The Central Dogma (#6 of 6): Mutation

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Objective

1) All cells contain genetic information in the form of DNA molecules. Genes are regions in the DNA that contain the instructions that code for the formation of proteins, which carry out most of the work of cells. (HS-LS1-1 & HS-LS3-1) 2) Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells. (HS-LS1-1)

Big Idea

Changes to the DNA code (mutation) have the potential to produce an alternate form of the original protein chain.

Learner Goals

Note: I recommend that you first check out this resource in order to get the most out of this lesson!

In high school I took several drafting classes and, for a while, I had hoped to become an architect. With respect to planning instruction and teaching, I feel that I can still live out the detailed approach to building something intricate and complex even though the product is a lesson rather than a certain "built environment".

The lesson-planning document that I uploaded to this section is a comprehensive overview of how I approach lesson planning. This template includes the "Big Three" aspects of the NGSS standards: Disciplinary Core Ideas, Crosscutting Concepts, and Science Practices. Of course, there are many other worthy learning goals, skills, instructional strategies, and assessments that can be integrated into a class session. I don't feel compelled to check every box but, rather, use it as a guide to consider various options and tailor the lesson in light of these.

With regard to this particular lesson, students will:

1. understand that cells store and use genetic information to guide their functions. Furthermore, the structure of DNA is a double-helix. Its shape explains how hereditary information is stored and passed along to offspring.

2.  be able to construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells. (HS-LS1-1)

From the perspective of instructional strategies, I want to emphasize the following challenges:

Teaching Challenge: How do I support my students to compose, communicate, and evaluate a clearly stated, evidence-based, compelling argument?

 

Teaching Challenge: How do I support my students in analyzing data in order to address a question of interest?

I hope you get some value from my work!

Anticipatory Set ("Hook")

10 minutes

Click here for the previous lesson in the series.

Peer Instruction Protocol (PIP): Leveraging an individual and group-oriented review strategy.

Yesterday's instruction focused on the relationship between the different forms of RNA (mRNA, tRNA, and rRNA) and the mechanism and purpose of translation. At this point I want to reflect on whether students learned what I intended. I regularly make use of the PIP review strategy as a way to assess student learning. A more detailed explanation is provided here.

I will progress through this review activity in stages and following each major topic taught in the near past. In this case, I will address only questions #11-12 (Translation).

Instructional Input/Student Activities

35 minutes

Teaching Challenge: How do I support my students to compose, communicate, and evaluate a clearly stated, evidence-based, compelling argument?

Teaching Challenge: How do I support my students in analyzing data in order to address a question of interest?

In light of the two teaching challenges presented, I believe that the Claim-Evidence-Reasoning teaching strategy brings together both parts of the learning goals (HS-LS-1 and 3).

To summarize, my students will have learned the purpose, location, and mechanisms for DNA replication. They should understand that cell division (either mitosis or meiosis) happens because of replication and this hinges on the base-pairing rules (A-T and C-G).

Furthermore, by understanding the slight variation in the base-pairing rules, my students will have learned that both transcription and translation are necessary for protein synthesis. The question of interest is what kind of dark magic is involved in turning the genoytype (e.g. "Aa") into the phenotype (e.g. hair color)? Well, we know it is NOT dark magic; rather it is the step-wise process of the Central Dogma: DNA -->mRNA--> protein chain.

Once students recognize that the code is interpreted to create a final product then a next logical question is, "If, and how, can we change the code to produce something REALLY cool?" (leading to some interesting genetic engineering discussions) or, "how has nature done the same thing?" If you change the gene, you change the protein. Kind of rhymes, right?

Intriguing question. Check.

Now for the evidence-based argument. 

CER: Claim-Evidence-Reasoning Model

The task with this assignment is to guide students toward the realization that mutations need not be extreme, grotesque, or extremely grotesque. Most commonly they are miniscule and imperceptible to the naked eye. Furthermore, not all changes to the genome result in any discernible difference to the phenotype and, if it does, most often it is a negative effect (e.g. Tay-Sachs disease with two missing nucleotide letters or Sickle Cell Anemia with 145/146 correct nucleotides).

This CER model requires students to examine five DNA codes and the complementary mRNA copies. Based on these transcripts, they are to examine the resulting protein chain and compare it to the original sequence (#1 of 5). Based on what they observe (Data), they are to choose the Claim that best suits the data. From here, they are to re-examine the Data and describe the most relevant Evidence that supports their claim and explain (Reason) their thinking as to why their evidence supports their claim.

To do justice to the learning objective, I am sure that there are myriad ways for students to progress from communicating "What they know" and "How they know" toward demonstrating "Why they know". I know that this graphic organizer has seemed pretty intuitive to students and makes the thinking process (justification) more transparent.

In short, the argument is whether all mutations lead to changes in the phenotype and whether it is dark, deep magic or the process of converting one genetic code to another and another that pops out a protein that may or may not be what was originally intended.

The CER model answer key is provided for your reference.

Closure: What did we learn? Where do we go from here?

10 minutes

Analogy Prompt: Giving students opportunities to think and talk about biology

I use analogies to relate complex and abstract ideas and processes to my students all the time! We make sense of our world in the terms that make sense to us; that is our common background experiences, the movies and TV shows we watch and books that we read* that are common to our community.

*(too few books read by too few folks in my opinion)

That being said, students should grapple with the purpose and process of the Central Dogma and how it relates to the things with which they are most familiar. I believe that this is when ownership of learning begins.

Prompt: "Transcription and translation are like ______ because ______ and transcription and translation ______."

There could be any number of responses such as "Transcription and translation are like writing a recipe and using it to make chocolate chip cookies with walnuts because hungry people need to know the steps to baking and transcription and translation must know what the DNA code (gene) wants to make (like a certain protein)."

Can you tell that it's almost snack time?

Lesson Extension & Follow-Up Activities

Formative Assessment: Protein Synthesis

Students will be directed to complete the assigned questions from the Transcription & Translation formative assessment. This will demonstrate if they grasped the mechanics of converting DNA code into mRNA, then use that to select the appropriate amino acids that result in the finished product (polypeptide).