Chapter 5 Activity: Identifying Macromolecules
Organic macromolecules can often seem large and overwhelming upon first inspection with possibly
hundreds of atoms comprising their complex structures. But a closer, more careful look will reveal
repeatable patterns of atoms which gives clues to the type of macromolecule. Learning a few simple rules
can go a long way to revealing the identity of the macromolecule. The following exercise will help you
figure out some of those rules. Work through the questions within your lab group and try to come to a
consensus on some ways you could distinguish different macromolecules, filling out the chart at the end.
1.) Which of the macromolecules can be composed of carbon (C), hydrogen (H) or oxygen (O) alone?
CARBOHYDRATES, SOME LIPIDS
2.) Which of the macromolecules must have their C, H, and O in a 1:2:1 ratio?
CARBOHYDRATES
3.) Which of the macromolecules must contain phosphorus (P)?
NUCLEIC ACIDS, PHOSPHOLIPIDS
4.) Which of the macromolecules must contain nitrogen (N)?
NUCLEIC ACIDS, PROTEINS
5.) If you wanted to label only the RNA in a cell and not DNA, what compound(s) could you label that are
specific for RNA?
URACIL; RIBOSE
6.) If you wanted to label only the DNA, what compound(s) could you label?
THYMINE; DEOXYRIBOSE
7.) An RNA virus contains only RNA and a protein covering. You want to label to tag only the RNA in the
virus. Which of the following would you use? Explain your answer.
A. Phosphorus
B. Nitrogen
C. Sulfur
D. Carbon
All macromolecules have carbon so D. is out. Proteins only have sulfur so C. is out. Both nucleic
acids and proteins have nitrogen so B. is out. That leaves only phosphorus which RNA but
proteins do not.
8.) You are given an unknown white powdery substance and are asked to identify it as a carbohydrate or
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a lipid. How could you distinguish between the two? (Hint: Assume you have a source of water)
Attempt to dissolve in water. If water is a good solvent for the substance, it is a carbohydrate. If it
doesn’t dissolve, it is a lipid.
9.) How could you distinguish a phospholipid from a fat? (Again, you have water.)
Fats are entirely hydrophobic so they will form a top or bottom layer with water. Phospholipids
are amphipathic and will form bilayers in water like cell membranes.
10.) Based on your answers to the previous questions, develop some simple rules you can use to identify
the following macromolecules.
Type of
Rules
macromolecule
Name of
Monomer
Carbohydrates Made only of carbon:hydrogen:oxygen Monosaccharide
Lipids
Proteins
Nucleic acids
in a 1:2:1 ratio. Possess a carbonyl
group, either a ketone or an aldehyde.
Are hydrophilic due to many hydroxyl
groups.
Can be made of just carbon, hydrogen No monomer
and oxygen in fats but not in a 1:2:1
ratio. Can have long, hydrophobic
hydrocarbons (fatty acids). Some
lipids are amphipathic and possess
hydrophilic
groups.
Proteins
arephosphate
made of amino
acids and Amino acid
Steroids
4 ring
structures
lack
all
animoare
acids
have
an aminothat
group
fatty acid
tails.
which
must
have N and a carboxyl
group. Some R groups can have
sulfur.
All nucleic acids are made of
Nucleotide
nucleotides which will have a 5C
sugar, a phosphate group so they will
all have phosphorus and one of the 5
possible nitrogenous bases so they
will have nitrogen.
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Name of bond b/t
monomers
Glycosidic linkage
Bond that joins fatty
acid tails to glycerol
is ester linkage
Peptide bond
Bond that joins
sugars and
phosphate is
phosphodiester
bond. H bonds b/t
complementary
bases.