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Biology
Name__________________
Date__________Hour_____
Mutations Change the Meaning of Genes
Background:
Genetic sleuths, Beadle and Tatum helped develop the theory that one-gene codes for one
polypeptide. These two scientists were also one of the first scientists to demonstrate that changes or
mutations in the sequence of nucleotides can change the shape of the resulting protein, which often
changes the function of the protein.
Some types of mutations in DNA are substitutions, insertions or deletions. Sometimes a base
substitution does not change the shape of the protein. Other substitutions can drastically change the shape
and function of a protein. Some mutations can be beneficial to the organism, while some mutations can be
harmful. A physical or chemical agent that causes a mutation is called a mutagen.
Directions: Pretend you are a scientist working on Beadle and Tatum’s team. Follow the steps below to
build a “healthy protein” and answer the questions. Then build each mutated protein and answer the
questions.
1. Build A Healthy Protein
 Transcribe the gene in the table into mRNA.
 Use the table on page 237 in your textbook to translate the mRNA into the resulting amino
acid chain.
 Using the bead color key, find the color bead that corresponds with each amino acid. Under
each amino acid write the color of the bead that represents each amino acid.
 String the beads together to represent a protein.
 When finished raise your hand to check your protein.
 DO NOT TAKE THE HEALTHY PROTEIN APART.
Healthy
Gene
(DNA)
TAC
GGA
TCT
TTC
AAA
GGT
CAT
TTT
MRNA
Amino Acid
Bead Color
a. Explain why the DNA in the chart is called a gene.
b. Where is the DNA copied into mRNA? What is this process called?
c. Where is the mRNA “decoded” into a polypeptide chain? What is this process called?
d. What is the name of the three bases that code for a specific amino acid called?
ATT
2. How Does Smoking Change A Protein?
A friend of Mrs. Minoletti’s has smoked for ten years. Some of the chemicals found in cigarette smoke are
known mutagens.
 Compare the healthy gene and the mutated gene in the table below. Circle all of the mutation(s) in
the mutated gene.
 Transcribe the DNA into mRNA and translate the mRNA into an amino acid sequence.
 Build the resulting mutated protein strand using the pop-beads.
Healthy
Gene
Mutated
Gene
TAC
GGA
TCT
TTC
AAA
GGT
CAT
TTT
ATT
TAC
AGG
TCT
TCT
AAA
GGT
ACT
TTT
ATT
mRNA
Amino Acid
Bead Color
a. Compare the mutated protein to the healthy protein. List the number of amino acids that are different in
the mutated protein compared with the healthy protein.
b. This type of mutation is called a base substitution. Explain why this is a good name for this kind of
mutation.
3. Discover how chemicals can change a protein.
A neighbor of Mrs. Minoletti’s works at an industrial plant. Workers at the plant use an unknown
mutagen.
 Compare the healthy gene and the mutated gene in the table below. Circle all of the mutation(s)
in the mutated gene.
 Transcribe the DNA into mRNA and translate the mRNA into a protein.
 Build the resulting mutated protein strand using the pop-beads.
Healthy
Gene
Mutated
Gene
mRNA
Amino Acid
Bead Color
TAC
GGA
TCT
TTC
AAA
GGT
CAT
TTT
TAC
GGG
ATC
TTT
CAA
AGG
TCA
TTT
ATT
TAT
T
a. Compare the mutated protein to the healthy protein. List the number of amino acids that are different in
the mutated protein compared to the healthy protein.
b. This type of mutation is called an addition or a base insertion. Explain why this is a good name for this
kind of mutation.
4. Discover how exposure to radiation affects a protein.
Radiation is a mutagen that can cause mutations in the DNA.
 Circle the mutation(s) in the mutated gene.
 Transcribe the DNA in the mutated gene and translate the mRNA into a protein.
 Build the resulting mutated protein strand using pop-beads.
Healthy
Gene
TAC
GGA
TCT
TTC
AAA
G G T C A T T T T A TT
Mutated
Gene
TAC
GGA
TCT
TCA
AAG
GGT ATT TTA
TT
mRNA
Amino
Acid
Bead
Color
a. Compare the healthy protein with the mutated protein strand. List the number of amino acids that
are different in the mutated strand compared with the healthy strand.
b. This type of mutation is called a deletion. Explain why this is a good name for this kind of mutation.
c. Of the three types of mutations, which two appear to change the protein the most drastically?
Describe why you think this happens?
d. What happened to the sequence of the bases in the genes that experienced a base insertion or a
deletion and what is this called?
AMINO ACID COLOR CODE
AMINO ACID
BEAD COLOR
Met (start, methionine)
Blue
Pro (proline)
Pink
Ser (serine)
Yellow
Lys (lysine) and Gly (glycine)
Black
Phe (phenylalanine)
Orange
Val (valine)
White
Arg (arginine)
stop
Green