The Coding of Protein Molecules By D.N.A.  

Glenn, Georgia S. Bogan High School

Objectives: Use paper models to demonstrate how DNA controls protein synthesis. Use paper models to show the role of mRNA in protein synthesis. Use paper models to show the role of tRNA in protein synthesis. Apparatus needed: Paper models to represent the following molecules: 5 deoxyribose thymine, 5 deoxyribose adenine, 1 deoxyribose cytosine, 1 deoxyribose guanine, 3 ribose uracil, 2 ribose adenine, 1 ribose cytosine, 2 tRNA molecules, 2 amino acid molecules. Cut out models beforehand and place in an envelope. Print the DNA Neucleotide sequence A,A,T,A,G,T on the envelope. Prepare a large "place mat" on which to assemble your protein molecule. Construct by taping two large sheets of construction paper together. Represent the nucleus by drawing a half circle on the left edge of your "place mat". Make it wide enough to accommodate a double strand of nucleotides. Make several circles to the left of the half circle to represent a few ribosomes in the cytoplasm. Strategies: Remove the puzzle pieces from the envelope. On the "place mat", start at the left edge inside the red half circle, arrange your DNA nucleotides in the linear sequence written on the envelope. Attach the corresponding nucleotides to make the right side of the DNA ladder. (Place the results on the board) Unzip the six nucleotides from the right half of your molecule. Attach the appropriate ribose nucleotides to the left half of your DNA nucleotides. (Record results on the board) Slide the ribose nucleotides to the right side of the half circle representing the nucleus and turn RNA nucleotides right side up. Attach the appropriate amino acid molecule to the appropriate tRNA molecule. Move the attached amino acid along with the tRNA to the appropriate bases on the RNA template. Try to arrange these molecules so that they will be built on top of a circle used to represent a ribosome. Students will identify what amino acids they have put together by looking at a chart showing the codons used to represent various amino acids. CONCLUSIONS: Each student has built a dipeptide made up of the amino acids leucine and serine. Large protein molecules are built the same way, but with many more amino acids being brought to the mRNA template by tRNA. EVALUATION: Answer the following questions to show understanding of protein synthesis: 1. To join tRNA molecules to the mRNA pattern, which sequence of tRNA molecules will match base pairs of the U,U,A sequence in mRNA? 2. Which tRNA sequence of bases can join U,C,A sequence in mRNA? 3. How does the sequence of bases on mRNA control the type of tRNA joining it? 4. A base sequence of A,A,A mRNA could only join with what sequence of bases in tRNA? 5. What specific amino acid is brought to the mRNA by a tRNA with a terminal sequence of A,G,U? (Use an amino acid - codon table) 6. What amino acid is brought to the mRNA by a tRNA terminal sequence of A,G,U? 7. How many half rungs of mRNA are responsible for the coding of one amino acid? 8. A protein molecule consists of the following amino acid sequence: leucine, glutamine, tyrosine, leucine, serine, serine. What would be the sequence of tRNA molecules responsible for forming this protein? 9. A ribosome receives the following mRNA message: AAA, CGA, GAA, GUU. What will be the sequence of tRNA bases joining the mRNA molecule? B. What will be the sequence of amino acids formed from this code? l0. Explain how a sequence of bases in DNA can instruct a cell to produce a certain protein.
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