Chapter 17 - 18 Study Questions
Which of the following statements is true about protein synthesis in prokaryotes?
Translation can begin while transcription is still in progress.
A particular triplet of bases in the coding strand of a gene is AAA. If an mRNA is made from this gene, the anticodon on the tRNA that will bind the codon on the mRNA is
UUU
A particular triplet of bases in the template strand of DNA is TTT. The anticodon on the tRNA that binds the mRNA codon is
UUU
Which of the following statements about the trp operon is TRUE?
When trp repressor protein binds tryptophan, it is stabilized in its active shape, preventing transcription of the genes of the trp operon from occurring.
A friend of yours is asked to conduct experiments to determine why a particular polypeptide is present in much higher levels in heart cells than in neural cells. She carefully measures the levels of mature mRNA from the gene that encodes the polypeptide and determines that heart and neural cells contain the same levels of the mature mRNA. She next measures the rate at which the mature mRNA that encodes the polypeptide is translated and finds that rates of translation of that mRNA are the same in heart and neural cells. Your friend now has no idea why the polypeptide is present at higher levels in heart versus neural cells and asks your advice on what to do next. What advice should you give her?
You should remind her that the levels of a polypeptide are determined not only by how frequently the mRNA encoding that polypeptide is translated, but also by the rate at which the polypeptide is degraded. So, she should consider conducting some experiments to determine whether the polypeptide is degraded more rapidly in neural cells than in heart cells.
Of the following, which is the most current description of a gene?
a DNA sequence that is expressed to form a functional product: either RNA or polypeptide
Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the LEAST serious effect on the polypeptide product?
a deletion of three nucleotides
Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the MOST serious effect on the polypeptide product?
a deletion of two nucleotides
Which of the following is most likely to have a small protein called ubiquitin attached to it?
a protein involved in glycine biosynthesis in a cell with lots of glycine
When a ribosome reaches the end of the coding region of an mRNA molecule, so that a stop codon is in the A site of the ribosome,
a release factor binds the stop codon at the A site and the polypeptide is freed from the tRNA in the P site
Which of the following mutations would be most likely to have a harmful effect on an organism?
a single nucleotide insertion downstream of, and close to, the start of the coding sequence
Which of the following are needed for the initiation of transcription?
all of these answers are correct
Which of the following chromatin modifications are possible?
all of these answers are correct
Which of the following statements about pre-mRNAs (primary mRNAs) is correct?
all of these answers are correct
Which of the following is very important in regulating gene expression?
all of these answers are correct.
Translation of mRNA
almost always begins at an AUG codon, which specifies methionine
A single gene is known to code for three different, but related, proteins. This could be due to which of the following?
alternative RNA splicing
The enzyme that catalyzes the formation of a covalent bond between a tRNA and a specific amino acid is
an aminoacyl tRNA synthetase
When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to be experimentally stopped at this point, which of the following would you be able to isolate?
an assembled ribosome with a polypeptide attached to the tRNA in the P site
Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the LEAST serious effect on the polypeptide product?
an insertion of three nucleotides
Ribosomal RNAs, or rRNAs
are not translated to form proteins
During translation, the role of release factors is to
bind the mRNA stop codon in the A site of the ribosome, causing release of the completed polypeptide
Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the
bonding of the anticodon to the codon and the attachment of amino acids to tRNAs.
Aminoacyl tRNA synthetases
catalyze the formation of a covalent bond between an amino acid and an appropriate tRNA molecule
Epigenetic inheritance includes inheritance of
changes in both DNA and histone modifications
The group of three nucleotides that specifies an amino acid is known as a
codon
The anticodon of a particular tRNA molecule is
complementary to the corresponding mRNA codon.
The "polyA" tail that is added to the 3' end of eukaryotic mRNA molecules
consists of a string of adenosine ribonucleotides
What would occur if the repressor of an inducible operon were mutated so it could not bind the operator?
continuous transcription of the operon's genes
A mutation that inactivates the regulatory (repressor) gene of a repressible operon in an E. coli cell would result in
continuous transcription of the structural gene controlled by that regulator.
A mutation that inactivates the function of a repressor protein involved in the regulation of a bacterial operon would result in
continuous transcription of the structural genes in the operon.
Which of the following is NOT a common mechanism of gene regulation?
control of gene duplication
A lack of which molecule would result in the cell's inability to "turn off" genes?
corepressor
The HXK gene is transcribed, resulting in production of HXK mRNA molecules. The total number of HXK mRNA molecules that are present in a cell at any given moment is
equally dependent on the rate at which the HXK mRNA molecules are made (transcribed) and the rate at which they are broken down
The SIS8 gene is transcribed to form SIS8 mRNAs. The SIS8 mRNAs are then translated to form SIS8 polypeptides. The total number of SIS8 polypeptides present in a cell at a given moment is
equally dependent on the rate at which the SIS8 polypeptides are made (translated) and the rate at which they are broken down
Which of the following types of RNA molecules have polyA tails?
eukaryotic mRNA molecules
Gene expression in eukaryotes is NOT regulated by
how efficiently trans-inducer molecules are transported to the correct part of the nucleus
What type of bonding is responsible for maintaining the shape of a tRNA molecule?
hydrogen bonding between base pairs
Transcriptional activators
increase the affinity of RNA polymerase for the promoter
Increasing the affinity of RNA polymerase for the promoter of a particular gene will
increase the rate at which that gene is transcribed.
Most repressor proteins are allosteric. Which of the following binds with the repressor to alter its conformation?
inducer
Which of the following, when taken up by the cell, binds to the repressor protein so that the repressor protein no longer binds to the operator?
inducer
A single aminoacyl tRNA synthetase can typically recognize
just one amino acid, but several tRNAs
A transcription unit that is 8,000 nucleotides long may use 1,200 nucleotides to make a protein consisting of approximately 400 amino acids. This is best explained by the fact that
many noncoding stretches of nucleotides are present in mRNA.
Changes in chromatin structure
may be inherited
In eukaryotes, transcriptional activators
may bind specific DNA sequences associated with genes and increase the affinity of RNA polymerase for the promoters for those genes.
What amino acid sequence will be generated, based on the following mRNA codon sequence?5' AUG-UCU-UCG-UUA-UCC-UUG 3'
met-ser-ser-leu-ser-leu
Which of the following are NOT found in operons?
miRNAs
Which of the following is NOT a typical modification of a eukaryotic primary (or precursor) mRNA?
phosphorylation
Ribosomes are composed of
polypeptides and RNAs
A part of an mRNA molecule with the following sequence is being read by a ribosome: 5' CCG-ACG 3' (mRNA). The charged transfer RNA molecules (with their anticodons shown in the 3' to 5' direction) shown in the table below are available. Two of them can correctly match the mRNA so that a dipeptide can form. The dipeptide that will form will be
proline-threonine.
A mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal phenylalanine. The consequence of this for the cell will be that
proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.
Transcription in eukaryotes requires which of the following in addition to RNA polymerase?
several transcription factors (TFs)
In eukaryotic cells, transcription cannot begin until
several transcription factors have bound to the promoter.
"Alternative splicing" refers to
slightly different sets of exons being present in different mature mRNA molecules made from a single gene.
The final product of an expressed gene can be which of the following?
tRNA, rRNA or polypeptide
The DNA strand to which ribonucleotides hydrogen bond during transcription is known as the
template strand
During translation, tRNAs leave the ribosome from
the E site
If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then
the amino acid acts as a corepressor.
Scientists sometimes transfer genes from one species to a different species. What property of the genetic code typically allows these genes to produce a protein of the same amino acid sequence in the new species as they did in the original species?
the genetic code is almost universal
In comparing DNA replication with transcription, which of the following is true only of DNA replication?
the growing polypeptide chain is transferred from the tRNA in the P ribosome site to the amino acid attached to the tRNA in the A ribosome site.
During translation, after the ribosome breaks the bond between the growing polypeptide chain and the tRNA in the P site and then forms a covalent (peptide) bond between the growing polypeptide chain and the amino acid attached to the tRNA in the A site,
the position of the ribosome on the mRNA shifts and a new, charged tRNA enters the A site of the ribosome
Within a cell, the amount of protein made using a given mature mRNA molecule depends partly on
the rate at which the mRNA is degraded.
During translation, after the ribosome breaks the bond between the growing polypeptide chain and the tRNA in the P site and then forms a covalent (peptide) bond between the growing polypeptide chain and the amino acid attached to the tRNA in the A site,
the ribosome shifts over one codon on the mRNA, such that the codon specifying the next amino acid is now lined up with the A site
During translation, after the ribosome breaks the bond between the growing polypeptide chain and the tRNA in the P site and then forms a covalent (peptide) bond between the growing polypeptide chain and the amino acid attached to the tRNA in the A site,
the tRNA that was in the P site is now in the E site and leaves the ribosome
The proteins that help RNA polymerase bind the DNA at the promoter site are known as
transcription factors
Which of the following help form a transcription complex at a promoter?
transcription factors and RNA polymerase
The tryptophan operon is a repressible operon that is
turned off whenever tryptophan is added to the growth medium.
Protein degradation may be mediated by
ubiquitin binding a protein and targeting it for degradation by a proteasome.
How many different amino acids could be specified if codons were two nucleotides in length?
16
The enzyme polynucleotide phosphorylase randomly assembles nucleotides into a polynucleotide polymer. You add polynucleotide phosphorylase to a solution of ATP, GTP, and UTP. How many artificial mRNA 3 nucleotide codons could possibly be made?
27
A possible sequence of nucleotides in the template strand of DNA that would code for the polypeptide sequence phe-leu-ile-val would be
3' AAA-GAA-TAA-CAA 5'.
A particular triplet of bases in the template strand of DNA is 5' GGT 3'. The corresponding codon for the mRNA transcribed is:
3' CCA 5'
A part of an mRNA molecule with the following sequence is being read by a ribosome: 5' CCG-ACG 3' (mRNA). The anticodon loop of the first tRNA that will complement this mRNA is
3' GGC 5'
A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is:
3' UCA 5'
A particular triplet of bases in the template strand of DNA is 5' AAT 3'. The corresponding codon for the mRNA transcribed is:
3' UUA 5'
Given the locally unwound double strand below, in which direction does the RNA polymerase move?
3' → 5' along the template strand
The nucleotide sequence of the coding strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' AATTCGGG 3'
5' AAUUCGGG 3'
The nucleotide sequence of the coding strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA?5' AATTCGGG 3'
5' AAUUCGGG 3'
The nucleotide sequence of the template strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' AATTCGGG 3'
5' CCCGAAUU 3'
The nucleotide sequence of the coding strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' TTTAAGG 3'
5' CCUUAAA 3'
The nucleotide sequence of the template strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' TTTAAGG 3'
5' CCUUAAA 3'
The nucleotide sequence of the template strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA?5' TTTAAGG 3'
5' CCUUAAA 3'
A peptide has the sequence NH2-phe-pro-lys-gly-phe-pro-COOH. Which of the following sequences in the coding strand of the DNA would code for this peptide?
5' TTT-CCC-AAA-GGG-TTT-CCC 3'
The figure below represents a tRNA that recognizes and binds a particular amino acid (in this instance, phenylalanine). Which codon on the mRNA strand codes for this amino acid?
5' UUC 3'
The nucleotide sequence of the coding strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA?5' TTTAAGG 3'
5' UUUAAGG 3'
Which of the following statements is TRUE?
5' and 3' untranslated regions (UTRs) are parts of exons, but do not code for proteins.
The nucleotide sequence of the template strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA?5' ATGCGTA 3'
5'UACGCAU 3'
The enzyme polynucleotide phosphorylase randomly assembles nucleotides into a polynucleotide polymer. You add polynucleotide phosphorylase to a solution of adenosine triphosphate and guanosine triphosphate. How many different artificial mRNA 3 nucleotide codons could possibly be made?
8
Which of the following is the best definition of a gene that is being "expressed"?
A gene that is producing its final product (protein or non-coding RNA) in a functional form is being expressed.
Which of the following would NOT be considered a gene that is being expressed?
A gene that is producing mRNA, but no protein.
Which of the following mutations would make it impossible for a bacterial cell to metabolize lactose?
A mutation in the promoter for the lac operon such that it can no longer bind RNA polymerase
Which of the following does not occur in prokaryotic gene expression, but does in eukaryotic gene expression?
A poly-A tail is added to the 3' end of an mRNA and a cap is added to the 5' end.
During translation (polypeptide elongation), charged tRNAs enter the ribosome at the
A site
A particular triplet of bases in the coding strand of a gene is TTT. If an mRNA is made from this gene, the anticodon on the tRNA that will bind the codon on the mRNA is
AAA
A particular triplet of bases in the template strand of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is
AAA
Why are chimpanzees and (most) humans so different?
All of these answers are correct
Transfer RNAs, or tRNAs
All of these answers are correct.
Which of the following statements about translation is TRUE?
All of these statements are true.
Which of the following statements about inheritance is TRUE?
All of these types of modifications may be inherited.
Allolactose, an isomer of lactose, is formed in small amounts from lactose. An E. coli cell is presented for the first time with the sugar lactose (containing allolactose) as a potential food source. Which of the following occurs when the lactose enters the cell?
Allolactose binds to the repressor protein.
Which of the following statements about repressor proteins is FALSE?
Binding of a corepressor stabilizes repressor proteins in their inactive shape
A particular triplet of bases in the coding strand of a gene is GGG. If an mRNA is made from this gene, the anticodon on the tRNA that will bind the codon on the mRNA is
CCC.
Which component is not directly involved in translation?
DNA
Which of the following statements is TRUE?
DNA is transcribed and RNA is translated
Which of the following correctly shows the flow of information in a cell?
DNA to RNA to protein
A transfer RNA (#1) attached to the amino acid lysine enters the ribosome. The lysine binds to the growing polypeptide on the other tRNA (#2) in the ribosome already. Where does tRNA #2 move to after this bonding of lysine to the polypeptide?
E site
What is meant by the statement that "the genetic code is not ambiguous"?
Each codon specifies just one amino acid.
Which of the following statements about RNA processing is FALSE?
Exons are cut out before mRNA leaves the nucleus.
A particular triplet of bases in the template strand of DNA is GGG. The anticodon on the tRNA that binds the mRNA codon is
GGG.
Which of the following statements about bacterial repressor proteins is FALSE?
High levels of inducers stabilize repressor proteins in their active state.
During certain types of cell division in Drosophila, studies have shown that there is phosphorylation of an amino acid in the tails of histones of gametes. A mutation in flies that interferes with this process results in sterility. Which of the following is the most likely hypothesis?
Histone tail phosphorylation prohibits chromosome condensation.
The "universal" genetic code is now known to have exceptions. Evidence for this can be found if which of the following is true?
If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only).
What is the function of the release factor?
It binds to the stop codon in the A site in place of a tRNA.
There is a mutation in the lac repressor gene that results in production of an altered lac repressor protein known as a "super-repressor" because it represses the lac operon permanently. Which of these would characterize such a mutant?
It cannot bind to the inducer.
Which of the following statements about a codon is FALSE?
It extends from one end of a tRNA molecule.
Which of the following statements about the DNA in one of your brain cells is certainly TRUE?
It is the same as the DNA in one of your heart cells.
Which of the following statements comparing mRNAs produced by prokaryotes versus eukaryotes is TRUE?
Mature prokaryotic mRNAs often code for multiple polypeptides whereas mature eukaryotic mRNAs typically code for only one polypeptide.
Which of the following statements about the genetic code is TRUE?
Mitochondrial genes use a slightly different genetic code than nuclear genes.
What is meant by the statement that "the genetic code is redundant"?
Most amino acids are specified by more than one codon.
Transfer RNAs, or tRNAs
None of these answers is correct.
Which of the following statements most accurately describes the components of an operon?
Operons have promoters, which are DNA sequences where RNA polymerase binds; operators, which are DNA sequences where transcriptional repressors bind; and structural genes that typically code for proteins that function together in a particular process.
Which of the following is NOT a major difference between transcription in prokaryotes versus eukaryotes?
Prokaryotic mRNA molecules are synthesized by RNA polymerase catalyzing the formation of phosphodiester bonds between ribonucleotides that are base paired with the DNA template strand; eukaryotic mRNA molecules are synthesized by RNA polymerase catalyzing the formation of phosphodiester bonds between ribonucleotides that are base paired with the DNA coding strand
For a repressible operon to be transcribed, which of the following must occur?
RNA polymerase must bind to the promoter, and the repressor must be inactive.
Which of the following statements best describes the termination of transcription in prokaryotes?
RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.
A geneticist introduces a transgene into yeast cells and isolates five independent cell lines in which the transgene has integrated into the yeast genome. In four of the lines, the transgene is expressed strongly, but in the fifth there is no expression at all. Which of the following is a likely explanation for the lack of transgene expression in the fifth cell line?
The 5th transgene integrated into a region of the genome where the chromatin is relatively inaccessible.
In comparing DNA replication with transcription, which of the following is true only of DNA replication?
The entire template molecule is represented in the product.
If a researcher moves the lac operator to a position upstream from the promoter for the lac operon, what would occur?
The lac operon will be expressed continuously.
If an experimenter moves the repressor gene (lac I) for the lac operon, along with its promoter, to a position some several thousand base pairs away from its normal position in the lac operon, which will you expect to occur?
The lac operon will function normally.
Which of the following statements comparing regulation of the lac and trp operons is TRUE?
The lac repressor protein is stabilized in its inactive shape by binding its inducer (allolactose), whereas the trp repressor protein is stabilized in its active shape by binding its corepressor (tryptophan).
You are studying the polypeptides produced by a particular human gene, and notice that about half of the polypeptides have a molecular mass of 200 kDa and the other half have a molecular mass of 150 kDa. One of your hypotheses for why this gene might produce proteins of different molecular masses might be
The primary transcripts encoded by the gene undergo alternative splicing and the different mature mRNAs that result encode proteins with different numbers of exons and thus different molecular masses.
An experimenter moves the operator for the lactose operon to the far end of the operon (past all of the structural genes in the lactose operon). Which of the following would likely occur when the cell is exposed to lactose?
The structural genes will be transcribed continuously.
When the genome of a particular species is said to include 20,000 protein-coding regions, what does this imply?
There are also genes for RNAs other than mRNA.