Standards: SC.912.L.16.5: Explain the basic processes of transcription and translation, and how they result in the expression of genes.

Transcription

1 Delicious DNA: Transcription and Translation Simulation Using an Edible Model Authors: Darcy Holoweski and Catherine Quist Standards: SC.912.L.16.5: Explain the basic processes of transcription and translation, and how they result in the expression of genes. Objectives: SWBAT describe how the processes of gene transcription and translation result in phenotypic expression. Grade Level: Biology 1, 9 th -11 th grade Overview: Students will learn about the processes of transcription and translation and then simulate these processes using an edible DNA model that they created during a previous lesson. Learning Outcomes: * Learning Performances: At the end of this lesson, students will understand and be able to simulate the production of an mrna sequence and protein translation through a model they have made. They will understand that a cell is dynamic and that proteins, which function as the structure and the machinery of the cell, must be constantly manufactured in order to support the cell's life processes. They will also be able to make connections between the importance of protein synthesis and evolution. Students' Prior Knowledge: * A basic knowledge of DNA structure, function, and location, and that DNA contains heritable instructions for building and maintaining an organism. * A basic knowledge of the organization of the cell; that DNA is stored in the nucleus and that ribosomes in the cytoplasm make protein. * Students should understandd that genes code for proteins, which are the structure and machinery of the cell. * Students should know that proteins are made by ribosomes, which are located in the cytoplasm. * Students should understand the process of cell division, including mitosis.

2 Establishing Purpose: The purpose of this lesson is to convey to the students that the cell is not static. The proteins, which function as the structure and the machinery of the cell, must be constantly manufactured in order to support the cell's life processes. Through the processes of transcription and translation, described in this lesson, the genetic code in the cell is decoded in order to construct these proteins. During this lesson, the students will be introduced to the "big picture" of protein synthesis through a hands-on activity in which they transcribe an mrna sequence from a DNA sequence and translate a protein from that mrna sequence. Finally, they will explore the evolutionary and regulatory reasons for the processes described by the Central Dogma. The students have also been working with the edible DNA models for two days previously. Therefore, links will be made between what the students have learned about DNA already and how they will use that knowledge to help them transcribe and translate the DNA code into proteins. In addition, the connection between cell division and protein translation will be made, emphasizing that the production of new proteins is necessary for the creation of new cells. Instructional Strategies: This lesson will combine a teacher lecture, and students working in pairs with DNA models to simulate how DNA is transcribed and translated. Materials Needed: Paper models of DNA previously built when DNA replication was introduced Time required: 3 50-miniute classes Instructional Seqence: * Introducing the lesson using guided inquiry to activate students' prior knowledge and to establish purpose for lesson: Establish the motivation for the transcription and translation process. "What happens during the process of cell division?" Students should say that DNA is replicated and new structures are built. "What are new cell structures made out of?" Students should mention protein. "How do cells know how to make new proteins?" Students should answer that instructions are in DNA. "How do cells use DNA to make proteins?" Students shouldn't have an answer to this. Explain that today we are going to learn about transcription and translation, which is the process by which the genetic code stored in DNA gets turned into protein. Explain how understanding the transcription and translation possible makes genetic engineering possible. Next establish the need for mrna to carry the genetic code from the nucleus to the cytoplasm. "What makes protein?" Students should know that proteins are made by ribosomes.

3 "Where are ribosomes located in the cell?" Students should know that ribosomes are located in the cytoplasm. "Where are genes located in the cell?" Students should know that genes are located on DNA, which is located in the nucleus. "How does the genetic code get out of the nucleus?" Students should understand that DNA never leaves the nucleus, but somehow the genetic code gets out of the nucleus into the cytoplasm. Students should suggest mechanisms. Students may suggest that a molecule must transcribe the genetic code and then take it into the cytoplams to be translated into protein, but if not, their curiousity has been peaked and they are ready to learn about how this phenomena occurs. At this point, the conceptual relationship between DNA, mrna and protein has been established, and it is time to introduce the Central Dogma. * Body of the Lesson: o Introduce Central Dogma: Using Figure 1 below, explain that DNA in the nucleus is transcribed into a single-stranded molecule called messenger RNA (mrna). The mrna travels out of the nucleus into the cytoplasm, where it is translated by the Ribosome and transfer RNA (trna) molecules into a peptide sequence. Once the peptide sequence is translated, it folds into a three dimensional protein, which acts to do work or provide structure to the cell.

4 Figure 1: Central Dogma of Biology *Understanding the Central Dogma by Analogy: Using Figure 2, explain the students the Central Dogma in terms of things and processes that the students already understand. The goal is to help them build connections between the new material and their prior knowledge. These symbols that describe the functions of the biological molecules may help students understand them better. Figure 2: Central Dogma Analogy Key: 1. DNA = Blueprint of Tinkertoy Structure 2. mrna = Messenger 3. Ribosome = Toy Factory 4. trna = Wrench 5. Amino Acids = Tinkertoy Parts 6. Protein = Tinkertoy Ferris Wheel *Connecting to the big picture: *Regulatory Implications: Explain to the students that the cell is not static. Proteins degrade and are digested over time so that new proteins must be manufactured all the time in order to support the life processes of the cell. For each of the following facts about transcription, think of a potential advantage for the cell: 1. Fact: mrna is transcribed from a particular gene in different amounts at different times. Correct Response: Cells can regulate the amount of different proteins, turning genes on and off. This leads to different cell types. It also leads to different developmental stages.

5 2. Fact: mrna travels to different parts of the cell to be translated. Correct Response: Proteins are made where they are needed in the cell, making it more likely that the protein will be available to do the necessary work. + Evolutionary Implications: Explain to the students that the relationship between DNA, RNA, and protein probably evolved for a reason. Most scientists believed that RNA evolved before DNA. 1. Why might RNA have evolved first? Answer: RNA is single stranded and is able to do work. 2. Why might DNA have evolved? Answer: DNA is double stranded and is more stable. Transitioning into an exploration of the details of transcription and translation: The teacher will point out that they have only explored the overall process of transcription and translatin and that they have not yet learned the detail. The teacher will next complete a detailed example of transcription and translation happening from a 9 or 12 nucleotide DNA sample. The students will be asked to follow along and provide answers to the teacher's leading questions for what happens at each step. To complete the example, the teacher will introduce the students to the Genetic Code chart in their textbooks and how to read the semi-complicated chart. Now students are ready to complete their own transcription and translation activity. o Implementing the activity: The students have been working with paper DNA models for the past two days. The first day they created a DNA model using different colored pieces of paper. The second day they learned about DNA replication and simulated it using their model. In this activity, the paper models will be used again to demonstrate how transcription and translation occur. They have seen the processes of transcription and translation demonstrated by the teacher using Figure 1, and they have problem-solved the different roles that each of the biological molecules have in the processes, and now they are given the opportunity to simulate the processes themselves. Before doing the activity the teacher will ask the students how they could use the models from the past two days to model transcription and translation. This will help them construct their own understanding of the models. The following activity sheet will guide the students in creating proteins from their DNA models: (Activity Sheet not included in this link as it does not correspond to the prior knowledge portion of the RWT). * Concluding the lesson using review: First, ask the students if they have any questions following the activity. Next, write a DNA sequence AGACTTATC on the board and project the genetic code, which gives the relationship between codons and amino acids on a screen. Ask the students to help transcribe and translate this DNA sequence. First, walk through the DNA sequence and transcribe it into mrna one nucleotide at a time. The corresponding mrna is UCUGAAUAG. Next, walk through the mrna translating it into protein one codon at a time. The corresponding protein is Ser Glu Stop. Ask students about the function of the 'Stop' codon to check for

6 understanding. Ask students what would happen if the first C in the sequence was changed to a G. Then the protein sequence would be Gln Glu Stop. This is an example of a mutation. Tell the students that they will be learning about mutation in the next lesson. Assessing Student Understanding: The worksheet for homework will ask the students to practice the process of transcribing DNA to yield mrna and translating mrna to yield protein and then ask the students to diagram the Central Dogma, the process of transcription and translation. * Routine practice: For the first three problems, give the students a DNA sequence and ask them to provide the corresponding mrna and protein. * Ask the students to diagram the Central Dogma of biology, including the cell membrane, nuclear membrane, mrna, DNA, protein, amino acids, trna, and ribosome. * Ask the students to label a diagram of an mrna being transcribed. * Ask the students to label a diagram of a protein being translated. Student Resources: The course textbook Biology: The Dynamics of Life, published by McGraw Hill: Glencoe Science, copyright Cautions: Students should be reminded not to eat their edible models. The models have touched the lab benches, which may have been the site of a chemical spill.