Intermediary metabolism is a complex subject that is often covered in general biology, cell biology, biochemistry, and animal and plant physiology courses. The functions of metabolism include the generation of usable energy, the degradation of complex nutrients into smaller intermediates, and the synthesis of new carbohydrates, amino acids, nucleotides, and lipids. Among the pathways most often studied are glycolysis, the citric acid cycle (tricarboxylic acid [TCA] or Krebs cycle), gluconeogenesis, the C3 (Calvin cycle) and C4 pathways of CO2 fixation, the β-oxidation cycle of fatty acid degradation, and the urea cycle. Most general biology textbooks include the structures of the key intermediates in these pathways along with the names of the enzymes that catalyze the individual reactions. More advanced textbooks provide additional details about each enzyme, such as its structure, reaction mechanism, and regulation. The breadth of this material can be overwhelming for both teachers and students.
In teaching a one-semester biochemistry course, I have found that using in-class poster sessions (Baird, 1991; Moneyham et al., 1996; Montúfar-Chaveznava et al., 2008) can greatly improve students' appreciation of metabolism and facilitate their mastery of both general principles and specific details. While I still give lectures with overviews of metabolic concepts and the general features of the major pathways, the precise descriptions of the individual steps in these pathways are covered in the poster sessions. Poster sessions have been found to be useful in a wide range of biology classes, from a high school course in which students look at the design of zoos (Slack, 2010) to an introductory college course focusing on stream ecology (Gorman, 2010) to an upper-level college course in cell biology (Wright & Boggs, 2002) to a more advanced course in cancer biology (Andraos-Selim et al., 2010). Poster sessions allow students not only to explore specific content areas in detail but also to develop their presentation and communication skills.
I usually divide the class into two groups so that half of the students can present their posters to the others on one day and the groups can be reversed a week later. Depending on the class size, the students might present posters individually or in pairs; the posters themselves can be limited to a few common pathways or expanded to cover more different pathways. I have a lottery near the beginning of the semester in which each student receives the name of one enzyme to study. The students are given written guidelines with the information to be covered in the poster, which in my course includes (1) a title and the author's name; (2) a one-paragraph abstract or summary; (3) a diagram of the chemical reaction involved; (4) a description of the human enzyme, including its gene, molecular size, amino acid sequence, and three-dimensional structure; (5) specific information about the enzyme's kinetics and mechanism; (6) a summary of its modes of regulation; (7) any available information about diseases associated with enzymatic defects; and (8) a list of references. Other instructors might have the students cover a different set of topics. The students also are provided with suggestions for the general format of the posters and can look at posters from previous years as examples. More general information about posters can be obtained from several books (e.g., McMillan, 2006; Knisely, 2009) and at websites such as the following:
A typical handmade poster is shown in Figure 1.
Posters also can be made using the PowerPoint software package in the Microsoft Office suite. However, because printing the poster either on campus or at an off-campus facility such as FedEx/Kinko's can be expensive, I have not made this a requirement for my class. Instructors who would like their students to learn to make posters in this way might provide them with a PowerPoint template, and circulate and grade electronic versions of the posters.
During the poster session itself, the posters are arranged in the order in which the enzymes and reactions occur within a pathway. The students and I go from poster to poster, discussing the information with each presenter. As is often true in poster sessions, the presenter is more relaxed than in a formal talk or PowerPoint presentation and the discussions are more open-ended and animated. While most students take the poster sessions seriously and actively participate, a few tend to hold back. This can be overcome by including questions about the posters on the exams and by having peer evaluations contribute to a student's overall grade. The students are graded using a simple rubric I have developed encompassing both the content of the poster and their interactions. Other rubrics are available online (e.g., http://www.readwritethink.org/lesson_images/lesson1076/rubric.pdf). While the students certainly do not master the details of every enzyme, they become the “class expert” on their particular enzyme and can use it as a case study for illustrating general biochemical principles (for a discussion and other examples of case studies, see http://ublib.buffalo.edu/libraries/projects/cases/case.html). I often refer the students to each other's posters so that they can see relationships between their enzyme and others that have been presented.
As an instructor, I have been quite satisfied with this approach, although it works best if the class has less than 25 students. Students' reactions to the poster sessions have been overwhelmingly positive, as indicated by their responses to open-ended questions on the course evaluations. I also think that it has improved performance on the regular in-class exams, although this is harder to prove because each class has its own distinctive mix of students. My exams usually consist of a mixture of multiple-choice questions and more open-ended short-answer questions. I use the multiple-choice questions to test the students' understanding of basic metabolic concepts such as the overall reaction of a pathway, its energetics, and its key points of regulation and major effectors. I use the short-answer questions to test the students' ability to do simple calculations, to describe enzyme mechanisms, and to interpret experimental data. In this section, I often include examples of enzymes or pathways that we have not discussed in class to see whether the students can apply the concepts they have learned from the lectures and from their posters to new situations. Thus, no student has a specific advantage over another student based on which enzyme they used for their poster presentation.