DNA and Protein Synthesis Grade 10

Transcription

1 Ohio Standards Connection: Life Sciences Benchmark C Explain the genetic mechanisms and molecular basis of inheritance. Indicator 5 Illustrate the relationship of the structure and function of DNA to protein synthesis and the characteristics of an organism. Lesson Summary: In this lesson, students will understand the role of DNA in protein synthesis. The relationship between protein synthesis and the characteristics of an organism will be analyzed through an activity that allows students to model the process. Estimated Time Duration: 75 minutes Commentary: This lesson provides students with the opportunity to use kinesthetic activity to deepen their understanding of how DNA is related to protein synthesis which builds and carries out the functions of living organisms. This lesson was field tested by teachers across the state of Ohio. One teacher commented: It is simple, but effective. I particularly like the tips that are included. Pre-Assessment: Group students in teams of two. Distribute three by five cards with the following steps of transcription and translation posted on them: DNA is unwound; mrna is made; mrna matures; mrna attaches at ribosome; trna matches codon; Peptide bonds are formed; Stop codon is read; mrna and protein are released. Scramble the cards when distributing them to students. Instruct the students to put these steps in the correct order. A timer can be used for this activity. 1

2 Scoring Guidelines: The correct sequence is as follows: DNA is unwound; mrna is made; mrna matures; mrna attaches at ribosome; trna matches codon; Peptide bonds are formed; Stop codon is read; mrna and protein are released. Observe students and make notes of their conversation to determine their level of understanding. Use this information to adjust instructional procedures where necessary. Post Assessment: Provide each student with the following DNA sequence: TAC GCT TTC CGA TGG CTA TGA (parent strand). Instruct the students to record the complementary DNA that would form during replication (complementary strand). Next, direct the students to record the resulting mrna sequence that would be formed. Then, explain to the students that a mutation will occur in the parent strand of DNA sequence. Instruct the students to change the 18 th letter in the sequence from A to G. Then, ask the students the following questions: 1. What initiates and terminates mrna coding? 2. If one base in the DNA is changed, describe what may happen to the protein that is formed. 3. When DNA changes, what does it do to the protein that is made? 4. Describe how this change may or may not affect the characteristics of the organism. Scoring Guidelines: 1. The amino acid sequence AUG is the start codon. The mrna begins coding at that point. Three specific amino acids (TAA, TAG and TGA) inform the mrna to stop reading the code and the amino acid chain is released. 2. If one base is changed, the amino acid that is coded for may be changed, changing the protein that is formed. This may or may not be an issue because many combinations of bases in a codon can code for the same amino acid. If this is the case, no change is made to the corresponding amino acid and the protein remains the same. If the base change alters the amino acid it is coding for, then the protein may be altered and the resulting protein may be changed which may initiate a change in the structure and the function of an organism. If the charges on the amino acid do not change, the tertiary structure of the protein does not change. 3. When DNA changes, the protein that is made during transcription and translation may be changed because of a change in the amino acid sequence. The rationale is the same as in the previous question. 4. Changes in the sequence of amino acids may change the shape or size of a protein and therefore may result in a change of the function or shape of the organism. 2

3 Instructional Procedures: Student Engagement 1. Ask students the following questions for a journal entry: a. How does your DNA relate to your physical characteristics such as eye color or the ability to roll your tongue? 2. Prepare the following materials: a. Make a banner with the following DNA sequence: AAAAA TAC GAT AGC TTT CCG ATG GCT ATT GGGGG. b. Make one card with the letter T to be used to cover up the G in the base triplet AGT in the banner. c. Make eight cards (approximately four by six) with one codon per card written in large letters. AUG, CUA, UCG, AAA, GGC, UAC, CGA, and UAA. d. Make at least eight, 4x6 cards with the following trna anti-codons and amino acid names written in large letters. Put one trna anticodon / amino acid pair to a card. AUG / Start; CUA / leucine; UCG / serine, AAA / lysine, GGC / glycine; UAC / tyrosine, CGA / arganine, and UAA / Stop. Additional cards with appropriate trna anti-codon/amino acid combinations should also be made so that all students will have a card with either an mrna codon or a trna anti-codon/amino acid. 3. Instruct students to work with a partner. Pass out one copy of Attachment A, Amino Acid Codon Table, or a table of your choosing, to each pair of students. At least eight students will be needed for this activity. Indicate to students that in this activity the class will be building a protein. Briefly discuss how an organism needs and uses proteins (muscle, cell structure, collagen in skin, hormones, etc.). Explain that the amino acids used to build those proteins come from food or may already be present in the organism. 4. Show the DNA strand banner with the following base sequence: AAAAA TAC GAT AGC TTT CCG ATG GCT ATT GGGGG. Instructional Tip: The repeating A s and the repeating G s are used here to indicate stretches of DNA between genes and therefore not transcribed into mrna. In addition, the activity is simplified from a natural system in that there are no introns to remove from the transcribed mrna before the mrna is matured and used at the ribosome for translation into a protein. The resulting mrna sequence then reads: AUG CUA UCG AAA GGC UAC CGA UAA. 5. Instruct the student pairs to record the complementary DNA sequence that would form during replication. Answer: TTTTT ATG CTA TCG AAA GGC TAC CGA TAA CCCCC. 6. Instruct the student pairs to record what the mrna base sequence would be if the DNA strand on the banner was being used as a mrna template between the repeating A s on the left and the repeating G s on the right. 7. Randomly pass out the necessary eight codon and eight trna anti-codon cards to the students. From the remaining students, pick one student to be the rrna. Distribute the anti-codon cards to all remaining students. Each student should have a card. 3

4 8. Have the students with the mrna codon cards arrange themselves in the appropriate order and hold hands (or hold ends of a short rope) to show a bond as determined by the DNA sequence on the banner. The line formed is then the full mrna strand. 9. Have the student that is the mrna start codon (AUG) find and go to the student that is the rrna. Then have the rrna student direct the appropriate trna to align with the mrna codon. Have each trna/amino acid student arrange themselves according to the mrna sequence to form the developing protein until a stop codon is reached. Have the rrna student then release the mrna from the amino acid chain, and translation is finished. 10. Tell the class that a ray (X-ray, UV ray, radiation, chemical exposure, etc.) just hit the DNA on the banner, resulting in the changing of one base in the sequence. The G in the ATG triplet was altered to a T (the triplet now is ATT). Cover the G on the card with a T to indicate the change. 11. Ask the class to determine what effect the change might have on the protein that is made. Direct the students to redo the above activity from forming the mrna through building the protein with the new DNA sequence. Instructional Tip: Real-life examples apply here. Why does the dentist cover individuals with a lead apron? Why does the X-ray technician stand behind a lead wall? Why should individuals use sun screen? Why should individuals avoid tanning beds? All of these are protections from radiation so that DNA is not mutated. The result should be a protein that is the same sequence of amino acids as the first but is composed of four amino acids instead of six because the cosmic ray changed the UAC codon (tyrosine) to a stop codon and therefore terminated the protein earlier than the original sequence. Additionally, you may choose to first re-do this activity changing the third base pair in the codon which does not change the amino acid showing students that the codon can change without changing the protein. 12. Direct the students to record their answer in their notes at each step. 13. To close this lesson, ask students to reflect through a journal entry or a class discussion on what happens when the sequence of amino acid sequence is changed. What happens to the shape or size of a protein? How does this change affect function or characteristics of the organism? Other changes may result in complications such as sickle cell anemia and cancer. Tie this information into the engagement question. How does your DNA relate to your physical characteristics such as eye color or the ability to roll your tongue? Differentiated Instructional Support: Instruction is differentiated according to learner needs to help all learners either meet the intent of the specified indicator(s) or, if the indicator is already met, to advance beyond the specified indicator(s). Have students work independently, in pairs or heterogeneous groups to complete the protein activity. Challenge students to explore a genetic or medical condition of interest and share with the class. 4

5 Extensions: Have students research other genetic diseases such as hemophilia, PKU or cystic fibrosis. Repeat this activity using an insertion or deletion in the sequence. Have students design an animation or dramatize the steps to protein synthesis. Homework Options and Home Connections: Invite students to examine the heritage of their pets or livestock, tracing physical characteristics and traits. Material and Resources: The inclusion of a specific resource in any lesson formulated by the Ohio Department of Education should not be interpreted as an endorsement of that particular resource, or any of its contents, by the Ohio Department of Education. The Ohio Department of Education does not endorse any particular resource. The Web addresses listed are for a given site s main page, therefore, it may be necessary to search within that site to find the specific information required for a given lesson. Please note that information published on the Internet changes over time, therefore the links provided may no longer contain the specific information related to a given lesson. Teachers are advised to preview all sites before using them with students. For the teacher: For the students: Copies of Amino Acid Table which can be obtained in the textbook, copies DNA sequences, index cards, banner. Copies of Amino Acid Table, copies of DNA sequences. Library Integration Tips: Have students use the school library to use Infohio s Access Science, NET Wellness and school library books to get information about genetic mechanisms and genetic diseases. Vocabulary: DNA RNA trna mrna rrna codon amino acid protein nucleotide transcription translation Technology Connections: Have students use on-line amino acid tables and charts Have students look at a gene bank Web site that shows specific mutations. 5

6 Research Connections: Marzano, R., Pickering, D., Pollock, J. (2001).Classroom Instruction that Works: Researchbased Strategies for Increasing Student Achievement, Alexandria, Va.: Association for Supervision and Curriculum Development. Nonlinguistic representations help students think about and recall knowledge. This includes the following: Creating graphic representations (organizers); Making physical models; Generating mental pictures; Drawing pictures and pictographs; Engaging in kinesthetic activity. Attachments: Attachment A, Amino Acid/Codon Table 6

7 Attachment A Amino Acid/Codon Table 20 Amino Acids with Their Corresponding DNA Codons Amino Acid DNA Codons Isoleucine Leucine Valine Phenylalanine Methionine Cysteine Alanine Glycine Proline Threonine Serine Tyrosine Tryptophan Glutamine Asparagine Histidine Glutamic acid Aspartic acid Lysine Arginine Stop codons ATT, ATC, ATA CTT, CTC, CTA, CTG, TTA, TTG GTT, GTC, GTA, GTG TTT, TTC ATG TGT, TGC GCT, GCC, GCA, GCG GGT, GGC, GGA, GGG CCT, CCC, CCA, CCG ACT, ACC, ACA, ACG TCT, TCC, TCA, TCG, AGT, AGC TAT, TAC TGG CAA, CAG AAT, AAC CAT, CAC GAA, GAG GAT, GAC AAA, AAG CGT, CGC, CGA, CGG, AGA, AGG TAA, TAG, TGA 7