Lesson 11

Nucleic Acid Structure and Function: Working with Models (Day 4 of 5)

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Objective

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.
  • For more information about the models, check out the website West Ed set up just for this project!  

The Classroom Flow: Introducing Today's Activity

10 minutes

1.  Ask students to take out their replication activity document from yesterday's lesson modeling DNA replication.

2. Show students again the DNA replication terminology list on the board we worked with yesterday.  Confirm their choices for where to spend our time in discussion.

3.  Ask students to move the desks out of the way and to sit in a circle on the floor.

  • Note:  You can move this activity outside as well. I did so for my afternoon classes and it was very exciting for students!

The Classroom Flow: Digging Deeper into the Process of DNA Replication

30 minutes

1.  Take a longer 3D model (approx 15 base pairs) and start passing out nucleotides to students (approximately one per student)

2.  Split the large model into two half strands (inserting vocabulary prompts/check ins constantly: template, helicase, nucelotide, DNA polymerase)

3.  Tell students they will be working together to create their DNA copies from the template strand and then allow them time to work. You will see students checking in on the other group's progress and technique, experimenting with nucleotide sequencing, and collaborating as they work and view the work of others.

Hints:  

  • No cheating by dismantling the DNA template or creating one long new strand to attach to the old strand!
  • Students will want to straighten the chain to make it easier to attach the bases--it isn't easier this way and in fact, it makes it nearly impossible to twist it into the double helix shape.  Remind students the shape and orientation matter (phosphates face out of the backbone)
  • Make sure that every kid gets their hands on the model, it is much more engaging and successful than when two or three kids each take hold of one half and work on it exclusively.
  • Orientation of the strands matters!  3' to 5' on one side, 5' to 3' on the other.  This is not vocabulary I tend to emphasize in introductory biology: i frame it as starting with a sugar on one half of the backbone and a phosphate group on the other so that they run opposite of each other on the strands.  Kids will immediately go back to their paper models and notice/confirm the numbers and flow of the molecule.
  • Setting this up as a friendly competition between the two halves of the DNA model teams helps move the process along.  However, I don't rush them; the learning comes from the doing! I continue to question throughout and also direct some students to read back through their documents/writing so far to help them synthesize and review.

 

 4.  Once both models have been created, put them side by side in the middle of the circle and look again at the board notes about this concept of semi-conservative.  This can be a tricky term for kids.  Use the brief Bozeman Science clip below for a short summary of what conservative vs. semi-conservative processes look like in the Meselson-Stahl experiment.  Students will be able to tell you that the benefits of the semi-conservative process is that you can use the older half of the DNA molecule to check for errors on the newer half.  Remind them that the word conservative used in this context is not the same as the political version of the word and that here, it means saved.

 

The Classroom Flow: Wrapping Up

15 minutes

1.  To review, ask students to make the shape of DNA before it replicates.  Have them turn to their partners and take turns sharing out their 'perfect' answer summarizing the steps and purpose of DNA replication using the vocabulary from the board. 

 2.  Ask for student volunteers to share out their team's best answer!  Alternatively, you share out your best version of this with gaps/questions for students to fill in with their verbal responses.

3.  To get a better sense of what this activity looked like in our classroom, check out my photo gallery selections below!

Students working 1

Students working 2

Students working 3

Students working 4

Students working 5

4.  Once the pair work time frame is over, repeat the process one last time as a class.  Prompt students to talk out each step with terminology, using prompts like:

  • What happens next? (any number of acceptable answers depending on when you ask it)
  • What is the name of the enzyme that unzips the DNA? Helicase
  • What do we call the name of the rule that tells us how the bases get together? Base pair rule
  • What kind of bonds do we find between the bases? Hydrogen

You can also use our small green board as a tool to trigger student memories about the definition of purines and pyrimidines and support them in identifying them by counting the number of rings in each nitrogen base along with the number of hydrogen bonds between each base pairing (A and T, C and G).

And now on to Day 5!