Which of the following statements about transcription is correct?
- The bacterial RNA holoenzyme is used during the elongation phase of transcription.
- During elongation, the RNA strand is extended in the 5' to 3' direction.
- Sigma factor is needed to recognize the transcriptional termination signal.
- The bacterial promoter lies just downstream of the start site of transcription.
answer
- During elongation, the RNA strand is extended in the 5' to 3' direction.
- Nucleotides are added to the 3' end of the growing RNA molecule.
question
How is a mutation in a bacterial cell that deletes three base pairs 10 base pairs upstream from the +1 site likely to affect transcription and why?
How is a mutation in a bacterial cell that deletes three base pairs 10 base pairs upstream from the +1 site likely to affect transcription and why?
answer
- Initiation will be inhibited because sigma cannot bind to the promoter.
- The +1 site is the transcription start site and the region 10 base pairs upstream is a region of the promoter critical for sigma binding and initiation.
question
During transcription in eukaryotes, a type of RNA polymerase called RNA polymerase II moves along the template strand of the DNA in the 3'→5' direction. However, for any given gene, either strand of the double-stranded DNA may function as the template strand.
answer
- the base sequence of the gene's promoter
question
Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus?
- A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA.
- A translation stop codon is added at the 3' end of the pre-mRNA.
- Coding sequences called exons are spliced out by ribosomes.
- A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA.
- Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes.
answer
- Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes.
- A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA.
- A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA.
question
During mRNA splicing ______.
answer
- snRNPs that make up the spliceosome recognize and remove introns
- The finished mRNA contains an uninterrupted message.
question
5' caps and 3' poly(A) tails of eukaryotic mRNAs ______.
answer
- protect mRNA from degradation and enhance translation
- Research has shown that mRNAs that have a cap and tail last longer in cells than mRNAs that don't
question
What is recognized by an aminoacyl tRNA synthetase?
answer
- one amino acid and the set of tRNAs that are coupled to that amino acid
- Aminoacyl tRNA synthetases "charge" tRNAs by catalyzing the addition of amino acids to them.
question
Which tRNA anticodon(s) could decode the mRNA codon CAG (recall that codons are always written in the 5'—>3' direction and anticodons are written in the 3'—>5' direction)?
- CUG only
- CUG or GUC
- GUC only
- GUU or GUC
answer
- GUU or GUC
- Non-standard ("wobble") base pairs between tRNA and mRNA (including G-U) are allowed at the third position of the codon.
question
How does the bacterial ribosome recognize where to start translation?
answer
- The small ribosomal subunit binds to a sequence in the mRNA just upstream of the start codon.
- The small ribosomal subunit binds to the Shine-Dalgarno sequence, which is about 6 nucleotides upstream from the start codon.
question
Why does cordycepin end transcription?
answer
- It lacks a 3' OH.
question
Where is an amino acid attached to a tRNA?
answer
- the 3' end
question
What would occur if a mutation caused an aminoacyl-tRNA synthetase to recognize both its normal amino acid and a different one?
answer
- One or more codons would sometimes be misread.
- The tRNA(s) recognized by this aminocacyl-tRNA synthetase could be attached to either amino acid, so the corresponding codon(s) could be read as either the correct or incorrect amino acid.
question
What enzyme catalyzes the attachment of an amino acid to tRNA?
answer
- aminoacyl-tRNA synthetase
- This enzyme matches a particular tRNA with a particular amino acid.
question
The tRNA anticodon, GAC, is complementary to the mRNA codon with the sequence _____.
answer
- CUG
- In RNA uracil replaces thymine.
question
The initiator tRNA attaches at the ribosome's _____ site.
answer
- P
- The initiator tRNA attaches to the ribosome's P site.
question
Which of these correctly illustrates the pairing of DNA and RNA nucleotides?
GTTACG
CAATCG
GTTACG
CAAUGC
GTTACG
GTTACG
GTTACG
ACCGTA
GTTACG
UAACAU
answer
- GTTACG
CAAUGC
- In RNA, uracil takes the place of thymine.
question
The direction of synthesis of an RNA transcript is _____.
answer
- 5' —> 3'
- Nucleotides are added to the 3' end of RNA.
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