produced by the
pancreas and cells in the wall of the small intestine
continue the breakdown of polypeptides until individual
amino acids result.
TEKS 7.6C: Recognize how large molecules are broken down into smaller molecules such as
carbohydrates can be broken down into sugars.
How are lipids broken down?
• Lipids are very large molecules that contain carbon, hydrogen,
and oxygen atoms. These atoms are bonded to one another,
forming molecules of fats, which are solid lipids, and oils, which
are liquid lipids.
• Many lipids are made up of smaller molecules called fatty acids
and glycerol. The bonds between these molecules are broken in
the small intestine by enzymes made by the pancreas and small
intestine.
• Bile, produced by the liver, aids this process. Bile breaks up
globs of lipids into tiny droplets. The larger surface area of the
droplets allows enzymes to more easily break down the lipids.
3. Infer In which organ does most digestion of food occur?