A Small Group Activity About Bacterial Regulation And Complementation

Abstract

As teachers, we well understand the need for activities that help develop critical-thinking skills in microbiology. In our experience, one concept that students have difficulty understanding is transcriptional regulation of bacterial genes. To help with this, we developed and evaluated a paper-based activity to help students understand and apply the concepts of bacterial transcriptional regulation. While we don’t identify it as such, we use a complementation experiment to assess student understanding of how regulation changes when new DNA is introduced. In Part 1 of this activity, students complete an open-book, take-home assignment that asks them to define common terminology related to regulation, and draw the regulatory components of different scenarios involving positive and negative regulation. In Part 2, students work in small groups of 3–4 to depict the regulatory components for a different scenario. They are asked to explain the results of a complementation experiment based on this scenario. They then predict the results of a slightly different experiment. Students who completed the Regulation Activity did significantly better on post-test questions related to regulation, compared to pre-test questions.

INTRODUCTION

This classroom activity was designed to help develop critical-thinking skills related to the transcriptional regulation of bacterial genes, using complementation as a tool for investigating regulation. A number of publications over the last decade have called for a greater emphasis on developing critical-thinking and problem-solving skills in college level biology classes (1, 2, 3, 4). In our experience, students have difficulty understanding and explaining transcriptional regulation in bacteria. To this end, we developed a classroom activity that first reviews basic concepts in bacterial regulation, then has students use those concepts to explain and predict the results of a genetic complementation experiment. Our hypothesis was that students who did this activity would be able to better explain the outcome of a similar experiment. While students might not be able to actually carry out such an experiment in a lab setting, they could get a sense of the thought process a scientist would go through, and could experience how the information generated in such an experiment is useful.

Intended audience/ prerequisite student knowledge

This activity was designed for microbiology and biology majors in a general microbiology class, but would be equally appropriate in a molecular biology or introductory genetics class. We assume that students had some exposure to the regulation of bacterial genes in introductory biology. While we use a complementation experiment to assess student understanding of bacterial regulation, we were not concerned that students might not know what a complementation experiment was. Instead, we wanted them to think about, and be able to explain, the consequences of introducing a regulatory sequence into a cell. How it was introduced and what it was called was not important to their understanding of how regulation is affected when new regulatory genes are introduced.

Learning time

The activity has two parts. Part 1 is a review of basic concepts and regulation scenario. In our classes, we give Part 1 to students as a homework assignment that takes about one hour to complete. In Part 2, students apply the basic concepts reviewed in Part 1 to an experimental situation. Students then discuss and write answers to questions in Part 2 during a 50-minute class period. While we had over 200 students divided into multiple sections, each with a facilitator, this activity could be used in smaller classes with one teacher as a facilitator for small group work. Students could work together on Part 1 in class, with Part 2 being given as a homework assignment. Alternatively, both sections could be done in class or as homework.

Learning objectives

Upon completion of this activity, students should be able to:

• ♦ describe how the components involved in the positive and negative regulation of bacterial genes work together to control transcription.

• ♦apply the basic concepts of positive and negative regulation of bacterial genes to explain the results of a complementation experiment involving regulatory mutants.

PROCEDURE

Materials

Students need the handout for Part 1 (1/student, given out as a homework assignment) and the handout for Part 2 (1/student). Instructors need the answer keys to both parts.

Student instructions

In our classes, students are instructed to download a pdf of Part 1 before class and answer the questions therein. The instructions for Part 1 are as follows: The goal of Part 1 is to make sure you have an adequate understanding of transcriptional regulation in bacterial cells. Answer these questions before you come to the small group discussion on regulation. We will briefly review this material before giving you Part 2 (which we will collect for a grade).

After reviewing the answers to Part 1, students are given Part 2, with these instructions: Talk among your group members to come to consensus on answers for each question. Then, using your own words, write out an answer and give this sheet to your instructor to be graded. Remember – you should discuss this with your group members, but the words you use must be your own.

Instructor instructions

In Part 1, we ask students to define common terminology associated with transcriptional regulation. They then draw in the regulatory components for three different scenarios involving positive and negative regulation. Students answer these questions as homework, using any resources, and bring them to class. This ensures that all students have some understanding of the concepts.

During our 50-minute class period, students meet in groups of 15–20 students led by Small Group Facilitators (in our case, graduate student teaching assistants). They first review the answers to Part 1. We then hand out Part 2, which students work through in groups of 3–4. In Part 2, students are asked to draw in the necessary components for a given regulatory scenario. They are then presented with an experiment based on this scenario, and are asked to explain the results. Finally, they are asked to predict the outcome of a slightly different scenario. While students are encouraged to discuss the answers to each question with their group members, each student must write his/her own answer to each question.

Suggestions for determining student learning

We collect and grade the answers based on a grading rubric (Appendix 4) out of a total of 10 points.

Sample data

Expected student outcomes, as well as partially correct answers, are given in the grading rubric (Appendix 3 and 4).

DISCUSSION

Field testing

We have been using variations of this activity in our General Microbiology Lecture Class (> 200 students) for about six years. To evaluate this activity, we gave 186 students a pre-test consisting of five questions (Fig. 1). Students were told that we were evaluating the next small group activity and were asked to answer the questions to the best of their ability. They were given time in class, but it was made clear that their performance would in no way affect their grade.

FIGURE 1:

Pre-test Questions

The percentage of correct answers for each question on the pre-test was as follows:

• Q1. A mutation in the signal-binding domain of the repressor that doesn’t allow signal to bind – 67% correct.

• Q2. A mutation in the DNA-binding domain of the repressor that allows the repressor to always bind to DNA – 71% correct.

• Q3. A mutation in the signal-binding domain of the activator that doesn’t allow signal to bind – 78% correct.

• Q4. A mutation in the activator-binding site that doesn’t allow the activator to bind to the activator-binding site – 64% correct.

• Q5. Would adding a wild-type repressor protein to this cell allow the cell to transcribe the gene? – 29% correct.

One week later, students were given Part 1 as a homework assignment (Appendix 1). Students answered these questions before coming to class. Students then met during our regular class period in groups of 15–20 students. A group facilitator reviewed the answers to Part 1 and students were allowed to ask any questions (Appendix 3). They were then divided into groups of 3–4 students and were given time to work through Part 2 (Appendix 2). Part 2 was collected and graded as part of the course (Appendix 4). The average score of the 186 students was 9/10 points.

Approximately one month later, students were given two questions on a final exam (Fig. 2). For these questions, 85% of students got Q1 (“In this case, what binds to the binding site?”) correct, while 30% of students got Q2 (“Draw in the results you would expect, and explain why you would expect those results”) totally correct, with another 50% getting partial credit, for an overall average of 1.35/2 points.

FIGURE 2:

Post-test questions

Evidence of student learning

To assess student learning, we performed pre-test/post-test statistical analyses. For our analysis of the first learning objective (“describe how components work together in the regulation of bacterial genes”), we looked at all the questions relating to the basic concepts of how positive and negative regulation works. We grouped these questions together, comparing the sum of Q1–Q4 on the pre-test to Q1 on the post-test. Using a paired t-test, we found that students’ scores on the post-test (90.1%) were significantly higher than their scores on the pre-test (70.1%; p = 0.05).

To address the second learning objective on applying these concepts to explain the results of an experiment, we compared student scores from the questions that dealt with interpreting and predicting experimental results (Q5 on the pre-test and Q2 on the post-test), this time using each student’s score on the Regulation Activity Q3 (“Based on the two experiments above, is the bfp operon under positive or negative control? What evidence do you have for your answer?”) and Q4 (“What would the results look like if the RegB gene was under the other form of regulation?”) as the covariate. Again, student scores on the post-test (67.8%) were significantly higher than scores on the pre-test (28.7%; p = 0.02). In addition, doing the Regulation Activity had a strong significant impact on student scores; that is, doing well on the Regulation Activity markedly improved their ability to answer the post-test question on explaining and predicting the results of a complementation experiment (p = 0.009).

Overall, our analysis shows that student understanding improved significantly after doing the Regulation Activity. We acknowledge that it is possible for some students to be passive observers in their groups, writing answers without truly understanding the concepts. In our case, students who did well on the Regulation Activity also did well on the critical-thinking questions on the post-test. Our results support the idea that during group work and peer discussions, students learned from each other and understood the material well enough to apply the concepts to new situations. Students themselves thought that the activity helped them to better understand the material.