Dr. Beatriz Gonzalez
In-Class Worksheet
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Name: __________________________
Just one nucleotide! Exploring the
effects of random single
nucleotide mutations
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Learning Objectives:
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Given a coding DNA sequence, determine the mRNA
•
Based on the transcribed mRNA, predict the resulting protein sequence
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Become proficient in using the codon chart to determine which codons code for which amino acids
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Recognize the importance of the START and the STOP codons
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Predict the effect that different types of mutations will have on the protein expressed
Introduction
The Central Dogma of molecular biology is the concept that cells are ruled by a cellular chain of
command that flow from DNA to RNA to protein. The information is housed in the DNA, transcribed
into a RNA molecule and translated into a protein. Therefore, protein synthesis occurs by means of
transcription and translation. Transcription occurs in the nucleus and produces RNA pairing
complementary bases to the coding DNA strand. This RNA is modified and processed in eukaryotes and
then goes to the cytoplasm where translation takes place (either in polyribosomes or in ribosomes
attached to the rough endoplasmic reticulum). Here the mRNA code is converted into a protein, a chain of
amino acids.
Activity 1: Review of base-pair rules
1. Fill out the following table to review the complementary base-pair rules during the processes of DNA
replication vs. transcription:
DNA Replication
If DNA template has
Newly made DNA
this base:
will have:
A
Transcription
If DNA template has mRNA will
this base:
have:
A
C
C
G
G
T
T
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Activity 2: Transcription: Making mRNA
In this simple exercise, you will “transcribe” the coding DNA sequence into an mRNA. This particular
region does not contain introns.
1. Using the following coding DNA sequence, determine the resulting mRNA.
DNA sequence: (provided sequence shown 3’→5’) nt = nucleotide
# 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
nt T T C A T A C G A C G T C T A C G T A A C T G C T
mRNA sequence: (5’→3’)
Activity 3: Translation: mRNA Universal Codon Chart
Translation is the process that takes the information that was passed from DNA into the
messenger RNA and turns it into a linear sequence of amino acids covalently joined by peptide bonds. It
really is a translation from one code, nucleotide sequence, to another code, amino acid sequence.
1. Name the three different types of RNA. Mention their functions.
2. Where are ribosomes made and what are they made of? How do they get to their final destination?
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3. Refer to the universal codon chart below. The AUG codon, codes both for methionine and serves as
an initiation site; the first AUG in an mRNA's coding region will be the site where translation (not
transcription) into protein begins.
Universal Codon Chart
Table 1 : Codon table. This table illustrates the 64 possible codon triplets.
2nd base
U
UUU Phenylalanine
UUC Phenylalanine
U
UUA Leucine
UUG Leucine
CUU Leucine
CUC Leucine
C
CUA Leucine
1st base CUG Leucine
AUU Isoleucine
AUC Isoleucine
A
AUA Isoleucine
1
AUG Methionine
GUU Valine
GUC Valine
G
GUA Valine
GUG Valine
C
A
G
UCU Serine
UCC Serine
UCA Serine
UCG Serine
UAU Tyrosine
UAC Tyrosine
UAA Stop
UAG Stop
UGU Cysteine
UGC Cysteine
UGA Stop
UGG Tryptophan
CCU Proline
CCC Proline
CCA Proline
CCG Proline
ACU Threonine
ACC Threonine
ACA Threonine
ACG Threonine
GCU Alanine
GCC Alanine
GCA Alanine
GCG Alanine
CAU Histidine
CAC Histidine
CAA Glutamine
CAG Glutamine
AAU Asparagine
AAC Asparagine
AAA Lysine
AAG Lysine
GAU Aspartic acid
GAC Aspartic acid
GAA Glutamic acid
GAG Glutamic acid
CGU Arginine
CGC Arginine
CGA Arginine
CGG Arginine
AGU Serine
AGC Serine
AGA Arginine
AGG Arginine
GGU Glycine
GGC Glycine
GGA Glycine
GGG Glycine
a) What is a “start” codon? How many are there? Name the codon and amino acid:
b) Name all the amino acids that have only one codon:
c) Name all the amino acids that have multiple codons:
d) What does it mean when a codon translates into STOP? Name the three STOP codons.
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Activity 4: Translation: Determining the Protein Sequence
Using the following coding DNA sequence, determine the mRNA and the polypeptide chain coded by
this region of the DNA. (You determined this sequence earlier in activity 2)
DNA sequence: (provided sequence shown 3’→5’) nt = nucleotide
# 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
nt T T C A T A C G A C G T C T A C G T A A C T G C T
mRNA sequence: (5’→3’) (the same as in activity 2)
Amino acid sequence (polypeptide):
Activity 5: Exploring Point Mutations
Procedure:
1. Mutate nucleotide #10 in the DNA sequence provided according to the rules in table 1.
2. Your instructor will provide you with rubber dice so you can simulate what happens when the
DNA sequence is mutated – if the number you roll does not result in a change, keep rolling until
it changes.
3. Every student in your group should roll the die to mutate their own DNA. In this way, there will
be more outcomes to compare.
4. Write down your newly mutated DNA sequence.
5. Determine and record the mRNA and the protein sequence coded by the mutated DNA sequence.
Table 1: Rules for determining which kind of mutation will take place
If you toss a … Then you must …
1
Substitute your nucleotide with an A
2
Substitute your nucleotide with a C
3
Substitute your nucleotide with a G
4
Substitute your nucleotide with a T
5
Delete the nucleotide
6
Insert a nucleotide right after (toss again until you get 1–4 to determine
which letter nucleotide to insert)
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DNA sequence: (provided sequence shown 3’→5’) nt = nucleotide
# 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
nt T T C A T A C G A C G T C T A C G T A A C T G C T
Write complete new DNA sequence with mutation at nucleotide 10 position:
(Depending on the mutation, you will end up with a 24-nt, 25-nt, or 26-nt DNA sequence.)
mRNA sequence from mutated DNA:
Amino acid sequence (polypeptide): Circle any differences from original protein
Activity 6: More Mutations!
Keeping the mutated nucleotide, mutate nucleotide #16 following the procedure outlined in activity 5.
Write the resulting DNA, mRNA, and protein sequences
Write complete DNA sequence (now with two mutations: one at nt 10 position, and the second at
the nt 16 position):
mRNA sequence with both mutations:
Amino acid sequence (polypeptide): Circle any differences from original protein
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Activity 7: Thought Questions
1. Write the definition of the term mutation.
2. If a mistake is made during transcription, will that mistake be permanent? During translation? Why or
why not? Will it be passed on to the next generation of cells? Explain your answers.
3. Why do you think you used a die to determine the mutations? Why did you keep the first mutation
when mutating the sequence a second time? In other words, why didn’t you “fix” it?
4. Did everyone in your group get the same mutation(s)? Explain. What are the odds of two people rolling
the same number? Of rolling the same mutation?
5. Deletions and insertions are also called _______ - ________ mutations.
6. What is a point mutation? Differentiate between the following types of point mutations:
a) Substitution
b) Deletion
c) Insertion
d) Missense
e) Nonsense
7. Explain the statement: "A mutation causes a change in the genotype, but that change does not always
cause a change in the phenotype".
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Reference: Gonzalez, B.Y. and J. H. van Oostrom 2009. Using Dice to Explore the Consequences of DNA
Mutations, Journal of College Science Teaching 38 (5): 56-59
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