Question 1

A researcher introduces double-stranded RNA into a culture of mammalian cells, and can identify its location or that of its smaller subsections experimentally, using a fluorescent probe.
-In addition, she finds what other evidence of this single-stranded RNA piece's activity?
A) She can measure the degradation rate of the remaining single strand.
B) She can measure the decrease in the concentration of Dicer.
C) The rate of accumulation of the polypeptide to be translated from the target mRNA is reduced.
D) The amount of miRNA is multiplied by its replication.
E) The cell's translation ability is entirely shut down.

Accepted Answer

The researcher can measure the rate of accumulation of the polypeptide to be translated from the target mRNA, which would be reduced if the introduced double-stranded RNA is causing RNA interference (RNAi). RNAi occurs when a double-stranded RNA triggers the degradation of the corresponding single-stranded mRNA, leading to reduced protein production. Options A, B, D, and E are not necessarily related to the activity of the introduced RNA and are not supported by the information given.

Question 2

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.
-Of the lines that express the transgene, one is transcribed but not translated. Which of the following is a likely explanation?
A) no promoter
B) no AUG in any frame
C) no compatible ribosome
D) high histone acetylation
E) missing transcription factor

Accepted Answer

If there is no AUG in any frame, then translation cannot occur, which would explain why transcription is happening but no protein is being produced.

Question 3

Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome.
-If she moves the promoter for the lac operon to the region between the beta galactosidase gene and the permease gene, which of the following would be likely?
A) Three structural genes will no longer be expressed.
B) RNA polymerase will no longer transcribe permease.
C) The operon will no longer be inducible.
D) Beta galactosidase will be produced.
E) The cell will continue to metabolize but more slowly.

Accepted Answer

Moving the promoter for the lac operon between the beta galactosidase gene and the permease gene would result in the expression of the beta galactosidase gene, as it will now be located upstream of the promoter. The proximity to the permease gene may also enhance the efficiency of lactose transport into the cell. Therefore, Option D is the most likely outcome. Option A is incorrect because the structural genes are still present, and Option B is incorrect because the permease gene is still present and can be transcribed by RNA polymerase. Option C is also incorrect because the lac operon will still be inducible, as the promoter has been moved but the overall operon structure is still intact. Option E is not supported by the information provided.

Question 4

Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome.
-If she moves the operator to a position upstream from the promoter, what would occur?
A) The lac operon will function normally.
B) The lac operon will be expressed continuously.
C) The repressor will not be able to bind to the operator.
D) The repressor will bind to the promoter.
E) The repressor will no longer be made.

Accepted Answer

Moving the operator upstream from the promoter will place it closer to the RNA polymerase binding site. This will increase the likelihood of the RNA polymerase binding to the promoter and transcribing the genes in the lac operon, leading to continuous expression of the operon. The repressor will still be able to bind to the operator, but it will not have an effect on gene expression as the RNA polymerase will bypass it.

Question 5

A researcher introduces double-stranded RNA into a culture of mammalian cells, and can identify its location or that of its smaller subsections experimentally, using a fluorescent probe.
-Within the first quarter hour, the researcher sees that the intact RNA is found in the cells. After 3 hours, she is not surprised to find that
A) Dicer enzyme has reduced it to smaller double-stranded pieces.
B) the RNA is degraded by 5' and 3' exonucleases.
C) the double-stranded RNA replicates itself.
D) the double-stranded RNA binds to mRNAs to prevent translation.
E) the double-stranded RNA binds to tRNAs to prevent translation.

Accepted Answer

After being introduced into mammalian cells, double-stranded RNA is recognized by the Dicer enzyme, which cleaves it into smaller double-stranded pieces known as siRNAs. This process occurs within the first quarter hour of introduction. Therefore, after 3 hours, it is expected that the RNA will have been reduced to smaller pieces by Dicer. Option B is incorrect because exonucleases degrade single-stranded RNA, not double-stranded RNA. Option C is incorrect because double-stranded RNA does not replicate itself in mammalian cells. Option D and E are incorrect because double-stranded RNA binds to mRNAs to trigger RNA interference and prevent translation, not bind to tRNAs.

Question 6

A researcher has arrived at a method to prevent gene expression from Drosophila embryonic genes. The following questions assume that he is using this method.
-The researcher in question measures the amount of new polypeptide production in embryos from 2-8 hours following fertilization and the results show a steady and significant rise in polypeptide concentration over that time. The researcher concludes that
A) his measurement skills must be faulty.
B) the results are due to building new cell membranes to compartmentalize dividing nuclei.
C) the resulting new polypeptides are due to translation of maternal mRNAs.
D) the new polypeptides were inactive and not measurable until fertilization.
E) polypeptides were attached to egg membranes until this time.

Accepted Answer

The method used by the researcher prevents gene expression from Drosophila embryonic genes, which means that the new polypeptides observed cannot be the result of transcription and translation of newly synthesized embryonic mRNA. However, there are already existing maternal mRNAs in the egg that are translated during early embryonic development, and this is likely the source of the observed increase in polypeptide concentration. Choice A is not a reasonable conclusion without any evidence, and choices B, D, and E do not account for the increase in polypeptide concentration.

Question 7

Use the following information to answer the following questions.
In Drosophila after ~100 minutes postfertilization, the embryo looks like the following diagram, with all nuclei having moved to the periphery and, subsequently, four of the nuclei being sequestered at the posterior end.
  
Drosophila embryo after about 2 hours.
-The developmental stages described for Drosophila illustrate
A) a hierarchy of gene expression.
B) homeotic developmental control.
C) the blockage of cell-to-cell communication.
D) homeotic developmental control and the blockage of cell-to-cell communication.
E) a hierarchy of gene expression and the blockage of cell-to-cell communication.

Accepted Answer

The answer of Use the following information to answer the...

Question 8

A researcher has arrived at a method to prevent gene expression from Drosophila embryonic genes. The following questions assume that he is using this method.
-The researcher continues to study the reactions of the embryo to these new proteins and you hypothesize that he is most likely to see which of the following (while embryonic genes are still not being expressed)?
A) The cells begin to differentiate.
B) The proteins are evenly distributed throughout the embryo.
C) Larval features begin to make their appearance.
D) Spatial axes (anterior → posterior, etc.) begin to be determined.
E) The embryo begins to lose cells due to apoptosis from no further gene expression.

Accepted Answer

Spatial axes (anterior → posterior, etc.) begin to be determined during embryonic development before gene expression from embryonic genes. Therefore, by preventing gene expression, the researcher may still observe the establishment of spatial axes in the embryo.

Question 9

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?
A) A transgene integrated into a heterochromatic region of the genome.
B) A transgene integrated into a euchromatic region of the genome.
C) The transgene was mutated during the process of integration into the host cell genome.
D) The host cell lacks the enzymes necessary to express the transgene.
E) A transgene integrated into a region of the genome characterized by high histone acetylation.

Accepted Answer

Heterochromatin is typically characterized by compacted chromatin structure with heavy methylation of histones and DNA. This can prevent access of the transcriptional machinery to genes within heterochromatic regions, leading to lack of expression. Therefore, it is likely that the transgene integrated into a heterochromatic region in the fifth cell line, leading to lack of expression.

Question 10

A researcher found a method she could use to manipulate and quantify phosphorylation and methylation in embryonic cells in culture.
-One of her colleagues suggested she try increased methylation of C nucleotides in a mammalian system. Which of the following results would she most likely see?
A) increased chromatin condensation
B) decreased chromatin condensation
C) abnormalities of mouse embryos
D) decreased binding of transcription factors
E) inactivation of the selected genes

Accepted Answer

Methylation of C nucleotides is associated with gene silencing and inactivation. Therefore, increased methylation of C nucleotides would most likely result in the inactivation of the selected genes.

Question 11

Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome.
-If she moves the repressor gene (lac I), along with its promoter, to a position at some several thousand base pairs away from its normal position, which will you expect to occur?
A) The repressor will no longer be made.
B) The repressor will no longer bind to the operator.
C) The repressor will no longer bind to the inducer.
D) The lac operon will be expressed continuously.
E) The lac operon will function normally.

Accepted Answer

Moving the repressor gene (lac I) along with its promoter does not inherently disrupt its function or its ability to be expressed, bind to the operator, or interact with the inducer. The lac operon can still be regulated normally because the repressor's action is not dependent on its physical location relative to the operon, as long as it is still being properly expressed.

Question 12

Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome.
-If she moves the operator to the far end of the operon (past the transacetylase gene), which of the following would likely occur when the cell is exposed to lactose?
A) The inducer will no longer bind to the repressor.
B) The repressor will no longer bind to the operator.
C) The operon will never be transcribed.
D) The structural genes will be transcribed continuously.
E) The repressor protein will no longer be produced.

Accepted Answer

Moving the operator to the far end of the operon would prevent the repressor from effectively blocking RNA polymerase from transcribing the structural genes, leading to continuous transcription.

Question 13

Use the following information to answer the following questions.
In Drosophila after ~100 minutes postfertilization, the embryo looks like the following diagram, with all nuclei having moved to the periphery and, subsequently, four of the nuclei being sequestered at the posterior end.
  
Drosophila embryo after about 2 hours.
-The next step after the embryo is formed would be
A) division of the embryo into five broad regions.
B) use of pair-rule genes to divide the embryo into stripes, each of which will become two segments.
C) use of zygotic segment polarity genes to divide each segment into anterior and posterior halves.
D) enclosure of the nuclei in membranes, forming a single layer over the surface.
E) separation of head, thoracic, and abdominal segments of the embryo.

Accepted Answer

After the embryo is formed, the next step involves the enclosure of the nuclei in membranes, which leads to the formation of a single layer over the surface of the embryo. This process is crucial for the further development and differentiation of the embryo into more complex structures.

Question 14

Use the following information to answer the following questions.
In Drosophila after ~100 minutes postfertilization, the embryo looks like the following diagram, with all nuclei having moved to the periphery and, subsequently, four of the nuclei being sequestered at the posterior end.
  
Drosophila embryo after about 2 hours.
-Formation of the pole cells (the four sequestered cells)demonstrates the role of
A) segmentation genes.
B) homeotic genes.
C) maternal effect genes.
D) zygotic genes.
E) all of the above.

Accepted Answer

The sequestration of the four pole cells at the posterior end of the embryo is a result of maternal effect genes, which are genes expressed in the mother's oocyte and play a role in early development before the activation of zygotic genes. Segmentation genes and homeotic genes are responsible for determining the body plan and specific identities of segments in later stages of development, while zygotic genes are activated after fertilization and play a role in the later stages of development. Therefore, the best choice is C, maternal effect genes.

Question 15

A researcher found a method she could use to manipulate and quantify phosphorylation and methylation in embryonic cells in culture.
-In one set of experiments using this procedure in Drosophila, she was readily successful in increasing phosphorylation of amino acids adjacent to methylated amino acids in histone tails. Which of the following results would she most likely see?
A) increased chromatin condensation
B) decreased chromatin condensation
C) abnormalities of mouse embryos
D) decreased binding of transcription factors
E) inactivation of the selected genes

Accepted Answer

Increased phosphorylation of amino acids adjacent to methylated amino acids in histone tails generally leads to decreased chromatin condensation. This is because phosphorylation adds negative charges to the histone tails, which can weaken the interaction between the histones and the DNA, leading to a more open chromatin structure that is accessible for transcription.

Question 16

A researcher has arrived at a method to prevent gene expression from Drosophila embryonic genes. The following questions assume that he is using this method.
-The researcher measures the concentration of the polypeptides from different regions in the early embryo and finds the following pattern (darker shading = greater concentration):

Which of the following would be his most logical assumption?
A) The substance has moved quickly from region 5 to region 1.
B) Some other material in the embryo is causing accumulation in region 1 due to differential binding.
C) The cytosol is in constant movement, dispersing the polypeptide.
D) The substance is produced in region 1 and diffuses toward region 5.
E) The substance must have entered the embryo from the environment near region 1.

Accepted Answer

The concentration gradient suggests that the substance is being produced in region 1 and diffusing toward region 5. This is a common pattern in many developmental processes, as different regions of an embryo produce and secrete different signaling molecules that guide the differentiation and patterning of adjacent tissues.

Question 17

One hereditary disease in humans, called xeroderma pigmentosum (XP), makes homozygous individuals exceptionally susceptible to UV-induced mutation damage in the cells of exposed tissue, especially skin. Without extraordinary avoidance of sunlight exposure, patients soon succumb to numerous skin cancers.
-Which of the following best describes this phenomenon?
A) inherited cancer taking a few years to be expressed
B) embryonic or fetal cancer
C) inherited predisposition to mutation
D) inherited inability to repair UV-induced mutation
E) susceptibility to chemical carcinogens

Accepted Answer

Xeroderma pigmentosum (XP) is an inherited disease that impairs the ability of cells to repair damage caused by ultraviolet (UV) light. Individuals with XP are exceptionally susceptible to UV-induced mutation damage in the cells of exposed tissue, especially skin. Without extraordinary avoidance of sunlight exposure, patients soon succumb to numerous skin cancers. Therefore, the best choice to describe this phenomenon is an inherited inability to repair UV-induced mutation.

Question 18

A researcher introduces double-stranded RNA into a culture of mammalian cells, and can identify its location or that of its smaller subsections experimentally, using a fluorescent probe.
-Some time later, she finds that the introduced strand separates into single-stranded RNAs, one of which is degraded. What does this enable the remaining strand to do?
A) attach to histones in the chromatin
B) bind to complementary regions of target mRNAs
C) bind to Dicer enzymes to destroy other RNAs
D) activate other siRNAs in the cell
E) bind to noncomplementary RNA sequences

Accepted Answer

The remaining single-stranded RNA can now bind to complementary regions in target mRNAs, leading to the degradation or repression of the targeted mRNA. This is the mechanism by which RNA interference (RNAi) operates.

Question 19

A researcher found a method she could use to manipulate and quantify phosphorylation and methylation in embryonic cells in culture.
-She tried decreasing the amount of methylation enzymes in the embryonic stem cells and then allowed the cells to further differentiate. Which of the following results would she most likely see?
A) increased chromatin condensation
B) decreased chromatin condensation
C) abnormalities of mouse embryos
D) decreased binding of transcription factors
E) inactivation of the selected genes

Accepted Answer

The answer of A researcher found a method she could...

Question 20

A researcher found a method she could use to manipulate and quantify phosphorylation and methylation in embryonic cells in culture.
-In one set of experiments she succeeded in decreasing methylation of histone tails. Which of the following results would she most likely see?
A) increased chromatin condensation
B) decreased chromatin condensation
C) abnormalities of mouse embryos
D) decreased binding of transcription factors
E) inactivation of the selected genes

Accepted Answer

The answer of A researcher found a method she could...

Quiz 18: Regulation of Gene Expression

A researcher introduces double-stranded RNA into a culture of mammalian cells, and can identify its location or that of its smaller subsections experimentally, using a fluorescent probe. -In addition, she finds what other evidence of this single-stranded RNA piece's activity?

Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome. -If she moves the promoter for the lac operon to the region between the beta galactosidase gene and the permease gene, which of the following would be likely?

Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome. -If she moves the operator to a position upstream from the promoter, what would occur?

A researcher found a method she could use to manipulate and quantify phosphorylation and methylation in embryonic cells in culture. -One of her colleagues suggested she try increased methylation of C nucleotides in a mammalian system. Which of the following results would she most likely see?

Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome. -If she moves the operator to the far end of the operon (past the transacetylase gene) , which of the following would likely occur when the cell is exposed to lactose?

A researcher found a method she could use to manipulate and quantify phosphorylation and methylation in embryonic cells in culture. -In one set of experiments she succeeded in decreasing methylation of histone tails. Which of the following results would she most likely see?