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Lesson 27: Biological Molecules (4.1.1)
All living things have in common several distinctive characteristics. The first among
these is the existence of cells. Each time you eat, you are providing your cells with what
is needed to carry out the basic functions of life. List the food(s) you and a classmate had
for breakfast this morning. It may be hard to believe, but each food that you listed
contains carbon! Let’s investigate further.
CHEMISTRY OF THE CELL
Carbon is especially important because one carbon atom can make covalent bonds with
four other atoms, resulting in the formation of very stable and complex structures.
Carbon is in all living things, as well as in the remains of living things. Molecules
containing carbon are called organic molecules (macromolecules). Those without
carbon are called inorganic molecules. Carbon dioxide, CO2, is the exception; it is
inorganic. Water is the most important inorganic molecule for living things, and serves
as the medium in which cellular reactions take place.
The four primary classes of organic compounds, often referred to as macromolecules, are
carbohydrates, lipids, proteins, and nucleic acids. Each of these is a polymer, a long
chain of small repeating subunits called monomers.
ORGANIC COMPOUNDS (BIOMOLECULES)
Carbohydrates are often called sugars, and are an
energy source. The simplest carbohydrates are subunits
called monosaccharides. Carbohydrates are composed
of carbon, hydrogen and oxygen in a ratio of 1:2:1.
Monosaccharides, such as glucose in the diagram above,
may join together to form disaccharides.
Monosaccharides are used as a quick source of energy.
When two monosaccharides join, they form a
disaccharide that function as transport sugars. Many
monosacchrides and disaccharides combine to form
polysaccharides. There are three main polysaccharides:
starch, cellulose, and glycogen. Each has a specific
function related to its shape. Table 27.1 summarizes a
few different types of carbohydrates.
Table 27.1 Different Types of Carbohydrates
Sugar
Type
Monosaccharide
Glucose
Polysaccharide
Starch
Polysaccharide
Cellulose
Glycogen
Polysaccharide
Cell
Plant and Animal
Plant
Plant
Animal
Use
Short term energy.
Glucose storage.
Structure and
support.
Glucose storage.
Lab Activity 1: Testing Starch
Iodine is useful in testing for the presence of starch. Use grapes, egg whites and butter. Place
these bits of food on a paper towel. Put a drop of iodine on each bit of food. Observe any
change in color
 Reddish- brown means the food contains little or no starch.
 Yellow means the food contains some starch
 Blue-black means the food contains a lot of starch
FOOD AND MACROMOLECULE TEST
To find the macromolecules present in different types of foods, several tests can be done.
Table 27.2 below summarizes the type of tests for each particular macromolecules.
Table 27.2 Food Tests
Macromolecule
Starch (polysaccharide)
Monosaccharide
Protein
Lipid
Testing substance
Iodine
Benedict’s Solutions
Biuret’s
Brown Paper Bag
Results
Yellow to black
“Carolina” blue to reddish-brown
“Duke” blue to purple
Translucent
PROTEINS
Proteins consist of long chains of amino acids
monomers called polypeptides. Figure 27.2 shows a
polypeptide; Figure 27.3 shows several polypeptides
linked together to form a protein. There are many
different types of proteins, which all have different
biological
functions. They
include:
structural proteins, regulatory proteins, contractile
proteins, transport proteins, storage proteins,
protective proteins, membrane proteins, toxins and
enzymes. Despite the wide variation in function,
shape and size, all proteins are made from the same
20 amino acids. The function of a protein is
determined by the order of amino acids, and the way
the polypeptides folds on itself. For example,
enzymes are specific to the substrate (reactant) they
bind to. The way an enzyme folds on itself determines what substrate it binds to.
Enzyme will be further discussed later. Since mammals cannot make all 20 amino acids
themselves, they must eat protein in order to maintain a healthy diet. Examples of
protein containing foods are beef, fish, poultry, beans, and cheese. Insulin and
Hemoglobin are two types of proteins.
Insulin is a protein released from the pancreas when blood sugar levels are too high.
Insulin communicates with the liver and muscle cells “telling” them both to remove
glucose from the bloodstream and store excess glucose as glycogen. Hemoglobin is
another protein found in the red blood cells of many animals. It is responsible for
bonding with oxygen and carrying this oxygen to body cells in order for aerobic cellular
respiration to occur. Aerobic cellular respiration is the process in which organisms use
oxygen in order to break down glucose and gain energy needed for life processes. It also
removes carbon dioxide, which is toxic to the body tissues.
LIPIDS
Lipids are fatty substances that have several functions but are most well known as fat
molecules that store long term energy. They are also the structural components of the
cell membrane. Lipids are fats composed of a glycerol and three fatty acids as seen in
Figure 27.4. Several important lipids have names that you may recognize: fats, oils,
waxes, and steroids. The excess of lipids strongly linked to heart disease and stroke.
Lab Activity 2: Testing for Fats in Food
Use a piece of brown paper bag to test for fat. Use grapes, egg whites and butter. Rub
the brown paper with each bit of food. Wait for 10 minutes. Hold the paper up to the
light.
 If not fat is present, the paper will appear opaque.
 If some fat is present, the paper will appear semi-translucent
 If a lot of fat is present, the paper will appear translucent.
Similar ACIDS
to resource from NC Biology SCOS Support Document: Unit 1 Life on a Cellular
NUCLEIC
Level, page 106-108. http://www.dpi.state.nc.us/curriculum/science/units/high/
Nucleic acids are found in the nucleus of a cell. The nucleic acid polymer is made up of
nucleotide monomers. The nucleotide monomer consists of a sugar, a phosphate group
and a nitrogenous base, Figure 27.5. Three examples of nucleic acids are:
a) DNA (deoxyribonucleic acid) directs
the activities of the cell and contains
the sugar deoxyribose.
b) RNA (ribonucleic acid) is involved
in protein synthesis and contains the
sugar ribose.
c) ATP (adenosine triphosphate)
provides energy for the cells
and is involved in almost every
reaction in the body
(See Lesson 30, Figure 30.1 for ATP diagram)
Now that the organic compounds present in the cell have been introduced, can you guess
which one makes up the bulk of a cell? Look at Figure 27.6. The bulk of a cell is not
made up of the
four organic
compounds, but is
mainly water.
Review Lesson 27: The Chemistry of the Cell
A. Define the following:
element
organic molecules
monomers
carbohydrates
polysaccharide
protein
lipids
nucleic acids
inorganic molecules
monosaccharide
insulin
nucleotides
polymers
disaccharides
hemoglobin
food nutrients
B. Select the best answer
1. Carbon chains are principal features of both carbohydrates and lipids. What is the
primary
difference between these two types of biomolecules?
A. Lipids always have a longer carbon chains than carbohydrates
B. Carbohydrates carry hydroxyl groups on their carbon backbone.
C. Carbohydrates cannot form rings as lipids can.
D. Lipids stores energy longer in the body as compared to carbohydrates
2. What molecules make up the bulk of a cell?
A. carbohydrates
C. proteins
B. lipids
D. water
3. Carbon is important to living things because
A. it metabolizes easily, creating a quick energy source\.
B. it is abundant on the earth’s surface.
C. it can form four covalent bonds with other atoms
D. it has twelve protons and neutrons.
4. Nucleotides are to nucleic acids as amino acids are to
A. DNA
C. proteins
B. polypeptides
D. carbohydrates
5. Organic compounds most often formed using which type of bond?
A. ionic bonds
C. peptide bonds
B. covalent bonds
D. hydrogen bonds
C. Complete the following exercises
1. All living things have a common tie with the Earth on which we live. Explain why this
is true.
2. What are the six elements commonly found in living things?
3. Why is carbon important to living things?