11 guided reading activity answers

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Chapter 11: How Genes Are Controlled

Guided Reading Activities

Big idea: Control of gene expression

Answer the following questions as you read modules 11.1–11.11:

1. True or false: The expression of genes can be turned on or off. If false, make it a correct statement.

2. Match the following terms to their description: operator, operon, promoter, repressor, and activator.

A protein that binds to DNA and stimulates transcription: ____________

Genes that serve a related function and the sequences that control them: ____________

Place where RNA polymerase begins transcription: ____________

Protein that blocks the RNA polymerase from binding the DNA: ____________

DNA sequence that determines whether RNA polymerase binds the promoter: ____________

3. A mutation in the bacterial gene that codes for the lac repressor creates a repressor that binds irreversibly to the lac operator. Briefly explain what effect, if any, this would have on the bac-terium’s metabolism of lactose.

4. The process by which a cell becomes specialized in structure and function is called ____________.

5. Briefly explain how the inactivation of the X chromosome in human females is an example of epigenetics.


The repressor would not detach from the operator, so the bacterium would be unable to me-tabolize lactose.

One of the female X chromosomes is randomly inactivated by methylation. Future genera-tions of cells born from this cell will have the same X chromosome inactivated. This process is an example of epigenetics.







6. A geneticist working for the National Institutes of Health (NIH) discovers a rare mutation of a human gene that leads to a high degree of methylation on the male Y chromosome. Briefly explain what effect this might have on gene expression on the Y chromosome.

7. Which of the following is a sequence of DNA that resides far away from the gene it helps to control?

a. Enhancer

b. Barr body

c. Transcription factor d. Promoter

8. A biologist is working to identify a single-celled organism that was discovered in a pond. After a series of experiments, she determines that every gene she has observed has its own promoter. What type of cell is this? Conversely, what type of cell is it not? Briefly explain your answer either way.

9. The default state of most eukaryotic genes is ____________.

10. Which of the following does not occur in the nucleus of a eukaryotic cell? a. Methylation

b. Alternative RNA splicing c. Regulation of transcription

d. RNA interference

11. True or false: miRNAs are small sequences of RNA that bind to complementary sequences of DNA to inactivate a gene. If false, make it a correct statement.

A mutation of this kind would most likely lead to significantly reduced expression of genes on the Y chromosome.

It is likely to be a eukaryotic organisms because related prokaryotic genes tend to be grouped together under the control of a single promoter, whereas eukaryotic genes tend to have their own promoter.

False, miRNAs bind to complementary sequences on mRNA and lead to the destruction of the mRNA or block its translation.


12. Complete the following table, which compares late-stage gene regulation mechanisms.

mRNA breakdown Initiation of translation Protein activation Protein breakdown

Description Enzymes degrade

mRNA relatively quickly, which helps to regulate the amount of proteins in a cell.

The initiation of translation can be regulated for a variety of reasons.

This is where a polypeptide requires modification before it becomes activated in its final form.

To control basic cellular

mechanisms, certain proteins need to be destroyed quicker than others.

Example Hemoglobin

mRNA is unusually stable and lasts a long time.

Blocking the translation of hemoglobin unless there is heme available

The activation of

insulin The breakdown of proteins that trigger metabolic changes in a cell

13. Briefly explain why control valves on a water pipe are a good analogy for control of gene expression in eukaryotes.

14. ______________ determine which end of the fruit fly becomes the head.

15. True or false: A mutation in a homeotic gene does not affect which end of the fly becomes the head. If false, make it a correct statement.

16. An oncologist wants to study how gene expression changes in pancreatic cancer cells. What technique might the oncologist use? Briefly explain how that would be of benefit to the oncologist.

17. cDNA is made from ____________ using reverse transcriptase.

a. mRNA

b. DNA c. cDNA d. miRNA

18. What can be inferred from the different color levels in the DNA microarray pictured in Figure 11.9 on page 219 in your textbook?

False, it could affect which end of the fly becomes the head.

The oncologist might use a DNA microarray, which would indicate what, if any, genes are changing in their expression.

This is a good analogy because the regulation of eukaryotic genes can occur at many different places along the entire process of transcription, translation, and beyond.


19. List the key events of a signal transduction pathway.

20. A cell has a mutation that causes a shape change in a cell-surface receptor protein that binds a signaling molecule. What effect is this likely to have on that particular signal transduction pathway?

21. What does the fact that many organisms on earth share similar mechanisms of signal trans-duction mean with respect to evolution?

Big idea: Cloning of plants and animals

Answer the following questions as you read modules 11.12–11.14:

1. True or false: Genes that are unexpressed retain the ability to be expressed. If false, make it a correct statement.

2. An organism produced from a single parent is referred to as a(n) ____________.

3. Briefly explain the genetic relationship between the two carrot plants in Figure 11.12 on page 221 in your textbook.

4. List the steps of nuclear transplantation.

5. A scientist trying to clone a Bengal tiger via nuclear transplantation obtains the donor nucleus from a gametic cell rather than a somatic cell. Briefly explain why this is not going to work.

6. Which of the following results in stem cells that can be used in treating medical ailments? a. Reproductive cloning

b. Regeneration

c. Therapeutic cloning

d. None of the above

A signaling molecule is released from the “sending” cell, the signaling molecule binds to a re-ceptor on the target cell, this initiates the activation of a series of relay proteins, the final relay protein activates a transcription factor, a gene is transcribed, and the mRNA is translated into a functional protein.

The signaling molecule will likely not be able to bind the cell-surface receptor, and the cell sig-naling pathway will be blocked.

This indicates that cell signaling evolved early in the history of life.


They are genetically identical.

The nucleus is removed from an egg, the nucleus from a somatic cell is inserted, and the cell is stimulated to divide and create a blastocyst.


7. Complete the following table, which compares embryonic stem cells to adult stem cells.

Embryonic stem cells Adult stem cells


Are not limited in what they can become. The harvesting of ES cells prevents an organism from possibly being born.

Are somewhat differentiated and are limited in the types of cells they can become. They can be obtained without harming the organism.

8. Ideally, a person would get ES cells made from one of his or her own donated somatic cells. Briefly explain why this is so advantageous.

Big idea: The genetic basis of cancer

Answer the following questions as you read modules 11.15–11.18:

1. A gene that causes cancer is known as a(n) ____________.

2. Proto-oncogenes and oncogenes are often misunderstood. Briefly describe the relationship between the two. Provide an example to help explain your answer.

3. A tumor-suppressor gene is mutated such that its expression is increased. Would this increase or decrease your chance of cancer? Briefly explain your answer.

4. True or false: Cancer usually develops as fast as a typical cold. If false, make it a correct statement.

5. Transformation is the process by which a cell goes from normal to cancerous. This is a grad-ual process based on the accumulation of DNA mutations. The effect of oncogenes is some-times described as the stuck gas pedal, and inactivated tumor-suppressor genes are referred to as the broken brake. Briefly explain how these two different analogies combine to explain transformation.

Because they were your cells, the DNA would match and there would not be any adverse reac-tions to any organ created as a result of therapeutic cloning.

Proto-oncogenes are normal genes found in an organism that have the potential to become mutated into oncogenes (genes that cause cancer).

It would decrease your chance because the control over cell division would be increased.

False, it usually takes a long period of time for cancer to develop.

The “stuck gas pedal” refers to a situation where cell division is being stimulated beyond nor-mal levels. The “broken brake” refers to a situation where a tumor suppressor gene is inacti-vated, which results in abnormal cell division. These kinds of mutations do not occur instantly at the same time. It takes a long time for transformation to occur due to the cumulative effect of the mutations.


6. Complete the Venn diagram that compares stimulatory with inhibitory signal transduction pathways.

7. Any substance that mutates DNA, which leads to cancer, is known as a(n) ____________.

8. True or false: Only women get breast cancer. If false, make it a correct statement.


Use your knowledge of the information contained within this chapter’s “Big Ideas” to answer this question.

Identical twins have been studied extensively to help us understand the inheritance of traits in humans. We have long believed that the sequence of nucleotides in our genes was the ultimate determinant of protein function. If that is true, what could explain the observations that one identi-cal twin can have asthma but not the other? What about when one identiidenti-cal twin has severe depres-sion and not the other?

Inhibitory signal transduction pathway Stimulatory signal

transduction pathway

This pathway normally produces a protein that stimulates cell


This pathway normally produces a protein that inhibits cell division. Both

pathways produce proteins that regulate the cell cycle by

interacting with components of

the cell cycle control system.



Figure 11.9 on page 219 in your textbook?

Figure 11.9

on page 219 in your textbook? p.3