Lesson 10

Nucleic Acid Structure and Function : Working with Models (Day 3 of 5)

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SWBAT identify the components of DNA and DNA replication using paper, puzzle piece, and 3-D DNA models.

Big Idea

Get your students communicating their knowledge of DNA structure and function through their analysis of a variety of DNA models!

Notes for the Teacher

This is a five day lesson series exploring the structure and function of DNA that I have been developing with my research partners at West Ed over the past three years.  By using multiple DNA models, this series gives students the opportunity for deeper exploration and discussion about the components and function of DNA as well as a chance to analyze the diverse ways each model reveals different pieces of information about DNA.  

On Day 1, we explore students' prior knowledge about DNA structure and examine paper models of DNA.  Standards: W.9-10.1SL.9-10.1SL.9-10.1dRST.9-10.1RST.9-10.4SP2SP7SP8XC-SF-HS-2

On Day 2, we utilize 3D models of DNA for comparison and deeper discussion.  Standards:  W.9-10.1SL.9-10.1SL.9-10.1dRST.9-10.1RST.9-10.4SP2SP7SP8XC-SF-HS-2

On Day 3 and Day 4, we delve into the process and scientific vocabulary of DNA replication using both paper and 3D models.  Standards:  W.9-10.1SL.9-10.1SL.9-10.1dRST.9-10.1RST.9-10.4SP2SP7SP8XC-SF-HS-2

on Day 5, we utilize puzzle piece models to compare and contrast DNA and RNA for greater depth of understanding and in preparation of for our next series of lessons on protein synthesis.  Standards:  W.9-10.1SL.9-10.1SL.9-10.1dRST.9-10.1RST.9-10.4SP2SP7SP8XC-P-HS-1XC-SF-HS-2

I am using the models I have on hand:  a classroom model found on any science education supply website, paper models that you can build for students to use or have them build on their own, puzzle piece models I found in a closet in my classroom, and a special set of 3D printer constructed models of DNA created by researchers at Scripps Research Institute in San Diego, CA and brought to my classroom through West Ed, a nonprofit research and development agency that is also over seeing the Smarter Balanced educational testing system in many states now embracing the CCSS.  You can use any models you have on hand or others that you are able to get on loan through nearby university partners.  

My students were very happy with this lesson series and especially the amount of information they were able to understand and discuss through the focused use of these models.  I can't wait to hear about the models you choose to use and how the lesson works for you and your kids! 

Check out a note one of my students wrote to me about our time with the DNA models and what she learned from the experience.  I was so excited to see a student who didn't always feel successful in our class feel completely confident about her knowledge and to hear her contribute in both small and large discussions and activities through this lesson series using these amazing models.

My deepest appreciation to the staff at West Ed including Jodi Davenport, Matt Silberglitt, and Jacqueline Powers along with the generous project funders of the 3D DNA models used in these lessons.   

  • This material is based upon work supported by the National Science Foundation under grant DRL-1108896 and by the Institute of Education Sciences, U.S. Department of Education, under grant R305A120047. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation, the Institute of Education Sciences, or the U.S. Department of Education.

The Classroom Flow: Introducing Today's Activity

10 minutes

1.  Tell students that today we will be exploring the concept of DNA replication.

2.  Before going through the activity directions for the day, spend a few minutes reviewing the work students did yesterday and link it back to our structure of DNA vocabulary that we have listed on the board.  In the Classroom Video: Spokesperson Protocol, you can see how my students and I check in about major questions they have that bridge yesterday's work and our goals for today.

2.  Using the spokesperson protocol, ask students to discuss briefly in their lab groups the following two prompts:  

What is DNA replication

When and where does it occur?

3.  Share out answers briefly.  You will get a large range of answers but most will show some familiarity with DNA.  There are specific terms I look for to write down.  As students say them, write them on the board.  Whatever words they do not say, add them to the list.  This list of DNA replication vocabulary should stay up on the board throughout the lesson series.  Let students know that by the end of the series, they will understand each of the terms.  You can see this process in person by viewing Classroom Video: Spokesperson Protocol (Whip Around Version).

4.  Ask students to move to their lab tables.

The Classroom Flow: Working with the 3D Models to Explore DNA Replication

25 minutes

1.  On each table, have out the paper and 3D models we have been using throughout this lesson series for each lab pair.

2. Pass out the DNA replication activity document.

3.  Tell students that they will be working with their 3D models to go through the initial steps of replication.  Tell them that you expect for partners to alternate roles for each of the steps.  In this way, no one person will dominate with the model.

4.  Remind students again that today's work is about using the models and discussing DNA replication and that the formalized writing piece of the assignment is the lowest priority today.  Share with them again that the writing will be easier to do and more accurate/correct once they have had a full conversation and collaborative session using the models.  

5.  As students work, check in on each group.  Typically, I have found that questions #2, 5, and 9 will give students the opportunity to really explore a deeper level of questioning and understanding.  You may also find students need support stemming from the DNA structure work they have been doing in previous sessions.  

6.  See the student work sample for typical student responses.  This second student work sample shows similar responses and themes.  Below you will find my tips for supporting students as they work through the more challenging prompts as a team using the models:

  • Question #2:  If any student groups struggle with this question, it is typically because they have not used their model to explore it.  Encourage them to handle the model and to experiment putting together the nucleotides first by hydrogen bond pairings and then by the covalent backbone connections.  At this point, they will begin to offer up why it has to be that that hydrogen bonds between base pairs happen first.
  • Question #5:  Again, students tend to get stuck here only if they haven't actually used the model to experiment according to the scenario listed in the question.  Once you encourage students to work with the model, they will see that incorrect base pairs can form, but that the connections are weaker than those between the correct base pairings, and that they don't fit correctly into the 3D shape of the entire model if they base pairs are wrong, causing lots of other construction issues.  
  • Question #9: If students express doubt on this question, again it is usually because they haven't worked with the model for the purpose described in the question.  You can lead them to the right idea by asking them again about the strength and weakness of covalent vs. hydrogen bonds.  They will almost immediately begin to see that if the entire molecule were made up of hydrogen bonds, it would not be stable enough to keep the base pair code in the correct order.  Alternatively, if the DNA was made up of covalent bonds, it would be very difficult and time and energy consuming for cells to break them apart to read the code each time they needed to replicate or make new proteins.


7.  I find that this base pair green board image helps as a reminder of how to figure out each part of the nucleotides represented on the 3D models. If students are not able to point out the four specific bases by name on the model, pull out the board as a hint and then ask again.  If needed, specifically point to the number of hydrogen bonds on the green board image and ask students to find the equivalent on the 3D model so that they can name each of the four bases on the model with confidence and consistency.  In the Classroom Video: Teacher Support, Student Collaboration, you can see one of my student teams working directly with me to go into this specific topic area in more depth and detail.  

8.  For this year's group of students, it was helpful for us to take a moment to stop in the middle of the class session and address specific comments and questions I heard as I observed student groups working with the models.  This brief break in the action can be a really great use of time to help students be more efficient, reach deeper understandings from their model work, and boost their confidence as they hear them mirrored back by other groups and you.  In the Classroom Video: Questioning, Using Models, you can see our class stop to check in about the differences between covalent and hydrogen bonds, how they are represented on the 3D and paper models, and how those differences relate to the structure and function of DNA.  

The Classroom Flow: Wrapping Up

15 minutes

1.  Ask students to look at the board for the major scientific terminology related to our exploration of DNA replication.  Using the spokesperson protocol, ask each group to pick the word they know best and the word they have the least knowledge of.  You can see this brief process in our classroom by viewing Classroom Video: Wrapping Up.

2.  Ask student spokespeople to share out their best known word first and using a green marker, put check marks next to it on the left of the word.  You will find that typically students feel that they are most familiar with template and base pair rule.  Ask student groups to share out their understanding of the top words check marked on the board. 

 3.  Repeat the same process for the words students are least familiar with, using a red pen and making checks on the right side of the word.  Typically, students will pick helicase/DNA polymerases and semi-conservative as the two words they need more support for deeper understanding. IN each of the steps below, see how you can address these two specific terms/concepts on a basic level to be revisited in the next day's lesson in more detail and depth:

4.  Ask students probing questions about the enzymes:

What do most enzymes end in?  -ase

What do enzymes do? Break things apart or put them together

Does the word helicase remind you of any word we already know?  Helix

5.  Ask students to make a shape with their arms that represents a DNA double helix (arms together) and then ask them to demonstrate the first step in DNA replication (arms apart).  They will immediately get what helicase does.  You can then input information about the role of DNA polymerases (add on nucleotides according to the base pair rule, edit new strands)

6. I draw this drawing on the board to support their initial understanding of the term semi-conservative.  We delve into it on a surface level due to time, but I tell them we will spend more time exploring it tomorrow.

6.  As a final wrap up, ask student groups to pick one word they would like to revisit tomorrow and have them come up to put a check mark by then using a blue pen (erase the other marks).  Typically, students pick semi-conservative or DNA polymerase.

7.  Student groups and I had many great conversations about DNA structure by observing our models and comparing their features.  In the Classroom Video: Observation, Deeper Questioning for Learning, you can see one of these discussions and hear a little more about my reflections about the many positive aspects of using models in the science classroom.

Now on to Day 4!