In today's lesson, students will continue the activity that they started yesterday by exploring how the hemoglobin protein is constructed using amino acids and mRNA instructions. After looking at the steps involved in translation, students will use origami to explore how the polypeptide made during the translation activity is folded to make a protein. Finally, students will write an analogy that is meaningful to them that will explain how the processes of replication, transcription, and translation work together to maintain a healthy cell.
Learning about cell processes like replication, transcription, and translation are important because many students struggle to understand how the cell acts as an unit of function. Also, it is highly important that students understand the basics of these natural cell processes to ensure they can take informed positions on the everyday application of molecular genetics, as well as the ethical implications of modifying living things. Using these hands-on activities really keep students engaged and allow students to gain a deeper understanding of the complexity of cell processes that they think they already know well. Here is what students will learn in this lesson.
Ask students to consider the following questions:
Have students use this graphic organizer in their lab notebook while watching the introduction video, 4 Primary Functions of Proteins. (Note: Here is an example of how the graphic organizer might be completed.)
Explain to students to truly understand the role of proteins in the body, they must understand how those proteins are made. Using the Frayer method, have students define translation.
Using the student worksheet and the manipulatives, students will role play the jobs of ribosomes and cytoplasm in making a portion of the hemoglobin molecule. Students should use the base pairing rules to show how the tRNA anti-codon temporarily binds with the mRNA to produce a polypeptide chain. (Note: Before the start of this activity, the teacher will need to have the ribosome, tRNA molecules, and amino acids precut and laminated. One set per group should be made.)
Give student groups the second part of the mRNA and have them combine it with the portion of mRNA that they made yesterday. While the student role playing the cytoplasm finds the correct transfer RNA for for mRNA codon, the student modeling the ribosome should place the amino acid into the P position on the ribosome. Then the ribosome should lightly the codon and anticodon together to represent the weak chemical bonds formed between them. The cytoplasm should hand the ribosome the correct tRNA for the next codon. The ribosome should firmly tape the two amino acids together. Next, he or she should cut the anticodon from the amino acid and shift the mRNA strand from the P position to the A position. Students should repeat these steps until the polypeptide chain is completed.
Following the completion of the model, students should compare their normal polypeptide chain with a polypeptide responsible for sickle cell anemia. Using the table provided on the student worksheet, they should compare the nucleotide sequence of the beginning of a normal hemoglobin gene with the beginning of the sickle cell hemoglobin gene. Students should note the only difference between the two genes.
Students should complete this activity by examining the model used in this simulation and comparing it to computer model of translation in real time.
This student activity is based on Walden, Ingrid, et al. 2014. Serendip Studios. "From Gene to Protein."
As a class, popcorn read the article Science of "Protein Origami" Unfolds from LiveScience. Have students complete a current events summary sheet while the article is being read. Next, hand each student a single sheet of origami paper. Explain that this paper is supposed to represent the unfolded polypeptide that has just left the ribosome. Next, explain that for the polypeptide to become a working protein that it might be folded and reshaped. Its basic amino acid sequence will not change, but will be used in determining the shape of the final protein.
To demonstrate the secondary structure, have students fold the paper into quarters and then along the diagonal. Explain to students what the secondary structure is and how it is formed. Have students continue to follow instructions found here. Explain tertiary structure and ask students what part of the rose design represents the tertiary structures. Finally, step 15 and 16 explain the quandary structure of the protein and ask the students how this step best models a protein.
Finally, show student images of a normal hemoglobin protein and a sickled hemoglobin protein. Ask them to describe the difference in their 3-D structures. Remind students that each came from a polypeptide that was folded to make a protein. Only one amino acid is different between them causing a huge difference in the final structure of the protein.
In their lab notebooks, students should create an analogy of common everyday practices that help demonstrate how the cell processes of DNA replication, RNA transcription, and protein translation works together.
(Note: To help my students begin to start thinking about what type of analogy may help them remember these processes, I share an analogy that I developed:
I make amazing sweet rolls called kolaches. So many people have asked me for the recipe that I decided I should have someone chisel the recipe into the wall of my classroom. I didn't want to lose the recipe. I provide recipe cards and pencils to whoever want to write the recipe down. However, the original recipe cannot leave my room. Students are free to take their copied recipe out of the room on recipe cards to their homes. At their homes, they can assemble the necessary ingredients and make their own kolaches.)
Next, students must compare their analogy with the three cell processes and explain them in light of what happens in the cell processes.
(Note: Here is how I explain my analogy to my students:
The kolaches are proteins. The recipe chiseled to the wall of my classroom represents the gene in the DNA template. My classroom represents the nucleus. When students copy the recipe onto recipe card, they are representing RNA polymerase making a mRNA template. The recipe card leaving the room is much like mRNA leaving the nucleus. The kitchen in the student's home represents the ribosome. When students assemble the supplies to make kolaches, it is like tRNA bringing amino acids to the ribosomes to make a polypeptide.)