Ask the Warm-Up question, “What monomer is the building block of proteins?” Remind students to recall information that they learned from the Macromolecules lesson. Use this question as a formative assessment to determine the depth of prior knowledge students possess about proteins. Listen to see if the class universally possesses a clear understanding of the relationship between amino acids and proteins. If students are not able to clearly explain that amino acids are the building blocks of proteins, spend 2-3 minutes reviewing the relationship of monomers and polymers. It might also be useful to review dehydration synthesis as the process that links the monomers, as well. Students should possess a clear understanding of the relationship of monomers and polymers before moving into the lesson.
Inform students that their learning targets for this lesson are:
Display visual information as you teach and instruct students to take notes using guided notes that you have provided or use a note-taking strategy that you have taught. Guided notes provide greater support for the different learning styles of students.
Complete a DNA and RNA graphic organizer, comparing DNA and RNA structure and function. Activating prior knowledge about DNA will help students compare and contrast what they know about DNA with the new knowledge being presented about RNA. Display the graphic organizer whole group and review the similarities of DNA and RNA as a check for understanding. As you lead students through the process of identifying which characteristics apply to DNA or RNA, listen for students’ ability to make the correct associations to each molecule.
Introduce the term, transcription. Give students a real world use of the term by pointing out that medical transcriptionists rewrite dictated notes from doctors into medical records. Emphasize that the instructions from DNA must be rewritten into RNA language because the languages are not based on the same “alphabet” or nitrogen bases. Just our English language is based on a set of letters that is different from the Japanese language, so is the difference between and RNA “language".
Explain transcription as it relates to protein synthesis, making sure students understand where this process occurs and what its product is. Make frequent checks for understanding throughout the teaching and note-taking process to identify gaps in students’ understanding of concepts.
Display a transcription animation and instruct students to watch it 2-3 times. Play the animation again and ask students to identify each of the 4 the colored molecules in the animation that are a part of protein synthesis. If needed, point out that the blue molecule appears to be a two-strand molecule before it is opened by the green molecule or that the red molecule that is formed is a single-strand. Look for students to identify DNA as the blue molecule, helicase as the green molecule, RNA polymerase as the yellow molecule and mRNA as the red molecule that is formed.
Introduce the term, translation, making sure students understand where this process occurs and what its product is. Using the prior example, remind students that transcription simply involved re-writing or “converting” the message into another language. Emphasize that de-coding of the message occurs during translation so that the re-written DNA message is understood in order to assemble the correct protein.
Expect that some students will struggle with these concepts. Deliberate use of modeling, visual aids, manipulatives, and foldables will help students grasp what occurs during protein synthesis. Plan to conduct 2-3 more lessons (Protein Synthesis Lab and protein synthesis, part 3) as a follow-up to this lesson to help reinforce conceptual understanding.
Distribute mRNA decoder charts to students. It’s a good idea to copy and laminate a set that can be reused each year. Display a DNA template strand on a LCD projector. Instruct students to copy the DNA template strand onto their papers. As a check for understanding, ask students to explain how DNA language is difference from RNA language.
Display a practice strand of DNA code. Perform a think aloud to allow students to observe how you walk through the process of transcribing each nitrogen base of the DNA strand into an mRNA strand. Make it a point to emphasize that transcription is re-writing DNA into RNA language. Use an interactive pen and pad write and display each letter that represents a nitrogen base as you explain how you transcribe the DNA template strand into the mRNA strand. Walk around the room as you work using an interactive writing pad to make sure that students are following along and writing as you write.
Note: I love using an interactive pen and pad because it frees me from standing at the board with my back to the class. It also allows me to walk around while writing to check that students are writing the correct information on their papers.
Instruct students to label and highlight the mRNA code strand. Remind students that this product was formed during transcription.
Next, perform a think aloud to allow students to observe your thinking process of translating each nitrogen base of the mRNA strand into a tRNA strand. Write each letter that represents the correct complementary nitrogen base as you explain how you translate the mRNA strand into its anticodon, tRNA.
Using an mRNA decoder chart that is displayed on an LCD projector, think aloud and model how to use the chart to identify the amino acid associated with each of the codons on the mRNA strand. Remind students that each group of three letters (nitrogen bases) represents a codon or triplet that is associated with a particular amino acid. Use an interactive pad to show students how to write the abbreviation of each amino acid in the sequence.
Distribute a codon practice worksheet and instruct students to use the mRNA decoder chart at the top of the page to identify the DNA, mRNA, tRNA or amino acid for each of the blank spaces on the chart.
Remind students that the circular table requires students to work outward from the center. Also, before releasing students to begin working independently, remind them to consider whether mRNA or tRNA is used to determine the amino acid sequence.
Walk around the room to observe students' decoding and assist students who have questions or need additional explanation.
As a class, review the correct answers to the practice. Ask for volunteers, as well as select those to respond to each line. Instruct students to correct their responses if they did not have the right answer.