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# 5.3: Activities and Answer Keys

Difficulty Level: At Grade Created by: CK-12

## Activity 4-1: Removing DNA from Thymus Cells

### PLAN

Summary Students treat fresh thymus tissue, (sweetbreads) to remove its DNA. They precipitate, spool, and observe the DNA in a test tube. Students design an alternative procedure to isolate thymus DNA. They also consider different tissue sources for obtaining DNA.

Objectives

Students:

\begin{align*}\checkmark\end{align*} extract the DNA from the nuclei of thymus cells.

\begin{align*}\checkmark\end{align*} describe the physical properties of DNA.

\begin{align*}\checkmark\end{align*} design an alternative procedure to isolate thymus DNA.

Student Materials

• Safety goggles
• Activity Report
• Sample of fresh thymus cells in a beaker; Sand; Liquid soap, clear, in a beaker with an eyedropper; Water in a beaker with an eyedropper; Alcohol; Cheesecloth square (several layers, \begin{align*}15 \times 15 \ cm\end{align*}); Mortar and pestle; Test tube; Small funnel; Test tube rack; Wooden skewer; Forceps; Eyedropper; Permanent marking pen; Paper towels; Black construction paper, \begin{align*}4 \times 4 \ cm\end{align*}; Transparent tape; Microscope, slides, and cover slips

Teacher Materials

• Serrated knife for cutting the thymus tissue
• Extra student materials, especially cheesecloth, skewers, test tubes, and fresh thymus cells
• You can substitute plastic or glass for the stirring rod.
• Methylene blue stain can be used to stain the thymus nuclei in Step 5.

Optional: DNA visuals, including models and/or posters Model of a cell with a large, distinct nucleus

Picture of a human torso to show the location of the thymus gland

Purchase fresh thymus tissue, also called sweetbreads, from your local butcher. You can freeze the thymus tissue if you do not plan to use right away.

Cut the thymus tissue into 2 cm cubes using a clean knife.

Keep all solutions cold prior to beginning the activity.

Estimated Time One to two class periods

Interdisciplinary Connection

Art Make a 3-D model of DNA.

Prerequisites and Background

Students should have good microscope skills. If the microscopes use mirrors and natural light, remind students not to point the mirror directly at the Sun. This activity is a great way to introduce and motivate the student to learn more about deoxyribonucleic acid (DNA).

DNA is not very soluble in 95-100% ethyl alcohol. It is at the interface where the DNA layer comes in contact with the alcohol layer that the DNA precipitates out of solution and can be spooled onto a clean, wooden skewer, glass rod, or pipette. Do not use plastic.

### IMPLEMENT

Introduce Activity 4-1 by reminding students of safety procedures in the lab, such as safety when using microscopes and wearing goggles when working with alcohol.

Point out the location of the thymus gland on a picture of a human torso.

Set up a slide to show intact thymus cells.

Steps 1-14 Be sure students are using their Activity Report as they progress through the Procedure.

Step 4 Monitor disposal of thymus tissue and clean up.

Step 5 This step can be done as a demonstration.

Steps 6-7 Make sure students only tap gently.

Step 8 Demonstrate how to trickle the alcohol down the inside of the test tube.

Steps 9-12 Monitor the disposal of materials and the general cleanup process. Again, make sure students are recording responses on their Activity Reports.

Step 13 Include a discussion of controls and variables to help students.

Step 14 Remind students to wash their hands thoroughly at the end of the activity.

• Use a clear detergent.
• Any alcohol such as ethanol, isopropanol, or rubbing alcohol can be used.
• Have students evaluate how they liked designing their own experiments and if it helped them learn more about DNA.

### ASSESS

Use the completion of the activity and written responses to the Activity Report to assess if students can

\begin{align*}\checkmark\end{align*} identify the location of DNA in thymus cells.

\begin{align*}\checkmark\end{align*} describe the physical properties of DNA.

\begin{align*}\checkmark\end{align*} design an alternative procedure to isolate thymus DNA.

\begin{align*}\checkmark\end{align*} identify different tissue sources for obtaining DNA.

## Activity 4-1: Removing DNA from Thymus Cells – Activity Report Answer Key

• Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
1. What is the purpose of the thymus tissue?
2. Make a drawing of your observations. You should be able to see the nuclei from the thymus cells. Be sure to label a few nuclei.
3. Which part of the cell was broken by the sand and grinding? Which part was broken by the soap?
4. Draw a labeled diagram and explain in words what happened when the alcohol was added to the test tube.
5. What is the purpose of twirling the wooden skewer?
6. Describe the appearance and texture of the DNA.
7. Describe your alternative procedure for removing thymus DNA. Include labeled diagrams as needed.
8. Explain how you would modify your original experimental design using different sources of DNA.

What Do You Think?

What other processes use templates to produce a copy of something?

## Activity 4-2: Building and Using a DNA Model

### PLAN

Summary Students make paper models of DNA nucleotides and use them to construct a DNA molecule consisting of twelve nucleotide pairs. They then use this DNA model to simulate the process of DNA replication.

Objectives

Students:

\begin{align*}\checkmark\end{align*} build models of DNA nucleotides.

\begin{align*}\checkmark\end{align*} construct a model of a DNA double helix.

\begin{align*}\checkmark\end{align*} simulate the replication of DNA.

Student Materials

• Resource
• Activity Report
• Scissors
• 6 different sets of colored paper
• Tape

Teacher Materials

• Models and diagrams of DNA molecules and nucleotides
• Extra supply of colored paper (6 colors noted below)

You can have students color the sugars, phosphates, and nitrogen bases as follows. Or you can copy them on the indicated colors of paper.

60 deoxyribose sugars (white)

60 phosphates (orange)

15 of each of the four nitrogenous bases:

adenine (red), thymine (blue), cytosine (yellow), and guanine (green)

Allow ample time to precut the template pieces.

Estimated Time One to two class periods, if template pieces have been precut

Interdisciplinary Connection

Math Relate the repeating patterns of nucleotides in DNA to other patterns in math.

Prerequisites and Background

Students should read and/or discuss the text material on DNA and replication before beginning this activity.

### IMPLEMENT

Students can work in lab teams of two to four. As indicated in the Advance Preparation, you can have students color the sugars, phosphates, and nitrogen bases as follows.

60 deoxyribose sugars (white)

60 phosphates (orange)

15 of each of the four nitrogenous bases:

adenine (red), thymine (blue), cytosine (yellow), and guanine (green).

It takes about one class period to color and cut out the templates. This can be done at home. It is important that the same color code is used for the different parts of the DNA nucleotides. Or you can copy them on paper of the colors indicated above.

Introduce Activity 4-2 by demonstrating how to put together a nucleotide and then how to combine the nucleotides into a DNA molecule.

Instead of using the colored paper for the copies of the templates, students can color both sides of the templates with pens or crayons.

Step 1-3 Remind students that they can sequence the nucleotides in any way they choose, but they should use no more than seven of each nucleotide.

Remind students to save extra nucleotides for simulating replication.

Step 4 Remind students to complete items 1 to 5 on their Activity Reports.

Step 5 Confirm students can explain replication.

Steps 6 Remind students to complete their Activity Reports and show them where they should store their completed models.

### ASSESS

Use the construction of the nucleotides and DNA double helix, the simulation of DNA replication, and the written answers on the Activity Report to assess if students can

\begin{align*}\checkmark\end{align*} build accurate models of nucleotides.

\begin{align*}\checkmark\end{align*} construct an accurate model of a DNA double helix.

\begin{align*}\checkmark\end{align*} explain the structure of DNA.

\begin{align*}\checkmark\end{align*} simulate the replication of DNA.

## Activity 4-2: Building and Using a DNA Model – Activity Report Answer Key

• Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
1. What are the three components of a nucleotide molecule?
2. What makes up the “rungs” of the DNA ladder?
3. What makes up the sides (uprights) of the DNA ladder?
4. What are the possible combinations of nitrogen bases?
5. Make a drawing of your completed DNA model. Be sure to include labels.
6. Make a drawing of the process of replication (Steps 5 and 6).
7. How do the replicated DNA molecules compare with the original DNA molecule?

Coding Students learn about the genetic code by using a variation of the mRNA code to solve a secret message. The secret message says, “HumBio is humming.”

A suggested response will be provided upon request. Please send an email to teachers-requests@ck12.org.

Write a sentence in which each word is made up of three letters, but do not leave spaces between the words, and do not use a period at the end of the sentence. Use the Code Key in the Mini Activity: Coding. What rules do you have to use to read this sentence? Explain why RNA polymerase must have start and stop signals. What start and stop signals would make it possible for someone to read your message correctly?

Building a Protein Model Pop beads can be obtained from any crafts store. Students may have pop beads at home. Students use 20 different colored pop beads or other colored plastic beads to simulate a protein chain of fifty amino acids and then compare their chains to see if they are similar, very different, or exactly alike. They relate their comparisons of the different pop bead proteins to the number of proteins that can be made from 20 different amino acids.

There are hundreds of different languages spoken around the world. Why do you think there are so many languages? How would you investigate which languages are related to each other? Can you speak more than one language, or would you like to be able to? What are some advantages of being able to speak more than one language?

A suggested response will be provided upon request. Please send an email to teachers-requests@ck12.org.

Consider your answer to the Journal Writing on this page with respect to how you would investigate whether different languages are related. How could you investigate whether different animals are related based on their genetic codes and proteins? How could you tell which animals were more and which were less closely related?

What does “poly” mean in the word polypeptide? What are some other words that use “poly” in this way?

1. Write a code using the letters A, U, G, and C for the nucleotides in mRNA.
2. Now design the triplets for the transfer RNAs that are complementary to this message.
3. What would happen if, in the first triplet, the A was missing and the message began with a U?
4. What else could you do that would change (mutate) the original message for making a functional protein into a meaningless message?

• Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
1. Describe how DNA makes a copy of itself.
2. Explain the role of DNA, mRNA, and amino acids in making a protein. DNA contains the code for making a particular protein.
3. What is the genetic code? How does it work?
4. How are amino acids brought into the sequence that is specified by the mRNA code?

## Activity 4-1 Report: Removing DNA from Thymus Cells (Student Reproducible)

1. What is the purpose of the thymus tissue?

2. Make a drawing of your observations. You should be able to see the nuclei from the thymus cells. Be sure to label a few nuclei.

3. Which part of the cell was broken by the sand and grinding? Which part was broken by the soap?

4. Draw a labeled diagram and explain in words what happened when the alcohol was added to the test tube.

5. What is the purpose of twirling the wooden skewer?

6. Describe the appearance and texture of the DNA.

In the space below, attach the paper containing your specimen. Label the DNA.

7. Describe your alternative procedure for removing thymus DNA. Include labeled diagrams as needed.

8. Explain how you would modify your original experimental design using different sources of DNA.

## Activity 4-2 Report: Building and Using a DNA Model (Student Reproducible)

1. What are the three components of a nucleotide molecule?

2. What makes up the “rungs” of the DNA ladder?

3. What makes up the sides (uprights) of the DNA ladder?

4. What are the possible combinations of nitrogen bases?

5. Make a drawing of your completed DNA model. Be sure to include labels.

6. Make a drawing of the process of replication (Steps 5 and 6).

7. How do the replicated DNA molecules compare with the original DNA molecule?

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6 , 7 , 8
Date Created:
Feb 23, 2012