In this activity, students investigate the gene that codes for CFTR and explore the transcription and translation of DNA.

Transcription

1 In this activity, students investigate the gene that codes for CFTR and explore the transcription and translation of DNA.

2 For each student: Science notebook Reproducible Master 6, Cooking Up a Protein For the class: Computer with large-screen monitor or projector that is connected to the Internet For each team: 5 different colors of 1.5 x 2 sticky notes Roll of thermal calculator paper, 2¼ wide meters of yarn Several copies of Reproducible Master 7, Amino Acids Computer with Internet access Set up a projector or a large-screen monitor and make sure that you have an Internet connection that will allow you to show the videos (the DNA Learning Center videos below, and the Scientific American video Genes vs. DNA vs. Chromosomes Instant Egghead #19 [ Preview the following videos from the DNA Learning Center, and determine whether the Basic or Advanced set is more appropriate for your class: o Basic DNA Transcription: o Basic mrna Translation: o Advanced DNA Transcription: o Advanced mrna Translation: Make a key that represents each base as a particular color of sticky note. You should have one sticky note color for each of the following bases: adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U). Make two displays: one for DNA that shows A, C, G, and T, and a second for RNA that shows A, C, G, and U. Bookmark the Cystic Fibrosis Mutation database ( on the class computers.

3 Photocopy the reproducible master, making several additional copies of page 4 for each team (students will cut the names of the amino acids from this page).

4 1. Remind students of the CFTR protein they explored in the previous session. Ask, What do you think is the connection between CFTR and our genes? 2. Keep track of students responses on chart paper or on the board. Students will likely understand that genes hold coded instructions to build organisms, though their level of understanding may vary. 3. Show the Scientific American video Genes vs. DNA vs. Chromosomes Instant Egghead #19 ( to the class. 4. Ask students to describe and explain the connection between DNA, genes, chromosomes, and proteins. 5. Explain that students will work in teams to explore how the genetic code of DNA is turned into proteins. Explain that some teams will be given a DNA sequence that codes for a normal protein, while others will be given a sequence that codes for an abnormal protein. It will be each team s job to transcribe and translate their sequence to determine whether they ve gotten a working or a non-working protein. 6. Pass out Reproducible Master 6, Cooking Up a Protein, to each student. Ask students to gather in their teams to discuss how they will undertake the activity. 7. Tell students that they will access the Cystic Fibrosis Mutation database online ( Assign each team an exon sequence to explore. Tell teams to copy their exon sequences, translate them into mrna, and then create chains of amino acids based on the genetic sequences they have been given. 8. Give teams time to create their sequence of amino acids. 9. Have teams combine their sequences (in the proper order) with the sequences made by other teams. Display the partial protein that the class created somewhere in the classroom. 10. Referring to the partial protein that the class made, ask students, How much of the full protein did we create? You may want to give them a hint that they could base their estimate on the fraction of the exons they ve translated and transcribed. 11. Explain that you re going to show some videos that are computer models of the actual processes of transcription and translation. Show the two videos you chose: Basic DNA Transcription: Basic mrna Translation: Advanced DNA Transcription: Advanced mrna Translation:

5 12. Ask students what they thought was interesting about the process and what questions they have about the process. Keep track of students responses on the board or on a piece of chart paper. 13. Discuss the Think About It questions. These questions should prompt students to start thinking about mutations, which they will explore in depth in the next lesson. What would happen to your amino acid chain if only one base was substituted? Does a substitution always lead to an incorrect amino acid? What would happen to your amino acid chain if a few base pairs were deleted? How do you think that might affect the protein?

6 Computer with Internet access Five different colors of sticky notes Roll of thermal calculator paper, 2¼ wide Yarn Scissors Tape or stapler Copies of Reproducible Master 7, Amino Acids DNA carries the genetic code of almost all organisms. It is found in the nucleus of each cell in your body. DNA is organized into chromosomes. Humans have 23 pairs of chromosomes, each with many genes that hold the instructions for many different traits. Your genetic makeup is stored in a genetic code made up of four chemical bases: adenine (A), cytosine (C), guanine (G), and thymine (T). The sequence of these four bases in your DNA is a code that holds the instructions for making and maintaining an organism. DNA consists of two complementary strands that form a long spiraling ladder shape called a double helix. Each base pairs with another: adenine with thymine, and cytosine with guanine. Each base is attached to a sugar molecule and a phosphate molecule that form the rails of the ladder. Source of graphic: U.S. National Library of Medicine (

7 When a cell divides, DNA is duplicated by splitting the ladder into two rails, with new, complementary rails forming for each original rail. This allows cells to divide and to each contain the full complement of DNA. Genes are made up of more than just the DNA that codes for their particular protein. In fact, some of the DNA in a gene doesn t code for anything. This part of the DNA is called an intron sequence. The part that codes for a protein is called an exon sequence. The gene that codes for the CFTR protein is on chromosome 7. When a protein is made, the DNA ladder splits into two rails, just like it does when it is being duplicated. However, during protein synthesis, the gene sequence is copied (transcribed) into messenger RNA (mrna). The intron sequences are then removed in a process called splicing, leaving only the exons, which code for the protein. The mrna then leaves the nucleus and is translated in a cellular organelle called the ribosome (found in the cytoplasm of the cell) into a protein made up of a series of amino acids. 1. Determine what exon your team has been assigned, and write that number here: 2. Go to the Cystic Fibrosis Mutation Database ( and find your exon. Click on the exon; you ll see that a red box appears on the CFTR gene that is represented, and a DNA sequence will appear below. Your exon is represented by capital letters in the sequence. 3. Collect the materials you will need to make your exon from your teacher. You will need a roll of paper and five different colors of sticky notes. 4. Consult the key for DNA that your teacher made. Roll out a length of paper and begin to construct your exon. Start at least six bases before the exon starts and continue at least six bases after it ends. Be sure to mark the start and end points of your exon on the paper roll. 5. It s now time to transcribe your exon. Roll out another piece of paper and mark it mrna. Transcribe your DNA by making a complementary strand of mrna with this

8 length of paper. Remember, in mrna, A pairs with U (uracil), T pairs with A, and G pairs with C. Your mrna starts at the start point of your exon and ends at the end point. 6. Now you have messenger RNA! The code of your mrna will be translated into a string of amino acids that will become the CFTR protein by a ribosome, which is an organelle in the cell. 7. Use the Amino Acid Wheel below or the Amino Acid Chart on the next page to create your part of the CFTR protein. If you are using the wheel, start in the center and work outward (for example, AAG codes for Lysine). Amino Acid Wheel

9 Amino Acid Chart 1 st 2 nd 3 rd U C A G U C A G UUU UCU UAU UGU U Phenylalanine Tyrosine Cysteine UUC UCC UAC UGC C Serine UUA UCA UAA UGA STOP A Leucine STOP UUG UCG UAG UGG Trytophane G CUU CCU CAU CGU U Histidine CUC CCC CAC CGC C Leucine Proline Arginine CUA CCA CAA CGA A Glutamine CUG CCG CAG CGG G AUU ACU AAU AGU U Asparagine Serine AUC Isoleucine ACC AAC AGC C AUA ACA Threonine AAA AUG Start Methionine AGA Lysine Arginine ACG AAG AGG G GUU GCU GAU Aspartic GGU U GUC GCC GAC Acid GGC C Valine Alanine Glycine GUA GCA GAA Glutamic GGA A GUG GCG GAG Acid GGG G A 8. As you identify each amino acid, cut out a paper version of it from Reproducible Master 7, Amino Acids and attach it to a piece of yarn using tape or a stapler. Make a chain of your amino acids. 9. Join your amino acid chain with the chains of other teams in the class (in the proper order, of course!). 1. What would happen to your amino acid chain if only one base was substituted? Does a substitution always lead to an incorrect amino acid? 2. What would happen to your amino acid chain if a few base pairs were deleted? How do you think that might affect the protein?

10 Phenylalanine Serine Tyrosine Cysteine Leucine Trytophane Leucine Proline Histidine Arginine Glutamine Isoleucine Threonine Asparagine Serine Lysine Arginine Methionine Valine Alanine Aspartic Acid Glycine Phenylalanine Serine Tyrosine Cysteine Leucine Trytophane Leucine Proline Histidine Arginine Glutamine Isoleucine Threonine Asparagine Serine Lysine Arginine Methionine Valine Alanine Aspartic Acid Glycine Phenylalanine Serine Tyrosine Cysteine Leucine Trytophane Leucine Proline Histidine Arginine Glutamine Isoleucine Threonine Asparagine Serine Lysine Arginine Methionine Valine Alanine Aspartic Acid Glycine