Problem Set 5: Transcription and Translation
General Instructions
- This is a group activity.
- Answer the problems shown below.
- Submit your answers in pdf/jpg formats only following the naming, Chem40_PS5_<Section>_<Group No.>
- Only one submission per group is needed.
Problems
1. The 5 -end of an mRNA has the sequence
...AGAUCCGUAUGGCGAUCUCGACGAAGACUCCUAGGGAAUCC...
What is the nucleotide sequence of the DNA template strand from which it was transcribed? If this mRNA is translated beginning with the first AUG codon in its sequence, what is the N-terminal amino acid sequence of the protein it encodes? Please refer to the codon table provided.
2. RNA polymerase has two binding sites for ribonucleoside triphosphates: the initiation site and the elongation site. The initiation site has a greater Km for NTPs than the elongation site. Suggest what possible significance this fact might have for the control of transcription in cells.
3. Make a list of the ways that transcription in eukaryotes differs from transcription in prokaryotes.
4. Review the evidence establishing that aminoacyl-tRNA synthetases bridge the information gap between amino acids and codons. Indicate the various levels of specificity possessed by aminoacyl-tRNA synthetases that are essential for high-fidelity translation of messenger RNA molecules.
5. Point out why Crick’s wobble hypothesis would allow fewer than 61 anticodons to be used to translate the 61 sense codons. How might “wobble” tend to accelerate the rate of translation?
6. In transpeptidation, which of the following seems the most apt account of the peptidyl transfer reaction: (a) The peptidyl-tRNA delivers its peptide chain to the newly arrived aminoacyl-tRNA situated in the A site, or (b) the aminoacyl end of the aminoacyl-tRNA moves toward the P site to accept the peptidyl chain? Which of these two scenarios makes more sense to you? Why?
7. Chloramphenicol inhibits the peptidyl transferase activity of the 50s ribosomal subunit. The 50S peptidyl transferase active site consists solely of functionalities provided by the 23S rRNA. What sorts of interactions do you think take place when chloramphenicol binds to the peptidyl transferase center? Which groups on chloramphenicol might be involved in these interactions?
8. Describe the mechanism of the following drugs/chemicals in inhibiting gene expression.
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- puromycin
- rifampicin
- ethidium bromide
- streptomycin
- chloramphenicol
- 5 April 2021, 5:25 PM