A play of protein synthesis in the classroom.
Because it involves several interconnected mechanisms that are not observable, protein synthesis is often reported to be poorly understood by students (Fisher, 1985). In a freshman General Biology class, my students encountered difficulties and misconceptions when confronted with this topic. Chapter delivery by lecture only was especially ineffective for getting the students to visualize these abstract concepts. So I decided to make protein synthesis come alive in the classroom by having the students role-play transcription and translation in the synthesis of a short polypeptide.
The role-play was done separately in two sections, with 12 and 16 students in each, and took about 10 minutes to complete. The students took on character roles of DNA and RNA while acting out complementary base pairing, splicing of introns and joining of exons, matching of mRNA codons to the corresponding amino acids, and assembly of amino acids on a growing polypeptide chain. At the end, the students were given a short quiz to assess what they had learned and a survey about their satisfaction with the activity. They performed well on factual-comprehension questions, but not in the concept application. This activity can be adapted for a larger class by using a longer DNA base sequence. Another variation is to have students dance to music while role-playing. They could also devise color-coded costumes for easy clarification of the sequences.
** Two large wooden hoops
** Several balloons with names of amino acids written on them
** Paper and marker pens
** Sticky tape
** Music (optional)
* Before the Role-Play
I briefly explained the meanings of sense and antisense DNA strands, genetic code, codon and anticodon, exon and intron, cap and tail on mRNA, and the codon chart for amino acids. Then I wrote a short sequence of bases on the DNA sense strand on the white board:
( A T G T T T T T G G C G A G G T G A ) 5' Intron stop 3'
An intron was included in the sequence. A chart of mRNA codon and amino acid was projected on the screen. The students already knew about complementary base pairing from a previous chapter, so I had them collaborate in pairs to work on the base pairing for DNA, mRNA, and tRNA, noting the replacement of thymine (T) by uracil (U) in RNA.
Each student was assigned to work on two roles. One became the genetic code (ATG) on the sense strand and the mRNA codon (AUG). His partner was the complementary code on the antisense strand (TAC), the tRNA anticodon (UAC), and the corresponding amino acid (methionine). The remaining bases (TTT, TTG, GCG, AGG, and TGA) were assigned in a similar manner to the other pairs of students. This activity engaged the students in learning that the sense strand was transcribed using the anti-sense strand as a template, and matching each mRNA codon to the correct amino acid using the mRNA codon chart. Two other students became the 5' cap and 3' poly-A tail, respectively on the processed mRNA.
* Role-Playing Transcription
Once all the base sequences were worked out, we pushed the desks and chairs against the wall to make space for the role-play. The bases were written on pieces of paper and taped onto the students' shirts for each role. The students lined up face-to-face in two rows, one representing the DNA sense strand and the other the antisense strand. Students were told that they were in the nucleus of the cell, the site of transcription. Hands were linked to represent hydrogen bonding between these bases, and unlinked to illustrate formation of the transcription bubble. Since there were not enough students, the sense strand moved away, but the students were told that the opening of the helix and transcription actually occur simultaneously The sense-strand students exchanged their DNA codes for mRNA codons and moved back in line, one by one, to face the antisense strand, demonstrating that the antisense strand was the template for transcription.
When all the mRNA codons were paired with the antisense codes, the antisense students walked away. The "intron" student was told to step out of the line, because introns are noncoding sequences that must be spliced from the mRNA. The remaining exons moved to close the gap left by the intron, so that the mRNA now contained only exons. The "cap" student joined the 5' end of mRNA (standing next to the initiator AUG student) and the "tail" student joined the 3' end (beside the UGA student). I explained that the purpose of the cap was to prevent enzyme digestion of mRNA and for its correct positioning by the 5' end on the ribosome. Thereafter, the students walked around to illustrate the movement of the modified mRNA out of the nucleus into the cytoplasm for translation.
* Role-Playing Translation
Two hoops were placed on the floor to represent the P and A ribosome sites in the cytoplasm. The 5' cap student stood beside the P hoop. I reiterated the function of the cap for positioning of mRNA on the ribosome. The initiator-codon student (AUG) stepped into the P hoop and was joined by the tRNA anticodon (UAC) carrying a balloon representing methionine (met). I repeated that translation always commences from the 5' end of mRNA with the codon AUG. Next, the first codon (AAA) stepped into the A hoop and was joined by a tRNA anticodon (UUU) with a balloon marked as lysine (lys). The first balloon (met) was transferred and stuck to the second one (lys). I explained that this step represented a chemical reaction that released the initial methionine from its tRNA and attached it to lysine by a peptide bond. The initial codon (AUG) and tRNA (UAC) stepped out of the P hoop while the first codon (AAA) and tRNA (UUU) translocated to the P hoop as the mRNA was read in the 5' [right arrow] 3' direction. The second-codon (CGC) student stepped into the vacated A hoop to be matched (translated) with anti-codon (GCG) and a balloon (arginine). The dipeptide (lys-met) attached to the tRNA at the P site was detached and taped to arginine (arg). The elongating polypeptide now consisted of three amino acids: met(first)-lys(second)-arg(third). The codon and tRNA then stepped out of the P hoop while the students in the A hoop translocated to the P hoop. The next was a stop codon (UGA). There was no corresponding tRNA for this codon, so the polypeptide was released from the ribosome and protein synthesis ended.
I explained and directed the first few rounds of the play. Repeating the entire role-play a few times allowed continual reflection upon earlier experiences in order to add to and transform them to develop deeper understanding. Once the students understood the process, they were able to continue it without direction from me. I encouraged the students to ask questions each time they went through the role-play.
After the final round of role-playing, the students watched a short animation of transcription and translation by John Kyrk (http://www.johnkyrk. com), which gave them an overview of the process.
To evaluate the effectiveness of the activity, I gave the students an unannounced quiz immediately after the debriefing. The students were required to write short answers to seven questions that tested their factual knowledge and concept application in a manner that reflected Bloom's cognitive process (Anderson & Krathwohl, 2001). I then used a paper-and-pen questionnaire to assess the students' attitudes and perceptions regarding the activity. They ranked their responses to 10 questions on a 10-point Likert scale (1 = strongly disagree; 10 = strongly agree). The last question invited them to provide additional comments.
Altogether, the pre-role-playing, role-playing, debriefing, and quiz took up an entire 90-minute class period.
* Results & Discussion
The students' answers to the quiz questions indicated that the basic concepts were well understood. Many were able to remember important details of the process, such as removal of introns, joining of all exons, addition of a cap and a tail, and the roles of the P and A sites during translation (Table 1, questions 1-6).
However, the activity did not help the students to adequately apply the concept in a new situation (question 7). In this final question, I deliberately presented a DNA sense strand with base sequences that were different from those used in the role-play. Also, the direction of the strand was reversed. Half the class correctly wrote base sequences of the transcribed mRNA, reflecting their understanding that both the sense and mRNA have similar base sequences, except for the replacement of T by U in RNA. The remaining students gave incorrect answers, writing the complementary base sequences of the antisense strand instead. Nonetheless, most (85%; Table 1) were able to write the correct base sequences on the tRNA and to use the codon chart. Only one student (4%) correctly translated the mRNA from the 5' end to produce a short polypeptide comprising met-his-lys-pro. All the others assembled the wrong sequence of amino acids, including those who produced the correct mRNA base sequences in the first part of this question, because they commenced translation from the 3' end of the mRNA. This clearly showed that more time is required for the students to reflect and assimilate scientific concepts into a higher level of cognitive functioning (Piaget, 1970). Perhaps the students might have performed better on question 7 if they had done it as a take-home assignment. A role reversal of each student in the second round of role-playing might also be helpful. For instance, the sense-DNA students could switch roles with the antisense students to better understand that the former was transcribed and the latter was the template.
Although no comparable data were available to determine the extent of the students' achievement when taught solely by PowerPoint, I had observed that the students generally struggled to comprehend and visualize the details of transcription and assembly of the amino acids on the polypeptide chain during the lecture period. There was also little active participation. By contrast, most of the students quickly grasped these concepts and were able to recall the details after role-playing. In addition, everyone was enthusiastic and motivated to participate, as they found role-playing enjoyable and memorable (Table 2). Overall, I was satisfied that role-playing was a worthwhile alternative teaching strategy that had enabled my students to visualize and understand the fundamental concepts in protein synthesis in a fun-filled environment.
RECOMMENDED READING FOR AP Teachers
Anderson, L.W. & Krathwohl, D.R., Eds. (2001). A Taxonomy for Learning, Teaching, and Assessing: A Revision of Bloom's Taxonomy of Educational Objectives. New York, NY: Longman.
Fisher, K.M. (1985). A misconception in biology: amino acids and translation. Journal of Research in Science Teaching, 22, 53-62.
Piaget, J. (1970). Genetic Epistemology. New York, NY: W.W. Norton.
BESSIE ONG is a Senior Lecturer in the American Degree Transfer Program at Taylor's College Subang Jaya, First Floor, Wisma Subang Jaya, Jalan SS15/4, 47 500 Subang Jaya, Selangor, Malaysia; e-mail: firstname.lastname@example.org.
Table 1. Learning outcomes according to Bloom's cognitive process (Anderson & Krathwohl, 2001). Bloom's Cognitive Quiz Question % Correct Answers Process (n = 28) Factual knowledge 1. State the site 96 of transcription and translation. Factual knowledge 2. What is the 77 product of transcription? Factual knowledge 3. List two One difference = 29 differences between Two differences = 52 DNA and RNA. None =19 Factual 4. Explain what a 81 comprehension codon is. Factual 5. Explain what 77 comprehension exons and introns are. Factual 6. Briefly summarize Incomplete = 31 comprehension the steps involved Complete = 50 in protein (with details) synthesis. Unacceptable = 19 Application of 7. A segment of DNA 54 (correct mRNA) factual knowledge sense strand with 85 (correct tRNA) its base sequence is 4 (correct amino given below. Show acid sequence) the base sequences for the transcribed mRNA & tRNAs. Label the direction of the mRNA strand. Identify the amino acid sequence after translation. DNA 3' ACC GAA CAC GTA 5' (sense strand) Answer: mRNA 3' ACC GAA CAC GUA 5' tRNA UGG CUU GUG CAU amino met- his- lys- pro acid start 1st 2nd 3nd Table 2. Students' perceptions of the role-play (1 = strongly disagree, 10 = strongly agree). Question Mean SD 1. I can remember the facts better from this 8.79 1.04 experience. 2. I understand the concept better than by 7.71 2.13 listening to lectures. 3. The activity helped me to visualize and relate 9.25 1.1 individual items together. 4. The activity allowed me to apply knowledge in a 8.71 1.17 new situation. 5. The activity revealed to me what I don't know 8.75 1.36 about the concepts. 6. I enjoyed myself. 9.1 1.15 7. The activity fostered my creativity. 8.37 1.94 8. I did not feel nervous or pressured. 9.22 1.28 9. The activity allowed me to learn from and to 8.71 1.36 teach my friends. 10. What is your overall attitude toward this 9.13 0.83 teaching strategy. 11. Additional comments * "It definitely was better than lectures and I had a lot of fun." * "This method could be used to explain other topics in biology to make the lesson more fun and easy to understand." * "Good lesson, I obviously grasped the facts and recognized the process more." * "I wish we could do more activities like this for the other chapters as I can understand better from this teaching method." * "Experiencing the process on my own helped me better understand the concept and remember the facts" * "It was such a different, but so interesting method of acquiring knowledge in biology." * "It helped me in visualizing how protein synthesis really works and enhanced my memory of this topic"
|Printer friendly Cite/link Email Feedback|
|Publication:||The American Biology Teacher|
|Date:||Nov 1, 2010|
|Previous Article:||A lantern-slide-inspired look into biology teaching's past.|
|Next Article:||Making biology teaching more "graphic".|