Bio 1 Chp 7 Quizzes and HW

Transcription in bacteria differs from transcription in a eukaryotic cell because __________________________.

RNA polymerase (along with its sigma subunit) can initiate transcription on its own.

RNA in cells differs from DNA in that ___________________.

it is single-stranded and can fold up into a variety of structures.

In eukaryotes, but not in prokaryotes, ribosomes find the start site of translation by ____________________________.

scanning along the mRNA from the 5′ end.

Which amino acid would you expect a tRNA with the anticodon 5′-CUU-3′ to carry? (Hint: you should use the codon table to answer)

As is conventional for nucleotide sequences, the anticodon is given reading from 5′ to 3′. The complementary base-pairing occurs between antiparallel nucleic acid sequences, and the codon recognized by this anticodon will therefore be 5′-AAG-3′. The correct answer is: lysine

Which of the following molecules of RNA would you predict to be the most likely to fold into a specific structure as a result of intramolecular base-pairing? Select one: a. 5′-CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3′ b. 5′-UGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUG-3′ c. 5′-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-3′ d. 5′-GGAAAAGGAGAUGGGCAAGGGGAAAAGGAGAUGGGCAAGG-3′

a. 5′-CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3′ Correct Choice (a) is correct. Choices (b) and (c) do not have any opportunity for intramolecular base-pairing and thus a specific structure is unlikely. Although there is some opportunity for intramolecular base-pairing in choice (d), choice (a) has much more intrastrand complementarity and is a better choice.

Which of the following does not occur before a eukaryotic mRNA is exported from the nucleus? a. The ribosome binds to the mRNA. b. The mRNA is polyadenylated at its 3′ end. c. 7-methylguanosine is added in a 5′-to-5′ linkage to the mRNA. d. RNA polymerase dissociates.

a. The ribosome binds to the mRNA. because, ribosomes are in the cytosol and will bind to the mRNA once it has been exported from the nucleus.

Which of the following statements about RNA splicing is false? a. Conventional introns are not found in bacterial genes. b. For a gene to function properly, every exon must be removed from the primary transcript in the same fashion on every mRNA molecule produced from the same gene. c. Small RNA molecules in the nucleus perform the splicing reactions necessary for the removal of introns. d. Splicing occurs after the 5′ cap has been added to the end of the primary transcript.

b. For a gene to function properly, every exon must be removed from the primary transcript in the same fashion on every mRNA molecule produced from the same gene. The primary transcript of a gene can sometimes be spliced differently so that different exons can be stitched together to produce distinct proteins in a process called alternative splicing.

A poison added to an in vitro translation mixture containing mRNA molecules with the sequence 5′-AUGAAAAAAAAAAAAUAA-3′ has the following effect: the only product made is a Met-Lys dipeptide that remains attached to the ribosome. What is the most likely way in which the poison acts to inhibit protein synthesis? a. It inhibits peptidyl transferase activity. b. It inhibits movement of the small subunit relative to the large subunit. c. It inhibits release factor. d. It mimics release factor.

b. It inhibits movement of the small subunit relative to the large subunit. Correct Choice (b) is correct. Choice (a) would prevent all peptide bond formation. Choice (c) would have no effect on translation until the stop codon was reached. Choice (d) would be likely to result in a mixture of polypeptides of various lengths; a poison mimicking a release factor could conceivably cause only Met-Lys to be made, but this dipeptide would not remain bound to the ribosome.

Which of the following statements about prokaryotic mRNA molecules is false? Select one: a. A single prokaryotic mRNA molecule can be translated into several proteins. b. Ribosomes must bind to the 5′ cap before initiating translation. c. Ribosomes can start translating an mRNA molecule before transcription is complete. d. mRNAs are not polyadenylated.

b. Ribosomes must bind to the 5′ cap before initiating translation. Correct

You have a bacterial strain with a mutation that removes the transcription termination signal from the Abd gene. Which of the following statements describes the most likely effect of this mutation on Abd transcription? a. The Abd RNA will not be produced in the mutant strain. b. The Abd RNA from the mutant strain will be longer than normal. c. Sigma factor will not dissociate from RNA polymerase when the Abd operon is being transcribed in the mutant strain. d. RNA polymerase will move in a backward fashion at the Abd operon in the mutant strain.

b. The Abd RNA from the mutant strain will be longer than normal. Correct (b) Without the termination signal, the polymerase will not halt and release from the DNA template at the normal location when transcribing the And gene. Most probably, the polymerase will continue to transcribe RNA until it reaches a sequence in the DNA that can serve as a termination sequence, either from the next downstream operon or in the intervening sequence between the Abd operon and the next gene. Dissociation of sigma factor occurs once an approximately 10-nucleotide length of RNA has been synthesized by RNA polymerase and should not be affected by the lack of a termination signal [choice (c)].

Which of the following statements about the genetic code is correct? Select one: a. All codons specify more than one amino acid. b. The genetic code is redundant. c. All amino acids are specified by more than one codon. d. All codons specify an amino acid.

b. The genetic code is redundant. Correct (b) Most amino acids can be specified by more than one codon. Each codon specifies only one amino acid [choice (a)]. Tryptophan and methionine are encoded by only one codon [choice (c)]. Some codons specify translational stop signals [choice (d)].

Where does translation take place in the eukaryotic cell?

ribosomes

The ribosome is important for catalyzing the formation of peptide bonds. Which of the following statements is true? Select one: a. The number of rRNA molecules that make up a ribosome greatly exceeds the number of protein molecules found in the ribosome. b. The large subunit of the ribosome is important for binding to the mRNA. c. The catalytic site for peptide bond formation is formed primarily from an rRNA. d. Once the large and small subunits of the ribosome assemble, they will not separate from each other until degraded by the proteasome.

c. The catalytic site for peptide bond formation is formed primarily from an rRNA. Correct Choice (c) is correct. A ribosome is built from many more proteins than rRNA molecules, although the ribosome is about two-thirds RNA and one-third protein by weight. Thus, (a) is incorrect. The small subunit binds to mRNA, so (b) is incorrect. Choice (d) is incorrect, as the assembly and disassembly of the small subunit with the large subunit occurs every time a protein is produced from an mRNA. When release factor binds to an mRNA, the ribosome will release the mRNA and dissociate into its two subunits, to be recycled during another round of protein synthesis.

Which of the following methods is not used by cells to regulate the amount of a protein in the cell? Select one: a. Genes can be transcribed into mRNA with different efficiencies. b. Many ribosomes can bind to a single mRNA molecule. c. Proteins can be tagged with ubiquitin, marking them for degradation. d. Nuclear pore complexes can regulate the speed at which newly synthesized proteins are exported from the nucleus into the cytoplasm.

d. Nuclear pore complexes can regulate the speed at which newly synthesized proteins are exported from the nucleus into the cytoplasm. Correct (d) Proteins are synthesized in the cytoplasm and therefore newly synthesized proteins would not be exported from the nucleus into the cytoplasm.

Where does RNA capping take place in the eukaryotic cell?

nucleus

Where does RNA splicing take place in the eukaryotic cell?

nucleus

Where does polyadenylation take place in the eukaryotic cell?

nucleus

Where does transcription take place in the eukaryotic cell?

nucleus

The sigma subunit of bacterial RNA polymerase ___________________.

recognizes promoter sites in the DNA.