UNIT 5 homework*Reminder: When answering these questions use your own words only!
False to True
The following statements are false. Explain why and rewrite the sentences so
that they read true.
1) All 64 codons specify an amino acid. (1 pt)
2) Ribosomal proteins are ‘running the show’ during translation. (1.5 pt)
3) The role of Elongation Factor-2 (EF-2) is to release the mRNA molecule from the ribosome.
(1.5 pt)
4) Misfolded proteins are marked with phosphorylation and delivered to the proteasome,
where they can attempt to refold. (1 pt)
5) The stop codon results in the addition of a terminating amino acid through peptide bond
formation. (1.5 pt)
6) In order to detect specific proteins in a cell sample, we use complementary amino acid
sequence to target the protein. (1 pt)
Multiple Choice Explained
7) The concentration of a particular protein, X, in a normal human cell rises gradually from a
low point, immediately after cell division, to a high point, just before cell division, and then
drops sharply. The level of its mRNA in the cell remains fairly constant throughout this time.
What is the best explanation of the drop in protein concentration? Explain your answer.
(1.5 pts)
A. Gene expression of Protein X was suppressed
B. There was a mutation in the gene of Protein X
C. Protein X was targeted for ubiquitination
D. After cell division, protein X was secreted out of the cell
8) There is a mutation in your ribosome! Instead of translating properly, you have only the
initiator tRNA (attached to methionine), and the next matching tRNA in the A site (carrying a
lysine). You are able to form a peptide bond between the lysine and methionine, but then
translation stalls. Given this scenario where do you predict the mutation is? Explain your
thinking. (1.5 pts)
A. A site
B. P site
C. E site
D. mRNA binding site
9) A mutation in the tRNA for the amino acid histidine results in the anticodon sequence 5′CUG-3′ (instead of 5′-AUG-3′). Which of the following aberrations in protein synthesis might this
tRNA cause? Explain your answer. (1.5 pts)
A. Read-through of stop codons
B. Substitution of histidine for lysine
C. Substitution of histidine for proline
D. Substitution of histidine for glutamine
Short Answer
10) If you used the following repeating nucleotide sequence in a cell-free translation system,
what amino acids would you get out? (Assume you do not need a start codon in this instance.)
5’ CUCUCUCUCUCUCUCU….3’ (1 pt)
11) (4 pts) Below is a piece of DNA from a gene.
3′-GTGCTACTTTAGACGGCTACCGCAT-5′
A. First transcribe the DNA into RNA. Write out the RNA sequence:
B. Next, using the amino acid chart, translate the RNA into a polypeptide. Write out the
polypeptide sequence:
C. Your gene sequence suffered a loss of the nucleotide shown in red. Write the amino acid
sequence that would now be translated.
3′-GTGCTACTTTAGACGGCTACCGCAT-5′
D. Explain what a ‘shift in the reading frame’ means for translation.
12) (1.5 pt) A. Look up the dictionary definition (Webster’s, etc.) of the word translation.
Write it below.
B. What special meaning does this word have when applied to the living cell?
13) Your research partner, George, is performing a Western blot to look for a thyroid protein in
various blood samples from mice. He ran the samples on the gel, transferred to the membrane,
and probed with an antibody to the thyroid protein. But when he developed the blot it had no
signal anywhere. What mistake did George make? What does he need to do to fix it? Explain.
(1.5 pts)
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