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C2. In bacteria, what event marks the end of the initiation stage of transcription?
The release of sigma factor marks the transition to the elongation stage oftranscription.
C8. A mutation within a gene sequence changes the start codon to a stop codon. How will this mutation affect the transcription of this gene?
This will not affect transcription. However, it will affect translation by preventing the initiation of polypeptide synthesis.
C16. The structure and function of DNA helicase and ρ protein are rather similar to each other. Explain how the functions of these two proteins are similar and how they are different.
Both DNA helicase and ρ protein break the hydrogen bonds of the DNA and move 5’ to 3’. They are different in that DNA helicase moves along the DNA and is used for DNA replication while ρ protein moves along the RNA and is used to promote transcriptional termination.
C18. Mutations that occur at the end of a gene may alter the sequence of the
gene and prevent transcriptional termination.
A. What types of mutations would prevent ρ-independent termination?
B. What types of mutations would prevent ρ-dependent termination?
C. If a mutation prevented transcriptional termination at the end of a gene, where would gene transcription end? Or would it end?
- A. Mutations that alter the uracil-rich region by introducing Gs and Cs, and mutations that prevent the formation of the stem-loop structure.
- B. Mutations that alter the termination sequence, and mutations that alter the ρ recognition site.
- C. Eventually, somewhere downstream from the gene, another transcriptional terminationsequence would be found, and transcription would terminate there. This secondtermination sequence might be found randomly or it might be at the end of an adjacentgene.
E16. A. gel retardation assay can be used to determine if a protein binds to DNA.
This method can also determine if a protein binds to RNA. In the combinations described here, would you expect the migration of the RNA to be retarded due to the binding of a protein?
A. mRNA from a gene that is terminated in a ρ-independent manner plus ρ protein.
B. mRNA from a gene that is terminated in a ρ-dependent manner plus ρ
C. pre-mRNA from a structural gene that contains two introns plus the
snRNP called U1.
D. Mature mRNA from a structural gene that contains two introns plus the snRNP called U1.
- A. No because rho will not bind to the RNA
- B. Yes rho will be there to attach to the RNA.
- C. It would be retarded because U1
- would bind to the pre-mRNA.
- D. It would not be retarded because U1 would not bind to mRNA that has already had
- its introns removed. U1 binds only to pre-mRNA.