The Central Dogma (#2 of 6): DNA Replication

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Objective

Systems of specialized cells within organisms help them perform the essential functions of life. (HS-LS1-1) 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)

Big Idea

The structure of DNA is a double helix. Its shape explains how hereditary information is stored and passed along to offspring.

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.  know that 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)

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

Teaching Challenge: How can I develop my students’ ability to apply unifying ideas to make connections across science content (among and between physics, chemistry, biology, earth and space science)?

Teaching Challenge: How do I support students to develop and use scientific models

I hope you get some value from my work!

Anticipatory Set ("Hook")

10 minutes

Click here for the previous lesson in the series.

3-2-1 Card: Allowing students time to think and write about biology.

I use the 3-2-1 Card strategy to allow students the equal opportunity to think about the learning from the previous day. In this case, students will respond to the following prompt:

Describe 3 similarities between DNA and RNA.

Describe 2 differences between DNA and RNA.

Identify 1 location in the cell that contains DNA (other than the nucleus).

More often than not, there are a handful of students who can come up with this information quite quickly however more students need time to process. They are encouraged to review the class work from yesterday before that work is turned in. This entry could be turned in for a grade or shared in a small group or large group setting (depending on the time and context of the lesson).

Click here to see a few examples of student responses!

Instructional Input/Student Activities

35 minutes

Central Dogma Notes (slides #1-9)

In this segment of the lesson, I spend some time using the strategy of direct instruction using the Cornell note-taking method. The topic is DNA replication and the context is to compare and contrast mitosis with meiosis (previously studied in this series).

In essence, students should recognize that meiosis makes unique haploid gametes; essentially that sex produces special offspring. In the case of mitosis, parent cells create daughter cells as clones for the purpose of repair of dead/damaged cells and for growth of the organism. In ideal circumstances the two generations of cells would be identical however mutation and other anomalies occur.

Therefore, if cells undergo mitosis then how does this happen? Students will learn how a single, double-helix (parent strands) produces a second, identical copy (daughter strands) that will be shipped off to the newly created cell. Without this process, an organism's cells could not be repaired for example.

The teaching challenge here is to connect the previous unit of study (Genetics) that has a macro focus with this study of molecular genetics with micro focus. If successful, students will have shown the ability to apply unifying ideas to make connections across these two related science topics.

The important cross-cutting concept here is that of pattern recognition (the base-pairing relationship between the parent and daughter strands' nucleotides (ATCG)).

Teaching Challenge: How do I support students to develop and use scientific models?

Students should recognize that the model of the double-helix structure allows for the pairing of complementary DNA strands when the interior (hydrogen) bonds are temporarily broken, thus exposing the parent/template strand for copying. Were it not for the occasional mismatch by DNA polymerase, all daughter and parent strands (and the resulting somatic cell copies) would be identical; a necessary function for replacement of dead or damaged cells.

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

10 minutes

Central Dogma Review

As we wrap up for today, I direct students to complete p. 1 ("Replication" questions only) to apply what they learned. This review packet will be completed in several stages as we progress through this lesson series. 

The answer key is provided for your reference. Click here for a sample of student work.

Click here for the next lesson in the series.

Lesson Extension & Follow-Up Activities

Students will be directed to finish the assigned questions from the Central Dogma Review packet if they did not do so in class.