TRANSCRIPTION AND TRANSLATION How does the sequence of bases in DNA determine the order of bases in mRNA? How does the sequence of bases in mRNA determine the order of amino acids in a protein? Materials: Colored pencils/crayons DNA nucleotide models (6 of each, total of 24) RNA nucleotide models (3 of each, total of 12) Scissors Clear tape Procedure: 1. Color the DNA nucleotide models. Use a different color of the each of the four bases. For example, color all the adenines red, the cytosines blue, the guanines yellow, and the thymines green. COLOR ONLY THE BASES, NOT THE SUGARS OR PHOSPHATE GROUPS. 2. Cut out each DNA nucleotide. 3. Use the 24 DNA nucleotides to construct a double-stranded DNA molecule. The first the 3 bases of the upper strand should be TAC and the last 3 bases should be ACT. In between, you may use any sequence of bases that you choose. Remember, the sequence of bases on the lower strand must be complementary to the bases of the upper strand. 4. Fasten the molecule together using clear tape to connect the nucleotides of each strand. Do not tape across base pairs. 5. Write the sequence of DNA bases below. Upper: ___________________________________________________________ Lower: ___________________________________________________________ 6. Now color the RNA nucleotide models. Use the same three colors you used before for the As, Cs, and Gs. Use a different color for the Us. AGAIN, COLOR ONLY THE BASES. 7. Cut out each RNA nucleotide. 8. Separate the upper and lower strands of DNA. 9. Using the upper strand of DNA, match complementary RNA nucleotides with the exposed bases of the DNA strand to make an mRNA molecule. 10. When you are finished, tape the mRNA molecule together. Write the sequence of RNA bases below: ___________________________________________________________________ 11. Now, use the codon chart on p. 292 of your textbook to determine the sequence of amino acids encoded by the mRNA. Fill in the amino acid sequence below. ____________________________________________________________________________________ Questions (answer on the back of this sheet) 1. Does the mRNA strand more closely resemble the DNA strand from which it was transcribed or the complementary DNA strand that wasn’t used? Explain. 2. In which step of the procedure did you simulate transcription? _____ 3. In which step did you simulate translation? _____ 4. Which would be more damaging to a cell, an error in DNA replication or transcription? Explain. 5. With regard to transcription and translation, describe how a change in the sequence of DNA bases in a gene (a mutation) could lead to a change in the functioning of a protein.
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