Chapter 17 Branched Tutorial: Gene Expression in Eukaryotes

Problem Statement

General Considerations and Tips

This type of problem is abstract, so drawing on the diagrams may be helpful for you, not just re-drawing a new gene order. For example, you could diagram arrows and “stop” signs on top of the original diagram to help you see the effect of each item.

It is better to draw the “stop” signs over the insulators first because a negative element will take precedence over the positive enhancer elements. Remember that insulators act as a type of barrier to stop an effect from traveling any farther.

Then draw arrows that indicate the positive influence of the enhancer, which is position independent. Make sure you pay attention to the insulator’s stop signal, which here stops the ability of the enhancer to affect gene D.

This way you can visualize which genes will be transcribed (A, B, C) and which will not (D).

An enhancer and insulator are located in the vicinity four genes (A, B, C, and D), as shown in the diagram below.

Question

a. On the basis of this diagram, which genes will be transcribed and which will not?

Gene A be transcribed because the enhancer activity blocked by the insulator.
Gene B be transcribed because the enhancer activity blocked by the insulator.
Gene C be transcribed because the enhancer activity blocked by the insulator.
Gene D be transcribed because the enhancer activity blocked by the insulator.

b. If the enhancer and insulator were switched in location, which genes would be transcribed and which would not be transcribed?

Gene A be transcribed because the enhancer activity blocked by the insulator.
Gene B be transcribed because the enhancer activity blocked by the insulator.
Gene C be transcribed because the enhancer activity blocked by the insulator.
Gene D be transcribed because the enhancer activity blocked by the insulator.

c. If the enhancer were now relocated from its current location to downstream of Gene D, which genes would be transcribed and which would not be transcribed?

Gene A be transcribed because the enhancer activity blocked by the insulator.
Gene B be transcribed because the enhancer activity blocked by the insulator.
Gene C be transcribed because the enhancer activity blocked by the insulator.
Gene D be transcribed because the enhancer activity blocked by the insulator.

1
Congratulations! You have correctly worked the problem.
Review Section 17.3 on The Initiation of Transcription is Regulated by Transcription Factors and Regulator Proteins. Pay particular attention to Figure 17.8. Ask yourself these questions:
What effect does an enhancer have on transcription of a gene? What is the range of an enhancer? Is an enhancer position-dependent or independent? What effect does an enhancer have on transcription of a gene? What is the range of an insulator? Is an insulator position-dependent or independent? How do insulators and enhancer affect each other when both are present?
Incorrect. Let’s work through the problem step-by-step.
false
If you think you know how to solve the problem, enter your answers above and click "Submit Answers." Your answers will be checked and, if there are any mistakes, you'll be given one chance to revise them. If there are still mistakes after your second attempt, you'll be guided through the process of solving the problem. If you want to go straight to that guided process, click "Work Problem Step-By-Step."

1
Congratulations! You have correctly worked the problem.
Review Section 17.3 on The Initiation of Transcription is Regulated by Transcription Factors and Regulator Proteins. Pay particular attention to Figure 17.8. Ask yourself these questions:
What effect does an enhancer have on transcription of a gene? What is the range of an enhancer? Is an enhancer position-dependent or independent? What effect does an enhancer have on transcription of a gene? What is the range of an insulator? Is an insulator position-dependent or independent? How do insulators and enhancer affect each other when both are present?
Incorrect. Let’s work through the problem step-by-step.
false

Step 1: Learn more about the terms you may not know or understand.

Question

In general, which genes can an enhancer affect?

A.
B.
C.
D.
2
Correct.
Incorrect. You have one more chance to answer correctly. Please try again.
Incorrect.

Instant TA

Most genetic elements function under certain conditions. Enhancers have a particular location, position, and range in which they enhance transcription.

Step 1 (continued)

Question

What effect does an insulator have on an enhancer’s activity?

A.
B.
C.
D.
2
Correct.
Incorrect. You have one more chance to answer correctly. Please try again.
Incorrect.

Instant TA

In the previous questions, you were asked separately about enhancers and insulators. Think about how an insulator’s activity and range will affect an enhancer’s activity and range.

Step 2: Understanding the problem

Question

An enhancer is surrounded by four genes (A, B, C, and D), as shown in the diagram below.

a. On the basis of this diagram, which genes will be transcribed and which will not?
b. If the enhancer and insulator were switched in location, which genes would be transcribed and which would no longer be transcribed?
c. If the enhancer were now relocated from its current location to downstream of Gene D, which genes would be transcribed and which would no longer be transcribed?

What are the questions in this problem asking you to solve for?

A.
B.
C.
D.
E.
2
Correct.
Incorrect. You have one more chance to answer correctly. Please try again.
Incorrect.

Instant TA

Read the original question carefully. You can take notes on the important points.

Step 3: Understand how insulators and enhancers act together on genes.

Question

An enhancer is surrounded by four genes (A, B, C, and D), as shown in the diagram below. An insulator lies between gene C and gene D.

1. If the insulator was not present or was deleted from the above diagram, which gene(s) could possibly be affected by the enhancer?

A.
B.
C.
D.
2
Correct.
Incorrect. You have one more chance to answer correctly. Please try again.
Incorrect.

Instant TA

Recall from Step 1 that most genetic elements function under certain conditions. Insulators and enhancers have particular locations, positions, and ranges in which they influence transcription. You can re-draw the diagram with the insulator missing and then evaluate the effect of just the enhancer on each gene separately. The new diagram would look like this.

Step 4: Solving the Problem

Question

An enhancer and insulator are located in the vicinity of four genes (A, B, C, and D), as shown in the diagram below.

a. On the basis of this diagram, which genes will be transcribed and which will not?

Gene A be transcribed because the enhancer activity blocked by the insulator.
Gene B be transcribed because the enhancer activity blocked by the insulator.
Gene C be transcribed because the enhancer activity blocked by the insulator.
Gene D be transcribed because the enhancer activity blocked by the insulator.

2
Correct.
Consider the range and position of the enhancer relative to the insulator and to each gene separately. Recall that enhancers activate transcription in a position-independent fashion. Does the enhancer have full access or has it been blocked?
Incorrect.

Instant TA

This type of problem is abstract, so drawing on the diagrams may be helpful for you, not just re-drawing a new gene order. For example, you could diagram arrows and “stop” signs on top of the original diagram to help you see the effect of each item.

It is better to draw the “stop” signs over the insulators first because a negative element will take precedence over the positive enhancer elements. Remember that insulators act as a type of barrier to stop an effect from traveling any farther.

Then draw arrows that indicate the positive influence of the enhancer, which is position independent. Make sure you pay attention to the insulator’s stop signal, which here stops the ability of the enhancer to affect gene D.

This way you can visualize which genes will be transcribed (A, B, C) and which will not (D).

Notes: