Laboratory Notes for BIO 6
Gene Problems in Transcription and Translation
1. For the segment of a strand of DNA whose nucleotide sequence is shown below, write the correct
mRNA sequence that would correspond to this DNA strand. What is the polypeptide strand that would
result? BE CAREFUL! You may have to replicate this DNA strand first!
5’ A T C A T G C G A G G G C T T A A A A C C G A C A T T A G C C T G A T T T A G 3’
3’T A G T A C G C T C C C G A A T T T T G G C T G T A A T C G G A C T A A A T C 5’
mRNA :
5’ A U C A U G C G A G G G C U U A A A A C C G A C A U U A G C C U G A U U U A G 3’
Polypeptide:
Met, Glu, Gly, Leu, Lys, Thr, Asp, Ile, Ser, Leu, Ile
2. Using a codon table, write the six different mRNA codons for serine.
UCU, UCC, UCA, UCG, AGU, AGC
3. How many codons are there for valine? for asparagine? for tryptophan?
Valine = 4
Asparagine = 2
Tryptophan = 1
4. Why must every mRNA begin with the codon AUG?
It is the part of the initiator tRNA that positions itself at the P site during Translation Initiation
5. Write the three different mRNA termination (STOP) codons. UAA, UAG, UGA
These six possible codons for arginine might appear in a molecule of mRNA. For each one, write the
anticodon on the tRNA molecule that will carry arginine to the ribosome when that particular codon is
read.
Codons Anticodons
CGU
GCA
CGC
GCG
CGA
GCU
6.
CGG
GCC
AGA
UCU
AGG
UCC
For the nucleotides in the mRNA molecule shown below, write the appropriate amino acid sequence in
the protein synthesized when this message is read by the ribosome (i.e. translated). Underline the
untranslated regions. Where would you modify this mRNA with a methylated cap and a poly-A tail?
5’ C C C G A G A U G G G A U U U C U C G G A A A A U U C A G G U A A A C A U G C 3’
Met
Gly
Phe
Leu
Gly
Lys
Phe
Arg
5’ end = methylated cap
3’ end = poly-A tail
7. The nucleotide sequence of a gene (segment of a strand of DNA) coding for a protein six amino acids
long is given below:
3’ T A C G T A C T G C G C A A G A A T A T C 5’
a. Write the appropriate sequence of nucleotides in the mRNA.
5’ A U G C A U G A C G C G U U C U U A U A G 3’
b. Write the appropriate amino acid sequence in the polypeptide strand encoded by this gene
sequence.
Met Asp Ala Phe Leu
c. Write the anticodons for the tRNAs bringing amino acids to the ribosome for the
synthesis of this protein.
UAC, GUA, CUG, CGC, AAG, AAU
d. Compare the anticodons with the original DNA sequence. Do you notice any similarity?
The same sequence as the anti-sense DNA except the T is replaced with a U
For questions 9—14. Five transformations of an original sequence of nucleotides in one half of an DNA
helix are given (a-e). The original DNA reads:
TACCGCAATGCTTGAGGC
mRNA:
AUGGCGUUACGAACUCCG
polypeptide:
Met
Choices :
Ala
Leu
Arg
Thr
Pro
e. A T G G C G T T A C G A A C T C C G
f. A U G G C G U U A C G A A C U C C G
g. T A C C G C A A A G C T T G A G G C
h. T A C G C A A T G C T T G A G G C
8. Which of the above choices would result by replicating the DNA sequence?
Choice e
9. Which of the above choices would be the result of a mutation known as a base substitution?
Choice g – the codon AAT is mutated to AAA
10. If you transcribed and translated the sequence you picked in question #9 - what amino acid is coded for
by the original DNA codon? What amino acid would result from the mutation?
The codon AAT is mutated to AAA; which means in the mRNA, the codon UUA is mutated to
UUU; this will change the leucine to phenylalanine
original:
Choice g :
mRNA:
polypeptide:
TACCGCAATGCTTGAGGC
TACCGCAAAGCTTGAGGC
AUGGCGUUUCGAACUCCG
Met
Ala
Phe Arg
Thr Pro
11. Which of the above would be the result of a mutation known as a nucleotide deletion causing a frame
shift?
Choice h – the C at base 3 is missing
12. If you transcribed and translated the sequence you picked in question #11, what would your new
polypeptide sequence be?
Original:
TACCGCAATGCTTGAGGC
Choice h:
TACGCAATGCTTGAGGC
mRNA:
AUGCGUUACGAACUCCG
polypeptide:
Met
Arg
Tyr
Glu
Leu
13. Which of the above is a primary transcript of mRNA from the original DNA? What is the polypeptide
sequence?
Choice f
14. Which of the mutations you identified above will have the greatest phenotypic effect? Explain your
answer.
Choice h the deletion results in a frame shift. Frame shifts have significant phenotype effects as the
resulting protein is frequently non-functional.